[Show abstract][Hide abstract] ABSTRACT: Complex structural properties of menisci can be characterized in part by their inhomogeneous strain response under compression. This pilot study explored the feasibility to quantify characteristic strain distributions on meniscus cross-sections subjected to static compression using electronic speckle pattern interferometry (ESPI). Cross-sectional specimens of 5-mm thickness were harvested from eight human menisci. After application of 20% pre-strain, strain maps in response to 10 μm compression were captured with ESPI. The 10 μm compression induced an aggregate strain of nominally 0.14% and resulted in highly non-uniform strain distributions. Local compressive strain captured by ESPI ranged from 0.03% to 0.7%. The highest strain was in the central region of meniscus cross-sections, and the lowest magnitude of strain was at the femoral surface of the meniscus. After stratifying for age, peak compressive strain in older menisci (71±6 years, n=4) was 0.33%±0.09, compared to 0.25%±0.06 in younger menisci (34±9 years, n=4).
Journal of Biomechanics 03/2015; 48(8). DOI:10.1016/j.jbiomech.2015.02.059 · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Axial dynamization of an osteosynthesis construct can promote fracture healing. This biomechanical study evaluated a novel dynamic locking plate that derives symmetric axial dynamization by elastic suspension of locking holes within the plate. Standard locked and dynamic plating constructs were tested in a diaphyseal bridge-plating model of the femoral diaphysis to determine the amount and symmetry of interfragmentary motion under axial loading, and to assess construct stiffness under axial loading, torsion, and bending. Subsequently, constructs were loaded until failure to determine construct strength and failure modes. Finally, strength tests were repeated in osteoporotic bone surrogates. One body-weight axial loading of standard locked constructs produced asymmetric interfragmentary motion that was over three times smaller at the near cortex (0.1 ± 0.01 mm) than at the far cortex (0.32 ± 0.02 mm). Compared to standard locked constructs, dynamic plating constructs enhanced motion by 0.32 mm at the near cortex and by 0.33 mm at the far cortex and yielded a 77% lower axial stiffness (p < 0.001). Dynamic plating constructs were at least as strong as standard locked constructs under all test conditions. In conclusion, dynamic locking plates symmetrically enhance interfragmentary motion, deliver controlled axial dynamization, and are at least comparable in strength to standard locked constructs. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Journal of Orthopaedic Research 02/2015; DOI:10.1002/jor.22881 · 2.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Impact damping by elastic fixation is a principal engineering strategy to increase the durability of load-bearing structures exposed to prolonged dynamic loading. This biomechanical study evaluated axial impact damping provided by a novel "dynamic" locking plate. In this design, locking screw holes are elastically suspended within a silicone envelope inside the locking plate. Axial impact damping was assessed for three fixation constructs applied to bridge a 10 mm fracture gap of a femoral diaphysis surrogate: a standard locking plate, an dynamic locking plate, and an Ilizarov ring fixator. First, the three fixation constructs were characterized by determining their axial stiffness. Subsequently, constructs were subjected to a range of axial impact loads to quantify damping of force transmission. Compared to standard locked plating constructs, dynamic plating constructs were 58% less stiff (p<0.01) and Ilizarov constructs were 88% less stiff (p<0.01). Impact damping correlated inversely with construct stiffness. Compared to standard plating, dynamic plating constructs and Ilizarov constructs dampened the transmission of impact loads by up to 48% (p<0.01) and 74% (p<0.01), respectively. In conclusion, lower construct stiffness correlated with superior damping of axial impact loads. Dynamic locking plates provide significantly greater impact damping compared to standard locking plates.
