Tarun Goswami

Temporomandibular Joint: Disorders, Treatments, and Biomechanics

Temporomandibular joint (TMJ) is a complex, sensitive, and highly mobile joint. Millions of people suffer from temporomandibular disorders (TMD) in USA alone. The TMD treatment options need to be looked at more fully to assess possible improvement of the available options and introduction of novel techniques. As reconstruction with either partial or total joint prosthesis is the potential treatment option in certain TMD conditions, it is essential to study outcomes of the FDA approved TMJ implants in a controlled comparative manner. Evaluating the kinetics and kinematics of the TMJ enables the understanding of structure and function of normal and diseased TMJ to predict changes due to alterations, and to propose more efficient methods of treatment. Although many researchers have conducted biomechanical analysis of the TMJ, many of the methods have certain limitations. Therefore, a more comprehensive analysis is necessary for better understanding of different movements and resulting forces and stresses in the joint components. This article provides the results of a state-of-the-art investigation of the TMJ anatomy, TMD, treatment options, a review of the FDA approved TMJ prosthetic devices, and the TMJ biomechanics.

Computed-tomography-based finite-element models of long bones can accurately capture strain response to bending and torsion

Finite element (FE) models of long bones constructed from computed-tomography (CT) data are emerging as an invaluable tool in the field of bone biomechanics. However, the performance of such FE models is highly dependent on the accurate capture of geometry and appropriate assignment of material properties. In this study, a combined numerical-experimental study is performed comparing FE-predicted surface strains with strain-gauge measurements. Thirty-six major, cadaveric, long bones (humerus, radius, femur and tibia), which cover a wide range of bone sizes, were tested under three-point bending and torsion. The FE models were constructed from trans-axial volumetric CT scans, and the segmented bone images were corrected for partial-volume effects. The material properties (Youngs modulus for cortex, density-modulus relationship for trabecular bone and Poissons ratio) were calibrated by minimizing the error between experiments and simulations among all bones. The R(2) values of the measured strains versus load under three-point bending and torsion were 0.96-0.99 and 0.61-0.99, respectively, for all bones in our dataset. The errors of the calculated FE strains in comparison to those measured using strain gauges in the mechanical tests ranged from -6% to 7% under bending and from -37% to 19% under torsion. The observation of comparatively low errors and high correlations between the FE-predicted strains and the experimental strains, across the various types of bones and loading conditions (bending and torsion), validates our approach to bone segmentation and our choice of material properties.

Distal-third clavicle fracture fixation: a biomechanical evaluation of fixation.

BACKGROUND Approximately 25% of distal clavicle fractures are unstable. Unstable patterns have longer times to union and higher nonunion rates. Stable restoration of the distal clavicle is important in decreasing the nonunion rate in distal clavicle fractures. The purpose of this study was to biomechanically compare operative constructs for the treatment of unstable, comminuted distal-third clavicle fractures in a cadaveric model using a locking plate and coracoclavicular reconstruction. We hypothesized that the combination of coracoclavicular reconstruction and a distal clavicle locking plate is biomechanically superior to either construct used individually. MATERIALS AND METHODS An unstable distal clavicle fracture was created in 21 thawed fresh-frozen cadaveric specimens. The 21 specimens were divided into 3 treatment groups of 7: distal-third locking plate, acromioclavicular (AC) TightRope (Arthrex, Naples, FL, USA), and distal-third locking plate and AC TightRope together. After fixation, each specimen was cyclically tested with recording of displacement to determine the stiffness and stability of each construct, followed by load-to-failure testing in tension and compression to determine the maximum load. RESULTS The combined construct of the locking distal clavicle plate and coracoclavicular reconstruction resulted in increased stiffness, maximum resistance to compression, and decreased displacement compared with either construct alone. CONCLUSION Greater fracture stability was achieved with the combination of the AC TightRope and locking clavicle plate construct than with either alone, suggesting a possibility for increased fracture-healing rates.

