ArticleLiterature Review

Instrumentation of the osteoporotic spine: Biomechanical and clinical considerations

January 2011
The Spine Journal 11(1):54-63

January 2011
11(1):54-63

DOI:10.1016/j.spinee.2010.09.024

Source
PubMed

Authors:

Karthikeyan Ponnusamy

Johns Hopkins Medicine

Sravisht Iyer

Hospital for Special Surgery

A. Jay Khanna

Georgetown University

Osteoporosis is a major health-care problem that is increasing in magnitude with the aging population. Such patients are more prone to develop painful and debilitating spinal deformities but are difficult to treat. Currently, no definitive treatment algorithm has been established. To review the failure modes of instrumentation and novel surgical treatments of spinal deformities in patients with osteoporosis with the goal of improving surgical care. Review article. We systematically searched PubMed for articles regarding instrumentation failure modes and surgical treatments of spinal deformities in patients with osteoporosis and summarized current treatment options. The surgical treatment options are severely limited because of the tendency for instrument failure secondary to pullout and subsidence, leading to revision procedures; multiple levels and multiple fixation points are recommended to minimize the risk. The literature supports the use of vertebroplasty in conjunction with pedicle screw-based instrumentation for treating more severe spinal deformities. Other techniques and modifications with evidence of reduced failure risk are bicortical screws, hydroxyapatite coatings, double screws, and expandable screws. Anterior approaches may provide another avenue of treatment, but only a few studies have been conducted on these implants in patients with osteoporosis. Spinal deformities in patients with osteoporosis are difficult to treat because of their debilitating and progressive nature. Novel surgical approaches and instruments have been designed to decrease construct failures in this patient population by reducing implant pullout, subsidence, and incidence of revision surgery. The success of these techniques depends on integrating biomaterial, biologic, and biomechanical aspects with clinical considerations. Synthesizing this myriad of aspects will lead to improved treatment options for patients with osteoporosis who are suffering from spinal deformities.

Konsep Diagnosis dan Penatalaksanaan Fraktur Osteoporosis Terkini

Article

Full-text available

Jan 2024

Osteoporosis is a metabolic bone disease that is caused by a decreased amount of bone mass, and microarchitectural damage to bone tissue that affects the bone to break easily. Osteoporosis can be divided into primary and secondary etiologies. Vertebral, hip, distal radius, and proximal humerus are the most common predilection of fracture complication due to osteoporosis. The diagnosis of osteoporotic fractures is established based on the identification of risk factors, general clinical manifestations, specific manifestation from each fracture predilection, and advanced examinations, including radiology imaging and dual-energy x-ray absorptiometry. The purpose of osteoporotic fractures management in elderly is a stable fixation with early mobilization that will induce an optimal activation of osteoblast for new bone formation

Long-Segmental Posterior Fusion Combined With Vertebroplasty and Wiring: Alternative Surgical Technique for Kummell’s Disease With Neurologic Deficits-A Retrospective Case Series

Article

Full-text available

Jun 2021

Purpose Various surgical methods have been reported for Kummell’s disease with neurologic deficits. The aim of this study was to introduce long-segmental posterior fusion (LPF) combined with vertebroplasty (VP) and wiring as an alternative surgical technique. Material and Methods We retrospectively analyzed 10 patients undergoing posterior decompression and LPF combined with VP and wiring for Kummell’s disease with neurologic deficits from January 2011 to December 2014. The radiologic outcomes included the local kyphotic angle (LKA) and segmental kyphotic angle (SKA). Clinical outcomes, including the visual analog scale (VAS), the Oswestry Disability Index (ODI) and the Frankel grade were assessed. Surgery-related complications were also evaluated. Results The mean age of the included patients was 77 ± 8 years with a mean follow-up period of 31.4 ± 4.9 months and a mean bone mineral density of −3.5 ± 0.7 (T-score). The mean operation time was 220 ± 32.3 minutes with a mean blood loss of 555 ± 125.7 mL. The preoperative LKA and SKA were significantly corrected postoperatively (37.9 ± 8.7° vs. 15.3 ± 5.3°, p = 0.005 for LKA; 21.3 ± 5.1° vs. 7.6 ± 2.8°, p = 0.005 for SKA) without a loss of correction at the last follow-up. The VAS and ODI were also significantly improved (7.7 ± 1.1 vs. 3.0 ± 1.6, p = 0.007 for VAS; 90.3 ± 8.9 vs. 49.6 ± 22.7, p = 0.007 for ODI). The Frankel grade of all patients was improved by at least 1 or 2 grades at the last follow-up. Surgery-related complications such as intraoperative cement leakage and implant loosening during the follow-up were not observed. Conclusions LPF combined with VP and wiring might be an effective surgical option for Kummell’s disease with neurologic deficits, especially for the elderly patients with morbidities. Level of Evidence level IV.

HOUNSFIELD UNITS USE IN SPINAL SURGERY PLANNING: SYSTEMATIC REVIEW AND META-ANALYSIS USO DAS UNIDADES HOUNSFIELD NO PLANEJAMENTO DA CIRURGIA ESPINHAL: REVISÃO SISTEMÁTICA E META-ANÁLISE USO DE LAS UNIDADES HOUNSFIELD EN LA PLANIFICACIÓN DE LA CIRUGÍA ESPINAL: REVISIÓN SISTEMÁTICA Y METANÁLISIS

Article

Full-text available

Oct 2022

Bone mineral density is a crucial factor in the success or failure of osteosynthesis in spine surgery; it shows the onset of osteoporosis and related complications. Its evaluation is verified by dual-energy X-ray absorptiometry (DEXA) and Hounsfield Unit (HU) measurement by CT scan. Objective: Determine the use of HU in surgical planning; compare utility in diagnosing osteoporosis by DEXA; and evaluate sensitivity in predicting complications. Method: A systemic literature review was conducted on PubMed, in line with PRISMA methodology. Including those who justified the use of pre-surgical planning, compared HU/DEXA, and assessed complications. For the statistical analysis, the χ² was used. Results: 57 articles were identified by selecting nine that met the inclusion criteria. In patients undergoing spinal surgery for fixation and fusion for degenerative pathology, HU measurement showed a prevalence of osteoporosis of 58.5% (sensitivity 93.26%; specificity 90.22%), osteoporosis-associated complications of 24.5%, proper diagnosis of 71.98%, and screw release rate of 82.31%. Conclusions: UH measurement for the diagnosis of osteoporosis turns out to be more sensitive, specific, and predictive compared to DEXA, especially in elderly patients; it represents a useful tool in planning spinal surgery, minimizing the risk of complications such as screw release, fractures, pseudoarthrosis, subsidence of intersomatic devices, and kyphosis of the proximal junction. Level of evidence II; Study Design: Systematic Review and meta-analysis. Keywords: Absorptiometry, Photon; Bone Density; Osteoporosis; Bone Screws; Tomography; Kyphosis

Biomechanical evaluation of reinsertion and revision screws in the subaxial cervical vertebrae

Article

Full-text available

May 2024
BMC MUSCULOSKEL DIS

Background This study aimed to evaluate the biomechanical effects of reinserted or revised subaxial cervical vertebral screws. Methods The first part aimed to gauge the maximum insertional torque (MIT) of 30 subaxial cervical vertebrae outfitted with 4.0-mm titanium screws. A reinsertion group was created wherein a screw was wholly removed and replaced along the same trajectory to test its maximum pullout strength (MPOS). A control group was also implemented. The second part involved implanting 4.0-mm titanium screws into 20 subaxial cervical vertebrae, testing them to failure, and then reinserting 4.5-mm revision screws along the same path to determine and compare the MIT and MPOS between the test and revision groups. Results Part I findings: No significant difference was observed in the initial insertion’s maximum insertion torque (MIT) and maximum pull-out strength (MPOS) between the control and reinsertion groups. However, the MIT of the reinsertion group was substantially decreased compared to the first insertion. Moderate to high correlations were observed between the MIT and MPOS in both groups, as well as between the MIT of the first and second screw in the reinsertion group. Part II, the MIT and MPOS of the screw in the test group showed a strong correlation, while a modest correlation was observed for the revision screw used in failed cervical vertebrae screw. Additionally, the MPOS of the screw in the test group was significantly higher than that of the revision screw group. Conclusion This study suggests that reinsertion of subaxial cervical vertebrae screws along the same trajectory is a viable option that does not significantly affect fixation stability. However, the use of 4.5-mm revision screws is inadequate for failed fixation cases with 4.0-mm cervical vertebral screws.

Craniocaudal cyclic load improve risk assessment of lumbar pedicle screw loosening：finite element analysis based on computer tomography

Preprint

Full-text available

Apr 2024

Background Screw loosening remains a prominent complication for osteoporotic patients with pedicle screw fixation surgeries, yet with limited risk assessment approach. The aim of this study was to investigate influence of craniocaudal cyclic load on pedicle screw fixation strength by computed tomography (CT) based finite element analysis (FEA) and we examined predict ability in pedicle screw loosening (PSL). Methods 12 clinical PSL cases (7 men, 5 women) and 12 age- and sex-matched controls were enrolled for CT based FEA. Simple axial pullout load and axial pullout load with preset craniocaudal cyclic load were applied to each model respectively, and the ultimate pullout force under both conditions is calculated as the fixed strength and compared. Besides, HU values of the vertebral body trabeculae and screw trajectory were measured as an assessment of osteoporosis. The ultimate pullout force and HU value were compared between PSL and controls cases. Results The cyclic load remarkably reduce the pullout force of pedicle screws (906.2 ± 180.2 N vs. 729.3 ± 172.3 N, p<0.0001) by CT based FEA. No significant difference between the PSL and the control group in the simple axial pull-out force and HU values of the vertebral body. But the pullout force with preset cyclic load (639.2 ± 169.4 N vs. 819.4 ± 125.1 N, p = 0.072) and the HU value of the screw trajectory (177.5 ± 43.8 vs. 217.2 ± 29.6, p = 0.016) in the PSL group is significantly lower than that in the control group. Area under receiver operating characteristic curve (ROC) revealed pullout force with preset cyclic load slightly better predicted PSL than HU value of the screw trajectory (AUC = 0.798 vs. 0.750). Conclusions The craniocaudal cyclic load significantly reduces the screw fixation strength. HU value of screw trajectory and pullout force with preset cyclic load by CT based FEA are helpful for the clinical prediction of PSL.

Surgical Management of Primary Thoracic Epidural Melanoma

Article

Full-text available

Feb 2024

In this study, we reported one of the first cases where a rare robotic-assisted platform with neuronavigation technology and carbon-fiber-polyetheretherketone (CF/PEEK) screws is employed to surgically treat multilevel thoracic primary spinal epidural melanoma. A 67-year-old male presented with left upper thoracic pain. His magnetic resonance imaging (MRI) of the thoracic spine revealed a dumbbell-shaped left epidural mass at the T2-3 level. Partial resection was performed due to tumor growth into the vertebral bodies and patient discretion for minimal surgery. The patient’s neurological conditions improved postoperatively, with reduced reported symptoms of pain and numbness. Postoperative imaging showed evidence of appropriate spinal stabilization. Patient underwent stereotactic body radiation therapy (SBRT), and no adverse events were reported. This case reflects one of the first examples of treating thoracic epidural melanoma with the use of robotic-assisted navigation. Further prospective studies are needed to determine the efficacy of robot-assisted navigation for patients with primary spinal malignant melanoma which may open the possibility of surgery to once presumed non-operative patients.

The effect of polymethylmethacrylate augmentation on the primary stability of stand-alone implant construct versus posterior stabilization in oblique lumbar interbody fusion with osteoporotic bone quality– a finite element study

Article

Full-text available

Jan 2024
SPINE J

BACKGROUND CONTEXT Oblique lumbar interbody fusion (OLIF) can provide an ideal minimally invasive solution for achieving spinal fusion in an older, more frail population where decreased bone quality can be a limiting factor. Stabilization can be achieved with bilateral pedicle screws (BPS), which require additional incisions and longer operative time. Alternatively, a novel self-anchoring stand-alone lateral plate system (SSA) can be used, where no additional incisions are required. Based on the relevant literature, BPS constructs provide greater primary biomechanical stability compared to lateral plate constructs, including SSA. This difference is further increased by osteoporosis. Screw augmentation in spinal fusion surgeries is commonly used; however, in the case of OLIF, it is a fairly new concept, lacking a consensus-based guideline. PURPOSE This comparative finite element (FE) study aimed to investigate the effect of PMMA screw augmentation on the primary stability of a stand-alone implant construct versus posterior stabilization in OLIF with osteoporotic bone quality. STUDY DESIGN The biomechanical effect of screw augmentation was studied inside an in-silico environment using computer-aided FE analysis. METHODS A previously validated and published L2-L4 FE model with normal and osteoporotic bone material properties was used. Geometries based on the OLIF implants (BPS, SSA) were created and placed inside the L3-L4 motion segment with increasing volumes (1–6 cm3) of PMMA augmentation. A follower load of 400 N and 10 Nm bending moment (in the three anatomical planes) were applied to the surgical FE models with different bone material properties. The operated L3-L4 segmental range of motion (ROM), the inserted cage's maximal caudal displacements, and L4 cranial bony endplate principal stress values were measured. RESULTS The non-augmented values for the BPS construct were generally lower compared to SSA, and the difference was increased by osteoporosis. In osteoporotic bone, PMMA augmentation gradually decreased the investigated parameters and the difference between the two constructs as well. Between 3 cm3 and 4 cm3 of injected PMMA volume per screw, the difference between augmented SSA and standard BPS became comparable. CONCLUSIONS Based on this study, augmentation can enhance the primary stability of the constructs and decrease the difference between them. Considering leakage as a possible complication, between 3 cm3 and 4 cm3 of injected PMMA per screw can be an adequate amount for SSA augmentation. However, further in silico, and possibly in vitro and clinical testing is required to thoroughly understand the investigated biomechanical aspects. CLINICAL SIGNIFICANCE This study sheds light on the possible biomechanical advantage offered by augmented OLIF implants and provides a theoretical augmentation amount for the SSA construct. Based on the findings, the concept of an SSA device with PMMA augmentation capability is desirable.

The role of concomitant vitamin D3 and K2 treatment after laminectomy in spinal stenosis surgery of patients with osteoporosis

Article

Full-text available

Aug 2023

Background: Readmission because of ongoing pain and complaints who undergone spinal surgery with osteoporosis is increasing. This study investigated the efficacy of concomitant vitamin D3 and K2 usage in the surgical treatment of patients with lumbar spinal stenosis who have osteoporosis. The aim of the study was to treatment strategy is to reduce the patient’s low back pain and decrease readmission rates due to ongoing pain. Methods: A total of 22 patients with osteoporosis included in the study who had lumbar decompression via laminectomy surgery with posterior instrumentation for spinal stenosis. Patients were divided into groups according to use additional supplement of vitamin D3+K2. Group 1 was control group who received only vitamin D3 and group 2 was patients who received vitamin D3+K2 treatment. Patients were called to their sixth month check-up and their pre-and post-treatment VAS scores and Roland-Morris scores were filled in and readmission rates due to ongoing pain were compared. Results: 9 male and 13 female participants with a mean age of 64.4 were in the study. The mean T-score in bone mineral density (BMD) was -2.7 in group 1 and -2.6 in group 2. A significant difference was found when the pre-operative and post-operative VAS and RM scores of all patients were compared (p<0.05). The mean readmission rates due to ongoing pain is 4 in group 1 and 7 in group 2. A significant difference was found when readmission rates due to ongoing pain were compared (p<0.05). Conclusions: Concomitant vitamin D3 and K2 usage in the surgical treatment of patients with lumbar spinal stenosis who have osteoporosis is a valuable treatment option to reduce the rate of admission to the hospital because of ongoing pain.

Screw Osteointegration—Increasing Biomechanical Resistance to Pull-Out Effect

Article

Full-text available

Aug 2023

Spinal disorders cover a broad spectrum of pathologies and are among the most prevalent medical conditions. The management of these health issues was noted to be increasingly based on surgical interventions. Spinal fixation devices are often employed to improve surgery outcomes, increasing spinal stability, restoring structural integrity, and ensuring functionality. However, most of the currently used fixation tools are fabricated from materials with very different mechanical properties to native bone that are prone to pull-out effects or fail over time, requiring revision procedures. Solutions to these problems presently exploited in practice include the optimal selection of screw shape and size, modification of insertion trajectory, and utilization of bone cement to reinforce fixation constructs. Nevertheless, none of these methods are without risks and limitations. An alternative option to increasing biomechanical resistance to the pull-out effect is to tackle bone regenerative capacity and focus on screw osteointegration properties. Osteointegration was reportedly enhanced through various optimization strategies, including use of novel materials, surface modification techniques (e.g., application of coatings and topological optimization), and utilization of composites that allow synergistic effects between constituents. In this context, this paper takes a comprehensive path, starting with a brief presentation of spinal fixation devices, moving further to observations on how the pull-out strength can be enhanced with existing methods, and further focusing on techniques for implant osteointegration improvement.

Biological principles of adult degenerative scoliosis

Article

Jun 2023
TRENDS MOL MED

The global aging population has led to an increase in geriatric diseases, including adult degenerative scoliosis (ADS). ADS is a spinal deformity affecting adults, particularly females. It is characterized by asymmetric intervertebral disc and facet joint degeneration, leading to spinal imbalance that can result in severe pain and neurological deficits, thus significantly reducing the quality of life. Despite improved management, molecular mechanisms driving ADS remain unclear. Current literature primarily comprises epidemiological and clinical studies. Here, we investigate the molecular mechanisms underlying ADS, with a focus on angiogenesis, inflammation, extracellular matrix remodeling, osteoporosis, sarcopenia, and biomechanical stress. We discuss current limitations and challenges in the field and highlight potential translational applications that may arise with a better understanding of these mechanisms.