[Show abstract][Hide abstract] ABSTRACT: Die Heilung von Frakturen wird wesentlich durch die mechanischen Bedingungen in der unmittelbaren Frakturumgebung beeinflusst, welche wiederum von der Art der Frakturstabilisation abhängt. Die Art und Ausführung einer Osteosynthese bestimmen die Steifigkeit und die Festigkeit des Verbunds aus Osteosynthese und frakturiertem Knochen. Während Erstere den zeitlichen Ablauf der Heilung beeinflussen kann, ist Letztere für die Belastungsfähigkeit der behandelten Extremität entscheidend und lässt Aussagen über den Versagensmechanismus des Osteosyntheseimplantats zu. Die Anforderungen an eine funktionierende Osteosynthese hängen entscheidend von der Anatomie und der physiologischen Belastung des heilenden Knochens ab und unterscheiden sich zwischen Frakturen im diaphysären und epi-/metaphysären Knochen. Bei diaphysären Frakturen kann die Wahl einer ausreichend dynamischen Osteosynthese über die Bildung eines periostalen Frakturkallus zu einer raschen Heilung führen. Bei Frakturen im Gelenkbereich stellen eine gute Wiederherstellung der Gelenkgeometrie und deren Retention die wesentlichen Aspekte für den Heilungserfolg dar. Basierend auf diesen Vorgaben lassen sich unter mechanischen Gesichtspunkten optimierte Implantate entwickeln und auf ihre sichere und Erfolg versprechende Anwendung untersuchen.
Trauma und Berufskrankheit 12/2013; 15(4). DOI:10.1007/s10039-013-2038-2
[Show abstract][Hide abstract] ABSTRACT: Document fixation and healing of distal femur fractures stabilized by plate osteosynthesis using Far Cortical Locking (FCL) screws.
Two level I and one level II trauma centers.
Thirty-two consecutive patients with 33 distal femur fractures (AO/OTA types 33-A,C).
Fractures were stabilized by plate osteosynthesis with MotionLoc FCL screws without supplemental bone graft or bone morphogenic proteins. Patients were followed up for a minimum of one year with functional and radiographic assessments obtained at postoperative weeks 6, 12, and 24 and computed tomography scans at week 12. If union was not confirmed within one year, follow-up was continued until union or revision surgery.
The primary endpoint was fracture union in absence of complications and secondary interventions. Fracture healing was defined by resolution of pain at the fracture site and cortical bridging on biplanar radiographs. Complications were defined by fixation failure, loss of reduction, implant breakage, infection, non-union, and need for revision.
Thirty-one fractures were available for follow-up. None of the 125 FCL screws used for diaphyseal fixation broke or lost fixation. One of 31 fractures displaced into varus (ΔVarus=5.8°). Thirty of 31 fractures healed within 15.6±6.2 weeks. At an average follow-up of 17±4 months there were two revisions, one to correct a mal-rotation at day 5, and one to treat a non-union at 6 months.
Absence of implant and fixation failure suggests that dynamic plating of distal femur fractures with FCL screws provides safe and effective fixation.
Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.
Journal of orthopaedic trauma 11/2013; DOI:10.1097/01.bot.0000438368.44077.04 · 1.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Angular acceleration of the head is a known cause of traumatic brain injury (TBI), but contemporary bicycle helmets lack dedicated mechanisms to mitigate angular acceleration. A novel Angular Impact Mitigation (AIM) system for bicycle helmets has been developed that employs an elastically suspended aluminum honeycomb liner to absorb linear acceleration in normal impacts as well as angular acceleration in oblique impacts. This study tested bicycle helmets with and without AIM technology to comparatively assess impact mitigation. Normal impact tests were performed to measure linear head acceleration. Oblique impact tests were performed to measure angular head acceleration and neck loading. Furthermore, acceleration histories of oblique impacts were analyzed in a computational head model to predict the resulting risk of TBI in the form of concussion and diffuse axonal injury (DAI). Compared to standard helmets, AIM helmets resulted in a 14% reduction in peak linear acceleration (p<0.001), a 34% reduction in peak angular acceleration (p<0.001), and a 22-32% reduction in neck loading (p<0.001). Computational results predicted that AIM helmets reduced the risk of concussion and DAI by 27% and 44%, respectively. In conclusion, these results demonstrated that AIM technology could effectively improve impact mitigation compared to a contemporary expanded polystyrene-based bicycle helmet, and may enhance prevention of bicycle-related TBI. Further research is required.
