Double-Bundle Medial Collateral Ligament Reconstruction Improves Anteromedial Rotatory Instability.

BACKGROUND: New techniques have been proposed to better address anteromedial rotatory instability in a medial collateral ligament (MCL)-injured knee that require an extra graft and more surgical implants, which might not be feasible in every clinical setting. PURPOSE: To investigate if improved resistance to anteromedial rotatory instability can be achieved by using a single-graft, double-bundle (DB) MCL reconstruction with a proximal fixation more anteriorly on the tibia, in comparison with the gold standard single-bundle (SB) MCL reconstruction. STUDY DESIGN: Controlled laboratory study. METHODS: Eight fresh-frozen human cadaveric knees were tested using a 6 degrees of freedom robotic simulator in intact knee, superficial MCL/deep MCL-deficient, and reconstruction states. Three different reconstructions were tested: DB MCL no proximal tibial fixation and DB and SB MCL reconstruction with proximal tibial fixation. Knee kinematics were recorded at 0°, 30°, 60°, and 90° of knee flexion for the following measurements: 8 N·m of valgus rotation (VR), 5 N·m of external tibial rotation, 5 N·m of internal tibial rotation, combined 89 N of anterior tibial translation and 5 N·m of external rotation for anteromedial rotation (AMR) and anteromedial translation (AMT). The differences between each state for every measurement were analyzed with VR and AMR/AMT as primary outcomes. RESULTS: Cutting the superficial MCL/deep MCL increased VR and AMR/AMT in all knee positions except at 90° for VR (P < .05). All reconstructions restored VR to the intact state except at 90° of knee flexion (P < .05). The DB MCL no proximal tibial fixation reconstruction could not restore intact AMR/AMT kinematics in any knee position (P < .05). Adding an anterior-based proximal tibial fixation restored intact AMR/AMT kinematics at ≥30° of knee flexion except at 90° for AMT (P < .05). The SB MCL reconstruction could not restore intact AMR/AMT kinematics at 0° and 90° of knee flexion (P < .05). CONCLUSION: In this in vitro cadaveric study, a DB MCL reconstruction with anteriorly placed proximal tibial fixation was able to control AMR and AMT better than the gold standard SB MCL reconstruction. CLINICAL RELEVANCE: In patients with anteromedial rotatory instability and valgus instability, a DB MCL reconstruction may be superior to the SB MCL reconstruction, without causing extra surgical morbidity or additional costs.

Central cone design demonstrates greater micromotion compared to keel design in cementless tibial baseplates: A biomechanical analysis.

PURPOSE: The purpose of this study was to compare micromotion of two new cementless tibial baseplates to a cementless design with well-published clinical success. METHODS: Three cementless tibial baseplate designs (fixed-bearing [FB] with keel and cruciform pegs, rotating-platform with porous central cone and pegs, FB with cruciform keel and scalloped pegs) were evaluated on sawbone models. Loading was applied to the baseplate at a rate of 1 Hz for 10,000 cycles, which represents 6-8 weeks of stair descent. This time frame also represents the approximate time length for the induction of biologic fixation of cementless implants. Compressive and shear micromotion at the sawbone-implant interface were measured. RESULTS: At the end of the loading protocol, the central cone rotating-platform design exhibited greater micromotion at the anterior (p < 0.001), posterior (p < 0.001) and medial locations (p = 0.049) compared to the other two implants. The central cone design also exhibited greater translational micromotion in the sagittal plane at the medial (p = 0.001) and lateral locations (p = 0.034) and in the coronal plane anteriorly (p = 0.007). CONCLUSION: The cementless central cone rotating-platform baseplate demonstrated greater vertical and translational micromotion compared to the two FB baseplates with a keel underloading. This may indicate lower initial mechanical stability in implants without a keel, which possibly affects osseointegration. The implication of this is yet unknown and requires further long-term clinical follow-up to correlate these laboratory findings. LEVEL OF EVIDENCE: V (biomechanical study).