Prevalence of osteoporosis in spinal surgery patients older than 50 years: A systematic review and meta-analysis

Article

Full-text available

May 2023
PLOS ONE

Introduction: In spine surgery, poor bone condition is associated with several complications like adjacent segment fractures, proximal junctional kyphosis, and screw loosening. Our study explored the prevalence of osteoporosis in spinal surgery patients older than 50 years through a systematic review and meta-analysis. Methods: This systematic review and meta-analysis were conducted according to the PRISMA criteria. Three electronic databases, including PubMed, EMBASE, and Web of Science, were searched from inception to August 2022. We used the random-effects model to calculate the overall estimates, and the heterogeneity was measured using Cochran's Q and I2 tests. Meta-regression and subgroup analyses were used to determine the source of the heterogeneity. Results: Based on the inclusion and criteria, we chose ten studies with 2958 individuals for our analysis. The prevalence of osteoporosis, osteopenia, and osteoporosis/osteopenia in the spinal surgery patients was 34.2% (95%CI: 24.5%-44.6%), 43.5% (95%CI: 39.8%-47.2%), and 78.7% (95%CI: 69.0%-87.0%), respectively. Regarding different diagnoses, the prevalence was highest in patients with lumbar scoliosis (55.8%; 95%CI: 46.8%-64.7%) and the lowest in patients with cervical disc herniation (12.9%; 95%CI: 8.1%-18.7%). In age groups 50-59, 50-69,70-79, the prevalence was 27.8%, 60.4%, 75.4% in females, and 18.9%, 17.4%, 26.1% in males. Conclusions: This study showed a high prevalence of osteoporosis in patients undergoing spine surgery, especially in females, people of older age, and patients who received degenerative scoliosis and compression fractures. Current osteoporosis screening standards for patients undergoing spine surgery may not be adequate. Orthopedic specialists should make more efforts regarding preoperative osteoporosis screening and treatment.

Transmission-Based Vertebrae Strength Probe Development: Far Field Probe Property Extraction and Integrated Machine Vision Distance Validation Experiments

Article

Full-text available

May 2023
SENSORS-BASEL

We are developing a transmission-based probe for point-of-care assessment of vertebrae strength needed for fabricating the instrumentation used in supporting the spinal column during spinal fusion surgery. The device is based on a transmission probe whereby thin coaxial probes are inserted into the small canals through the pedicles and into the vertebrae, and a broad band signal is transmitted from one probe to the other across the bone tissue. Simultaneously, a machine vision scheme has been developed to measure the separation distance between the probe tips while they are inserted into the vertebrae. The latter technique includes a small camera mounted to the handle of one probe and associated fiducials printed on the other. Machine vision techniques make it possible to track the location of the fiducial-based probe tip and compare it to the fixed coordinate location of the camera-based probe tip. The combination of the two methods allows for straightforward calculation of tissue characteristics by exploiting the antenna far field approximation. Validation tests of the two concepts are presented as a precursor to clinical prototype development.

Safety and Osteointegration of Titanium Screws Coated with a Fibroblast Growth Factor-2–Calcium Phosphate Composite Layer in Non-Human Primates: A Pilot Study

Article

Full-text available

May 2023

Spinal instrumentation surgery for older patients with osteoporosis is increasing. Implant loosening may occur due to inappropriate fixation in osteoporotic bone. Developing implants that achieve stable surgical results, even in osteoporotic bone, can reduce re-operation, lower medical costs, and maintain the physical status of older patients. Fibroblast growth factor-2 (FGF-2) promotes bone formation; thus, coating pedicle screws with an FGF-2–calcium phosphate (FGF-CP) composite layer is hypothesized to enhance osteointegration in spinal implants. We designed a long-term implantation pilot study that estimated the safety and bone-forming efficacy of pedicle screws coated with an FGF-CP composite layer in cynomolgus monkeys. Titanium alloy screws, either uncoated (controls) or aseptically coated with an FGF-CP composite layer, were implanted in the vertebral bodies of six female adult cynomolgus monkeys (three monkeys per group) for 85 days. Physiological, histological, and radiographic investigations were performed. There were no serious adverse events, and no radiolucent areas were observed around the screws in either group. The bone apposition rate in the intraosseous region was significantly higher in the FGF-CP group than in the controls. Moreover, as analyzed by Weibull plots, the bone formation rate of the FGF-CP group exhibited a significantly higher regression line slope than the control group. These results demonstrated that there was significantly less risk of impaired osteointegration in the FGF-CP group. Our pilot study suggests that FGF-CP-coated implants could promote osteointegration, be safe, and reduce the probability of screw loosening.

Avoiding Spinal Implant Failures in Osteoporotic Patients: A Narrative Review

Article

Full-text available

Apr 2023

Study design: Narrative review. Objectives: With an aging population, the prevalence of osteoporosis is continuously rising. As osseous integrity is crucial for bony fusion and implant stability, previous studies have shown osteoporosis to be associated with an increased risk for implant failure and higher reoperation rates after spine surgery. Thus, our review's purpose was to provide an update of evidence-based solutions in the surgical treatment of osteoporosis patients. Methods: We summarize the existing literature regarding changes associated with decreased bone mineral density (BMD) and resulting biomechanical implications for the spine as well as multidisciplinary treatment strategies to avoid implant failures in osteoporotic patients. Results: Osteoporosis is caused by an uncoupling of the bone remodeling cycle based on an unbalancing of bone resorption and formation and resulting reduced BMD. The reduction in trabecular structure, increased porosity of cancellous bone and decreased cross-linking between trabeculae cause a higher risk of complications after spinal implant-based surgeries. Thus, patients with osteoporosis require special planning considerations, including adequate preoperative evaluation and optimization. Surgical strategies aim towards maximizing screw pull-out strength, toggle resistance, as well as primary and secondary construct stability. Conclusions: As osteoporosis plays a crucial role in the fate of patients undergoing spine surgery, surgeons need to be aware of the specific implications of low BMD. While there still is no consensus on the best course of treatment, multidisciplinary preoperative assessment and adherence to specific surgical principles help reduce the rate of implant-related complications.

Biomechanical investigation of the hybrid modified cortical bone screw–pedicle screw fixation technique: Finite-element analysis

Article

Full-text available

Jul 2022

Background Hybrid fixation techniques including the both modified cortical bone trajectory (MCBT) and traditional trajectory (TT) at the L4 and L5 lumbar segment are firstly proposed by our team. Therefore, the purpose of this study is to evaluate and provide specific biomechanical data of the hybrid fixation techniques including the MCBT and TT. Methods Four human cadaveric specimens were from the anatomy laboratory of Xinjiang Medical University. Four finite-element (FE) models of the L4–L5 lumbar spine were generated. For each of them, four implanted models with the following fixations were established: TT-TT (TT screw at the cranial and caudal level), MCBT-MCBT (MCBT screw at the cranial and caudal level), hybrid MCBT-TT (MCBT screw at the cranial level and TT screw at the caudal level), and TT-MCBT (TT screw at the cranial level and MCBT screw at the caudal level). A 400-N compressive load with 7.5 N/m moments was applied to simulate flexion, extension, lateral bending, and rotation, respectively. The range of motion (ROM) of the L4–L5 segment and the posterior fixation, the von Mises stress of the intervertebral disc, and the posterior fixation were compared. Results Compared to the TT-TT group, the MCBT-TT showed a significant lower ROM of the L4–L5 segment ( p ≤ 0.009), lower ROM of the posterior fixation ( p < 0.001), lower intervertebral disc stress ( p < 0.001), and lower posterior fixation stress ( p ≤ 0.041). TT-MCBT groups showed a significant lower ROM of the L4–L5 segment ( p ≤ 0.012), lower ROM of the posterior fixation ( p < 0.001), lower intervertebral disc stress ( p < 0.001), and lower posterior fixation stress ( p ≤ 0.038). Conclusions The biomechanical properties of the hybrid MCBT-TT and TT-MCBT techniques at the L4–L5 segment are superior to that of stability MCBT-MCBT and TT-TT techniques, and feasibility needs further cadaveric study to verify.

Türk Kadınlarının Yaş Dağılımının Farklı İskelet sistemi T Skor Değişikliklerine etkisi

Article

Full-text available

Apr 2021

Amaç: Osteopeninin hangi vücut kemiğinde ve ne zaman başladığını anlamak ve üreme çağındaki kadınların menopoz dönemine geçişleri sırasında T-skor korelasyonlarının derecesini belirlemek için genç kadınları kapsayan Dual Enerji X-Ray Absorbsiyometri (DXA) çalışmaları yetersizdir. Çalışmamızın amacı farklı yaşlarda femur boynu, femur trokanter, lomber omurgada en düşük T-skoru ve yaş artışı ile korelasyonunu DXA kullanarak değerlendirmektir. Gereç ve Yöntem: Bu retrospektif kohort çalışmasında, İstanbul Eğitim ve Araştırma Hastanesi Kadın Hastalıkları ve Doğum Kliniği'ne başvuran 45-80 yaş arasındaki hastaların DXA sonuçlarını değerlendirdik. kemik mineral yoğunluğu (KMY) ölçümleri DXA cihazı ile anterior-posterior yönde yapıldı. Bulgular: Dört hasta grubunda farklı bölgelerin T-skorları arasında lomber omurga (p=0.025) hariç istatistiksel anlamlı fark bulundu (p<0.005). Tüm yaş gruplarında lomber bölge T-skoru en düşük saptandı. 45-50 ve 51-60 yaşlarında femur trokanter, 61-70 ve 71-80 yaşlarında femur boynu en az osteopeniden etkilenen bölgeler olarak saptandı. Dört yaş grubunda lomber omurga kemik KMY artan yaştan etkilenmemiş saptandı. Öte yandan femur boynu ve ftrokanter bölgelerinde artan yaş ile KMY' da progresif düşüş saptandı. Tartışma: Doğru bir KMY analizi gerçekleştirilmesi için test sınırlaması mevcut olduğunda, belirli bir lokalizasyondaki kemik yoğunluk değerlerlerinden varsayım yapılabileceğini saptadık. Farklı iskelet sistemi bölgelerinin T-skor fark aralıklarının kendi içlerinde yaş ile azalmadığını tespit ettiğimiz ve osteopeniye en duyarlı bölge olduğu için tüm yaş gruplarında öncelikle lomber KMY'nin kontrol edilmesini önermekteyiz. Bu nedenle klinisyenlere önerimiz, özellikle femur ve femur trokanter bölgelerinde yaşla artan KMY dansitesinde progresif azalmaya dikkat etmeleri ve lomber bölgedeki KMY’ nun daha genç yaşlarda azaldığını göz önüne bulundurmalarıdır.

A novel bone cement injector augments Chinese osteoporotic lumbar pedicle screw channel: a biomechanical investigation

Article

Full-text available

Apr 2022
BMC MUSCULOSKEL DIS

Background: The study aimed to (1) create a series of pedicle injectors with different number of holes on the sheath especially for the Chinese elderly patients and (2) further investigate the effects of the injectors on the augmentation of pedicle screw among osteoporotic lumbar pedicle channel. Methods: This study used the biomechanical test module of polyurethane (Pacific Research Laboratory Corp, USA) to simulate the mechanical properties of human osteoporotic cancellous bone. The bone cement injectors were invented based on anatomical parameters of lumbar pedicle in Chinese elderly patients. Mechanical test experiments were performed on the bone cement injectors according to the three groups, namely, a local augmentation group, a full-length augmentation group, and a control group. The local augmentation group included three subgroups including 4-hole group, 6-hole group, and 8-hole group. All holes were laterally placed. The full-length augmentation group was a straight-hole injector. The control group was defined that pedicle screws were inserted without any cement augmentation. Six screws were inserted in each group and the maximum insertion torque was recorded. After 24 h of injecting acrylic bone cement, routine X-ray and CT examinations were performed to evaluate the distribution of bone cement. The axial pull-out force of screws was tested with the help of the material testing system 858 (MTS-858) mechanical tester. Results: The bone cement injectors were consisted of the sheaths and the steel rods and the sheaths had different number of lateral holes. The control group had the lowest maximum insertion torque as compared with the 4-hole, 6-hole, 8-hole, and straight pore groups (P < 0.01), but the differences between the 4-hole, 6-hole, 8-hole, and straight pore groups were no statistical significance. The control group had the lowest maximum axial pull-out force as compared with the other four groups (P < 0.01). Subgroup analysis showed the 8-hole group (161.35 ± 27.17 N) had the lower maximum axial pull-out force as compared with the 4-hole group (217.29 ± 49.68 N), 6-hole group (228.39 ± 57.83 N), and straight pore group (237.55 ± 35.96 N) (P < 0.01). Bone cement was mainly distributed in 1/3 of the distal end of the screw among the 4-hole group, in the middle 1/3 and distal end of the screw among the 6-hole group, in the proximal 1/3 of the screw among the 8-hole group, and along the long axis of the whole screw body in the straight pore group. It might indicate that the 8-hole and straight-hole groups were more vulnerable to spinal canal cement leakage. After pullout, bone cement was also closely connected with the screw without any looseness or fragmentation. Conclusions: The bone cement injectors with different number of holes can be used to augment the pedicle screw channel. The pedicle screw augmented by the 4-hole or 6-hole sheath may have similar effects to the straight pore injector. However, the 8-hole injector may result in relatively lower pull-out strength and the straight pore injector has the risks of cement leakage as well as cement solidarization near the screw head.

The predictive value of psoas and paraspinal muscle parameters measured on MRI for severe cage subsidence after standalone lateral lumbar interbody fusion

Article

Mar 2022
SPINE J

BACKGROUND CONTEXT: The effect of psoas and paraspinal muscle parameters on cage subsidence after minimally invasive techniques, such as standalone lateral lumbar interbody fusion (SA-LLIF), is unknown. PURPOSE: This study aimed to determine whether the functional cross-sectional area (FCSA) of psoas and lumbar spine extensor muscles (multifidus and erector spinae), and psoas FCSA normalized to the vertebral body area (FCSA/VBA) differ among levels with severe cage subsidence after SA-LLIF when compared to levels without severe cage subsidence. STUDY DESIGN: Retrospective single center cohort study. PATIENT SAMPLE: Patients who underwent SA-LLIF between 2008 and 2020 for degenerative conditions using exclusively polyetheretherketone (PEEK) cages, had a lumbar magnetic resonance imaging (MRI) scan within 12 months, a lumbar computed tomography (CT) scan within 6 months prior to surgery, and a postoperative clinical and radiographic follow-up at a minimum of 6 months were included. OUTCOME MEASURES: Severe cage subsidence. METHODS: MRI measurements included psoas and combined multifidus and erector spinae (paraspinal) FCSA and FCSA/VBA at the L3-L5 pedicles. Following manual segmentation of muscles on axial T2-weighted images using ITK-SNAP (version 3.8), the FCSA was calculated using a custom written program on MatlabTM (version R2019a, The MathWorks, Inc.) that used an automated pixel intensity threshold method to differentiate between fat and muscle. Mean volumetric bone mineral density (vBMD) at L1/2 was measured by quantitative CT. The primary endpoint was severe cage subsidence per level according to the classification by Marchi et al. Multivariable logistic regression analysis was performed using generalized linear mixed models. All analyses were stratified by biological sex. RESULTS: 95 patients (45.3% female) with a total of 188 operated levels were included in the analysis. The patient population was 92.6% Caucasian with a median age at surgery of 65 years. Overall subsidence (Grades 0-III) was 49.5% (53/107 levels) in men versus 58.0% (47/81 levels) in women (p = 0.302), and severe subsidence (Grades II-III) was 22.4% (24/107 levels) in men versus 25.9% (21/81 levels) in women (p = 0.608). In men, median psoas FCSA and psoas FCSA/VBA at L3 and L4 were significantly greater in the severe subsidence group when compared to the non-severe subsidence group. No such difference was observed in women. Paraspinal muscle parameters did not differ significantly between non-severe and severe subsidence groups for both sexes. In the multivariable logistic regression analysis with adjustments for vBMD and cage length, psoas FCSA at L3 (OR 1.002; p = 0.020) and psoas FCSA/VBA at L3 (OR 8.655; p = 0.029) and L4 (OR 4.273; p = 0.043) were found to be independent risk factors for severe cage subsidence in men. CONCLUSIONS: Our study demonstrated that greater psoas FCSA at L3 and psoas FCSA/VBA at L3 and L4 were independent risk factors for severe cage subsidence in men after SA-LLIF with PEEK cages. The higher compressive forces the psoas exerts on lumbar segments as a potential stabilizer might explain these findings. Additional pedicle screw fixation might be warranted in these patients to avoid severe cage subsidence.

Comprehensive analysis of pedicle screw implantation in the C7 vertebra using computed tomography-based three-dimensional models

Article

Full-text available

Mar 2022
BMC Surg

Background From a biomechanical point of view, pedicle screws (PS) are better than other kinds of screws for implantation in the seventh cervical vertebra (C7). However, the application of PS is limited because of the high risk of severe complications. It is essential to define the optimal entry point and trajectory. The aim of this study was to comprehensively analyze the starting point and trajectory for C7 PS insertion using three dimensional (3D) models. Methods Overall, 60 subjects aged 18 to 67 years old were included. All CT images were used to construct 3D computer models of the C7 vertebrae. A new coordinate system was established for the next evaluation. The pedicle axis was calculated with respect to the entire pedicle; then, the ideal entry point, screw diameter and length, sagittal angle and lateral angle were assessed. Results All the ideal entry points were located at the medial superior to lateral notch (LN), and the mean distance between the entry point and LN was 5.86 ± 1.67 mm in the horizontal direction and 3.47 ± 1.57 mm in the vertical direction. The mean distance between the entry point and the middle point of the inferior edge of the C6 articular process (MP) was 0.74 ± 1.83 mm in the horizontal direction. The mean sagittal angle of the pedicle axis was 90.42°, and the mean pedicle transverse angle was 30.70°. The average diameter and length of the PS were 6.51 ± 0.76 mm and 31.58 ± 4.40 mm, respectively. Conclusions This study provided a novel method to calculate the ideal starting point and trajectory for C7 PS insertion. These measurements may be helpful for preoperative planning. It is recommended that 3D CT imaging is used preoperatively to carefully evaluate the anatomy of each individual.