[Show abstract][Hide abstract] ABSTRACT: Periprosthetic distal femur fractures are severe injuries occurring in the often osteoporotic bone of the elderly. Far cortical locking (FCL) screws, which have been shown to promote increased callus formation in animal models, have recently become available for clinical use. The purpose of this study is to report preliminary healing and complication rates of periprosthetic distal femur fractures treated with FCL constructs.
A retrospective review of 20 patients who underwent open reduction and internal fixation of periprosthetic distal femur fractures using FCL constructs was performed. Healing was assessed radiographically and clinically at 6, 12 and 24 weeks post-operatively. Construct failure was defined as any hardware breakage or bone-implant dissociation leading to loss of reduction.
Complete data through the 24 week study period was available for 18/20 patients. Bridging callus was identified in 16/18 patients by the 24 week follow up for a healing rate of 88.9%. In patients that healed, the average time to medial bridging callus formation was 10.7±6.7 weeks, 11.0±6.6 weeks for anterior fracture line and 13.4±7.5 weeks for the posterior fracture line. both patients that failed to heal underwent revision surgery.
The initial results of this study are comparable to results reported for distal femur periprosthetic fractures treated with locking plate fixation without FCL screws, although it was difficult to compare time to healing between previously published studies. It is the impression of the authors that callus appears earlier and is more robust and uniform between the three cortices in FCL cases compared to their previous experiences with traditional locking plate periprosthetic distal femur fractures. This work suggests that FCL screws may be superior to traditional locking constructs but further studies are needed to directly compare the two methods.
[Show abstract][Hide abstract] ABSTRACT: Locked plate constructs used for fixation of periprosthetic fractures show high rates of healing difficulties. This is especially true in the distal femur, where modern studies show a revision rate of 15% to 22%. The combination of residual fracture gaps created by using biological fixation techniques and the high stiffness of locked plates is thought to result in decreased motion at the fracture site. Concern that the increased stiffness of locked plates contributes to the high nonunion rate lead to changes in the surgical technique (longer working length) and implant materials (titanium). These changes result in plate bending at the fracture site and induce callus at the cortex opposite the plate, with very little callus forming at the cortex near the plate. Far cortical locking (FCL) was developed out of the need to decrease construct stiffness and increase callus formation by allowing symmetric fracture site motion within the optimal range for secondary bone healing. The use of FCL constructs requires only minor changes in surgical technique from standard locked plating. Early outcomes using FCL screws for both nonperiprosthetic and periprosthetic fractures suggest the screws are safe in osteoporotic bone with increased callus formation and no screw breakage or pull out.
Techniques in Orthopaedics 01/2013; 28(3):260-264. DOI:10.1097/BTO.0b013e3182a25e65
[Show abstract][Hide abstract] ABSTRACT: To develop a reliable, easy to use bedside, office, or field system that allows the rapid measurement of cervical and ocular vestibular evoked myogenic potentials (cVEMP and oVEMP) using a bone-conduction stimulus.
Prospective bioengineering design and proof of concept of the test system with saccular and utricular otolith response studies in human subjects.
Private practice, tertiary neurotology referral center.
Twenty healthy adult controls without history of auditory or vestibular dysfunction and 5 preoperative and postoperative patients with confirmed superior canal dehiscence (SCD) participated.
The subjects underwent auditory stimuli-based cVEMP and oVEMP studies using a commercially available system as well as testing with a novel bone-conduction cVEMP and oVEMP head striker system.
Duration of each study, healthy subject and patient comfort, reproducibility, latency, and amplitude of auditory and striker evoked cVEMP and oVEMP responses.
