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ABSTRACT: This study compared the effect of 2 techniques of pulley management--venting and pulley enlargement (complete A2 incision with pulley repair and sheath closure using a retinacular graft)--on gliding resistance and on the incidence of triggering following zone 2 flexor tendon repairs in human cadaver specimens.
In vitro gliding resistance and the incidence of triggering were determined in 10 human cadaver specimens under 5 progressive conditions: (1) intact, (2) tendon repair (both tendons cut and repaired with the sheath intact), (3) condition 2 plus 50% venting of the distal A2 pulley, (4) condition 2 with venting extended to 66% of distal A2, and (5) condition 4 plus pulley enlargement. Triggering was determined in the same specimens by 2 computational algorithms that detected force changes in the load cells used to measure gliding resistance.
Tendon repair increased gliding resistance from the intact condition by an average of 229%. Gliding resistance was reduced in conditions 3, 4, and 5 from the repair condition by 15%, 25%, and 22%, respectively. Triggering commenced with tendon repair in some specimens, and its incidence increased with 50% venting. Further venting reduced triggering, but not as effectively as pulley enlargement did.
In this cadaveric study, venting and pulley enlargement reduce gliding resistance by equivalent amounts. Triggering persisted despite venting. The surgeon should carefully examine tendon repairs for free gliding. Pulley enlargement might be more effective than venting in reducing the incidence of triggering.
The Journal of hand surgery 06/2011; 36(8):1316-22. · 1.33 Impact Factor
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ABSTRACT: Falls, many of which are caused by balance problems, are a leading cause of injuries in elderly persons. Few studies have investigated osteopathic manipulative treatment (OMT) for patients with balance problems.
To test whether an OMT protocol with an emphasis on cranial manipulation can improve vestibular balance control structures and postural stability in a healthy elderly population. Design: A pilot prospective clinical trial.
Research laboratories of the University of North Texas Health Science Center Texas College of Osteopathic Medicine in Fort Worth.
Forty healthy elderly patients aged 65 or older were enrolled and separated into an OMT group and a control group. Owing to the recruitment process and limited time for the study, the first 20 patients to enroll were in the OMT group, and the next 20 were in the control group. Patients were excluded if they had a condition that could impair balance.
The OMT protocol comprised 7 OMT techniques applied weekly by the same osteopathic physician before balance tests. Patients in the control group received no treatment.
Patients were asked to stand on a force plate and to perform 3 balance tests: (1) eyes open, (2) eyes closed, and (3) a modified Romberg test. The center of pressure between their feet was recorded for 30 seconds. The average center of pressure displacement for each test was used to determine anteroposterior (AP) sway and mediolateral (ML) sway. Balance tests were performed each week for 4 weeks. Tests were performed at the same time of day as the first test.
Changes in AP sway values between visits 1 and 4 were as follows: eyes open, -0.72 and 0.75 mm for the control and OMT groups, respectively; eyes closed, -0.49 and 0.44 mm; and Romberg test, -0.17 and 0.52 mm. The changes in ML sway values between visits 1 and 4 were as follows: eyes open, -0.58 and 0.07 mm for the control and OMT groups, respectively; eyes closed, -0.21 and 0.03 mm; and Romberg test, -0.15 and 0.39 mm. The OMT group had significantly reduced sway for the eyes-open test after 4 visits (P=.001).
The OMT protocol used in the present study improved the postural stability of healthy elderly patients, as measured by changes in sway values. (ClinicalTrials.gov number NCT01153412).
The Journal of the American Osteopathic Association 06/2011; 111(6):382-8.
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ABSTRACT: To investigate our hypothesis that primary pulley enlargement and repair using an extensor retinaculum graft will reduce tendon repair gliding resistance. The benefit of pulley enlargement has been tested in experimental animals, but its effect on gliding resistance in vitro using human fingers is not known.
In vitro gliding resistance in the proximal tendon sheaths (A1 through A3) was measured and compared in 7 cadaver fingers using the method of Uchiyama and colleagues at a fixed 50 degrees over the proximal sheath under 3 conditions: (1) intact tendons with intact proximal sheath; (2) laceration and 2-strand core plus running epitenon repair of the tendons with intact sheath; and (3) repaired tendons with enlargement of the A2 pulley and adjacent proximal sheath by incision and repair with an extensor retinacular graft. Results were analyzed statistically.