The relationship between S1 screw loosening and postoperative outcome in patients with degenerative lumbar scoliosis

Article

Full-text available

Feb 2022
BMC MUSCULOSKEL DIS

Abstract Background When choosing S1 as the lowest level of instrumentation, there are many complications may come out such as S1 screw loosening. Facing this problem, there has been various techniques for the protection of S1 screw including sacropelvic fixation, bicortical or tricortical insertion of S1 screw. Objective This study aimed to explore the risk factors for the S1 screw loosening, then to demonstrate the relationship between S1 screw loosening and postoperative outcome for patients with degenerative lumbar scoliosis (DLS). Methods Patients who underwent lumbosacral fixation for DLS were evaluated retrospectively. They were divided into two groups according to the S1 pedicle screw at the follow-up. Age, gender, bone mineral density, body mass index, history of smoking, the number of instrumented levels, comorbidities, complications and radiological parameters were collected. We established logistic regression analysis to determine independent risk factors for S1 screw loosening and multiple linear regression to identify whether S1 screw loosening would influence postoperative clinical outcome. Results S1 screw loosening rate was up to 41.0% (32/78). Patients were older in the S1 screw loosening group than those in the control group (P

The accuracy and effectiveness of automatic pedicle screw trajectory planning based on computer tomography values: an in vitro osteoporosis model study

Article

Full-text available

Feb 2022
BMC MUSCULOSKEL DIS

Abstract Background Pedicle screw placement in patients with osteoporosis is a serious clinical challenge. The bone mineral density (BMD) of the screw trajectory has been positively correlated with the screw pull-out force, while the computer tomography (CT) value has been linearly correlated with the BMD. The purpose of this study was to establish an in vitro osteoporosis model and verify the accuracy and effectiveness of automated pedicle screw planning software based on CT values in this model. Methods Ten vertebrae (L1-L5) of normal adult pigs were randomly divided into decalcification and control groups. In the decalcification group, the vertebral bodies were decalcified with Ethylenediaminetetraacetic acid (EDTA) to construct an in vitro osteoporosis model. In the decalcification group, automatic planning (AP) and conventional manual planning (MP) were used to plan the pedicle screw trajectory on the left and right sides of the pedicle, respectively, and MP was used on both sides of the control group. CT values of trajectories obtained by the two methods were measured and compared. Then, 3D-printed guide plates were designed to assist pedicle screw placement. Finally, the pull-out force of the trajectory obtained by the two methods was measured. Results After decalcification, the BMD of the vertebra decreased from − 0.03 ± 1.03 to − 3.03 ± 0.29 (P

Craniospinal Surgery in Hajdu-Cheney Syndrome: A Review of Case Reports

Article

Full-text available

Dec 2021

Hajdu-Cheney syndrome (HCS) is a rare metabolic bone disorder that results in severe osteoporosis and various skeletal deformities. Craniospinal pathology is commonly associated with it, but surgical management is challenging due to the distorted anatomy, reduced bone strength, and fusion failure due to osteolysis. Hence, the surgical difficulty in these patients requires careful consideration. In this study, we systematically review all published operative cases and complications to provide a comprehensive review pertaining to the spine and/or cranium in patients with HCS. By highlighting these cases and their associated complications, we aim to prepare practitioners who treat this difficult pathology.

The Accuracy and Effectiveness of Automatic Pedicle Screw Trajectory Planning Based on CT Values: An in Vitro Osteoporosis Model Study.

Preprint

Full-text available

Nov 2021

Background Pedicle screw placement in patients with osteoporosis is a serious clinical challenge. The bone mineral density (BMD) of the screw trajectory has been positively correlated with the screw pull-out force, while the CT value has been linearly correlated with the BMD. The purpose of this study was to establish an in vitro osteoporosis model and verify the accuracy and effectiveness of automated pedicle screw planning software based on CT values in this model. Methods Ten vertebrae (L1-L5) of normal adult pigs were randomly divided into a decalcification group and a control group. In the decalcification group, the vertebral bodies were decalcified with Ethylenediaminetetraacetic acid (EDTA) to construct an in vitro osteoporosis model. In the decalcification group, automatic planning (AP) and conventional manual planning (MP) were used to plan the pedicle screw trajectory on the left and right sides of the pedicle, respectively, and MP was used on both sides of the control group. CT values of trajectories obtained by the two methods were measured and compared. Then, 3D-printed guide plates were designed to assist pedicle screw placement. A biomechanical instrument was used to measure the pull-out force of the trajectory obtained by the two methods. Results After decalcification, the T' value of the vertebral body decreased from -0.03 ± 1.03 to -3.03 ± 0.29 (P <0.05). In the decalcification group, the MP trajectory CT value was 2167.28 ± 65.62 Hu, the AP trajectory CT value was 2723.96 ± 165.83 Hu, and the MP trajectory CT value in the control group was 2242.94 ± 25.80 Hu (P<0.05). In the decalcified vertebrae, the screw pull-out force of the MP group was 48.6% lower than that of the control group (P <0.05). The pull-out force of the AP trajectory was 44.7% higher than that of the MP trajectory (P <0.05) and reached 97.4% of the MP trajectory in the control group (P >0.05). Conclusion Automatic planning of the pedicle screw trajectory based on the CT value can obtain a higher screw pull-out force, which is a valuable new method of pedicle screw placement in osteoporotic vertebral bodies.

Biomechanical Evaluation of Cortical Bone Trajectory Fixation with Traditional Pedicle Screw in the Lumbar Spine: A Finite Element Study

Article

Full-text available

Nov 2021

Cortical bone trajectory (CBT) is increasingly used in spinal surgery. Although there are many biomechanical studies, the biomechanical effect of CBT in combination with traditional pedicle screws is not detailed. Therefore, the purpose of this study was to investigate the effects of the traditional pedicle screw and CBT screw implantation on the lumbar spine using finite element methods. Based on the combination of the traditional pedicle screw and the CBT system implanted into the lumbar spine, four finite element spinal lumbar models were established. The models were given four different load conditions (flexion, extension, lateral bending, and axial rotation), and the deformation and stress distribution on the finite element model were observed. The results show that there was no significant difference in the structural stability of the lumbar spine model between the traditional pedicle screw system and the CBT system. In addition, CBT may reduce stress on the endplate. Different movements performed by the model may have significant biomechanical effects on the spine and screw system. Clinical spinal surgeons may also consider using the CBT system in revision spinal surgery, which may contribute to smaller wounds.

A Novel Bone Cement Injector Augments Osteoporotic Lumbar Pedicle Screw Channel: A Biomechanical Investigation

Preprint

Full-text available

Oct 2021

Background: The study aimed to invent a series of pedicle injectors and investigated the effects of the injectors with different number of holes on the augmentation of pedicle screw using bone cement in osteoporotic lumbar pedicle channel. Methods: This study used the biomechanical test module of polyurethane (Pacific Research Laboratory Corp, USA) to simulate the mechanical properties of human osteoporotic cancellous bone. The bone cement injectors were invented based on anatomical parameters of lumbar pedicle in Chinese. Mechanical test experiments were divided into three groups, namely, a local augmentation group, a full-length augmentation group, and a control group. The local augmentation group included three subgroups including 4 holes, 6 holes, and 8 holes and all holes were laterally placed. The full-length augmentation group was a straight-hole injector. The control group was defined that pedicle screws were inserted without any cement augmentation. Six screws were inserted in each group and the maximum insertion torque was recorded. After 24 hours of injecting acrylic bone cement, routine X-ray and CT examinations were performed to evaluate the distribution of bone cement. The axial pull-out force of screws was tested with the help of the MTS 858 mechanical tester. Results: The bone cement injectors were consisted of the sheaths and the steel-rods and the sheaths had different number of lateral holes. The control group had the lowest maximum insertion torque as compared with the 4-hole, 6-hole, 8-hole, and straight pore groups (P<0.01), but the difference between the 4-hole, 6-hole, 8-hole, and straight pore groups was no statistical significance. The control group had the lowest maximum axial pull-out force as compared with the other four groups (P<0.01). Subgroup analysis showed the 8-hole group (161.35±27.17 N) had the lower maximum axial pull-out force as compared with the 4-hole (217.29±49.68 N), 6-hole (228.39±57.83 N), and straight pore groups (237.55±35.96 N) (P<0.01). Bone cement was mainly distributed in 1/3 of the distal end of the screw among the 4-hole group, in the middle 1/3 and distal end of the screw among the 6-hole group, in the proximal 1/3 of the screw among the 8-hole group, and along the long axis of the whole screw body in the straight pore group. It might indicate that the 8-hole and straight-hole groups were more vulnerable to spinal canal cement leakage. After pullout, bone cement was also closely connected with the screw without any looseness or fragmentation. Conclusions: The bone cement injectors with different number of holes can be used to augment the pedicle screw channel. The pedicle screw augmented by the 4-hole or 6-hole sheath may have similar effects to the straight pore injector. However, the 8-hole injector may result in relatively lower pull-out strength and the straight pore injector has the risks of cement leakage as well as cement solidarization near the screw head.

Prognostic Factors of Surgical Treatment of Lumbar Spondylolithesis

Article

Aug 2021

The Safety and Effectiveness of Automatic Pedicle Screw Trajectory Planning Based on CT Values: An in Vitro Osteoporosis Model Study.

Preprint

Full-text available

Aug 2021

Background Pedicle screw placement in patients with osteoporosis is a serious clinical challenge. The bone mineral density (BMD) of the screw trajectory has been positively correlated with the screw pull-out force, while the CT value has been linearly correlated with the BMD. The purpose of this study was to establish an in vitro osteoporosis model and verify the safety and effectiveness of automated pedicle screw planning software based on CT values in this model. Methods Ten vertebrae (L1-L5) of normal adult pigs were randomly divided into a decalcification group and a control group. In the decalcification group, the vertebral bodies were decalcified with Ethylenediaminetetraacetic acid (EDTA) to construct an in vitro osteoporosis model. In the decalcification group, automatic planning (AP) and manual planning (MP) were used to plan the pedicle screw trajectory on the left and right sides of the pedicle, respectively, and MP was used on both sides of the control group. CT values of trajectories obtained by the two methods were measured and compared. Then, 3D-printed guide plates were designed to assist pedicle screw placement. A biomechanical instrument was used to measure the pull-out force of the trajectory obtained by the two methods. Results After decalcification, the T' value of the vertebral body decreased from -0.03 ± 1.03 to -3.03 ± 0.29 (P <0.05). In the decalcification group, the MP trajectory CT value was 2167.28 ± 65.62 Hu, the AP trajectory CT value was 2723.96 ± 165.83 Hu, and the MP trajectory CT value in the control group was 2242.94 ± 25.80 Hu (P<0.05). In the decalcified vertebrae, the screw pull-out force of the MP group was 48.6% lower than that of the control group (P <0.05). The pull-out force of the AP trajectory was 44.7% higher than that of the MP trajectory (P <0.05) and reached 97.4% of the MP trajectory in the control group (P >0.05). Conclusion Automatic planning of the pedicle screw trajectory based on the CT value can obtain a higher screw pull-out force, which is a valuable new method of pedicle screw placement in osteoporotic vertebral bodies.

Stand-Alone Rod Augmentation for Instrumentation Failure after Pedicle Subtraction Osteotomy: A Case Report with a 2-Year Follow-up

Article

Full-text available

Aug 2021

Background: Revision surgery of spine can be a complex procedure and has known complications. It involves hardware revision, removal of scar/callus tissue, realignment of sagittal balance, and anterior augmentation. However, through this report, we aim to demonstrate that a stand-alone rod augmentation at the failure site without removal of scar/callus tissue and/or anterior fixation can achieve excellent results in select cases. Case Report: A 66-year-old woman underwent L2 pedicle subtraction osteotomy (PSO) + T9-iliac fixation for fixed sagittal imbalance and osteoporotic collapse of L3. One year later, she developed progressive axial lumbar pain and difficulty in mobilization. The patient was diagnosed with pseudoarthrosis and instrumentation failure and underwent revision spine surgery with stand-alone rod augmentation. She had an uneventful rehabilitation and showed complete radiographic union and excellent clinical outcome in the 2-year follow-up. Conclusion: Stand-alone rod augmentation can provide stable posterior construct to prevent future pseudoarthrosis and/or instrumentation failure after revision spine surgery in selected cases. Anterior augmentation or resection dural scar tissue or dissection through callus tissue is not always necessary.

Osteoporosis is Associated with Increased Minor Complications and Pulmonary Embolism Following Single Level ALIF and PSIF Spine Stabilization: An Analysis of 7004 Patients

Article

Full-text available

Aug 2021

Background: Osteoporosis is a prevalent disease that predisposes patients to fracture and additional post-operative complications, potentially contributing to decreased quality of life. The objective of the current study is to (I) characterize the demographic trends of individuals with osteoporosis undergoing single level posterior spine instrumentation and fusion (PSIF) and anterior lumbar interbody fusion (ALIF); (II) determine the association between osteoporosis and postoperative complications; (III) identify whether the use of bone strengthening medications is associated with improved outcomes. Methods: A retrospective review of the Mariner Claims Database was conducted on patients undergoing single level ALIF (CPT 22558) and PSIF (CPT 22840) between 2011 and 2017. Diagnosis of osteoporosis (CPT 77080, CPT 77801, CPT 77082) included a bone density scan within two years of surgery. Patients with osteoporosis were 1:1 matched to controls. Patients taking bone enhancing medications prior to surgery were compared to those that did not take medications. Multivariable logistic regression analyses were performed to evaluate post-operative complication risk factors. Results: 3,502 patients with diagnosed osteoporosis underwent ALIF and PSIF, of which 788 (22.5%) were treated with supplemental medication. Diagnosis of osteoporosis was associated with an increased risk of pulmonary embolism [1.1% vs. 0.4%, odds ratio (OR) 2.48, 95% confidence interval (CI): 1.36-4.53, P=0.003] and minor complications (16.7% vs. 12.9%, OR 1.15, 95% CI: 1.01-1.30, P=0.039). Revision rates two-years post-operatively were not significantly different between patients with osteoporosis and matched controls (P>0.05). There were no differences in outcomes between osteoporotic patients who received medications and those who did not receive medication (P>0.05). Conclusions: Osteoporosis is common in a nationally-representative Medicare database cohort. Pre-operative diagnosis of osteoporosis is associated with increased minor complications following ALIF and PSIF. Pre-operative osteoporosis treatment is not associated with a significant difference in post-operative outcomes. The current study can guide pre-operative counseling in this cohort.

Prevalencia e influencia de la osteoporosis y la deficiencia de vitamina D en pacientes intervenidos de artrodesis vertebral

Thesis

Full-text available

Jun 2021

La osteoporosis (OP) una enfermedad muy frecuente y representa un gran desafío para los cirujanos de columna. Las cirugías de fusión vertebral en pacientes con OP no diagnosticada o tratada se asocian a un aumento de las complicaciones y una deficiente fusión ósea. Actualmente no existen estudios que aborden el diagnóstico de OP con criterios actualizados que integren medición de DMO por DXA, de calidad ósea o microarquitectura por TBS y factores de riesgo para OP mediante el FRAX. Adicionalmente, pesar de contar con tratamientos farmacológicos eficaces para OP e innovaciones en las técnicas quirúrgicas, el conocimiento y concienciación de los cirujanos de columna respecto a la OP parece insuficiente. En la primera parte de nuestro estudio se realizó un estudio transversal con recolección prospectiva en 104 pacientes mayores de 50 años candidatos a cirugía de fusión espinal mediante una evaluación clínica-radiológica completa (DXA, TBS, FRAX) y la medición de niveles séricos de vitamina D. Los resultados principales fueron que la prevalencia de osteoporosis según los criterios de DXA fue del 9,6%, y de osteopenia en el 34,6%. Integrando en el diagnóstico al TBS y FRAX, el 37,5% de pacientes resultaron tener de una deficiente calidad ósea. Además, que un 80% padecieron de hipovitaminosis D. Concluimos que la DXA por sí sola es insuficiente para la identificación preoperatoria de casos de deterioro de la calidad ósea. El FRAX es útil para identificar pacientes de alto riesgo de OP y el TBS es un complemento valioso de la DXA al agregar la dimensión de la calidad ósea. En la segunda parte de nuestro estudio evaluamos los patrones de práctica en el diagnóstico y tratamiento de la OP en los cirujanos de columna. Se realizó una encuesta electrónica de diez preguntas de opción múltiple a cirujanos de columna a nivel nacional (77 participantes) e internacional (122). Los resultados fueron que en el supuesto de los pacientes con sospecha de OP, aproximadamente un tercio de los cirujanos aún no se plantea ninguna medida para diagnosticarla antes de una artrodesis vertebral. Solo la mitad de los encuestados optaría por modificar su estrategia quirúrgica en los pacientes con OP. La técnica quirúrgica preferida en caso de OP fue la colocación de tornillos cementados. En la pseudoartrosis, casi la mitad de cirujanos no considera necesario el diagnóstico de OP para una reintervención. Por otra parte, en las fracturas vertebrales osteoporóticas por compresión (FVC) el 80% de los cirujanos se plantearía alguna medida que facilitaría el tratamiento de la OP. Hubo una mayor concienciación sobre la optimización de la OP en el caso FVC. Existen oportunidades potenciales de mejorar el diagnóstico y tratamiento de la OP en pacientes con cirugía de artrodesis de columna.

Biomechanical performance of bicortical versus pericortical bone trajectory (CBT) pedicle screws

Article

Full-text available

Aug 2021
EUR SPINE J

PurposeThe cortical bone trajectory (CBT) is an alternative to the traditional pedicle screw trajectory (TT) in posterior spinal instrumentation, enhancing screw contact with cortical bone and therefore increasing fixation strength. Additional to the trajectory, insertion depth (pericortical vs. bicortical placement) could be a relevant factor affecting the fixation strength. However, the potential biomechanical benefit of a bicortical placement of CBT screws is unknown. Therefore, the aim of this study was to quantify the fixation strength of pericortical- versus bicortical-CBT (pCBT versus bCBT) screws in a randomized cadaveric study.Methods Pedicle screws were either placed pericortical or bicortical with a CBT in 20 lumbar vertebrae (2 × 20 instrumented pedicles) from four human spine cadavers by using patient-specific templates. Instrumented specimens underwent physiological cyclic loading testing (1′800′000 cycles, 10 Hz), including shear and tension loads as well as bending moments. Translational and angular displacements of the screws were quantified and compared between the two techniques.ResultsThere was a slight decrease in translational (0.2 mm ± 0.09 vs. 0.24 mm ± 0.11) and angular displacements (0.06° ± 0.05 vs. 0.13° ± 0.11) of bCBT screws when compared with pCBT screws after 1′800′000 cycles. However, the results were non-significant (p > 0.05).Conclusion The authors do not recommend placing CBT screws bicortically, as no relevant biomechanical advantage is gained while the potential risk for iatrogenic injury to structures anterior to the spine is increased.