Implant wear mechanisms—basic approach

Numerous parameters control the long-term performance of a total hip joint arthroplasty. The articulating motions between the femoral and the acetabular components produce wear debris in a hip implant. Surface roughness, clearance, coefficient of friction and sliding distance are found to be contributing parameters that affect wear rates. Wear produced in a hip implant leads to the loosening of a hip prosthesis and thus failure of the hip implant. Ultra-high-molecular-weight polyethylene (UHMWPE) has been successfully used as an acetabular weight bearing component in the THR applications. Cross-linked UHMWPE was found to improve the lifespan of an artificial hip. A gradient cross-linking of UHMWPE has been observed to be a recent development in implant bearing materials. During in vitro studies, gradient cross-linked UHMWPE showed nearly undetectable wear rates.

Biomechanical comparison of a proximal humeral locking plate using two methods of head fixation

HYPOTHESIS Locking plates have emerged as the implant of choice for stabilization of proximal humeral fractures. The biomechanical properties of a locked plating system using smooth pegs vs threaded screws for fixation of the humeral head were compared to test the hypothesis that there would be no biomechanical difference between pegs and threaded screws. MATERIALS AND METHODS Sixteen pairs of fresh frozen cadaveric humeri were randomized to have a surgical neck gap osteotomy stabilized with a locked plate using threaded screws (n=8) or smooth pegs (n=8). The intact contralateral humerus served as a control. Each specimen was tested with simultaneous cyclic axial compression (40 Nm) and torsion (both +/-2 Nm and +/-5 Nm) for 6000 cycles. All specimens were loaded to failure. Interfragmentary motion and load-displacement curves were analyzed to identify differences between the groups. Our data were then compared to previously published forces across the glenohumeral joint to provide evidence based recommendations for postoperative use of the shoulder. RESULTS There was a statistically significant difference between test specimens and their paired control (P < .001) in cyclic testing and load to failure. Differences between the smooth pegs and threaded screws were not statistically significant. DISCUSSION There is no biomechanical difference between locked smooth pegs and locked threaded screws for proximal fragment fixation in an unstable 2-part proximal humeral fracture model. CONCLUSION Our study contributes to the published evidence evaluating forces across the glenohumeral joint and suggests that early use of the affected extremity for simple activities of daily living may be safe. Use of the arm for assisted ambulation requiring a crutch, cane, walker, or wheelchair should be determined on a case-by-case basis.

Biomechanical evaluation of a pre-contoured clavicle plate

Recent attention has been focused on the operative treatment of mid-shaft fractures of the clavicle. This study compares the in-vitro biomechanical properties of a pre-formed titanium clavicle plate (Acumed) to a Synthes 3.5 mm limited-contact dynamic-compression (LCDC) plate using a cadaveric osteotomy model. An osteotomy was performed on 7 pairs of human clavicles and were randomly plated with either a Synthes 3.5 mm LCDC stainless steel plate or an Acumed titanium pre-contoured clavicle plate. After plating, specimens were tested on an EnduraTEC material testing apparatus for axial compression and tension strength, as well as torsional strength in compression and tension. Biomechanical test results for plated specimens are reported for the LCDC plate and the Acumed plate, and the 2 plates are compared. This exploratory study supports investigations with larger sample sizes to determine if the Acumed pre-contoured plate differs from the LCDC plate in biomechanical properties and the clinical implications of such differences.

Use of the Reamer-Irrigator-Aspirator for Bone Graft Harvest: A Mechanical Comparison of Three Starting Points in Cadaveric Femurs

Objectives: The mechanical behavior of cadaveric femurs after intramedullary reaming using the Reamer-Irrigator-Aspirator (RIA) for autogenous bone graft harvest has not been fully described. We hypothesized that reamed femurs, regardless of starting point, would adequately withstand cyclic loading simulating postoperative single-leg stance. Methods: Twenty-one cadaveric pairs were randomly assigned to one of three groups based on starting point: Group 1 (trochanteric), Group 2 (piriformis fossa), and Group 3 (retrograde). Each femur underwent dual-energy x-ray absorptiometry scanning and radiographs. Each test femur was reamed to 15 mm using the RIA with the contralateral femur serving as the control. The specimens were loaded to 1400 N of axial compression with 2° simultaneous torsion for 10,000 cycles. If the femur survived cyclic loading, it was then loaded to failure in axial compression. Comparisons regarding survival of cyclic loading were made using Fisher exact test. Results: No differences were seen between groups regarding age, sex, and T-score. The mean T-score for the femurs was -2.531 ± 1.372. Overall, 18 of 21 (86%) test femurs and 20 of 21 (95%) control femurs withstood cyclic loading (P = 0.606). Statistical significance was not reached for the three pairwise comparisons between test groups. The femurs failed in patterns consistent with simple pertrochanteric, basicervical, midcervical, or subcapital fractures. Conclusions: Intramedullary reaming for bone graft harvest using the RIA without subsequent intramedullary stabilization did not significantly degrade the mechanical behavior of cadaveric femurs in simulated single-leg stance regardless of reamer starting point. It appears safe to allow single-leg stance weightbearing on a reamed, unstabilized femur after bone graft harvesting using the RIA.