Early Postoperative Activities of Daily Living Do Not Adversely Affect Joint Torques or Translation Regardless of Capsular Condition: A Cadaveric Study.

PURPOSE: To evaluate the impact of capsular management on joint constraint and femoral head translations during simulated activities of daily living (ADL). METHODS: Using 6 (n = 6) cadaveric hip specimens, the effect of capsulotomies and repair was then evaluated during simulated ADL. Joint forces and rotational kinematics associated with gait and sitting, adopted from telemeterized implant studies, were applied to the hip using a 6-degrees of freedom (DOF) joint motion simulator. Testing occurred after creation of portals, interportal capsulotomy (IPC), IPC repair, T-capsulotomy (T-Cap), partial T-Cap repair, and full T-Cap repair. The anterior-posterior (AP), medial-lateral (ML), and axial compression DOFs were operated in force control, whereas flexion-extension, adduction-abduction, and internal-external rotation were manipulated in displacement control. Resulting femoral head translations and joint reaction torques were recorded and evaluated. Subsequently, the mean-centered range of femoral head displacements and peak signed joint restraint torques were calculated and compared. RESULTS: During simulated gait and sitting, the mean range of AP femoral head displacements with respect to intact exceeded 1% of the femoral head diameter after creating portals, T-Caps, and partial T-Cap repair (Wilcoxon signed rank P < .05); the mean ranges of ML displacements did not. Deviations in femoral head kinematics varied by capsule stage but were never very large. No consistent trends with respect to alterations in peak joint restrain torques were observed. CONCLUSIONS: In this cadaveric biomechanical study, capsulotomy and repair minimally affected resultant femoral head translation and joint torques during simulated ADLs. CLINICAL RELEVANCE: The tested ADLs appear safe to perform after surgery, regardless of capsular status, because adverse kinematics were not observed. However, further study is required to determine the importance of capsular repair beyond time-zero biomechanics and the resultant effect on patient-reported outcomes.

Lateral Subvastus Lateralis versus Medial Parapatellar Approach for Total Knee Arthroplasty: Patient Outcomes and Kinematics Analysis.

The conventional approach for total knee arthroplasty (TKA) is a medial parapatellar approach (MPA). We aimed to study patient outcomes and kinematics with a quadriceps sparing lateral subvastus lateralis approach (SLA). Patients with neutral/varus alignment undergoing primary TKA were consented to undergo the SLA. At 1-year postoperative, patients underwent radiostereometric analysis. Patients were administered the Short Form 12 (SF-12), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Knee Society Score (KSS). Kinematics and outcome data were compared to a group undergoing TKA via conventional MPA. Fourteen patients underwent TKA via SLA with a mean age 71.5 ± 8.0 and mean body mass index (BMI) 31.0 ± 4.5. The MPA group had 13 patients with mean age 63.4 ± 5.5 (p = 0.006) and mean BMI 31.2 ± 4.6 (p = 0.95). The SLA resulted in a significantly more posterior medial contact point at 0 (p = 0.011), 20 (p = 0.020), and 40 (p = 0.039) degrees of flexion. There was no significant difference in medial contact point from 60 to 120 degrees, lateral contact point at any degree of flexion, or axial rotation. There was no difference in improvement in postoperative WOMAC, SF-12, KSS function, and total KSS knee scores between groups. The MPA group had a significantly greater improvement in KSS knee scores at 3 months (p < 0.001), 1 year (p = 0.003), and 2 years (p = 0.017). The SLA resulted in increased medial femoral rollback early in flexion. Although both approaches resulted in improved postoperative outcomes, the MPA group showed significantly greater improvements in KSS knee scores at 3 months, 1 year, and 2 years. Further studies are required to identify any benefits that the SLA may offer. LEVEL OF EVIDENCE: Therapeutic Level II.

Reliability of the Sigmoid Notch Classification of the Distal Radioulnar Joint.