Gliding resistance increased from an average of 0.44 N +/- 0.07 in the intact condition to an average of 1.51 N +/- 0.23 (a mean increase of 243%) when the tendons were cut and repaired. Enlarging the proximal sheath by sheath incision and graft repair reduced the gliding resistance from the repair condition to 1.04 N +/- 0.15 (a mean decrease of 31%). These changes are statistically significant.
In vitro, repaired tendons had a greater resistance to gliding than that of the intact tendons through the proximal sheath when tested by the method of Uchiyama and colleagues. Enlargement and repair with an extensor retinacular graft of the A2 pulley and adjacent sheath significantly reduced resistance to repaired tendon gliding. These findings support further investigation into the concept that primary pulley enlargement may improve tendon function after repair.
The Journal of hand surgery 09/2009; 34(8):1436-43. · 1.33 Impact Factor
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ABSTRACT: Anterior spinal infection (prevertebral abscess and/or discitis) after posterior instrumentation for vertebral fractures is a challenging complication, since a new implant may become necessary anteriorly, in a septic environment. Generally accepted management guidelines are yet to be established. The authors present a case of posterior instrumentation for fractures of T12 and L1, complicated after 9 months with an anterior infection (prevertebral abscess and discitis) with extended-spectrum beta-lactamase (ESBL) producing Escherichia coli (E. coli). This case is unique in that the multi-resistant organism was isolated only after the second stage of infection treatment, which consisted of anterior débridement and anterior implantation of titanium cages and rods. In this particular case, infection was controlled despite implantation of multiple cages, screws and rods, and fusion was achieved, by means of intravenous antibiotic treatment for 12 months. At the latest follow-up, 24 months post surgery, there was no evidence of infection. This problem case may be helpful for surgeons confronted with spinal deformities secondary to infections with multi-resistant organisms.
Acta orthopaedica Belgica 08/2009; 75(4):566-70. · 0.40 Impact Factor
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ABSTRACT: Interspinous devices have been introduced to provide a minimally invasive surgical alternative for patients with lumbar spinal stenosis or foraminal stenosis. Little is known however, of the effect of interspinous devices on intersegmental range of motion (ROM). The aim of this in vivo study was to investigate the effect of a novel minimally invasive interspinous implant, InSwing, on sagittal plane ROM of the lumbar spine using an ovine model. Ten adolescent Merino lambs underwent a destabilization procedure at the L1-L2 level simulating a stenotic degenerative spondylolisthesis (as described in our earlier work; Spine 15:571-576, 1990). All animals were placed in a side-lying posture and lateral radiographs were taken in full flexion and extension of the trunk in a standardized manner. Radiographs were repeated following the insertion of an 8-mm InSwing interspinous device at L1-L2, and again with the implant secured by means of a tension band tightened to 1 N/m around the L1 and L2 spinous processes. ROM was assessed in each of the three conditions and compared using Cobb's method. A paired t-test compared ROM for each of the experimental conditions (P < 0.05). After instrumentation with the InSwing interspinous implant, the mean total sagittal ROM (from full extension to full flexion) was reduced by 16% from 6.3 degrees to 5.3 +/- 2.7 degrees. The addition of the tension band resulted in a 43% reduction in total sagittal ROM to 3.6 +/- 1.9 degrees which approached significance. When looking at flexion only, the addition of the interspinous implant without the tension band did not significantly reduce lumbar flexion, however, a statistically significant 15% reduction in lumbar flexion was observed with the addition of the tension band (P = 0.01). To our knowledge, this is the first in vivo study radiographically showing the advantage of using an interspinous device to stabilize the spine in flexion. These results are important findings particularly for patients with clinical symptoms related to instable degenerative spondylolisthesis.