Georg Schmorl Prize of the German Spine Society (DWG) 2020: new biomechanical in vitro test method to determine subsidence risk of vertebral body replacements

Article

Full-text available

May 2021
EUR SPINE J

Purpose Prevention of implant subsidence in osteoporotic (thoraco)lumbar spines is still a major challenge in spinal surgery. In this study, a new biomechanical in vitro test method was developed to simulate patient activities in order to determine the subsidence risk of vertebral body replacements during physiologic loading conditions. Methods The study included 12 (thoraco)lumbar (T11-L1, L2-L4) human specimens. After dorsal stabilisation and corpectomy, vertebral body replacements (VBR) with (a) round centrally located and (b) lateral end pieces with apophyseal support were implanted, equally distributed regarding segment, sex, mean BMD ((a) 64.2 mgCaHA/cm ³ , (b) 66.7 mgCaHA/cm ³ ) and age ((a) 78 years, (b) 73.5 years). The specimens were then subjected to everyday activities ( climbing stairs , tying shoes, lifting 20 kg ) simulated by a custom-made dynamic loading simulator combining corresponding axial loads with flexion–extension and lateral bending movements. They were applied in oscillating waves at 0.5 Hz and raised every 100 cycles phase-shifted to each other by 50 N or 0.25°, respectively. The range of motion (ROM) of the specimens was determined in all three motion planes under pure moments of 3.75 Nm prior to and after implantation as well as subsequently following activities. Simultaneously, subsidence depth was quantified from fluoroscope films. A mixed model (significance level: 0.05) was established to relate subsidence risk to implant geometries and patients’ activities. Results With this new test method, simulating everyday activities provoked clinically relevant subsidence schemes. Generally, severe everyday activities caused deeper subsidence which resulted in increased ROM. Subsidence of lateral end pieces was remarkably less pronounced which was accompanied by a smaller ROM in flexion–extension and higher motion possibilities in axial rotation ( p = 0.05). Conclusion In this study, a new biomechanical test method was developed that simulates physiologic activities to examine implant subsidence. It appears that the highest risk of subsidence occurs most when lifting heavy weights, and into the ventral part of the caudal vertebra. The results indicate that lateral end pieces may better prevent from implant subsidence because of the additional cortical support. Generally, patients that are treated with a VBR should avoid activities that create high loading on the spine.

Vertebral Augmentation for Osteoporotic Vertebral Compression Fractures

Article

Apr 2024
RADIOL CLIN N AM

Microwave Vertebrae Strength Probe Development: Robust and Fast Phase Unwrapping Technique

Article

Mar 2024

We have developed a new transmission-based, open-ended coaxial probe for assessing vertebrae strength during spinal fusion surgery. The approach exploits the fact that the probes are within the far field of each other implying that the phase varies linearly with respect to propagation distance. Determining the absolute phase is critical for recovering the associated tissue dielectric properties from which bone strength will be determined. Unfortunately, unwanted multi-path signals corrupt the signals at the lower end of the operating frequency range from which our conventional unwrapping strategy depends. Our new approach requires only three measurements within the prime frequency range and can be determined robustly with a minimum of computations. This will be vital to developing a commercial device since the signal levels will be extremely low power requiring longer than usual data acquisition times, which will be mitigated by measuring the data at only a few frequencies. Fast and efficient operation will be critical for clinical success.

Temel Spinal Enstrüman Bilgisi

Book

Full-text available

Jul 2023

Türkiye’de Spinal Enstrümantasyonun Tarihi Sait NADERİ Mekanik ve Biyomekaniğin Temelleri Bozkurt Burak ÖZHAN Spinal İmplantların Elemanları Cumhur KILINÇER Lisa FERRARA Metalurji ve Alaşım Bilgisi Enver ATİK Klasik Üretim Yöntemleri Enver ATİK Katmanlı İmalat (Kİ) - Additive Manufacturing (AM) Cüneyt TEMİZ Peyker TEMİZ Cerrahide 3D Printer Destekli İmplant Üretimi ve Kaplama Yöntemleri Hasan Emre AYDIN Deniz AKKAYA Ali ARSLANTAŞ Biyouyumlu Malzemeler ve Mekanik Özellikleri Melis YURDDAŞKAL Hülya DURMUŞ Biyomalzemelerin Karakterizasyonu Hüseyin Erdem YALKIN Patoloji ve Enstruman Biyomekaniği Serdar ÇEVİK Hakan HANIMOĞLU Hakan BOZKUŞ Cerrahi Teknik - Enstruman İlişkisi Ömer AKÇALI Enstrüman, Füzyon, Psödoartroz Burak TAHMAZOĞLU Taha Şükrü KORKMAZ Murat HANCI Osteoporotik Omurga Cerrahisinde Kullanılan İmplantlar Varol AYDIN Kadir KOTİL Geçiş Bölgelerinde Enstrüman Sorunları, Yük Yoğunlaşması ve Proksimal Bileşke Sorunları Seymur NİFTALİYEV Erkan KAPTANOĞLU Spinal Enstrümantasyonda Yetmezlik Mehdi HEKİMOĞLU Ahmet Tulgar BAŞAK Ali Fahir ÖZER Enstrüman Kurgusunun Komplikasyonlarla İlişkisi Muhammed Taha ESER Süleyman Rüştü ÇAYLI Spinal İmplant Teknolojisi : Gelişmeler Cüneyt TEMİZ Peyker TEMİZ Mehmet EMİNOĞLU Ömer Emre YAĞLI Spinal Araştırma Geliştirme, Sertifikasyon ve İnovasyon Süreçleri Cüneyt TEMİZ Mehmet EMİNOĞLU Ömer Emre YAĞLI Burak TÜLÜ Spinal Cerrahide Yeni Teknolojik Gelişmeler; Teletıp, Robotik Sistemler ve Genişletilmiş Gerçeklik-Karma Gerçeklik Macit TERZİ Emre BAHİR METE Murat ZAİMOĞLU Yusuf Şükrü ÇAĞLAR Spinal Cerrahide Enstrümantasyon ile İlgili Hekim Sorumluluğu Serdar IŞIK

Treatment Strategies in the Osteoporotic Spine

Article

Jul 2024
ORTHOP CLIN N AM

Optimization of Pedicle Screw Parameters for Enhancing Implant Stability Based on Finite Element Analysis

Article

Dec 2023

Team Approach: Bone Health Optimization in Orthopaedic Surgery

Article

Dec 2023

» Bone health optimization (BHO) has become an increasingly important consideration in orthopaedic surgery because deterioration of bone tissue and low bone density are associated with poor outcomes after orthopaedic surgeries. » Management of patients with compromised bone health requires numerous healthcare professionals including orthopaedic surgeons, primary care physicians, nutritionists, and metabolic bone specialists in endocrinology, rheumatology, or obstetrics and gynecology. Therefore, achieving optimal bone health before orthopaedic surgery necessitates a collaborative and synchronized effort among healthcare professionals. » Patients with poor bone health are often asymptomatic and may present to the orthopaedic surgeon for reasons other than poor bone health. Therefore, it is imperative to recognize risk factors such as old age, female sex, and low body mass index, which predispose to decreased bone density. » Workup of suspected poor bone health entails bone density evaluation. For patients without dual-energy x-ray absorptiometry (DXA) scan results within the past 2 years, perform DXA scan in all women aged 65 years and older, all men aged 70 years and older, and women younger than 65 years or men younger than 70 years with concurrent risk factors for poor bone health. All women and men presenting with a fracture secondary to low-energy trauma should receive DXA scan and bone health workup; for fractures secondary to high-energy trauma, perform DXA scan and further workup in women aged 65 years and older and men aged 70 years and older. » Failure to recognize and treat poor bone health can result in poor surgical outcomes including implant failure, periprosthetic infection, and nonunion after fracture fixation. However, collaborative healthcare teams can create personalized care plans involving nutritional supplements, antiresorptive or anabolic treatment, and weight-bearing exercise programs, resulting in BHO before surgery. Ultimately, this coordinated approach can enhance the success rate of surgical interventions, minimize complications, and improve patients' overall quality of life.

In vitro fatigue behavior and in vivo osseointegration of the auxetic porous bone screw

Article

Full-text available

Aug 2023
ACTA BIOMATER

The incidence of screw loosening, migration, and pullout caused by the insufficient screw-bone fixation stability is relatively high in clinical practice. To solve this issue, the auxetic unit-based porous bone screw (AS) has been put forward in our previous work. Its favorable auxetic effect can improve the primary screw-bone fixation stability after implantation. However, porous structure affected the fatigue behavior and in vivo longevity of bone screw. In this study, in vitro fatigue behaviors and in vivo osseointegration performance of the re-entrant unit-based titanium auxetic bone screw were studied. The tensile-tensile fatigue behaviors of AS and nonauxetic bone screw (NS) with the same porosity (51%) were compared via fatigue experiments, fracture analysis, and numerical simulation. The in vivo osseointegration of AS and NS were compared via animal experiment and biomechanical analysis. Additionally, the effects of in vivo dynamic tensile loading on the osseointegration of AS and NS were investigated and analyzed. The fatigue strength of AS was approximately 43% lower while its osseointegration performance was better than NS. Under in vivo dynamic tensile loading, the osseointegration of AS and NS both improved significantly, with the maximum increase of approximately 15%. Preferrable osseointegration of AS might compensate for the shortage of fatigue resistance, ensuring its long-term stability in vivo. Adequate auxetic effect and long-term stability of the AS was supposed to provide enough screw-bone fixation stability to overcome the shortages of the solid bone screw, developing the success of surgery and showing significant clinical application prospects in orthopedic surgery.

Peri-operative optimization in adult spinal deformity surgery

Article

Apr 2023
Semin Spine Surg

Study on Auxetic Bone Screw's Good Balance of Osseointegration and Anti-Pullout Stability

Preprint

Jan 2023

Percutaneous Cement-Augmented Screws Short Fixation for the Treatment of Severe Osteoporotic Vertebral Burst Fractures

Article

Apr 2022

Objective (Background) This study aims to evaluate the therapeutic reliability of posterior percutaneous cement-augmented screws short fixation(PASF) in patients with severe osteoporotic vertebral burst fractures(OVBFs). Methods Single-level OVBFs with an anterior vertebral body height(VBH) reduction equal or superior to 60% were included. A frailty index was employed for preoperative frailty assessment. Back pain and related disability were assessed through the VAS scale and Oswestry low-back pain disability index(ODI), being administered at injury time, preoperative, postoperative, twelfth-month and last patient follow-up evaluations. The main radiological outcomes were represented by Cobb angle(CA) and anterior vertebral body compression percentage(AVBC%), being measured at injury time, preoperative, postoperative and twelfth-month examinations. Among the others, the incidence of cement leakages and hardware failures was assessed. Results Thirty-three patients met the inclusion criteria. All patients resulted frail(76%) or semi-frail(24%). Significant VBH restoration and segmental kyphosis improvement after PASF was documented (AVBC%:-40(-43;-37) VS -67(-70;-65), P = 0.0001; CA: 10(8-12) VS 24(23-26), P = 0.0001). The mean VAS and ODI scores documented optimal and long-enduring pain relief and related disability reduction after PASF (VAS: 2(2-3) VS 8(7-8), P = 0.0001; ODI: 22(17-26) VS 64(60-69), P = 0.0001). Only one cement leakage (3%), asymptomatic, occurred. After a mean follow-up of 33 months, no early/late hardware failures were reported. Conclusions The clinical and radiological results of this study suggest that PASF could be a safe and effective treatment option for severe OVBFs when conservative treatments failed.

Metabolic Bone Disease

Chapter

Jan 2017

Investigation on Bending Strength Between Different Designs of Pedicle Screw to Obtain an Optimum Design

Chapter

Jul 2021

Pedicle screw is made from titanium alloy which gives support in the treatment of specific condition like lumbar, acute and chronic instabilities or deformities of thoracic, sacral spine. Mostly, the screw comes with rods act as connector, nuts, sleeves and plates. As a system, it increases the rigidity and holds the bone in placed while the bone heals itself over time. Over the years, many researchers have studied the pullout strength and the bending strength of pedicle screw. They found out that factors like core design, thread design, geometry and insertion techniques influenced the strength in pullout and bending. Failure of a screw is unavoidable. Sometime breakage happened at the neck or at the radial hole of pedicle screw due to high local stress. Thus, this project focused on the finding the most optimize diameter and position of radial in cylindrical screw to increase its bending strength. The pedicle screw inserted 40 mm into cylindrical block as a replacement for real human bone. It was then validated using Ansys software after gone through several simulation until the error become less than 10%. As a validated model, it was modified into pedicle screw with 2 radial holes varied diameter of 1.0 mm, 1.5 mm and 2.0 mm at 3 different position of radial hole. It was given bending moment of 1.29 Nm for starters and increase 0.3 Nm until the pedicle screw reached the yield stress at 790 Mpa. The head fixed at all directions and bending moment applied at tip of pedicle screw. As a result, high stress mostly distributed around the radial holes. All of the proposed designs able to withstand bending moment of 1.29 Nm–2.79 Nm while maintaining its original shape. Unlike the original pedicle screw, it can only resist bending moment at best 2.03 Nm before it broke. Finally, the most optimized diameter and position of radial hole was 1.0 mm at parallel positioned with improvement of 10.75% and 21.51% better than 1.5 mm and 2.0 mm respectively despite any position of radial hole.

Instrumentation Options

Chapter

Jan 2022

Revision lumbar spine surgery can be challenging, with high patient, provider, and socioeconomic burden. Surgeons must accurately identify goals of revision surgery to recognize which instrumentation options may assist in favorable patient outcomes. Various pedicle and pelvic fixation options, rod and crosslink devices, and interbody or corpectomy instrumentation may assist with goals of revision surgery including neural element decompression, solid arthrodesis, and correction of iatrogenic or untreated deformity. Given the quickly expanding profile of instrumentation available to the treating surgeon, a thorough understanding of options is paramount to successful surgical planning.

Impact of preoperative treatment of osteoporosis on re-operations, complications and health care utilization in patients undergoing thoraco-lumbar spine fusions. A 5-year national database analysis

Article

Sep 2021

Objective Identify the impact of preoperative treatment of Osteoporosis (OP) on reoperation rates, complications and healthcare utilization following thoraco-lumbar (TL) spine fusions. Materials and Methods We used ICD9/10 and CPT codes to extract data from MarketScan (2000–2018). Patients were divided into two groups based on preoperative treatment of OP within one year prior to the index spinal fusion: medication (m-OP) cohort and non-medication (nm-OP) cohort. Outcomes (re-operation rates, re-admission, complications, healthcare utilization) were analyzed at 1-, 12-, 24- and 60-months. Results Of 3606 patients, 65% (n = 2330) of patients did not receive OP medications (nm-OP). At index hospitalization, there were no difference in LOS (median nm-OP: 3 days vs. m-OP:4 days), discharge to home (nm-OP 80% vs. m-OP 75%) and complications (nm-OP 13% vs. m-OP 12%). Reoperation rates were not different among the cohorts at 1- (nm-OP 5.7% vs. m-OP 4.2%), 2- (nm-OP 9.4% vs. m-OP 7.8) and 5 years (nm-OP 16.9% vs. m-OP 14.8%). Patients in m-OP cohort incurred higher overall median payments at 1 year ($17,866 vs. $ 16,010), 2 years ($38,634 vs. $34,454) and 5 years ($94,797 vs. $91,072) compared to nm-OP cohort. Conclusion Preoperative treatment of OP had no impact on complications, LOS, discharge disposition following TL fusions at index hospitalization. Similarly, no impact of preoperative treatment was noted in terms of reoperation rates at 12-, 24- and 60 months following the index spine fusion. Patients who received preoperative treatment for OP incurred higher health care utilization at 12-, 24- and 60 months following surgery.

Alternatives to Traditional Pedicle Screws for Posterior Fixation of the Degenerative Lumbar Spine

Article

Jul 2021

Background: Traditional pedicle screws are currently the gold standard to achieve stable 3-column fixation of the degenerative lumbar spine. However, there are cases in which pedicle screw fixation may not be ideal. Due to their starting point lateral to the pars interarticularis, pedicle screws require a relatively wide dissection along with a medialized trajectory directed toward the centrally located neural elements and prevertebral vasculature. In addition, low bone mineral density remains a major risk factor for pedicle screw loosening, pullout, and pseudarthrosis. The purpose of this article is to review the indications, advantages, disadvantages, and complications associated with posterior fixation techniques of the degenerative lumbar spine beyond the traditional pedicle screws. Methods: Comprehensive literature searches of the PubMed, Scopus, and Web of Science databases were performed for 5 methods of posterior spinal fixation, including (1) cortical bone trajectory (CBT) screws, (2) transfacet screws, (3) translaminar screws, (4) spinous process plates, and (5) fusion mass screws and hooks. Articles that had been published between January 1, 1990, and January 1, 2020, were considered. Non-English-language articles and studies involving fixation of the cervical or thoracic spine were excluded from our review. Results: After reviewing over 1,700 articles pertaining to CBT and non-pedicular fixation techniques, a total of 284 articles met our inclusion criteria. CBT and transfacet screws require less-extensive exposure and paraspinal muscle dissection compared with traditional pedicle screws and may therefore reduce blood loss, postoperative pain, and length of hospital stay. In addition, several methods of non-pedicular fixation such as translaminar and fusion mass screws have trajectories that are directed away from or posterior to the spinal canal, potentially decreasing the risk of neurologic injury. CBT, transfacet, and fusion mass screws can also be used as salvage techniques when traditional pedicle screw constructs fail. Conclusions: CBT and non-pedicular fixation may be preferred in certain lumbar degenerative cases, particularly among patients with osteoporosis. Limitations of non-pedicular techniques include their reliance on intact posterior elements and the lack of 3-column fixation of the spine. As a result, transfacet and translaminar screws are infrequently used as the primary method of fixation. CBT, transfacet, and translaminar screws are effective in augmenting interbody fixation and have been shown to significantly improve fusion rates and clinical outcomes compared with stand-alone anterior lumbar interbody fusion. Level of evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Comparison of Percutaneous Kyphoplasty and Pedicle Screw Fixation for Treatment of Thoracolumbar Severe Osteoporotic Vertebral Compression Fracture with Kyphosis

Article

Jun 2021

Background Pedicle screw fixation (PSF) was considered to be the preferred surgery for treatment of severe osteoporotic vertebral compression fracture (sOVCF), while sOVCF was traditionally regarded as a relative contraindication to minimally invasive percutaneous kyphoplasty (PKP). Debate continues on the selection of surgical methods for sOVCF. This study aimed to compare the efficacy and safety between PKP and PSF. Methods PKP was carried out in 376 patients in Group 1, and 121 underwent PSF in Group 2. Visual analogue scale (VAS), Oswestry Disability Index (ODI), local kyphotic angle (LKA), fractured vertebral body height (FVBH) and complications were evaluated. Results In the immediate postoperative analysis, the mean VAS in Group 1 was 2.4 that was significantly lower than 4.7 in Group 2; the mean ODI score was 44.4 in Group 1 that was lower than 57.1 in Group 2. Besides, the patients in Group 1 acquired significantly better ODI score at 1-year follow-up. The LKA and FVBH were better recovered in Group 2. In Group 1, 113 patients showed cement leakage; 29 patients underwent PKP for adjacent new vertebral fractures. In Group 2, two patients suffered from wound infections, four pneumonia, two urinary tract infection, three asymptomatic screws loosening, seven undergoing PKP to treat new vertebral fractures and one removal of internal fixation due to back pain. Conclusions Based on clinical and radiological evaluations, PKP was comparable to PSF for treatment of sOVCF with kyphosis, while PKP has the advantages of minimal invasion, quick post-operative pain relief and functional recovery.