Background The Tolat sigmoid notch classification is a commonly used classification to characterize the distal radioulnar joint (DRUJ). This classification was based on a limited assessment of the entire joint, which may lead to inaccuracies in sigmoid notch evaluation. Questions/Purposes The purpose of this study is to assess the reliability of the Tolat classification for sigmoid notch characterization. Methods The sigmoid notch of 52 models of cadaveric forearms was assessed by applying the Tolat classification to the three-dimensional (3D) modeled notch and then slices at the start of the notch (0 mm) and 4 mm more proximal. The inter- and intrarater agreement was assessed using Cohen's and Fleiss' kappa statistic. Results Agreement between iterations regardless of slices or surgeons/radiologists was moderate. Intrarater agreement between pairs of slices (0 vs 4 mm, 0 mm vs 3D, 4 mm vs 3D) was moderate, whereas agreement between all slices was slight. Agreement between surgeons and between radiologists was moderate, while agreement across all raters and slices was fair. Models described as "other" were more consistent in 3D classifications and were commonly classified as a reverse ski slope. Conclusions Classification using the Tolat scheme is fair to moderate at best. Classification of the sigmoid notch using an axial view of the distal radius may not accurately reflect the anatomy throughout the notch. Clinical Relevance The Tolat classification supplies a limited analysis of the sigmoid notch, and does not represent a comprehensive evaluation of the entire joint. Future classification systems should characterize the entire sigmoid notch.

Analysis of Intramedullary Beam Designs Using Customized Finite Element Models for Medial Column Arthrodesis of the Foot.

Intramedullary beaming is a surgical option for medial column arthrodesis; however, disagreement exists about which beam design should be used. This computational study aimed to analyze the effects that common beam parameters have on medial column arthrodesis using a set of 5 subject-specific finite element models. A full-factorial design of experiments was conducted with 3 factors: implant stiffness (114 GPa Titanium vs 193 GPa Stainless Steel), threaded portion (25 mm Partially Threaded vs 130 mm Fully Threaded) and cannulation (Cannulated vs Solid). Increasing implant stiffness, threaded portion and using a solid beam all significantly increased medial column stiffness from 13.9 to 20.0 N/mm (p < .001), 15.2 to 18.8 N/mm (p = .001) and 13.6 to 20.4 N/mm (p < .001), respectively. Moreover, simultaneously increasing all 3 factors resulted in a 172% increase in medial column stiffness, as well as a 33% decrease in maximum von-Mises stress, 70% decrease in strain energy and 44% decrease in the average normal force in the implant during bending; all of which were significant. There was no significant increase in contact area in any of the joints, but there was a significant decrease in micromotion in each joint, ranging from 63% to 66%. Based on the parameters tested, a stainless steel, fully threaded (design that can apply compression), solid intramedullary device would produce the most stable construct for medial column arthrodesis under ideal conditions. Future studies simulating neuropathic conditions are needed before clinical use; however, this study shows the potential benefits of altering the implant design.

Does surgical approach affect patient outcomes of total knee arthroplasty?

BACKGROUND: Surgical approaches for total knee arthroplasty (TKA) include the medial parapatellar (MPA), subvastus (SV), midvastus (MV), and lateral parapatellar approach (LPA); it remains unclear which approach is superior. METHODS: Patients having undergone TKA at our institution were retrospectively organized into matched groups according to surgical approach (MPA, MV, SV, or LPA). Outcomes between the groups were compared using the Short-Form 12 (SF-12), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Knee Society Score (KSS), and range of motion (ROM) up to 2 years postoperative. RESULTS: Sixty-eight MV patients, 8 SV patients, and 4 LPA patients were matched with groups of MPA patients. There was no difference in outcomes between the MPA and MV groups up to 2 years. The SV group had significantly higher SF-12 Physical Composite Score (PCS; p = 0.036) and WOMAC stiffness score (p = 0.014) at 2 years, but significantly lower flexion at 1 year (p = 0.022) than the MPA group. The LPA group had significantly lower SF-12 PCS (p = 0.011) and WOMAC function scores (p = 0.022) at 1 year than the MPA group. CONCLUSION: There was no significant difference between the MPA and MV approach. The SV approach had some improved long-term outcomes over the MPA aproach (SF-12 and WOMAC), but had significantly lower flexion at 1 year. The LPA group showed inferior outcomes than the MPA group but had more severe valgus preoperative deformity (p = 0.024). Further studies are required to investigate the potential benefit of quadriceps-sparing approaches.