The mean age of the healthy controls was 43.8, with a range of 19 to 69 years (10 male and 10 female subjects). The mean age of the SCD patient group was 46, with a range of 25 to 54 years; all female subjects. Although the cVEMP responses were similar using either the auditory or head strike stimuli, the healthy subjects preferred the latter, but the SCD patients became more symptomatic. The oVEMP data showed more consistent responses using the striker system. A statistically significant reduction in latency for the striker-evoked cVEMP occurred compared with the auditory cVEMP evoked response in the 5 SCD preoperative patients. All normalized postoperatively.
Recording the cVEMP and oVEMP responses using the striker system was much more rapid than with auditory stimuli and was more comfortable for the healthy subjects. The striker system and the acoustic method elicited strong otolithic receptor dysfunction symptoms in all SCD patients; however, they preferred the shorter striker studies. The striker system, because of the statistically shorter latency of p13 during the striker evoked cVEMP, which normalized after SCD closure, suggests that this method may be useful in identifying SCD patients before imaging studies. In addition, based on our biomechanical data, the striker was able to reliably produce a consistent and defined head striker impact.
Otology & neurotology: official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology 08/2012; 33(8):1392-400. DOI:10.1097/MAO.0b013e318268d234 · 1.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND: Surgical stabilization of flail chest injury with generic osteosynthesis implants remains challenging. A novel implant system comprising anatomic rib plates and intramedullary splints may improve surgical stabilization of flail chest injuries. This observational study evaluated our early clinical experience with this novel implant system to document if it can simplify the surgical procedure while providing reliable stabilization. METHODS: Twenty consecutive patients that underwent stabilization of flail chest injury with anatomic plates and intramedullary splints were prospectively enrolled at two Level I trauma centres. Data collection included patient demographics, injury characterization, surgical procedure details and post-operative recovery. Follow-up was performed at three and six months to assess pulmonary function, durability of implants and fixation and patient health. RESULTS: Patients had an Injury Severity Score of 28±10, a chest Abbreviated Injury Score of 4.2±0.4 and 8.5±2.9 fractured ribs. Surgical stabilization was achieved on average with five plates and one splint. Intra-operative contouring was required in 14% of plates. Post-operative duration of ventilation was 6.4±8.6 days. Total hospitalization was 15±10 days. At three months, patients had regained 84% of their expected forced vital capacity (%FVC). At six months, 7 of 15 patients that completed follow-up had returned to work. There was no mortality. Among the 91 rib plates, 15 splints and 605 screws in this study there was no hardware failure and no loss of initial fixation. There was one incidence of wound infection. Implants were removed in one patient after fractures had healed. CONCLUSIONS: Anatomic plates eliminated the need for extensive intraoperative plate contouring. Intramedullary rib splints provided a less-invasive fixation alternative for single, non-comminuted fractures. These early clinical results indicate that the novel implant system provides reliable fixation and accommodates the wide range of fractures encountered in flail chest injury.
[Show abstract][Hide abstract] ABSTRACT: Biological activity can be added to synthetic scaffolds by incorporating functional peptide sequences that provide enzyme-mediated degradation sites, facilitate cellular adhesion or stimulate signaling pathways. Poly(ethylene glycol) diacrylate is a popular synthetic base for tissue engineering scaffolds because it creates a hydrophilic environment that can be chemically manipulated to add this biological functionality. Furthermore, the acrylate groups allow for encapsulation of cells using photopolymerization under physiological conditions. One complication with the addition of these peptides is that aromatic amino acids absorb light at 285 nm and compete with the ultraviolet (UV)-sensitive photoinitiators such as IrgacureTM 2959 (I2959), the most commonly used initiator for cytocompatible photoencapsulation of cells into synthetic scaffolds. In this study we define non-toxic conditions for photoencapsulation of human mesenchymal stem cells (hMSC) in PEGDA scaffolds using a visible light photoinitiator system composed of eosin Y, triethanolamine and 1-vinyl-2-pyrrolidinone. This visible light photoinitiator produced hydrogel scaffolds with an increased viability of encapsulated hMSCs and a more tightly crosslinked network in one-third the time of UV polymerization with I2959.