Pullout Strength of Pedicle Screws using Cadaveric Vertebrae with or without Artificial Demineralization

Article

Apr 2021
SPINE J

OBJECTIVES To evaluate the differences in the pullout strength and displacement of pedicle screws in cadaveric thoracolumbar vertebrae with or without artificial demineralization. METHODS Five human lumbar and 5 thoracic vertebrae from one cadaver were divided into two hemivertebrae. The left-side specimens were included in the simulated osteopenic model group and the right-side bones in a control group. In the model group, we immersed each specimen in HCl (1 N) solution for 40 min. We measured bone mineral density (BMD) using dual-energy X-ray absorptiometry and quantitative computerized tomography. We inserted polyaxial pedicle screws into the 10 pedicles of the cadaveric lumbar spine after measuring the BMD of the 2 hemivertebrae of each specimen. We measured the pullout strength and displacement of the screws before failure in each specimen using an Instron system. RESULTS The average pullout strength of the simulated osteopenic model group was 76% that of the control group. In the control and model groups, the pullout strength was 1678.87 ± 358.96 N and 1283.83 ± 341.97 N, respectively, and the displacement was 2.07 ± 0.34 mm and 2.65 ± 0.50 mm, respectively (P < 0.05). We detected positive correlations between pullout strength and BMD in the control group and observed a negative correlation between displacement and BMD in the model group. CONCLUSION By providing an anatomically symmetric counterpart, the human cadaveric model with or without demineralization can be used as a test bed for pullout tests of the spine. In the simulated osteopenic model group, pullout strength was significantly decreased compared with the untreated control group. CLINICAL SIGNIFICANCE Decreased bone mineral density may significantly reduce the pullout strength of a pedicle screw, even though the range is osteopenic rather than osoteoporotic.

Low-Dose MDCT of Patients With Spinal Instrumentation Using Sparse Sampling: Impact on Metal Artifacts

Article

Mar 2021

OBJECTIVE. The purpose of our study was to evaluate simulated sparse-sampled MDCT combined with statistical iterative reconstruction (SIR) for low-dose imaging of patients with spinal instrumentation. MATERIALS AND METHODS. Thirty-eight patients with implanted hardware after spinal instrumentation (24 patients with short- or long-term instrumentation-related complications [i.e., adjacent segment disease, screw loosening or implant failure, or postoperative hematoma or seroma] and 14 control subjects with no complications) underwent MDCT. Scans were simulated as if they were performed with 50% (P50), 25% (P25), 10% (P10), and 5% (P5) of the projections of the original acquisition using an in-house-developed SIR algorithm for advanced image reconstructions. Two readers performed qualitative image evaluations of overall image quality and artifacts, image contrast, inspection of the spinal canal, and diagnostic confidence (1 = high, 2 = medium, and 3 = low confidence). RESULTS. Although overall image quality decreased and artifacts increased with reductions in the number of projections, all complications were detected by both readers when 100% of the projections of the original acquisition (P100), P50, and P25 imaging data were used. For P25 data, diagnostic confidence was still high (mean score ± SD: reader 1, 1.2 ± 0.4; reader 2, 1.3 ± 0.5), and interreader agreement was substantial to almost perfect (weighted Cohen κ = 0.787-0.855). The mean volumetric CT dose index was 3.2 mGy for P25 data in comparison with 12.6 mGy for the original acquisition (P100 data). CONCLUSION. The use of sparse sampling and SIR for low-dose MDCT in patients with spinal instrumentation facilitated considerable reductions in radiation exposure. The use of P25 data with SIR resulted in no missed complications related to spinal instrumentation and allowed high diagnostic confidence, so using only 25% of the projections is probably enough for accurate and confident diagnostic detection of major instrumentation-related complications.

The Effect of Risedronate on Posterior Lateral Spinal Fusion in a Rat Model

Article

Full-text available

Aug 2009

To evaluate the potential effects of risedronate (RIS) which shows a higher anti-resorptive effect among bisphosphonates, after a posterolateral lumbar intertransverse process spinal fusion using both autograft and allograft in a rat model. A totoal of 28 Sprague-Dawley rats were randomized into 2 study groups. A posterolateral lumbar intertransverse process spinal fusion was peformed using both autograft and allograft in a rat model. Group I (control) received 0.1 mL of steril saline (placebo) and Group II (treatment) received risedronate, equivalent to human dose (10 microg/kg/week) for 10-weeks period. The fusion rates as determined by manual palpation were 69% in the group I and 46% in the group II (p = 0.251). According to radiographic score, the spinal segment was considered to be fused radiographically in 7 (53%) of the 13 controls and 9 (69%) of the 13 rats treated with RIS (p = 0.851). The mean histological scores were 5.69 +/- 0.13 and 3.84 +/- 0.43 for the control and treatment groups, respectively. There was a significant difference between the both groups (p = 0.001). The mean bone density of the fusion masses was 86.9 +/- 2.34 in the control group and 106.0 +/- 3.54 in the RIS treatment group. There was a statistical difference in mean bone densities of the fusion masses comparing the two groups (p = 0.001). In this study, risedronate appears to delay bone fusion in a rat model. This occurs as a result of uncoupling the balanced osteoclastic and osteoblastic activity inherent to bone healing. These findings suggest that a discontinuation of risedronate postoperatively during acute fusion period may be warranted.

An Experimental Study of a Combination Method Using a Pedicle Screw and Laminar Hook for the Osteoporotic Spine

Article

Full-text available

Jun 1997

Using human cadaver spines, the authors compared the effect of using a combination of pedicle screw and laminar hook on the same vertebra with that of using a pedicle screw alone in reference to bone mineral density of the vertebra under nondestructive cyclic loading. To quantify stiffness obtained by pedicle screw alone and by the combination method and to clarify a relationship between stiffness obtained by each instrumentation method and bone mineral density of the vertebra. The use of pedicle screws apparently improves the union rate of spinal fusion. Instrumentation failures sometimes occur, however, such as loosening or loss of correction of the spine, especially in patients with osteoporosis. Some augmentation method in instrumentation is necessary to overcome bone fragility in the osteoporotic spine. Thirteen cadaver lumbar vertebrae were used for this study. Bone mineral density was measured by dual-energy X-ray absorptiometer. After separating each vertebrae, the pedicle screw was screwed into a vertebra. Five cycles of cephalocaudal loading were performed to the shank of the screw with a cross-head speed of 3 mm/min under a maximum load control of 29.4 N using an Instron type testing machine, and the stiffness obtained with the pedicle screw (Kj) was calculated from the load-deformation curve. Then, a laminar hook was set and connected to the screw via a rod. Mechanical testing was performed in the same way, and the stiffness obtained with the combination method (Kf) was determined. Kj and Kf were compared using the paired t test. The relationship between Kj, Kf, or the stiffness improvement ratio ([Kf-Kj]/Kj) by the combination method and bone mineral density was analyzed by linear regression analysis. Stiffness obtained by the combination method was significantly greater than that obtained by pedicle screw alone (89.8 +/- 35.0 N/mm by the combination method, 60.2 +/- 19.6 N/mm by pedicle screwing alone; P < 0.0001). Stiffness, whether obtained by pedicle screw alone or by the combination method, was positively correlated with bone mineral density (with pedicle screw alone, R2 = 0.614, P < 0.0001; with the combination method, R2 = 0.645, P < 0.0001). However, there was no significant correlation between stiffness improvement ratio and bone mineral density. Instrumentation stiffness obtained by the combination method was significantly greater than that obtained by the use of pedicle screw alone. There was no significant correlation between the improvement ratio by the combination method and bone mineral density. These results suggest that the combination method is valuable irrespective of the presence of spinal osteoporosis.

Compressive strength of interbody cages in the lumbar spine: The effect of cage shape, posterior instrumentation and bone density

Article

Full-text available

Feb 1998

One goal of interbody fusion is to increase the height of the degenerated disc space. Interbody cages in particular have been promoted with the claim that they can maintain the disc space better than other methods. There are many factors that can affect the disc height maintenance, including graft or cage design, the quality of the surrounding bone and the presence of supplementary posterior fixation. The present study is an in vitro biomechanical investigation of the compressive behaviour of three different interbody cage designs in a human cadaveric model. The effect of bone density and posterior instrumentation were assessed. Thirty-six lumbar functional spinal units were instrumented with one of three interbody cages: (1) a porous titanium implant with endplate fit (Stratec), (2) a porous, rectangular carbon-fibre implant (Brantigan) and (3) a porous, cylindrical threaded implant (Ray). Posterior instrumentation (USS) was applied to half of the specimens. All specimens were subjected to axial compression displacement until failure. Correlations between both the failure load and the load at 3 mm displacement with the bone density measurements were observed. Neither the cage design nor the presence of posterior instrumentation had a significant effect on the failure load. The loads at 3 mm were slightly less for the Stratec cage, implying lower axial stiffness, but were not different with posterior instrumentation. The large range of observed failure loads overlaps the potential in vivo compressive loads, implying that failure of the bone-implant interface may occur clinically. Preoperative measurements of bone density may be an effective tool to predict settling around interbody cages.

Improved extraction torque of hydroxyapatite-coated pedicle screws

Article

Full-text available

Dec 2000

Loosening of the screws is a problem in instrumentation with pedicle screws. Coating with hydroxyapatite improves the holding characteristics for metal implants, but the possible effects on the anchorage of pedicle screws have not been described. In this study, seven patients were operated on with spinal instrumentation using four stainless steel pedicle screws. Hydroxyapatite-coated screws were used in either the upper or the lower of the instrumented levels. The insertion torque was measured. In four cases the screws were removed after 10-22 months and the extraction torque was measured. The mean insertion torque was found to be significantly greater in the hydroxyapatite-coated screws (107 Ncm) than in the standard screws (76 Ncm). In three cases, the extraction torque for the hydroxyapatite-coated screws exceeded the range for the torque wrench (600 Ncm), while the conventional screws were loose (< 5 Ncm). In one case, the extraction torque was 475 and 550 Ncm for the coated screws, and 5 and 25 Ncm for the conventional screws. The difference in extraction torque was significant. Hydroxyapatite coating was shown to have improved the purchase of pedicle screws very effectively. By using fully coated screws, as in the present study, extraction was extremely difficult compared to extraction of conventional stainless steel screws, which were regularly loose. By reducing the area of the screws that is coated, it may be possible to achieve an enhanced purchase while extraction will be easier when compared to fully coated screws.

Effect of Parathyroid Hormone (1-34) on Fractures and Bone Mineral Density in Postmenopausal Women with Osteoporosis

Article

Full-text available

Jun 2001

Once-daily injections of parathyroid hormone or its amino-terminal fragments increase bone formation and bone mass without causing hypercalcemia, but their effects on fractures are unknown. We randomly assigned 1637 postmenopausal women with prior vertebral fractures to receive 20 or 40 microg of parathyroid hormone (1-34) or placebo, administered subcutaneously by the women daily. We obtained vertebral radiographs at base line and at the end of the study (median duration of observation, 21 months) and performed serial measurements of bone mass by dual-energy x-ray absorptiometry. New vertebral fractures occurred in 14 percent of the women in the placebo group and in 5 percent and 4 percent, respectively, of the women in the 20-microg and 40-microg parathyroid hormone groups; the respective relative risks of fracture in the 20-microg and 40-microg groups, as compared with the placebo group, were 0.35 and 0.31 (95 percent confidence intervals, 0.22 to 0.55 and 0.19 to 0.50). New nonvertebral fragility fractures occurred in 6 percent of the women in the placebo group and in 3 percent of those in each parathyroid hormone group (relative risk, 0.47 and 0.46, respectively [95 percent confidence intervals, 0.25 to 0.88 and 0.25 to 0.861). As compared with placebo, the 20-microg and 40-microg doses of parathyroid hormone increased bone mineral density by 9 and 13 more percentage points in the lumbar spine and by 3 and 6 more percentage points in the femoral neck; the 40-microg dose decreased bone mineral density at the shaft of the radius by 2 more percentage points. Both doses increased total-body bone mineral by 2 to 4 more percentage points than did placebo. Parathyroid hormone had only minor side effects (occasional nausea and headache). Treatment of postmenopausal osteoporosis with parathyroid hormone (1-34) decreases the risk of vertebral and nonvertebral fractures; increases vertebral, femoral, and total-body bone mineral density; and is well tolerated. The 40-microg dose increased bone mineral density more than the 20-microg dose but had similar effects on the risk of fracture and was more likely to have side effects.

Hydroxyapatite coating improves fixation of pedicle screws - A clinical study

Article

Full-text available

May 2002

We investigated the effects of hydroxyapatite (HA) coating on the purchase of pedicle screws. A total of 23 consecutive patients undergoing lumbar fusion was randomly assigned to one of three treatment groups. The first received uncoated stainless-steel screws, the second screws which were partly coated with HA, and the third screws which were fully coated. The insertion torque was recorded. After 11 to 16 months, 21 screws had been extracted. The extraction torque was recorded. Radiographs were taken to assess fusion and to detect loosening of the screws. At removal, the extraction torques exceeded the upper limit of the torque wrench (600 Ncm) for many HA-coated screws. The calculated mean extraction torque was 29 +/- 36 Ncm for the uncoated group, 447 +/- 114 Ncm for the partly-coated group and 574 +/- 52 Ncm for the fully-coated group. There were significant differences between all three groups (p < 0.001). There were more radiolucent zones surrounding the uncoated screws than the HA-coated screws (p < 0.001). HA coating of pedicle screws resulted in improved fixation with reduced risk of loosening of the screws.

Clinical practice. Postmenopausal osteoporosis

Article

Jan 2016

Factors affecting the pullout strength of self-drilling and self-tapping anterior cervical screws

Article

Jan 2003

Study design. A biomechanical comparison of 12-, 14-, and 16-mm self-tapping and self-drilling screws in cadaveric cervical spines was performed. Objective. This study compared self-drilling and self-taping screw designs used in anterior cervical locking plates in terms of insertion torque and pullout strength. In addition to screw design, the effects to screw length (12, 14, and 16 mm) and bone mineral density were examined. Methods. A total of 201 screws were implanted and tested. Nineteen cadaver spine specimens (C2 through C7) were radiographed and their bone mineral density measured. In each vertebral level, two screws of the same length were implanted and their insertion torque measured. One of each screw design (self-drilling or self-tapping) was randomly placed in each vertebra for side-by-side comparison. Vertebrae then were individually potted and mounted on an MTS machine for accurate measurement of maximum pullout strength. Results. Pullout strength was strongly related to screw length (P=0.0002). There was no significant difference in pullout strength between the self-drilling and self-tapping screw designs at any length (P=0.9352). A significant correlation (Pless than or equal to0.0077) exists between insertion torque and bone mineral density for the self-drilling and self-tapping 14- and 16-mm screws. A significant correlation exists between pullout strength and bone mineral density for 14- and 16-mm screw lengths of both screw types. (P<0.001). Conclusions. It would appear that the longest screw feasible should always be used clinically for maximum pullout strength. There is no difference in pullout strength between self-drilling and self-tapping screws. Bone mineral density significantly influences screw performance.

Osteoporosis prevention, diagnosis, and therapy

Article

Jan 2001

Surgical Anatomy of the Sacrum

Article

Jun 1991

Anterior sacral anatomy was studied to allow safe sacral screw placement. The study included 27 bony sacra. Intrapelvic dissections were performed. Cadaveric specimens were dissected and photographed. The position and angulation of the first sacral foramen was extremely variable. After the position of the L5 root, sacral roots, and iliac vessels, was considered, safe posterior sacral screw implantation could be assured through placement above the level of the first sacral foramen directed medially toward the promontory, parallel to the superior sacral end-plate. Complications of indiscriminate screw placement included L5-root damage, iliac vein penetration, and intractable perineal pain due to sacral root injury. Preoperative computed tomography with the scanner gantry tilted to parallel the superior sacral end-plate defined the great vessels, neural foramens, inclination of the superior sacral end-plate, and prominence of the posterior ileum. Surgical accuracy was evaluated after surgery with computed tomography.

Internal Fixation in the Osteoporotic Spine

Article

Dec 1997

Serena S Hu

The presence of osteoporosis in patients who are candidates for spinal surgery can affect preoperative planning. These patients may not need instrumentation for a successful surgical result, but if use of instrumentation is indicated because of instability or deformity, certain principles should be observed. These include using multiple sites of fixation, accepting lesser degrees of deformity correction, and avoiding ending the instrumentation within kyphotic segments. Advances in perioperative medical management, as well as improved instrumentation systems, may also contribute to improving patient outcomes.

Future Directions

Article

Dec 1997

Because current medical and surgical treatments of vertebral body fractures are less than adequate, there is a need for interventions that decrease the likelihood of occurrence of these fractures and improve the treatment options once they have occurred. One such broad category of intervention involves the fortification or augmentation of the vertebral bodies. In addition to prophylactically stabilizing osteoporotic vertebral bodies at risk for fracture, augmentation of vertebral bodies that have already fractured may prove to be useful by reducing pain, improving function, and preventing further collapse and deformity. Vertebral body augmentation can also be used as an adjunct to fixation of internal hardware‐for example, pedicle screws‐in osteoporotic spines. A number of products are now available or are in clinical trials. The most promising products are injectable materials‐polymethylmethacrylate or mineral bone cement. The early clinical results using polymethylmethacrylate in percutaneous vertebroplasty for fractured vertebral bodies and the results in vitro using an injectable mineral cement for vertebral body fortification are encouraging. Although the principle of vertebral body augmentation remains encouraging, data to support the widespread use of these techniques remain sparse, and the indications for their use should be more clearly defined.

Anterior Vertebral Body Screw Pullout Testing

Article

Apr 1998

Study Design. A biomechanical study of pullout of anteriorly implanted screws in cadaveric vertebral bodies. Objectives. To investigate and compare the pullout strength of the Zielke, Kaneda, Universal Spine System (USS) pedicle screw, and USS pedicle screw with a new pullout‐resistant nut. Summary of Background Data. A common problem with anterior purchase regardless of the implant system is screw pullout at the proximal and distal ends of multilevel constructs. There is limited information on a solution to this problem. Methods. The L1 to L4 vertebral bodies from four cadavers had one each of Zielke and Kaneda pedicle screws (Acromed Corp., Cleveland, OH), USS pedicle screw (Synthes Spine, Paoli, PA), and USS pedicle screw with pullout‐resistant nut implanted transversely across the center of the vertebral body with bicortical purchase in a similar fashion as would be used clinically. The screws were extracted using a servohydraulic material testing system. The maximum axial forces were recorded. Results. The Zielke and Kaneda screws had no significant difference in mean pullout strength (P = 0.542). The USS screw alone was less strong (P = 0.009). The USS screw and pullout‐resistant nut increased the pullout strength by twofold (P = 0.00006). In the screw pullout tests, the mode of failure was at the screw thread's interface. The USS screw and pullout‐resistant nut failed by imploding the body around the nut. With the USS screw and pullout‐resistant nut, the pullout strength was determined by the compressive strength of the bone. Conclusions. The addition of a pullout‐resistant nut to an anterior vertebral body screw improves the pullout strength by twofold and changes the mode of failure to rely ultimately on the inherent vertebral body strength rather than the screw's characteristics. The addition of a pullout‐resistant nut may be applicable to multilevel implant constructs to prevent screw pullout at the top and bottom.