Load to Failure of the Ankle Joint Complex After Fusion of the Subtalar and Talonavicular Joints: A Cadaveric Study.

Recent literature has proposed that restriction of joints in the rearfoot secondary to coalitions may lead to increased risk for severe ankle fracture after trauma. There is a paucity of literature regarding the rigidity of the ankle joint after arthrodesis of the subtalar and talonavicular joints. In this study, load-to-failure testing of cadaveric ankle joints with and without fusion of the subtalar and talonavicular joints was performed to determine if clinically relevant fracture patterns could be reproduced. Of the 3 fixation patterns studied, combined subtalar and talonavicular joint fusion resulted in a measurable increase in joint stiffness; however, this was not statistically significant. Clinical and radiographic examination postloading revealed that all tested ankle joints sustained a dislocation type injury rather than a specific bone fracture pattern. It was determined that a pure low-speed bending and compression model does not produce clinically relevant fracture patterns, and that higher energy mechanisms are required.

Characterizing the trade-off between range of motion and stability of reverse total shoulder arthroplasty.

BACKGROUND: The trade-off between range of motion (ROM) and stability of reverse total shoulder arthroplasty (RSA) has long been hypothesized to exist but has not yet been well characterized. The goal of this study was to use design optimization techniques to obtain a Pareto curve, which quantifies the trade-off between 2 competing objectives and is defined by the performance of optimum designs that maximize one surgical outcome without sacrificing the other. METHODS: Multi-objective design optimization techniques were used; 4 design and surgical parameters including glenoid lateralization (GLat), neck-shaft angle (NSA), inferior offset of the center of rotation (CORinf), and humerus lateralization (HLat) were tuned simultaneously. The ROM and stability, the objectives to be optimized, of any candidate design were characterized computationally using a combination of finite element models, musculoskeletal models, analytical equations, and surrogate models. Optimum designs and Pareto curves were determined separately for a standard cup depth and a shallow cup depth. The performance of the optimum designs, in terms of ROM and stability, was compared with a representative commercially available design. RESULTS: A Pareto curve was obtained for each cup depth, confirming there is a trade-off between ROM and stability of RSA. In comparison to the commercially available design (cup depth, 8.1 mm; GLat, 5 mm; NSA, 155°; CORinf, 0 mm; HLat, 0 mm), the designs optimized for ROM offered 38.8% (cup depth, 6 mm; GLat, 16 mm; NSA, 163.6°; CORinf, 4 mm; HLat, 0.6 mm) and 35.2% (cup depth, 8.1 mm; GLat, 16 mm; NSA, 160.5°; CORinf, 4 mm; HLat, -0.2 mm) improvement in ROM. The designs optimized for stability (cup depth of 6 mm with GLat of 16 mm, NSA of 170°, CORinf of 4 mm, and HLat of 3 mm and cup depth of 8.1 mm with GLat of 16 mm, NSA of 170°, CORinf of 4 mm, and HLat of 3 mm) both offered 12.4% improvement in stability over the commercially available design. Designs in the toe region of the Pareto curve offered between 75% and 90% of the maximum possible improvement over the commercially available design for both objectives. CONCLUSION: It was confirmed that a trade-off exists between ROM and stability of RSA, in which maximizing one outcome requires a sacrifice in the other. The relative gains and sacrifices in the competing outcomes when traversing the Pareto front could aid in understanding clinically optimum designs based on patient-specific needs.