European Spine Journal 02/2009; 18(5):696-703. · 1.97 Impact Factor
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ABSTRACT: The aim of this study was to compare our experience with minimally invasive transforaminal lumbar interbody fusion (MITLIF) and open midline transforaminal lumbar interbody fusion (TLIF). A total of 36 patients suffering from isthmic spondylolisthesis or degenerative disc disease were operated with either a MITLIF (n = 18) or an open TLIF technique (n = 18) with an average follow-up of 22 and 24 months, respectively. Clinical outcome was assessed using the visual analogue scale (VAS) and the Oswestry disability index (ODI). There was no difference in length of surgery between the two groups. The MITLIF group resulted in a significant reduction of blood loss and had a shorter length of hospital stay. No difference was observed in postoperative pain, initial analgesia consumption, VAS or ODI between the groups. Three pseudarthroses were observed in the MITLIF group although this was not statistically significant. A steeper learning effect was observed for the MITLIF group.
International Orthopaedics 12/2008; 33(6):1683-8. · 2.03 Impact Factor
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ABSTRACT: Vertebroplasty and kyphoplasty have been reported to alter the mechanical behavior of the treated and adjacent-level segments, and have been suggested to increase the risk for adjacent-level fractures. The intervertebral disc (IVD) plays an important role in the mechanical behavior of vertebral motion segments. Comparisons between normal and degenerative IVD motion segments following cement augmentation have yet to be reported. A microstructural finite element model of a degenerative IVD motion segment was constructed from micro-CT images. Microdamage within the vertebral body trabecular structure was used to simulate a slightly (I = 83.5% of intact stiffness), moderately (II = 57.8% of intact stiffness), and severely (III = 16.0% of intact stiffness) damaged motion segment. Six variable geometry single-segment cement repair strategies (models A-F) were studied at each damage level (I-III). IVD and bone stresses, and motion segment stiffness, were compared with the intact and baseline damage models (untreated), as well as, previous findings using normal IVD models with the same repair strategies. Overall, small differences were observed in motion segment stiffness and average stresses between the degenerative and normal disc repair models. We did however observe a reduction in endplate bulge and a redistribution in the microstructural tissue level stresses across both endplates and in the treated segment following early stage IVD degeneration. The cement augmentation strategy placing bone cement along the periphery of the vertebra (model E) proved to be the most advantageous in treating the degenerative IVD models by showing larger reductions in the average bone stresses (vertebral and endplate) as compared to the normal IVD models. Furthermore, only this repair strategy, and the complete cement fill strategy (model F), were able to restore the slightly damaged (I) motion segment stiffness above pre-damaged (intact) levels. Early stage IVD degeneration does not have an appreciable effect in motion segment stiffness and average stresses in the treated and adjacent-level segments following vertebroplasty and kyphoplasty. Placing bone cement in the periphery of the damaged vertebra in a degenerative IVD motion segment, minimizes load transfer, and may reduce the likelihood of adjacent-level fractures.
European Spine Journal 12/2008; 18(1):59-68. · 1.97 Impact Factor
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ABSTRACT: Intertransverse posterolateral fusion along with instrumentation is a common technique used for spinal fusion. Iliac crest bone graft (ICBG) offers good fusion success rates with a low risk for disease transmission but is, however, linked with certain morbidity. In an effort to eliminate or reduce the amount of iliac graft needed, bone substitutes including demineralized bone matrix (DBM) have been developed. This study evaluates a novel DBM (Accell Connexus used in one or two-level instrumented posterolateral lumbar fusion.
A total of 59 consecutive patients were studied as two groups. Group 1 consisted of 33 patients having Accell Connexus used to augment either ICBG or local decompression material. Group 2 consisted of 26 consecutive patients, operated prior to the introduction of this novel DBM, having either ICBG alone or local decompression material. Fusion was assessed by two independent observers, blinded to graft material, using standardized criteria found in the literature. All adverse events were recorded prospectively.
The results show no statistically significant differences between the two groups in fusion rates, complications, surgery duration, ODI, or pain on VAS. Logistical regression showed no relation between fusion and age, smoking status or comorbidities. Furthermore, no adverse events related to the use of the novel DBM were observed.
The results from this study demonstrate that the novel DBM presented performs equally as well as that of autologous bone, be it either ICBG or a local decompression material, and can therefore be used as a graft extender.