[Show abstract][Hide abstract] ABSTRACT: Elevation of a locking plate over the bone surface not only supports biological fixation, but also decreases the torsional strength of the fixation construct. Biplanar fixation by means of a staggered screw hole arrangement may combat this decreased torsional strength caused by plate elevation. This biomechanical study evaluated the effect of biplanar fixation on the torsional strength of locking plate fixation in the femoral diaphysis.
Custom titanium plates were manufactured with either a linear or staggered hole pattern to evaluate planar and biplanar fixation, respectively. Fixation strength under torsional loading was evaluated in surrogates of the femoral diaphysis representative of osteoporotic and non-osteoporotic bone. Furthermore, fixation strength was determined for plate fixation with unicortical or bicortical locking screws. Five specimens per configuration were loaded to failure in torsion to determine their strength, stiffness, and failure mode.
In osteoporotic bone, biplanar fixation was 32% stronger (P=0.01) than planar fixation when unicortical screws were used and 9% stronger (P=0.02) when bicortical screws were used. In non-osteoporotic bone, biplanar fixation was 55% stronger (P<0.001) than planar fixation when unicortical screws were used and 42% (P<0.001) stronger when bicortical screws were used.
A biplanar screw configuration improves the torsional strength of diaphyseal plate fixation relative to a planar configuration in both osteoporotic and normal bone. With biplanar fixation, unicortical screws provide the same fixation strength as bicortical screws in non-osteoporotic bone.
[Show abstract][Hide abstract] ABSTRACT: To characterize scleral biomechanics in both eyes of eight monkeys in which chronic intraocular pressure (IOP) elevation was induced in one eye.
Each posterior sclera was mounted on a pressurization apparatus, IOP was elevated from 5 to 45 mm Hg while the 3D displacements of the scleral surface were measured by speckle interferometry. Finite element (FE) models of each scleral shell were constructed that incorporated stretch-induced stiffening and multidirectionality of the collagen fibers. FE model predictions were then iteratively matched to experimental displacements to extract unique sets of scleral biomechanical properties.
For all eyes, the posterior sclera exhibited inhomogeneous, anisotropic, nonlinear biomechanical behavior. Biomechanical changes caused by chronic IOP elevation were complex and specific to each subject. Specifically: (1) Glaucomatous eyes in which the contralateral normal eyes displayed large modulus or thickness were less prone to biomechanical changes; (2) glaucomatous scleral modulus associated with an IOP of 10 mm Hg decreased (when compared with that of the contralateral normal) after minimal chronic IOP elevation; (3) glaucomatous scleral modulus associated with IOPs of 30 and 45 mm Hg increased (when compared with that of the contralateral normal) after moderate IOP elevation; and (4) FE-based estimates of collagen fiber orientation demonstrated no change in the glaucomatous eyes.
Significant stiffening of the sclera follows exposure to moderate IOP elevations in most eyes. Scleral hypercompliance may precede stiffening or be a unique response to minimal chronic IOP elevation in some eyes. These biomechanical changes are likely to be the result of scleral extracellular matrix remodeling.
[Show abstract][Hide abstract] ABSTRACT: Several mechanical studies suggest locking plate constructs may inhibit callus necessary for healing of distal femur fractures. However, the rate of nonunion and factors associated with nonunion are not well established.
We (1) determined the healing rate of distal femur fractures treated with locking plates, (2) assessed the effect of patient injury and treatment variables on fracture healing, and (3) compared callus formation in fractures that healed with those that did not heal.
We retrospectively reviewed 82 patients treated with 86 distal femur fractures using lateral locking plates. We reviewed all charts and radiographs to determine patient and treatment variables and then determined the effects of these variables on healing. We quantitatively measured callus at 6, 12, and 24 weeks. The minimum time for telephone interviews and SF-36v2(TM) scores was 1 year (mean, 4.2 years; range, 1-7.2 years).