The Medial structures of the knee have a significant contribution to posteromedial rotational laxity control in the PCL-deficient knee.

PURPOSE: Various reconstruction techniques have been employed to restore normal kinematics to PCL-deficient knees; however, studies show that failure rates are still high. Damage to secondary ligamentous stabilizers of the joint, which commonly occurs concurrently with PCL injuries, may contribute to these failures. The main objective of this study was to quantify the biomechanical contributions of the deep medial collateral ligament (dMCL) and posterior oblique ligament (POL) in stabilizing the PCL-deficient knee, using a joint motion simulator. METHODS: Eight cadaveric knees underwent biomechanical analysis of posteromedial stability and rotatory laxity using an AMTI VIVO joint motion simulator. Combined posterior force (100 N) and internal torque (5 Nm) loads, followed by pure internal/external torques (± 5 Nm), were applied at 0, 30, 60 and 90° of flexion. The specimens were tested in the intact state, followed by sequential sectioning of the PCL, dMCL, POL and sMCL. The order of sectioning of the dMCL and POL was randomized, providing n = 4 for each cutting sequence. Changes in posteromedial displacements and rotatory laxities were measured, as were the biomechanical contributions of the dMCL, POL and sMCL in resisting these loads in a PCL-deficient knee. RESULTS: Overall, it was observed that POL transection caused increased posteromedial displacements and internal rotations in extension, whereas dMCL transection had less of an effect in extension and more of an effect in flexion. Although statistically significant differences were identified during most loading scenarios, the increases in posteromedial displacements and rotatory laxity due to transection of the POL or dMCL were usually small. However, when internal torque was applied to the PCL-deficient knee, the combined torque contributions of the dMCL and POL towards resisting rotation was similar to that of the sMCL. CONCLUSION: The dMCL and POL are both important secondary stabilizers to posteromedial translation in the PCL-deficient knee, with alternating roles depending on flexion angle. Thus, in a PCL-deficient knee, concomitant injuries to either the POL or dMCL should be addressed with the aim of reducing the risk of PCL reconstruction failure.

Embedded sensing package for temporary bone cement spacers in infected total knee arthroplasty.

The re-infection rate of total knee arthroplasty (TKA) after two stage revision (15%) remains high as it can be challenging to determine whether the infection has been fully cleared between the first and second stage procedures. Temporary embedded sensor systems could be a potential solution to indicate whether the infection has been cleared. In this study a telemetric sensor system to integrate with a bone cement spacer and measure knee joint temperature was designed and evaluated. The sensor package precision, accuracy, hysteresis, and thermal equilibrium were empirically determined. Cadaveric testing was performed with the sensor package implanted inside the femoral notch alongside a pre-formed femoral and tibial bone cement spacer. The limb was tested though 30,000 cycles at 0.5 Hz under a 500 N load. Accuracy and precision of the sensing package were found to be ±0.24 °C and 0.09 °C respectively with negligible hysteresis. Thermal insulation caused by the implant itself was found to produce a thermal time constant of 263 ± 5 s, resulting in a 17 min rise time. Memory capacity enabled data logging every 20 s for a 6 week period before necessitating data transfer. Bluetooth was suitable for data transmission while the package was implanted. Following cyclic loading of the cadaveric specimen, imaging and debridement revealed no issues related to mechanical integrity of the bone cement spacer or encapsulated sensor package. While additional validation is required before use in patients, the concept of temporary embedded sensing technology to aid management of infection treatments is promising.

Rotational Anatomy of the Radius and Ulna: Surgical Implications.