Lumbosacral fixation using expandable pedicle screws

Article

Mar 2001
SPINE J

Background context: Pedicle screw fixation in osteoporotic bone and in revision of previous pedicle screw fixation cases presents a significant challenge to spine surgeons. Biomechanical tests have shown that a pedicle screw that expands within the vertebrae body can substantially improve fixation in the presence of compromised bone.Purpose: To review the clinical and radiographic results with the use of expandable pedicle screws.Study design: One hundred forty-five patients received one or more expandable pedicle screws from the Omega21 spinal fixation system (EBI, L.P., Parsippany, NJ) to obtain thorocolumbar or lumbosacral stabilization.Patient sample: The indications for use of the expandable screws were osteoporosis (21 cases), reoperation of previous pedicle instrumentation (27 cases), intraoperative screw relocation (17 cases), construct reinforcement (23 cases), and sacral anchoring to avoid the necessity of anterior penetration of the sacral cortex (57 cases).Outcome measures: The presence of radiographic fusion and complications arising from the instrumentation were reviewed at a mean follow-up period of 35 months (range, 24–72 months).Methods: A retrospective clinical and radiographic review was performed. Fusion was evaluated based on anterior-posterior and lateral radiographs as well as dynamic radiographs in flexion and extension.Results: Radiographic evidence of fusion was obtained in 125 of the 145 cases (86%). Eighty-six percent of patients with osteoporosis and 89% of reoperations fused. There were no instances of screw loosening or pullout of the expandable screws. Screw breakage occurred in four patients (2.8%), including three patients where fusion was not obtained. In six patients the expandable screws were removed without difficulty after fusion because of local discomfort.Conclusion: The results of this study have shown that expandable pedicle screws can be efficacious in cases in which pedicle screw fixation is difficult and adds a valuable tool to the growing armamentarium of spinal instrumentation.

Effect of Endplate Conditions and Bone Mineral Density on the Compressive Strength of the Graft–Endplate Interface in Anterior Cervical Spine Fusion

Article

Apr 2001

Study Design. Destructive compression tests and finite element analyses were conducted to investigate the biomechanical strength at the graft–endplate interface in anterior cervical fusion. Objectives. To investigate the effect of endplate thickness, endplate holes, and bone mineral density of the vertebral body on the biomechanical strength of the endplate–graft interface in an anterior interbody fusion of the cervical spine. Summary of Background. Subsidence of the graft into the vertebral body is a well-known complication in anterior cervical fusion. However, there is no information in the literature regarding the compressive strength of the graft–endplate interface in relation to the endplate thickness, holes in the endplate, and bone mineral density of the vertebral body. Methods. Biomechanical destructive compression tests and finite element analyses were performed in this study. Cervical vertebral bodies (C3–C7) isolated from seven cadaveric cervical spines (age at death 69–86 years, mean 79 years) were used for compression tests. Bone mineral density of each vertebral body was measured using a dual energy radiograph absorptiometry unit. Endplate thickness was measured using three coronal computed tomography images of the middle portion of the vertebral body obtained using a computer-assisted imaging analysis. Then each vertebral body was cut into halves through the horizontal plane. A total of 54 specimens, consisting of one endplate and half of the vertebral body, were obtained after excluding eight vertebrae with gross pathology on plain radiograph. Specimens were assigned to one of three groups with different endplate conditions (Group I, intact; Group II, partial removal; and Group III, complete removal) so that group mean bone mineral density became similar. Each endplate was slowly compressed until failure using an 8-mm-diameter metal indenter, and the load to failure was determined as a maximum force on a recorded force–displacement curve. The effect on the strength of the graft–endplate interface of various hole patterns in the endplate was studied using a finite element technique. The simulatedhole patterns included the following: one large central hole, two lateral holes, two holes in the anterior and posterior portion of the endplate, and four holes evenly distributed from the center of the endplate. Stress distribution in the endplate was predicted in response to an axial compressive force of 110 N, and the elements with von Mises stress greater than 4.0 MPa were determined as failed. Results. The endplate thickness and bone mineral density were similar at all cervical levels, and the superior and inferior endplates had similar thickness at all cervical levels. There was no significant association between bone mineral density and endplate thickness. Load to failure was found to have a significant association with bone mineral density but not with endplate thickness. However, load to failure tends to decrease with incremental removal of the endplate, and load to failure of the specimens with an intact endplate was significantly greater than that of the specimens with no endplate. Finite element model predictions showed significant influence of the hole pattern on the fraction of the upper endplate exposed to fracture stress. A large hole was predicted to be more effective than the other patterns at distributing a compressive load across the remaining area and thus minimizing the potential fracture area. Conclusion. Results of this study suggest that it is important to preserve the endplate as much as possible to prevent graft subsidence into the vertebral body, particularly in patients with poor bone quality. It is preferable to make one central hole rather than multiple smaller holes in the endplate for vascularity of the bone graft because it reduces the surface area exposed to fracture stresses.

Augmented pin fixation with Cortoss® for an unstable AO-A3 type distal radius fracture in a patient with a manifest osteoporosis

Article

Sep 2008

Distal radius fractures are one of the most common fractures in the elderly females. In this article, we report a case of a distal radius fracture type AO-A3 with dorsal instability, in an older woman with manifest osteoporosis, treated with minimally invasive Cortoss composite and FFS-wires(R). A 63-year-old woman sustained an unstable distal radial fracture of her left wrist after falling from a kitchen step. She underwent an open reduction of the fracture and fixation with two crossed-fixation pins and Cortoss composite. Post-operative plaster cast immobilization was given for 2 weeks, after which the plaster cast and the fixation pins were removed. At 4 weeks follow-up, she had a good functional result of her left wrist, after 11 months there was a complete return of grip strength with also, except for the palmar flexion, a full return of function. We report here the first case of a successful surgical treatment with Cortoss composite of an AO-A3 type distal radius fracture.

Effect of Teriparatide [rhPTH(1,34)] and Calcitonin on Intertransverse Process Fusion in a Rabbit Model

Article

Jan 2010
SPINE

Randomized, double-blinded, placebo controlled animal study. To evaluate the effect of teriparatide and calcitonin after an intertransverse process spinal fusion in a rabbit model. It is widely recognized that some osteoporosis medications, including bisphosphonates, can interfere with bone healing. Although prescribed frequently in the treatment of osteoporosis, the effect of teriparatide and calcitonin on spinal fusion has not been fully elucidated. We hypothesized that teriparatide, being the only anabolic medication for osteoporosis treatment, would have a beneficial effect on spine fusion. Fifty-one New Zealand white rabbits underwent a posterolateral L5-L6 intertransverse process arthrodesis using autogenous iliac crest bone graft. The rabbits were randomly divided into 3 groups. All animals received daily subcutaneous injections of group I (n = 17) 1 mL of saline placebo; group II (n = 17) 10 microg/kg/day of teriparatide; group III (n = 17) 14 IU/animal of calcitonin during the 8-week postoperative period. Postmortem analyses included manual palpation, radiographic, biomechanical, and histologic assessment. Three random 10x fields were examined/graded within the cephalad, middle, and caudal regions of each section (810 fields). Fusion quality was graded using the Emery histologic scale (0-7 based on fibrous/bone content of the fusion mass). Histologic fusion rates for teriparatide averaged 86.7% and was significantly greater than the autograft control group (50%) (P = 0.033). Radiographically, there was a strong trend towards teriparatide being superior to the calcitonin group (85.7% vs. 56.3%, respectively; P = 0.07). The average Emery grading score was 5.99 +/- 1.46 SD for the autologous group and 6.26 +/- 0.93 SD for the teriparatide group (P = 0.031). Although not significant, the teriparatide group showed less motion in flexion/extension, lateral bending, and axial rotation. Our results suggest that teriparatide enhances spinal fusion while calcitonin has a neutral effect. The teriparatide group had the best histologic fusion rate and Emery scores, while the calcitonin group was similar to the saline controls. Although not significant, the teriparatide group had a strong trend towards superior radiographic fusion over the calcitonin group.

Robotic Approaches to the Posterior Spine

Article

Oct 2009
SPINE

This anatomic study described robotic approaches to the posterior thoracolumbar spine in a porcine model. Ergonomics, control, and approach and technical difficulties were noted. The objective of this study was to develop a robotic approach to the posterior thoracolumbar spine maximizing surgeon ergonomics and control. Surgery is both physically and mentally demanding, and strains from ergonomics and the aging process may negatively impact surgical skills. In spine surgery, control and precision are extremely important due to the close proximity to the spinal cord. The da Vinci robotic surgery system has offered better ergonomics and control in urology, gynecology, and cardiac surgery, and is rapidly gaining adoption. To date, there have been no published reports of da Vinci robotic spine surgery, motivating us to assess its potential in posterior spine surgery. Posterior spine da Vinci approaches were tested on a pig without spinal pathology with an open subperiosteal dissection. A laser instrument and prototype robotic burr and rongeur instruments were tested on laminotomy, laminectomy, disc incision, and dural suturing procedures. Open dissection of the posterior spine provided sufficient access to successfully perform laminotomy, laminectomy, disc incision, and dural suturing procedures. Prototype burr and rongeur instruments were effective with good control. The laser instrument coagulated the epidural venous plexus and incised the anulus. Robot ergonomics allowed the surgeon to perform procedures for a full day with significantly less fatigue and reduced hand tremor. The da Vinci could perform the major noninstrumented procedures of the posterior spine with improved ergonomics and control. Surgeon fatigue and tremor were reduced. With some modification of prototype and commercial instruments a posterior spine surgery instrument kit can be developed. Future clinical studies can better assess patient and surgeon benefits of using the da Vinci robot for posterior spine surgeries.

The Pedicle Screw Fixation With Vertebroplasty Augmentation in the Surgical Treatment of the Severe Osteoporotic Spines

Article

Sep 2009

Retrospective clinical study. To present the early clinical results of pedicle screw fixation augmented by vertebroplasty using polymethylmethacrylate in severely osteoporotic patients requiring spine surgery due to the neurologic deficit. It is postulated that combining a formal vertebroplasty-that is, maximum filling of the trabecular space with polymethylmethacrylate-with pedicle screw placement in osteoporotic vertebrae could result in resistance to pullout forces significantly. Between the years 2003 and 2006, pedicle screw placement with vertebroplasty augmentation was performed in 49 patients who had severe osteoporosis and who required spine surgery due to neurologic deficit. Eleven patients with less than 2 years of follow-up and 2 patients who died from unrelated illness were excluded from the study. Thirty-six of 49 patients having minimum 2 years of follow-up were included. Cement augmentation was also performed in segments proximal and distal to instrumentation to prevent junctional segment fractures. Early and late postoperative complications were recorded during follow-up. The mean postoperative follow-up was 37 (24 to 48) months. The average age of the patients was 66 (59 to 78) years. The instrumentation was performed meanly at 5 segments and vertebroplasty was performed averagely at 7 segments. All patients had the T-score value of less than -2.5 from the anteroposterior and lateral lumbar spine and hip views, so regarded as severe osteoporosis. In our study group, there were no extravasation and subsequent thermal neural injury. Four superficial wound infections have been observed and they responded well to local debridement and antibiotics. There were no proximal and distal junctional segment fractures during the follow-up course. Postoperatively, all patients with neurologic symptoms had complete relief of their nerve compression symptoms. In patients requiring spine surgery due to neurologic deficit and having no sufficient time for the medical treatment of severe osteoporosis, pedicle screw fixation with vertebroplasty augmentation and vertebroplasty in segments proximal and distal to the instrumented segments can be good alternative methods to provide well fixation and fusion while preventing proximal and distal junctional fractures. One should be careful about pulmonary cement embolism after such kind of procedures.

The effect of ethyl cyanoacrylate on experimental posterior lateral spinal fusion, in a rat model

Article

Jan 2009

Cyanoacrylates (CAs) are a type of tissue adhesives which are currently the most commonly used for cutaneous closings. The use of CAs was reported in other clinical procedures such as odontology, neurological surgery, maxillary surgery, orthopaedics, plastic surgery, etc. In this experimental study the authors carried out posterolateral spinal fusion in a rat model to test the usefulness of ethyl-cyanoacrylate (ECA) in fixation of allograft/autograft fusions. 25 Sprague-Dawley rats were randomized into two study groups. Bilateral posterolateral lumbar intertransverse process spinal fusion was performed with both autograft and allograft in both groups. ECA gel was dropped in the fusion area in a rat model in group II. The fusion rates as determined by manual palpation were 75% in controls and 46% in the ECA group (p = 0.322). According to radiographic score, the spinal segment was considered to be fused radiographically in 66% of controls and in 46% of animals in the ECA group (p = 0.43). The mean histological scores were 5.58 +/- 0.14 and 4.53 +/- 0.18 for the control and treatment group, respectively (p = 0.001). The mean bone density of the fusion masses was 101.3 +/- 2.5 in the control group and 92.0 +/- 3.3 in the ECA treatment group (p = 0.044). Ethyl-cyanoacrylate appeared to retard the osteogenic fusion but was well tolerated and did not induce necrosis, allergic reaction, infection, necrosis or neurological deficit in a rat model of posterolateral spinal fusion.

Evaluation of a silica-containing bone graft substitute in a vertebral defect model

Article

Feb 2009
J BIOMED MATER RES A

Orthopedic and spine surgeons are in need of supplements or replacements for autograft. We investigated the histological properties of three formulations of Calcium Sodium Phosphosilicate [calcium sodium phosphosilicate putty with or without autograft and NovaBone 45S5 Bioglass particulate (NovaBone, LLC, Jacksonville, FL)] using a sheep vertebral bone void model. Bone voids were surgically created in L3, L4, and L5 in each of 22 sheep, and the voids were filled with one of the tested biomaterials or left empty as a control. Histological evaluations were performed at either: 0, 6, or 12 weeks after surgery. Undecalcified sections were digitized, and the areas of the original defect and new bone were quantified. Decalcified sections were evaluated qualitatively. Histomorphometry showed a significant increase in the amount of bone between 6 and 12 weeks in all groups, but there was no significant difference in new bone formation among the formulations or between any formulation and the empty defects. The granules of all three formulations were associated with an inflammatory reaction. Many of the particles appear to have a hollow center, and the narrow tunnel through the center of the particles was sometimes associated with acute inflammation especially at 6 weeks. These particles were also associated with chronic inflammation at both 6 and 12 weeks, although the extent of inflammation decreased between 6 and 12 weeks. The search for the optimum bone graft substitute/extender will continue.

Pitfalls of Pedicle Screw Fixation in the Sacrum

Article

Sep 1992

Five male cadavers were used to evaluate anatomically structures at risk using sacral pedicle screw fixation. Risk was defined as the likelihood of penetration by K-wires placed through the pedicles and cortices at the S1, S2, and S3 levels. A scale based on the distance from the wire to the vital structure was developed to quantify risk. Instrument insertion techniques were classified as direct and lateral. The direct technique at S1 placed the left common iliac vein and the sympathetic chain at high risk. The sympathetic chain was also at high risk at the S2 and S3 levels. The lateral technique placed the lumbosacral trunk at high risk at the S1 level, as well as the S1 nerve root with screw placement at the S2 level. Anterior cortical penetration during sacral pedicle screw fixation places anatomic structures at variable risk depending on the technique used.

Surgical anatomy of the sacrum. A guide for rational screw fixation

Article

Jul 1991

Influence of Bone Mineral Density on the Fixation of Thoracolumbar Implants A Comparative Study of Transpedicular Screws, Laminar Hooks, and Spinous Process Wires

Article

Oct 1990

Posteriorly directed load to failure testing of four different types of spinal implants was performed in individual T5 to S1 vertebra harvested from seven fresh-frozen human cadaveric spines. The implants tested were: 1) Drummond spinous process wires, 2) Harrington laminar hooks, 3) Cotrel-Dubousset transpedicular screws, and 4) Steffee VSP transpedicular screws. The ultimate failure of each implant was compared with the bone mineral density of each vertebra to determine which implants, if any, were particularly advantageous in osteoporotic vertebrae. Before biomechanical testing, the spines were analyzed in vitro by dual photon absorptiometry to determine the bone mineral densities (gm/cm2) of each vertebra. The mean tensile loads to failure for each of the implants tested were as follows: Cotrel-Dubousset transpedicular screws: 345 Newtons; spinous process wire/button: 382 Newtons; Steffee transpedicular screws: 430 Newtons; and laminar hooks: 646 Newtons. The difference between the loads to failure for laminar hooks and the other implants was significant (P less than 0.05) using one-way analysis of variance. The overall correlation coefficient for bone mineral density with ultimate load to failure was 0.30 (P less than 0.001). The correlation coefficients were 0.47 (P less than 0.001) for spinous process wires alone; 0.096 (not significant) for laminar hooks alone; 0.37 (P less than 0.001) for Cotrel-Dubousset pedicle screws; and 0.48 (P less than 0.001) for Steffee pedicle screws. Of the four different implants tested, laminar hooks were most resistant to failure from posteriorly directed forces.(ABSTRACT TRUNCATED AT 250 WORDS)

A Biomechanical Study of Intrapeduncular Screw Fixation in the Lumbosacral Spine

Article

Mar 1986

This laboratory experiment was undertaken to identify factors contributing to intrapeduncular screw fixation in the vertebra. Testing was performed in axial pull-out and cyclic loading modes using multiple screw designs inserted to various depths into fresh human lumbosacral vertebra. The degree of osteoporosis played a major role in pull-out strength. Larger diameter, full-threaded screws inserted deep enough to engage the anterior vertebral cortex resulted in the most secure fixation. In the sacrum, the second sacral pedicle was the weakest location of insertion. Screws aimed laterally into the ala at 45 degrees or medially into the first sacral pedicle resisted larger axial pull-out loads than those inserted straight anteriorly into the ala. Methyl methacrylate was found to restore secure fixation in previously-loosened screws and pressurization of cement doubled the pull-out force. In cyclic load tests, deeper-inserted screws were found to withstand a greater number of cycles before loosening. Measurements of pedicle outer cortical diameters were found in many specimens to be smaller than both the 4.5-mm and 6.5-mm diameter screws.