Fourteen fractures (20%) failed to unite. Demographics and comorbidities were similar in patients who achieved healing compared with those who had nonunions. There were more empty holes in the plate adjacent to fractures that healed; comminuted fractures failed to heal more frequently than less comminuted fractures. Less callus formed in fractures with nonunions and in patients treated with stainless steel plates compared with titanium plates. Complications occurred in 28 of 70 fractures (40%), 19 of which had additional surgery.
We found a high rate of nonunion in distal femur fractures treated with locking plates. Nonunion presented late without hardware failure and with limited callus formation suggesting callus inhibition rather than hardware failure is the primary problem. Mechanical factors may play a role in the high rate of nonunion.
Clinical Orthopaedics and Related Research 03/2011; 469(6):1757-65. DOI:10.1007/s11999-011-1870-6 · 2.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The high stiffness of periarticular locked plating constructs can suppress callus formation and fracture healing. Replacing standard locking screws with far cortical locking (FCL) screws can decrease construct stiffness and can improve fracture healing in diaphyseal plating constructs. However, FCL function has not been tested in conjunction with periarticular plating constructs in which FCL screws are confined to the diaphyseal segment. This biomechanical study evaluated if diaphyseal fixation of a periarticular locking plate with FCL screws reduces construct stiffness and induces parallel interfragmentary motion without decreasing construct strength. Periarticular locking plates were applied to stabilize distal femur fractures in 22 paired femurs using either a standard locked plating approach (LP group) or FCL for diaphyseal fixation (FCL group) using MotionLoc screws (Zimmer, Warsaw, IN). Each specimen was evaluated under quasiphysiological loading to assess construct stiffness, construct durability under dynamic loading, and residual strength after dynamic loading. FCL constructs had an 81% lower initial stiffness than LP constructs. They induced nearly five times more interfragmentary motion than LP constructs under one body weight loading (P < 0.001). FCL constructs generated parallel interfragmentary motion, whereas LP constructs exhibited 48% less motion at the near cortex than at the far cortex (P = 0.002). Seven LP constructs and eight FCL constructs survived 100,000 loading cycles. The residual strength of surviving constructs was 4.9 ± 1.6 kN (LP group) and 5.3 ± 1.1 kN (FCL group, P = 0.73). In summary, FCL screws reduce stiffness, generate parallel interfragmentary motion, and retain the strength of a periarticular locked plating construct. Therefore, FCL fixation may be advisable for stiffness reduction of periarticular plating constructs to promote fracture healing by callus formation.
[Show abstract][Hide abstract] ABSTRACT: The development of far cortical locking (FCL) was motivated by a conundrum: locked plating constructs provide inherently rigid stabilization, yet they should facilitate biologic fixation and secondary bone healing that relies on flexible fixation to stimulate callus formation. Recent studies have confirmed that the high stiffness of standard locked plating constructs can suppress interfragmentary motion to a level that is insufficient to reliably promote secondary fracture healing by callus formation. Furthermore, rigid locking screws cause an uneven stress distribution that may lead to stress fracture at the end screw and stress shielding under the plate. This review summarizes four key features of FCL constructs that have been shown to enhance fixation and healing of fractures: flexible fixation, load distribution, progressive stiffening, and parallel interfragmentary motion. Specifically, flexible fixation provided by FCL reduces the stiffness of a locked plating construct by 80% to 88% to actively promote callus proliferation similar to an external fixator. Load is evenly distributed between FCL screws to mitigate stress risers at the end screw. Progressive stiffening occurs by near cortex support of FCL screws and provides additional support under elevated loading. Finally, parallel interfragmentary motion by the S-shaped flexion of FCL screws promotes symmetric callus formation. In combination, these features of FCL constructs have been shown to induce more callus and to yield significantly stronger and more consistent healing compared with standard locked plating constructs. As such, FCL constructs function as true internal fixators by replicating the biomechanical behavior and biologic healing response of external fixators.