PURPOSE: The rotational anatomy of the forearm bones is not well defined. This study aims to further the understanding of the torsion of the radius and ulna to better guide treatment. METHODS: Computed tomography images of 98 cadaveric forearms were obtained and 3-dimensional models of the radius and ulna were generated and analyzed. The rotation of the radius was evaluated by comparing the orientation of the distal radius central axis (DRCA) with the volar cortex of the distal radius (DR) and biceps tuberosity (BT). The rotation of the ulna was evaluated by assessing the orientation of the ulnar head with respect to the proximal ulna. RESULTS: The DR volar cortex pronates from distal to proximal. The BT was 43.8° ± 16.9° supinated from the DRCA (range, 2.7°-86.5°). The mean difference in rotation between contralateral biceps tuberosities was 7.0° ± 7.1°. The volar cortex of the DR was 12.6° ± 5.4° supinated compared with the DRCA. The ulnar head was pronated 8.4° ± 14.9° with respect to the greater sigmoid notch (range, 50.3° pronation-22.0° supination). CONCLUSIONS: The BT has a variable orientation relative to the DR, but it is generally located anteromedially in a supinated arm or 136° opposite the radial styloid. Understanding the rotational anatomy of the radius and ulna can play an important role in surgical planning and implant design. The rotational anatomy of the radius and ulna varies significantly between individuals, but is similar in contralateral limbs. CLINICAL RELEVANCE: Distal radius volar cortex rotational anatomy can help guide treatment of DR fractures and malunions as well as assist in positioning of wrist arthroplasty implants, particularly in the presence of bone loss. The side-to-side similarities demonstrated in this study should be helpful in managing patients with segmental bone loss or fracture malunion and those requiring joint reconstruction.

Sensitivities of lumbar segmental kinematics and functional tissue loads in sagittal bending to design parameters of a ball-in-socket total disc arthroplasty prosthesis.

Lumbar total disc arthroplasty (TDA) is an attractive option for the treatment of spinal disorders. However, post-operative complications may cause revision surgery. In this study, an in-depth biomechanical analysis was performed to test how sensitive post-operative spinal responses in sagittal bending were to design parameters of a widely used ball-in-socket TDA design. Our simulation results revealed that lowering the intervertebral distraction, posteriorly positioning the implant, or decreasing the radius of curvature of the metal-on-polyethylene bearing surface could result in spinal responses which better matched normal spinal kinematics, but deviated further from the normal spinal tissue load-sharing pattern.

A Smart Knee Implant Using Triboelectric Energy Harvesters.

Although the number of total knee replacement (TKR) surgeries is growing rapidly, functionality and pain-reduction outcomes remain unsatisfactory for many patients. Continual monitoring of knee loads after surgery offers the potential to improve surgical procedures and implant designs. The goal of this study is to characterize a triboelectric energy harvester under body loads and to design compatible frontend electronics to digitize the load data. The harvester prototype would be placed between the tibial component and polyethylene bearing of a TKR implant. The harvester generates power from the compressive load. To examine the harvester output and the feasibility of powering a digitization circuitry, a triboelectric energy harvester prototype is fabricated and tested. An axial tibiofemoral load profile from normal walking (gait) is approximated as a 1 Hz sine wave signal and is applied to the harvester. Because the root mean square of voltages generated via this phenomenon is proportional to the applied load, the device can be simultaneously employed for energy harvesting and load sensing. With an approximated knee cyclic load of 2.3 kN at 1 Hz, the harvester generated output voltage of 18 V RMS, and an average power of 6 µW at the optimal resistance of 58MΩ. The harvested signal is rectified through a negative voltage converter rectifier and regulated through a linear-dropout regulator with a combined efficiency of 71%. The output of the regulator is used to charge a supercapacitor. The energy stored in the supercapacitor is used for low resolution sensing of the load through a peak detector and analog-to-digital converter. According to our analysis, sensing the load several times a day is feasible by relying only on harvested power. The results found from this work demonstrate that triboelectric energy harvesting is a promising technique for self-powering load sensors inside knee implants.

The Effect of Dorsal Angulation on Distal Radioulnar Joint Arthrokinematics Measured Using Intercartilage Distance.