Archives of Orthopaedic and Trauma Surgery 07/2008; 128(6):621-5. · 1.37 Impact Factor
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ABSTRACT: Total disc replacement (TDR) clinical success has been reported to be related to the residual motion of the operated level. Thus, accurate measurement of TDR range of motion (ROM) is of utmost importance. One commonly used tool in measuring ROM is the Oxford Cobbometer. Little is known however on its accuracy (precision and bias) in measuring TDR angles. The aim of this study was to assess the ability of the Cobbometer to accurately measure radiographic TDR angles. An anatomically accurate synthetic L4-L5 motion segment was instrumented with a CHARITE artificial disc. The TDR angle and anatomical position between L4 and L5 was fixed to prohibit motion while the motion segment was radiographically imaged in various degrees of rotation and elevation, representing a sample of possible patient placement positions. An experienced observer made ten readings of the TDR angle using the Cobbometer at each different position. The Cobbometer readings were analyzed to determine measurement accuracy at each position. Furthermore, analysis of variance was used to study rotation and elevation of the motion segment as treatment factors. Cobbometer TDR angle measurements were most accurate (highest precision and lowest bias) at the centered position (95.5%), which placed the TDR directly inline with the x-ray beam source without any rotation. In contrast, the lowest accuracy (75.2%) was observed in the most rotated and off-centered view. A difference as high as 4 degrees between readings at any individual position, and as high as 6 degrees between all the positions was observed. Furthermore, the Cobbometer was unable to detect the expected trend in TDR angle projection with changing position. Although the Cobbometer has been reported to be reliable in different clinical applications, it lacks the needed accuracy to measure TDR angles and ROM. More accurate ROM measurement methods need to be developed to help surgeons and researchers assess radiological success of TDRs.
European Spine Journal 06/2008; 17(8):1066-72. · 1.97 Impact Factor
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ABSTRACT: Relatively small amounts of microdamage have been suggested to have a major effect on the mechanical properties of bone. A significant reduction in mechanical properties (e.g. modulus) can occur even before the appearance of microcracks. This study uses a novel non-linear microdamaging finite-element (FE) algorithm to simulate the low-cycle fatigue behavior of high-density trabecular bone. We aimed to investigate if diffuse microdamage accumulation and concomitant modulus reduction, without the need for complete trabecular strut fracture, may be an underlining mechanism for low-cycle fatigue failure (defined as a 30% reduction in apparent modulus). A microCT constructed FE model was subjected to a single cycle monotonic compression test, and constant and variable amplitude loading scenarios to study the initiation and accumulation of low-cycle fatigue microdamage. Microcrack initiation was simulated using four damage criteria: 30%, 40%, 50% and 60% reduction in bone element modulus (el-MR). Evaluation of structural (apparent) damage using the four different tissue level damage criteria resulted in specimen fatigue failure at 72, 316, 969 and 1518 cycles for the 30%, 40%, 50% and 60% el-MR models, respectively. Simulations based on the 50% el-MR model were consistent with previously published experimental findings. A strong, significant non-linear, power law relationship was found between cycles to failure (N) and effective strain (Deltasigma/E(0)): N=1.394x10(-25)(Deltasigma/E(0))(-12.17), r(2)=0.97, p<0.0001. The results suggest that microdamage and microcrack propagation, without the need for complete trabecular strut fracture, are mechanisms for high-density trabecular bone failure. Furthermore, the model is consistent with previous numerical fatigue simulations indicating that microdamage to a small number of trabeculae results in relatively large specimen modulus reductions and rapid failure.
Journal of Biomechanics 02/2008; 41(3):515-22. · 2.43 Impact Factor
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ABSTRACT: Accurate clinical measurement of spinal range of motion (ROM) is essential in the evaluation of artificial disc performance. The effect of patient placement with respect to the X-ray beam source is yet to be reported and may be an influencing factor in radiographic artificial disc angle measurements. This study aims to evaluate how radiographic patient placement influences artificial disc angle measurements. An anatomically accurate synthetic L4-L5 motion segment was instrumented with an artificial disc and two pins. The instrumented motion segment was mounted onto a frame allowing for independent rotation and elevation while holding the artificial disc angle and anatomical position between L4 and L5 fixed. Analyses included descriptive statistics, evaluation of uncertainty, intra- and inter-observer, and a 2-way analysis of variance (ANOVA). The mean angle measurement range at the various positions was 1.26 degrees for the pin, and 2.74 degrees for the artificial disc endplates. The centered patient position had the highest inter- and intra-observer reliability. ANOVA results showed elevation effects to be statistically significant (P = 0.021), and rotational effects to be extremely statistically significant (P < 0.0001) for the pin angles. In terms of the mean artificial disc angle, however, the ANOVA showed a highly statistically significant interaction term (P = 0.002). A significant difference was found in the angle measurements of a fixed artificial disc prosthesis based on a sample of patient radiographic placement positions. Since it is important to assess the success of an artificial disc replacement by evaluating the relatively small ROM present, it is crucial to aim at minimizing the error by placing the patient parallel to the plate with the beam centered not at the mid lumbar spine, but at the level of the arthroplasty, for both flexion and extension views.