Laparoscopic Discectomy With Anterior Lumbar Interbody Fusion

Article

Sep 1995

Patients presenting with L5-S1 anterior column disease with or without herniation into the spinal canal but without stenosis underwent magnetic resonance imaging screening before surgery to determine surgical suitability for laparoscopic anterior lumbar interbody fusion relative to the aortic bifurcation and approach to the disc space. To analyze and evaluate the laparoscopic approach, technique, and benefit of anterior lumbar discectomy and interbody fusion by distraction and compression-loading of autograft only as compared with cage-spacer-enhanced autograft fusion. Advancement in minimally invasive spine surgery techniques has provided options with less morbidity for posterior lumbar procedures. General surgical advancements in laparoscopy and advantages of traditional anterior lumbar interbody fusion, including restoration of disc height and exposure for safe nerve decompression, provided a basis for an integrated procedure that would address anterior column abnormality with low surgical morbidity. Five patients underwent technically successful laparoscopic anterior lumbar interbody fusion with approach to the disc space by an experienced laparoscopic general surgeon. A sixth patient in the study group was unable to undergo laparoscopic fusion because of an iliac vein tear during the surgical approach. After the approach, a spine surgeon followed with complete manual discectomy and interbody autogenous fusion laparoscopically. Two to three Cloward-type dowels were obtained by separate incision from the anterior iliac crest. All patients by 6-month follow-up examination were clinically fused with no motion on flexion-extension radiographs. One patient had slight anterior retropulsion of one dowel without the necessity of reoperation. Laparoscopic L5-S1 anterior lumbar interbody arthrodesis may represent a viable option for patients with abnormality, including anterior column and degenerative disc disease.

Osteoporotic vertebral collapse with late neurological complications

Article

Jun 1995
Paraplegia

This paper describes 27 patients who had a spinal fracture and underwent an anterior or a posterior spinal decompression, with or without spinal instrumentation, for late neurological compromise secondary to post-traumatic vertebral collapse associated with osteoporosis. Five males and 22 females were studied, with an average follow-up of 3.7 years. The patients developed delayed neurological compromise due to osteoporotic vertebral collapse 1 month to 1.5 years following insignificant spinal fractures. Abnormal hypermobility at the collapsed spinal level with gradual retropulsion of fracture fragments into the spinal canal appeared to contribute to late paralysis. This pathology is treated surgically either anteriorly or posteriorly, but we recommend transpedicular posterolateral decompression and stabilization with a screw-rod construct because of technical ease and minimum invasion.

Effects of Bone Mineral Density on Pedicle Screw Fixation

Article

Dec 1994

In an attempt to evaluate the effects of bone mineral density on the quality of fixation of pedicle screws in the lumbar spine, the axial pullout force was determined and compared in normal and osteoporotic human lumbar spines. Four techniques of screw hole preparation were evaluated. Two pedicle screw/offset laminar hook constructs also were evaluated to determine whether the adjunct fixation of the laminar hooks would improve quality of fixation to a level sufficient to allow their use in the osteoporotic lumbar spine. Pedicle screws were inserted by one of the listed techniques into fresh frozen cadaveric human spines. The fixation strength then was evaluated by pullout on a uniaxial testing frame. Bone mineral density was a strong influence on axial pullout force. In normal bone, the method of screw hole preparation did not significantly affect the quality of fixation. However, in the osteoporotic spine, either an untapped screw hole or the tapping of a screw hole with a 5.5 mm tap improved the pullout force a statistically significant amount (P < 0.003). Also, a pedicle screw with offset hooks at two adjacent levels improved the fixation significantly, increasing the pullout force to twice the expected value. Pedicle screw pullout strength was highly correlated with bone mineral density. A 5.5 mm tap or preparation with a ganglion knife improved pullout strength. Use of pedicle screws in conjunction with laminar hooks at two levels improved pullout strength.

Relation of Vertebral Bone Screw Axial Pullout Strength to Quantitative Computed Tomographic Trabecular Bone Mineral Content

Article

Jan 1994
J Spinal Disord

Noninvasive prediction of the maximum axial load that a spinal bone screw will be able to withstand after anterior surgical placement would be highly useful. To investigate if this is feasible, we first performed preliminary experiments to distinguish the trabecular and cortical contributions to overall stiffness; the trabecular component was found to dominate. We then used a commercial computed tomography bone mineral package to determine the mineral density of the trabecular region of 41 porcine vertebrae in terms of equivalent K2HPO4 concentration; values ranged from 104 to 343 mg/cm3. A 6.5-mm diameter cancellous bone screw was then inserted laterally in each vertebra, and the ultimate tensile strength (UTS) of the screw/bone interface was measured using a tensile testing machine. The UTS values ranged from 589 to 2,620 Newtons. A superlinear relation was found between UTS and the projected K2HPO4 concentration in the direction of the screw axis, expressed in units of mg/cm2.

Anterior Cervical Plate Fixation with the Titanium Hollow Screw Plate System

Article

Sep 1993

Although anterior cervical plates provide excellent fixation for the anterior column, the potential risk for injury to the spinal cord or soft tissues involved with their use has been the reason they have not gained universal acceptance. Morscher introduced a system that attempts to prevent the migration and loosening of screws by using a cross-split screw head that can be locked into the plate. The secondary advantage of this system is that it eliminates the requirement for posterior cortex purchase and thereby decreases the risk for spinal cord injury. This article reports the authors' experience using the Morscher titanium hollow screw cervical plate system. Forty-two patients in the series underwent anterior cervical arthrodesis for degenerative disease or trauma. The average number of levels fused were two. The fusion rate was 100%. Significant hardware loosening occurred in two patients. There was no iatrogenic injury to the spinal cord or esophagus. In conclusion, the titanium hollow screw cervical plate provides immediate stable fixation with minimal complications. Its use should be considered in the surgical treatment of patients requiring multilevel anterior cervical arthrodesis.

Prevalence and incidence of vertebral deformities

Article

Jun 1993

There is a need to identify vertebral fractures from radiographs taken at a single point in time, but considerable controversy surrounds the methods to be used. We extended a data set to comprise baseline radiographs of the thoracic and lumbar spine on an age-stratified random sample of 762 Rochester, Minnesota, women and used revised methods to define vertebral deformities morphometrically. Changes in the method of measuring vertebral heights, changes in the source of normal values for vertebral measurements and changes in the criteria for assessing vertebral deformity had little impact on estimated prevalence and incidence in this population. The prevalence of any vertebral deformity was estimated at 25.3 per 100 Rochester women aged 50 years and over (95% CI, 22.3-28.2), while the incidence of a new deformity in this group was estimated at 17.8 per 1000 person-years (95% CI, 16.0-19.7). Projected nationally, these data suggest that over 500,000 white women in the United States develop vertebral deformities for the first time each year and that over 7 million white women aged 50 years and over might be affected at any given time. These estimates are limited by the absence of a reliable 'gold standard' with which to determine false positive and false negative rates associated with this or any other morphometric method. Information on the health consequences of vertebral deformities of various sorts would be most helpful in choosing between alternative approaches to defining them.

Instrumented Laparoscopic Spinal Fusion

Article

Oct 1995

Seventeen consecutive patients underwent laparoscopic instrumented interbody fusions using custom-designed delivery instrumentation and "BAK" fusion cages; both are manufactured by Spinetech and the former was developed by the authors. The cases were performed at two spine centers under Food and Drug Administration investigational device evaluation clinical trials. We expect this approach will maintain a high fusion rate with diminished hospitalization time, recovery time, patient discomfort, and expense. The rehabilitative aspects of the procedure are a great improvement over traditional fusion approaches. Extraordinary advances in many endoscopic surgical fields have resulted in many endoscopic surgical fields have resulted in lowered morbidity, expense, and suffering associated with their open surgery counterparts. The authors have developed prototype of delivery instruments for the current laparoscopic fusion cage delivery system. The procedure is performed transperitoneally with carbon dioxide insufflation to enable video-assisted visualization through a 10-mm endoscope. Three 10-mm incisions and one 13- to 20-mm incision are required for one-level procedures. Two hollow titanium-threaded interbody implants are packed with autologous bone and inserted into the diseased interspace. Seventeen patients, with an average follow-up period of 8 months and a range of 6-12 months, underwent the procedure. There were 14 single-level fusions and three two-level fusions, all involving L4-S1 levels. There were two cases that required conversion to open procedures without sequelae; two patients had remote donor site wound infections eradicated with incision and drainage and antibiotics, and one patient required subsequent posterior spinal decompression because of a displaced endplate fracture. Average hospital stay was an average of 2 days, excluding two patients with complications and very prolonged stay. Although this procedure is associated with a long learning curve, the technique, once mastered, is effective and advantageous over current approaches to lumbar fusion. Operative time and hospital stay are expected to decrease with future instrumentation development and surgeon experience.

Biomechanical Study of Screws in the Lateral Masses: Variables Affecting Pull-out Resistance*

Article

Oct 1996

The purpose of this study was to investigate the effects of the design of the screw, the depth of insertion, the vertebral level, and the quality of the host bone on the pull-out resistance of screws used in the lateral masses. The study included twelve fresh cervical spines from human cadavera. Radiographs were made of each specimen to ensure the absence of defects, and then the cancellous-bone density of the vertebral bodies was measured at each level with quantitative computed tomography scanning. Six commercially available screws of various diameters and thread configurations (2.7, 3.2, 3.5, and 4.5-millimeter cortical-bone screws; a 3.5-millimeter cancellous-bone screw; and a 3.5-millimeter self-tapping screw) that are currently used for fixation of the cervical lateral masses were tested for axial load to failure. A twelve-by-twelve Latin square design was used to randomize the screws with regard to level (second through seventh cervical vertebrae), side (right and left), and depth of insertion (unicortical or bicortical purchase). Each screw was then subjected to uniaxial load to failure. The data were analyzed to determine if the diameter of the screw, the thread configuration, the number of cortices engaged, the cervical level, or the bone density was associated with the load to failure. Three major subgroups (greatest, intermediate, and lowest pull-out resistance) were identified. The subgroup with the greatest pull-out resistance included only screws with bicortical purchase; the 3.2, 3.5, and 4.5-millimeter cortical-bone screws and the 3.5-millimeter cancellous-bone screw were in this subgroup. Regardless of the thread configuration, no screw with unicortical purchase was in the group with the greatest pull-out resistance. Two of the three values in the subgroup with the lowest pull-out resistance were for the 3.5-millimeter self-tapping screw (with unicortical or bicortical purchase). The cancellous-bone density of the vertebral body was not associated with pull-out resistance and it did not vary significantly according to the cervical level, with the numbers available. However, the pull-out resistance of the screws varied significantly (p = 0.004) by level: it was the greatest at the fourth cervical level, decreasing cephalad and caudad to that level.

Biomechanical evaluation of Caspar and Cervical Spine Locking Plate systems in a cadaveric model

Article

Jul 1996
J NEUROSURG

There exist two markedly different instrumentation systems for the anterior cervical spine: the Cervical Spine Locking Plate (CSLP) system, which uses unicortical screws with a locking hub mechanism for attachment, and the Caspar Trapezial Plate System, which is secured with unlocked bicortical screws. The biomechanical stability of these two systems was evaluated in a cadaveric model of complete C5-6 instability. The immediate stability was determined in six loading modalities: flexion, extension, right and left lateral bending, and right and left axial rotation. Biomechanical stability was reassessed following fatigue with 5000 cycles of flexion-extension, and finally, the spines were loaded in flexion until the instrumentation failed. The Caspar system stabilized significantly in flexion before (p < 0.05) but not after fatigue, and it stabilized significantly in extension before (p < 0.01) and after fatigue (p < 0.01). The CSLP system stabilized significantly in flexion before (p < 0.01) but not after fatigue, and it did not stabilize in extension before or after fatigue. The moment needed to produce failure in flexion did not differ substantially between the two plating systems. The discrepancy in the biomechanical stability of these two systems may be due to differences in bone screw fixation.

Factors affecting the pullout strength of cancellous bone screws

Article

Sep 1996

Screws placed into cancellous bone in orthopedic surgical applications, such as fixation of fractures of the femoral neck or the lumbar spine, can be subjected to high loads. Screw pullout is a possibility, especially if low density osteoporotic bone is encountered. The overall goal of this study was to determine how screw thread geometry, tapping, and cannulation affect the holding power of screws in cancellous bone and determine whether current designs achieve maximum purchase strength. Twelve types of commercially available cannulated and noncannulated cancellous bone screws were tested for pullout strength in rigid unicellular polyurethane foams of apparent densities and shear strengths within the range reported for human cancellous bone. The experimentally derived pullout strength was compared to a predicted shear failure force of the internal threads formed in the polyurethane foam. Screws embedded in porous materials pullout by shearing the internal threads in the porous material. Experimental pullout force was highly correlated to the predicted shear failure force (slope = 1.05, R2 = 0.947) demonstrating that it is controlled by the major diameter of the screw, the length of engagement of the thread, the shear strength of the material into which the screw is embedded, and a thread shape factor (TSF) which accounts for screw thread depth and pitch. The average TSF for cannulated screws was 17 percent lower than that of noncannulated cancellous screws, and the pullout force was correspondingly less. Increasing the TSF, a result of decreasing thread pitch or increasing thread depth, increases screw purchase strength in porous materials. Tapping was found to reduce pullout force by an average of 8 percent compared with nontapped holes (p = 0.0001). Tapping in porous materials decreases screw pullout strength because the removal of material by the tap enlarges hole volume by an average of 27 percent, in effect decreasing the depth and shear area of the internal threads in the porous material.

Restoration of Pedicle Screw Fixation With an in Situ Setting Calcium Phosphate Cement

Article

Sep 1997

Pedicle screws were pulled out of human cadaveric vertebrae before and after augmentation with polymethylmethacrylate or in situ-setting calcium phosphate cement. The fixation strength of screws augmented with calcium phosphate cement was compared with that of screws augmented with polymethylmethacrylate. To determine whether a new in situ-setting calcium phosphate cement might be suitable for augmenting the fixation of pedicle screws. The principle objective was to compare the pull-out resistance of screws augmented with calcium phosphate cement with the pull-out behavior of screws augmented with polymethylmethacrylate. Polymethylmethacrylate augmentation was chosen as the standard because of its current clinical use. Five types of screws were tested to determine whether screw design had an effect on the efficacy of augmentation. Although many factors affect the pull-out resistance of pedicle screws, a key determinant of their performance is the strength of their attachment to the spine. In elderly, osteopenic patients, the screw-bone interface is especially at risk for stripping during insertion or pull-out after surgery. In these patients, polymethylmethacrylate has been used to augment pedicle screw fixation, although its use is not without risk. In situ-setting calcium phosphate cements may provide an alternative to polymethylmethacrylate in this application. Like polymethylmethacrylate, calcium phosphate cements can be injected into the prepared screw hole. They have the added advantage of being resorbed and replaced during healing and normal bone remodeling. Thirty human lower lumbar vertebrae (L3-L5) were implanted bilaterally with one of five types of pedicle screws (n = 6 for each screw type). The screws were pulled out 3.0 mm at 0.25 mm/sec with a servohydraulic materials testing machine. The 3.0-mm pull-out distance, which was slightly longer than one thread pitch, was designed to strip the screw-bone interface but to leave the pedicle otherwise intact. After the initial testing, the screws in each vertebrae were removed, and the screw tracks were filled with 2.0 cc of polymethylmethacrylate (one side) or calcium phosphate cement (contralateral side). After augmentation, the screws were reinserted, and the cements were allowed to harden for 24 hours. Postaugmentation testing followed the protocols for preaugmentation testing, and the pull-out resistance of screws augmented with calcium phosphate cement was compared with the pull-out resistance of screws augmented with polymethylmethacrylate. Mechanically, calcium phosphate cement compared favorably with polymethylmethacrylate for augmenting pedicle screws. Both restored the strength of the screw-bone interface: across all screw types, the average increase in pull-out strength was 147% with polymethylmethacrylate augmentation and 102% with calcium phosphate cement. There were no significant differences because of screw type with either type of augmentation. The in situ-setting calcium phosphate cement investigated in this study compared favorably with polymethylmethacrylate in a single-cycle, pull-out test of augmented pedicle screws in senile trabecular bone. With further evaluation, this cement may offer an alternative to polymethylmethacrylate for the enhancement of pedicle screw fixation clinically.

The mechanical role of laminar hook protection of pedicle screws at the caudal end vertebra

Article

Feb 1997

Biomechanical studies have shown hooks to be superior to pedicle screws in pull-out, especially in osteoporosis. This study evaluates the possible increase in stiffness of pedicle screws provided by laminar hooks while applying non-destructive forces to a vertebrectomy model assembled with Compact Cotrel Dubousset (CCD) instrumentation. Synthetic vertebrae were employed in a three-level vertebrectomy model. CCD screw-based three-level constructs with and without sublaminar hooks in the caudal element were tested in flexion, extension, compression, lateral bending, and torsion. There was no statistically significant advantage in adding inferior laminar hooks to a caudal end vertebra that had bilateral pedicle screws in any of the testing modes. Torsional stability, however, was augmented, but not significantly. Torsional instability and osteoporotic bone may be the clinical justifications for adding laminar hooks below screws in the caudal end vertebra.

Future directions: Augmentation of osteoporotic vertebral bodies

Article

Jan 1998

Because current medical and surgical treatments of vertebral body fractures are less than adequate, there is a need for interventions that decrease the likelihood of occurrence of these fractures and improve the treatment options once they have occurred. One such broad category of intervention involves the fortification or augmentation of the vertebral bodies. In addition to prophylactically stabilizing osteoporotic vertebral bodies at risk for fracture, augmentation of vertebral bodies that have already fractured may prove to be useful by reducing pain, improving function, and preventing further collapse and deformity. Vertebral body augmentation can also be used as an adjunct to fixation of internal hardware--for example, pedicle screws-in osteoporotic spines. A number of products are now available or are in clinical trials. The most promising products are injectable materials-polymethylmethacrylate or mineral bone cement. The early clinical results using polymethylmethacrylate in percutaneous vertebroplasty for fractured vertebral bodies and the results in vitro using an injectable mineral cement for vertebral body fortification are encouraging. Although the principle of vertebral body augmentation remains encouraging, data to support the widespread use of these techniques remain sparse, and the indications for their use should be more clearly defined.