Finite element analysis of stress and wear characterization in total ankle replacements.

Total Ankle Arthroplasty is performed in order to reduce the pain and loss of ambulation in patients with various forms of arthritis and trauma. Although replacement devices fail by a number of mechanisms, wear in the polyethylene liner constitutes one of the dominating failure modes. This leads to instability and loosening of the implant. Mechanisms that contribute to wear in the liners are high contact and subsurface stresses that break down the material over time. Therefore, it is important to understand the gait that generates these stresses. Methods to characterize and decrease wear in Ohio Total Ankle Replacements (TARs) have been performed in this research. This research utilizes finite element analysis of Wright State University (WSU) patented TAR models. From the Finite element analysis (FEA) results, mathematical models of contact conditions and wear mechanics were developed. The maximum wear rate values obtained in the study (at 25.598MPa, 3.74mm(3)/year) and maximum surface Mises stress obtained with new optimization model (11.52MPa) seem to be comparable with the maximum wear values obtained in other similar studies. These models were used to determine the best methods for wear characterization and reduction. Furthermore, optimization models were developed based on geometry of the implants. These equations optimize geometry, thus congruency and anatomical simulations for total ankle implants.

Mechanical evaluation of fourth-generation composite femur hybrid locking plate constructs

Locking compression plates are routinely used for open reduction and internal fixation of fractures. Such plates allow for locking or non-locking screw placement in each hole. A combined use of both types of screw application for stabilization of a fracture is commonly applied and referred to as hybrid internal fixation. Locking screws improve the stability of the fixation construct but at the expense of significant additional cost. This study experimentally analyzes various combinations of locking and non-locking screws under simultaneous axial and torsional loading to determine the optimal hybrid locking plate—screw construct in a fourth generation composite femur. Clinically it is necessary to ensure adequate fixation stability in a worse case fracture-bone quality scenario. A locking screw near the fracture gap increased the axial and torsional strength of the locked plate system. Greater removal torque remained in non-locked screws adjacent to locked screws compared to an all non-locking screws control group.

Failure modes for total ankle arthroplasty: a statistical analysis of the Norwegian Arthroplasty Register

BackgroundIt is imperative to understand the most common failure modes of total ankle arthroplasty (TAA) to appropriately allocate the resources, healthcare costs, enhancing surgical treatment methods, and improve design and longevity of the implant. The objective of this study was to investigate the primary mode or modes of failure (Loose talar component, loose tibial component, dislocation, instability, misalignment, deep infection, Fracture (near implant), Pain, defect polyethylene (PE), other, and missing information) of TAA implants, so these failure mode/modes can be targeted for future improvement.MethodsThe Norwegian Total Hip Arthroplasty Register 2008 was chosen as the primary source of data since the register have been in existence for 20 years and also gives more specific failure modes than other registries. Tukey–Kramer method was applied to Norwegian Arthroplasty Register.ResultsAfter the application of the Tukey–Kramer method, it is evident that there is no significant difference between any of the failure modes that are pertinent to the ankle. However, there is significant evidence that the number of ankle arthroplasties are increasing with time.ConclusionsSince there is no statistical evidence showing which failure mode contributes most to revision surgeries, it is concluded that more information/data is needed to further investigate failure modes in ankle arthroplasties. Since the numbers of such surgeries are increasing, sufficient data should become available in time.