European Spine Journal 01/2008; 17(1):30-5. · 1.97 Impact Factor
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ABSTRACT: Studies evaluating the mechanical behavior of the trabecular microstructure play an important role in our understanding of pathologies such as osteoporosis, and in increasing our understanding of bone fracture and bone adaptation. Understanding of such behavior in bone is important for predicting and providing early treatment of fractures. The objective of this study is to present a numerical model for studying the initiation and accumulation of trabecular bone microdamage in both the pre- and post-yield regions. A sub-region of human vertebral trabecular bone was analyzed using a uniformly loaded anatomically accurate microstructural three-dimensional finite element model. The evolution of trabecular bone microdamage was governed using a non-linear, modulus reduction, perfect damage approach derived from a generalized plasticity stress-strain law. The model introduced in this paper establishes a history of microdamage evolution in both the pre- and post-yield regions.
Medical Engineering & Physics 10/2007; 30(6):725-32. · 1.62 Impact Factor
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ABSTRACT: This study aims to evaluate the influence of bone harvesting on postoperative pain and fusion rates. Group 1 patients received iliac crest bone graft (ICBG) either alone or augmented with local bone. Group 2 received only local bone. No statistical significance was found in radiological union or in the Oswestry Disability Index scores. Visual Analogue Scale scores showed less pain in group 2. Logistic regression showed no correlation between residual pain and occurrence of fusion. Harvesting ICBG did not appear to increase fusion rates and no relation was found between radiological non-union and pain.
International Orthopaedics 09/2007; 33(1):187-9. · 2.03 Impact Factor
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ABSTRACT: Pedicle screw insertion in spinal surgery is a demanding technique with potential risks to neurological structures, for example, within the spinal canal. Assessing screw placement in clinical practice has been performed using plain radiographs and/or mainly axial computed tomography (CT) images. Screw placement using CT image reconstructions in multiple planes has been described, but its reliability has yet to be studied. This study aimed at addressing the clinical issue of interobserver and intraobserver reliability in the use of axial and coronal CT images for the assessment of pedicle screw placement. Fifty nine pedicle screws were studied by two experienced radiologists on two separate occasions. Screw placement was classified as "in", "out" or "questionable". On average, 88% and 92% of the screws were classified as "in" by the first and second radiologist, respectively. Intraobserver agreement strength was almost perfect for both observers using either axial or coronal images. Interobserver agreement strength was almost perfect (axial) and substantial (coronal) in the first reading and substantial (axial, coronal) in the second reading. Assessing screw placement in more than one CT imaging plane is not only useful but reliable. Routine use may enhance reporting quality of screw placement by surgeons and radiologists.
International Orthopaedics 09/2007; 31(4):531-6. · 2.03 Impact Factor
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ABSTRACT: Chance fractures are relatively rare injuries and can be treated either conservatively, with a cast, or surgically, especially when posterior ligament injury is present. This paper presents two cases of lumbar Chance fractures treated using recently developed percutaneous cannulated pedicle screws. The first patient suffered associated abdominal injuries that required surgery, while the second had associated stable spinal fractures. Intraoperative blood loss was minimal. Both patients progressed to osseous union without implant failure. Following minimally invasive implant removal 9 months after injury, both patients remained asymptomatic without any evidence of instability on flexion and extension images obtained during their latest follow-up. This technique may be useful in selected cases in which bone grafting is not necessary; it allows early mobilization and stable fixation while minimizing morbidity.