Anterior vertebral body screw pullout testing. A comparison of Zeilke, Kaneda, Universal Spine System, and Universal Spine System with pullout-resistant nut

Article

May 1998

A biomechanical study of pullout of anteriorly implanted screws in cadaveric vertebral bodies. To investigate and compare the pullout strength of the Zielke, Kaneda, Universal Spine System (USS) pedicle screw, and USS pedicle screw with a new pullout-resistant nut. A common problem with anterior purchase regardless of the implant system is screw pullout at the proximal and distal ends of multilevel constructs. There is limited information on a solution to this problem. The L1 to L4 vertebral bodies from four cadavers had one each of Zielke and Kaneda pedicle screws (Acromed Corp., Cleveland, OH), USS pedicle screw (Synthes Spine, Paoli, PA), and USS pedicle screw with pullout-resistant nut implanted transversely across the center of the vertebral body with bicortical purchase in a similar fashion as would be used clinically. The screws were extracted using a servohydraulic material testing system. The maximum axial forces were recorded. The Zielke and Kaneda screws had no significant difference in mean pullout strength (P = 0.542). The USS screw alone was less strong (P = 0.009). The USS screw and pullout-resistant nut increased the pullout strength by twofold (P = 0.00006). In the screw pullout tests, the mode of failure was at the screw thread's interface. The USS screw and pullout-resistant nut failed by imploding the body around the nut. With the USS screw and pullout-resistant nut, the pullout strength was determined by the compressive strength of the bone. The addition of a pullout-resistant nut to an anterior vertebral body screw improves the pullout strength by twofold and changes the mode of failure to rely ultimately on the inherent vertebral body strength rather than the screw's characteristics. The addition of a pullout-resistant nut may be applicable to multilevel implant constructs to prevent screw pullout at the top and bottom.

A Biomechanical Study of Anterior Thoracolumbar Screw Fixation

Article

Oct 1998

The pullout strength of unicortical and bicortical screws in thoracic and lumbar vertebral bodies was measured as a function of bone mineral density. To determine the influence of bone mineral density and screw insertion technique on the stability of anterior thoracolumbar spine screw fixation. No previous study has addressed the specific technique of screw insertion or stability of screw fixation in the anterior spine. Fifty-one human thoracic vertebral bodies were tested in pullout with 6.55-mm cancellous screws inserted using unicortical and bicortical techniques. Pullout force increased exponentially with increasing bone mineral density for unicortical and bicortical screws. Bicortical screws were significantly stronger in resisting pullout than unicortical screws. Advancing an anterior vertebral body screw to engage the second cortex increases resistance to pullout by 25-44%, depending on vertebral bone mineral density. The difference in resistance between unicortical and bicortical techniques was smaller in specimens with low mineral densities.

The Effect of Locking Fixation Screws on the Stability of Anterior Cervical Plating

Article

Feb 1999

Current anterior cervical plate systems were tested with locked and unlocked fixation screws and with unicortical and bicortical fixation screws to determine fixation rigidity and pull-off strengths. To evaluate the effects of screw-plate locking and screw length on fixation strength and stability of anterior cervical plates. New plate systems provide for rigid locking of the screw-plate interface, theoretically increasing construct rigidity, allowing unicortical fixation, and preventing screw back-out. There are few data on the effects of locking screws on the stability of anterior cervical plating. Eighty fresh lamb vertebrae (C3-T1) were used. Test systems included: Cervical Spine Locking Plate (CSLP; Synthes, Paoli, PA, Orion plate (Sofamor-Danek, Memphis, TN), and Acroplate (AcroMed, Cleveland, OH). The CSLP and Orion plates were tested with fixation screws, locked and unlocked, and the AcroMed plate with unicortical and bicortical screw purchase. Biomechanical testing of the screw-plate constructs was performed to determine the initial bone-plate rigidity and pull-off strength. A 2.5-Nm cyclic bending moment was then applied to additional constructs for 10(5) cycles, and these constructs retested. Locked CSLP and Orion constructs were more rigid than all unlocked unicortical systems initially and after cyclic loading (P < 0.05). After cycling, the rigidity of all unlocked unicortical constructs decreased significantly (P < 0.05). There was no significant difference in pull-off strengths between the CSLP, the Orion, and the unicortical AcroMed plate. However, all had significantly less pull-off strength than the AcroMed plate with bicortical screws. A negative correlation was observed between initial pull-off strength and sagittal vertebral body diameter. Locking screws significantly increased the rigidity of the tested screw-plate systems initially and after cyclic loading. Because pull-off strength was affected by the vertebral body diameter, use of longer unicortical screws may be clinically beneficial in the patient with larger cervical vertebrae.

Effect of Implant Design and Endplate Preparation on the Compressive Strength of Interbody Fusion Constructs

Article

May 2000

A human cadaveric study on the compressive strength of different lumbar interbody fusion implants and endplate preparation techniques was performed. To assess the axial compressive strength of an implant with peripheral endplate contact as opposed to full surface contact, and to assess whether removal of the central bony endplate affects the axial compressive strength. The compressive strength of interbody fusion constructs has been compared between implants and bone grafts. Neither implant design nor endplate preparation has been shown to affect strength. Removal of the central bony endplate for bone grafts was noted to improve graft incorporation but also to facilitate subsidence. A total of 44 vertebrae were tested in four experimental groups by combining two interbody implants (full-surface vs peripheral surface support) with two endplate preparation techniques (intact bony endplate vs removal of the central bony endplate). Specimens were tested to ultimate compressive failure using a 50 N/second ramped load. Yield strength and ultimate compressive strength were compared between groups using two-factor analysis of covariance. A P value less than 0.05 was considered significant. Stepwise linear regressions assessed the predictive power of age, bone mineral content, and the implant's normalized endplate coverage on yield strength and ultimate compressive strength. Neither implant design nor endplate preparation technique affected yield strength or ultimate compressive strength. Age, bone mineral content, and the normalized endplate coverage were strong predictors of yield strength (P < 0. 0001; r2 = 0.459) and ultimate compressive strength (P < 0.0001; r2 = 0.510). An implant with only peripheral support resting on the apophyseal ring offers axial mechanical strength similar to that of an implant with full support. Neither supplementary struts nor a solid implant face has any additional mechanical advantage, but reduces graft-host contact area. Removal of the central bony endplate is recommended because it does not affect the compressive strength and promotes graft incorporation.

The Use of Pedicle-Screw Internal Fixation for the Operative Treatment of Spinal Disorders*

Article

Nov 2000

Robert W Gaines

Pedicle screws have dramatically improved the outcomes of spinal reconstruction requiring spinal fusion. Short-segment surgical treatments based on the use of pedicle screws for the treatment of neoplastic, developmental, congenital, traumatic, and degenerative conditions have been proved to be practical, safe, and effective. The Funnel Technique provides a straightforward, direct, and inexpensive way to very safely apply pedicle screws in the cervical, thoracic, or lumbar spine. Carefully applied pedicle-screw fixation does not produce severe or frequent complications. Pedicle-screw fixation can be effectively and safely used wherever a vertebral pedicle can accommodate a pedicle screw--that is, in the cervical, thoracic, or lumbar spine. Training in pedicle-screw application should be standard in orthopaedic training programs since pedicle-screw fixation represents the so-called gold standard of spinal internal fixation.

Use of cylindrical titanium mesh and locking plates in anterior cervical fusion: Technical note

Article

Feb 2001
J NEUROSURG

After performing anterior cervical corpectomy or discectomy for cervical spondolytic myelopathy or radiculopathy, iliac crest bone graft and fibular auto- or allograft is often used to achieve arthrodesis in the cervical spine. The purpose of this study was to evaluate the use of a cylindrical titanium mesh and locking plate system as an alternative technique in achieving anterior cervical fusion and maintaining lordosis. Hospital records and radiographs of 38 patients who underwent anterior cervical discectomies (28 patients) or corpectomies (10 patients) from 1995 to 1997 were reviewed retrospectively. All patients had undergone arthrodesis in which autograft and a cylindrical titanium mesh and anterior locking plate fixation were used after discectomy or corpectomy. There were 20 men and 18 women (mean age 46.1 years; range 34–72 years). Presenting symptoms included radiculopathy (61%), myelopathy (37%), and neck pain (2%). Preoperative and postoperative radiographs were studied, and data were obtained on the following: overall lordosis or kyphosis of the cervical spine, segmental lordosis or kyphosis at each surgically treated level, and evidence of fusion. In all of the patients in whom lordosis was present preoperatively, lordosis was maintained during the follow-up period. The overall fusion rate was 100%. The average change in overall lordosis or kyphosis related to the fixation devices was 1.2° (range 1–5°); the average segmental change was 2.3° (range 0–5°); and the mean follow up was 16 months (range 12–36 months). Anterior cervical fusion with cylindrical titanium mesh and cervical locking plate system is an effective method of achieving arthrodesis and maintaining alignment in the cervical spine. The construct may provide additional load-sharing function, and it avoids the use of cadaveric bone or the need for harvesting tricortical iliac crest autograft.

Biomechanical testing and clinical experience with the OMEGA-21 spinal fixation system

Article

Jun 2001

The role of spinal instrumentation is to provide mechanical stability, obtain and maintain anatomic alignment, and promote fusion. The American Society for Testing and Materials (ASTM) introduced guidelines and procedures so that biomechanical properties of different implant designs could be compared in a consistent manner. Combined with biomechanical analyses, clinical evaluation allows the safety and efficacy of a spinal implant system to be determined before construction. The objective of our study was to determine the biomechanical properties and clinical performance of the OMEGA-21 Spinal Fixation System. Static and dynamic (fatigue) biomechanical testing was performed per ASTM guidelines and recommendations on individual components and on the system assembled in a corpectomy model. Clinical and radiographic evaluation of 57 consecutive patients with indications for instrumented spinal arthrodesis of the lower dorsal lumbar and sacral segments of the spine was performed at a mean follow-up of 31.9 months. Static and fatigue testing revealed superior biomechanical properties of the individual components and of the assembled system. The mechanical-strength values of the system were comparable with maximum reported values for existing implant designs. At final clinical follow-up, 86% of patients obtained relief of their symptoms; 84% considered their clinical results to be excellent or good. Ninety-one percent of patients satisfied radiographic criteria for bony fusion. There were 5 implant-related complications: 2 misplaced screws (2 patients), local pain above the implant (2 patients), and 2 broken expansive screws (1 patient). Biomechanical and clinical results indicate that the OMEGA-21 system is feasible and performs well as a spinal instrumentation system for the lower dorsal, lumbar, and sacral spine.

Comparison of a new bisphenol-a-glycidyl dimethacrylate-based cortical bone void filler with polymethyl methacrylate

Article

Nov 2001

A newly formulated and reinforced bisphenol-a-glycidyl dimethacrylate (bis-GMA) resin (Cortoss/Orthovita, Malvern, Pa.) was compared with Simplex P polymethyl methacrylate (Stryker Howmedica Osteonics, East Rutherford, N.J.) in rabbits for up to 52 weeks and in sheep for up to 78 weeks. As seen in scanning electron microscopy and histology examinations, both implant materials were surrounded by bone at late time periods, with fibrous layers of connective tissue seen in half the Simplex P specimens. No clinically significant safety differences between implant materials were apparent. Interfacial bond strengths between the implant and bone generally increased with time, but were 4.5-fold greater with Cortoss than Simplex P at 24 weeks, and 100-fold greater at 52 weeks. Forces required to displace 316SS rods held in place with Cortoss were consistently greater than forces to displace rods held in place with Simplex P. No statistically significant differences in displacement forces were found between rods held in place with Cortoss polymerized in situ and rods held with prepolymerized Cortoss. Interfacial bond strengths were greater for Simplex P that was polymerized in situ than for prepolymerized polymethyl methacrylate specimens. Cortoss synthetic cortical bone void filler is a good candidate material to fix implants in bone. It has characteristics consistent with long-term safety and has a better ability to bond to bone than Simplex P.

Augmentation of Anterior Vertebral Body Screw Fixation by an Injectable, Biodegradable Calcium Phosphate Bone Substitute

Article

Dec 2001

A biomechanical study to evaluate the effects of a biodegradable calcium phosphate (Ca-P) bone substitute on the fixation strength and bending rigidity of vertebral body screws. To determine if an injectable, biodegradable Ca-P bone substitute provides significant augmentation of anterior vertebral screw fixation in the osteoporotic spine. Polymethylmethacrylate (PMMA) augmented screws have been used clinically; however, there is concern about thermal damage to the neural elements during polymerization of the PMMA as well as its negative effects on bone remodeling. Injectable, biodegradable Ca-P bone substitutes have shown enhanced fixation of pedicle screws. Sixteen fresh cadaveric thoracolumbar vertebrae were randomly divided into two groups: control (no augmentation) (n = 8) and Ca-P bone substitute augmentation (n = 8) groups. Bone-screw fixation rigidity in bending was determined initially and after 10(5) cycles, followed by pullout testing of the screw to failure to determine pullout strength and stiffness. The bone-screw bending rigidity for the Ca-P bone substitute group was significantly greater than the control group, initially (58%) and after cyclic loading (125%). The pullout strength for Ca-P bone substitute group (1848 +/- 166 N) was significantly greater than the control group (665 +/- 92 N) (P < 0.01). Stiffness in pullout for the Ca-P bone substitute groups (399 +/- 69 N/mm) was significantly higher than the control group (210 +/- 51 N/mm) (P < 0.01). This study demonstrated that augmentation of anterior vertebral body screw fixation with a biodegradable Ca-P bone substitute is a potential alternative to the use of PMMA cement.

Advantage of Pedicle Screw Fixation Directed Into the Apex of the Sacral Promontory Over Bicortical Fixation: A Biomechanical Analysis

Article

May 2002
SPINE

A biomechanical study of human cadaveric sacra using insertional torque and bone mineral density was conducted to determine the optimal sagittal trajectory of S1 pedicle screws. To measure the maximal insertional torque of sacral promontory versus bicortical pedicle screw fixation. Fixation of instrumentation to the sacrum is commonly accomplished using S1 pedicle screws, with previous studies reporting biomechanical advantages of bicortical over unicortical S1 screws. The biomechanical effect of bicortical screws (paralleling the endplate) versus screws directed into the apex of the sacral promontory is unknown. For this study, 10 fresh frozen cadaver sacra were harvested and evaluated with dual-energy radiograph absorptiometry to assess bone mineral density. Matched 7.5-mm monoaxial stainless steel pedicle screws then were randomly assigned by side (left versus right) and placed bicortically or into the apex of the sacral promontory under direct visualization. Maximum insertional torque was recorded for each screw revolution with a digital torque wrench (TQJE1500, Snap-On Tools, Kenosha, WI). Maximum bicortical S1 screw insertional torque averaged 5.22 +/- 0.83 inch-pounds, as compared with the maximum sacral promontory S1 screw insertional torque of 10.34 +/- 1.94 inch-pounds. This resulted in a 99% increase in maximum insertional torque (P = 0.005) using the "tricortical" technique, with the screw directed into the sacral promontory. Mean bone mineral density was 940 +/- 0.25 mg/cm2 (range, 507-1428 mg/cm2). The bone mineral density correlated with maximal insertional torque for the sacral promontory technique (r = 0.806; P = 0.005), but not for the bicortical technique (r = 0.48; P = 0.16). The screws directed into the apex of the sacral promontory of the S1 pedicle resulted in an average 99% increase in peak insertional torque (P = 0.005), as compared with bicortical S1 pedicle screw fixation. Tricortical pedicle screw fixation correlates directly with bone mineral density.

Increased pedicle screw pullout strength with vertebroplasty augmentation in osteoporotic spines

Article

May 2002
J NEUROSURG

The authors conducted a biomechanical study to evaluate pedicle screw pullout strength in osteoporotic cadaveric spines. Nonaugmented hemivertebrae were compared with pressurized polymethylmethacrylate (PMMA)-augmented hemivertebrae. Six formalin-fixed cadaveric thoracolumbar spines at least two standard deviations below the mean bone mineral density (BMD) for age were obtained. Radiographic and BMD studies were correlated to grades I, II, and III osteoporosis according to the Jekei scale. Each of the 21 vertebrae underwent fluoroscopic placement of 6-mm transpedicular screws with each hemivertebra serving as the control for the contralateral PMMA-augmented hemivertebra. Pedicle screws were then evaluated for biomechanical axial pullout resistance. Augmented hemivertebrae axial pullout forces were increased (p = 0.0005). The mean increase in pullout force was 181% for Grade I, 206% for Grade II, and 213% for Grade III osteoporotic spines. Augmented Grade I osteoporotic spines demonstrated axial pullout forces near those levels reported in the literature for nonosteoporotic specimens. Augmented Grade II osteoporotic specimens demonstrated increases to levels found in nonaugmented vertebrae with low-normal BMD. Augmented Grade III osteoporotic specimens had increases to levels equal to those found in nonaugmented Grade I vertebrae. Augmentation of osteoporotic vertebrae in PMMA-assisted vertebroplasty can significantly increase pedicle screw pullout forces to levels exceeding the strength of cortical bone. The maximum attainable force appears to be twice the pullout force of the nonaugmented pedicle screw for each osteoporotic grade.

The effects of bone density and disc degeneration on the structural property distributions in the lower lumbar vertebral endplates

Article

Sep 2002

In this study, we hypothesized that vertebral bone density and disc degeneration would affect the structural property distributions of the lower lumbar vertebral endplates (L3-L5). The results may have implications for improving interbody implant designs to better resist subsidence. A 3 mm diameter hemispherical indenter was used to perform indentation tests at 0.2 mm/s to a depth of 3 mm at 27 standardized locations in 55 bony endplates of intact human lumbar vertebrae (L3-L5). The resulting load-displacement curves were used to extract the failure load and stiffness of each test site. Bone density was measured using lateral DEXA scans. Disc condition was determined using a four-point grading scale. Three-way analyses of variance were used to analyze the relationships between the data. The overall failure load decreased with bone mineral density (BMD) in the superior (p < 0.0001) and inferior (p = 0.011) lumbar endplates. In both endplates, the posterolateral regions were significantly stronger than more central regions. With increasing BMD, this difference became more pronounced in the superior endplates only (p = 0.005). Increased disc degeneration was associated with an overall failure load decrease in the inferior lumbar endplates (p = 0.002). The strength in the central regions of the superior endplates was reduced with increasing degeneration, but this was not observed peripherally (p = 0.001). Stiffness magnitude or distribution was not significantly affected by BMD or disc degeneration. The locations of the strongest regions of the endplate did not change with either bone density or disc degeneration. This implies that implant shapes designed using the basic structural property maps for the L3-L5 endplates are appropriate for use in patients with a wide range of pathologies, even though overall failure loads are generally lower in patients with reduced bone density and greater degrees of disc degeneration.

Instrumentation of the osteoporotic spine: Biomechanical and clinical considerations

Abstract

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