Journal of Neurosurgery Spine 08/2007; 7(1):71-4. · 1.53 Impact Factor
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ABSTRACT: Percutaneous insertion of cannulated pedicle screws has been recently developed as a minimally invasive alternative to the open technique during instrumented fusion procedures. Given the reported rate of screw misplacement using open techniques (up to 40%), we considered it important to analyze possible side effects of this new technique. Placement of 60 pedicle screws in 15 consecutive patients undergoing lumbar or lumbosacral fusion, mainly for spondylolisthesis, were analyzed. Axial, coronal, and sagittal reformatted computer tomography images were examined by three observers. Individual and consensus interpretation was obtained for each screw position. Along with frank penetration, we also looked at cortical encroachment of the pedicular wall by the screw. Thirteen percent of the patients (2/15) had severe frank penetration from the screws, while 80% of them (12/15) had some perforation. On axial images the incidence of severe frank pedicle penetration was 3.3% while the overall rate of screw perforation was 23%. In coronal images the overall screw perforation rate rose to 30% while the rate of severe frank pedicle penetration remained unchanged. One patient (6.6%) suffered S1 root symptoms due to a frankly medially misplaced screw, requiring re-operation. This study has shown that percutaneous insertion of cannulated pedicle screws in the lumbar spine is an acceptable procedure. The overall rate of perforation in axial images is below the higher rates reported in the literature but does remain important. Frank penetration of the pedicle was nevertheless low. It remains a demanding technique and has to be performed with extreme care to detail.
European Spine Journal 06/2007; 16(5):613-7. · 1.97 Impact Factor
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ABSTRACT: Several studies have looked at accuracy of thoracic pedicle screw placement using fluoroscopy, image guidance, and anatomical landmarks. To our knowledge the upper thoracic spine (T1-T6) has not been specifically studied in the context of screw insertion and placement accuracy without the use of either image guidance or fluoroscopy. Our objective was to study the accuracy of upper thoracic screw placement without the use of fluoroscopy or image guidance, and report on implant related complications. A single surgeon inserted 60 screws in 13 consecutive non-scoliotic spine patients. These were the first 60 screws placed in the high thoracic spine in our institution. The most common diagnosis in our patient population was trauma. All screws were inserted using a modified Roy-Camille technique. Post-operative axial computed tomography (CT) images were obtained for each patient and analyzed by an independent senior radiologist for placement accuracy. Implant related complications were prospectively noted. No pedicle screw misplacement was found in 61.5% of the patients. In the remaining 38.5% of patients some misplacements were noted. Fifty-three screws out of the total 60 implanted were placed correctly within all the pedicle margins. The overall pedicle screw placement accuracy was 88.3% using our modified Roy-Camille technique. Five medial and two lateral violations were noted in the seven misplaced screws. One of the seven misplaced screws was considered to be questionable in terms of pedicle perforation. No implant related complications were noted. We found that inserting pedicle screws in the upper thoracic spine based solely on anatomical landmarks was safe with an accuracy comparable to that of published studies using image-guided navigation at the thoracic level.
European Spine Journal 06/2007; 16(5):625-9. · 1.97 Impact Factor
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ABSTRACT: A meta-analysis of the published literature was conducted specifically looking at accuracy and the postoperative methods used for the assessment of pedicle screw placement in the human spine.
This study specifically aimed to identify postoperative methods used for pedicle screw placement assessment, including the most common method, and to report cumulative pedicle screw placement study statistics from synthesis of the published literature.
Safety concerns have driven specific interests in the accuracy and precision of pedicle screw placement. A large variation in reported accuracy may exist partly due to the lack of a standardized evaluation method and/or the lack of consensus to what, or in which range, is pedicle screw placement accuracy considered satisfactory.
A MEDLINE search was executed covering the span from 1966 until 2006, and references from identified papers were reviewed. An extensive database was constructed for synthesis of the identified studies. Subgroups and descriptive statistics were determined based on the type of population, in vivo or cadaveric, and separated based on whether the assistance of navigation was employed.
In total, we report on 130 studies resulting in 37,337 total pedicle screws implanted, of which 34,107 (91.3%) were identified as accurately placed for the combined in vivo and cadaveric populations. The most common assessment method identified pedicle screw violations simply as either present or absent. Overall, the median placement accuracy for the in vivo assisted navigation subgroup (95.2%) was higher than that of the subgroup without the use of navigation (90.3%).
Navigation does indeed provide a higher accuracy in the placement of pedicle screws for most of the subgroups presented. However, an exception is found at the thoracic levels for both the in vivo and cadaveric populations, where no advantage in the use of navigation was found.
Spine 03/2007; 32(3):E111-20. · 2.08 Impact Factor
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ABSTRACT: The mechanical behavior of a thoracic motion segment following cement augmentation was studied using the finite-element method.
To examine effects of cement augmentation on motion segment stiffness and load transfer.
Vertebroplasty and kyphoplasty procedures are meant to stiffen and strengthen the vertebral body, but the optimal cement volume and placement to achieve these goals without altering load transfer to adjacent segments are unknown.
A microstructural finite-element model of a vertebral motion segment was constructed from micro-CT images. Microdamage within the vertebral body trabecular structure was modeled using an elasto-plastic modulus reduction scheme. Three motion segment damage models were created: I = 18% apparent modulus reduction (least damage), II = 45%, and III = 85% (most damage); and several one- and two-segment polymethylmethacrylate cement repair strategies (partial fill kyphoplasty, replacement of bone and marrow; and both partial fill and complete fill vertebroplasty, replacement of marrow only) were studied. Average disc and bone stresses and motion segment apparent compressive stiffness were compared with baseline (undamaged and untreated) simulation results.
In terms of maximizing stiffness and minimizing stress alterations in the adjacent vertebral body and increasing motion segment apparent stiffness, we found that, other than complete fill, the most effective single-segment cement repair strategy was vertebroplasty on the periphery of the superior segment overlying the disc anulus (<0.1% overall vertebral body bone stress alteration and 83% stiffness increase, respectively, damage Model III). Two-segment vertebroplasty (all repair models) restored motion segment stiffness to baseline levels in all damage models, while single-segment vertebroplasty (all repair models) restored stiffness to baseline levels only in damage Model I. Single- and two-segment kyphoplasty was effective in restoring stiffness to baseline levels for Model I only. Compared with the baseline model, cement augmentation decreased average treated segment bone stresses (up to 66%, complete fill vertebroplasty elasto-plastic modulus reduction Model III), increased average intervertebral disc nucleus stresses (up to 59%, kyphoplasty elasto-plastic modulus reduction Model III), and increased average adjacent segment, endplate region stresses (up to 2.8%, kyphoplasty elasto-plastic modulus reduction Model II). Adjacent (untreated) segment peak bone stresses were increased (up to 45%, kyphoplasty, Model III) in endplate regions underlying the intervertebral disc nucleus.
The damage-repair simulations indicated that cement augmentation improves motion segment stiffness but substantially alters bone stress distributions in treated and adjacent segments.
Spine 06/2005; 30(11):1258-65. · 2.08 Impact Factor
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ABSTRACT: Cement augmentation of hip lag screws to avoid cut-out displacement is classically described, along with a number of technical drawbacks. In a series of six elderly patients with hip fractures in osteoporotic bone, we illustrate catheter-assisted delivery of limited amounts of a new bisphenol-a-glycidyl dimethacrylate (bis-GMA)-based composite into hip compression screw threads, enabling significant increase in insertional torque compared with unaugmented screws. In two patients, unaugmented screws that did not initially purchase were tightened with a minimum torque of 1 N-m after augmenting with bis-GMA-based composite. No screw or femoral head displacement relative to baseline (2 days postoperative) was seen in any patient on serial x-rays taken up to 6 months after surgery. This technique adds approximately 10 minutes to surgery time. Advantages of bis-GMA-based composite over traditional PMMA augmentation include mixing on-demand, the ability to make repeated injections over extended periods in the event of femoral head perforations (in one patient in this series), precise placement of adequately small volumes of material, and a lower exotherm. Potentially, this bis-GMA-based composite may reduce the frequency of cut-out complications by enhancing bone-implant interface.
Journal of Orthopaedic Trauma 02/2004; 18(1):34-40. · 2.13 Impact Factor