Background The effects of dorsal angulation deformity on in vitro distal radioulnar joint (DRUJ) contact patterns are not well understood. Purpose The purpose of this study was to utilize intercartilage distance to examine the effects of forearm rotation angle, distal radius deformity, and triangular fibrocartilage complex (TFCC) sectioning on DRUJ contact area and centroid position. Methods An adjustable implant permitted the creation of simulated intact state and dorsal angulation deformities of 10, 20, and 30 degrees. Three-dimensional cartilage models of the distal radius and ulna were created using computed tomography data. Using optically tracked motion data, the relative position of the cartilage models was rendered and used to measure DRUJ cartilage contact mechanics. Results DRUJ contact area was highest between 10 and 30 degrees of supination. TFCC sectioning caused a significant decrease in contact area with a mean reduction of 11 ± 7 mm 2 between the TFCC intact and sectioned conditions across all variables. The position of the contact centroid moved volarly and proximally with supination for all variables. Deformity had a significant effect on the location of the contact centroid along the volar-dorsal plane. Conclusion Contact area in the DRUJ was maximal between 10 and 30 degrees of supination during the conditions tested. There was a significant effect of simulated TFCC rupture on contact area in the DRUJ, with a mean contact reduction of 11 ± 7 mm 2 after sectioning. Increasing dorsal angulation caused the contact centroid to move progressively more volar in the sigmoid notch.

Biomechanical Comparison of Intramedullary Beaming and Plantar Plating Methods for Stabilizing the Medial Column of the Foot: An In Vitro Study.

Charcot neuroarthropathy often results in a rocker-bottom foot deformity, which leads to ulceration, infection, and amputation. Surgical techniques to reconstruct the medial column include intramedullary beaming and plantar plating, with disagreement regarding which approach provides a stronger construct with superior stability and fixation. The objective of the present cadaveric study was to compare the construct rigidity and strength of beaming and plantar plating of the medial column of 5 paired bilateral feet. Cannulated titanium beams and plates were implanted in the right and left feet, respectively. The specimens underwent interval testing to generate load-displacement and load-strain curves, cyclic loading at low loads, and then were loaded to failure. The beamed and plated specimens had statistically similar stiffness (p = .80) with a mean of 11.1 ± 3.9 N/mm and 11.3 ± 5.9 N/mm, respectively. The beamed and plated specimens had a statistically similar mean strain of -164 ± 75.1 µÎµ and -208 ± 87.8 µÎµ on the dorsal (p = .45) and 92 ± 90.4 µÎµ and 221 ± 100.5 µÎµ on the plantar (p = .08) surfaces of the first metatarsal. Three beamed specimens failed from talus fracture (60%), and 2 beams plastically deformed (40%). Two plated specimens failed from talus fracture (40%), and 3 experienced screw pullout (60%). The beamed and plated specimens withstood a mean load to failure of 234 ± 111.4 N and 140 ± 68.9 N, respectively, with the difference statistically significant (p = .04). Overall, beaming was more robust than plantar plating, because it was less sensitive to specimen size and bone quality.

Development of a hybrid computational/experimental framework for evaluation of damage mechanisms of a linked semiconstrained total elbow system.

BACKGROUND: Long-term durability of total elbow arthroplasty (TEA) is a concern, and bearing wear or excessive deformations may necessitate early revision. The current study used experimental wear testing and computational finite element modeling to develop a hybrid computational and experimental framework for the evaluation of TEA damage mechanisms. METHODS: Three Coonrad-Morrey (Zimmer-Biomet Inc., Warsaw, IN, USA) TEA implants were used for experimental wear testing for 200,000 cycles. Gravimetric measurements were performed before and after the tests to assess the weight change caused by wear. A finite element model of the implant was also developed to analyze ultrahigh-molecular-weight polyethylene (UHMWPE) damage. RESULTS: High localized contact pressures caused visible creep and plastic flow, deforming bushings and creating unintended UHMWPE-on-UHMWPE contact surfaces where considerably high wear rates were observed. Average experimentally measured vs. model-predicted wear was 9.5 ± 1.0 vs. 14.1 mg for the of the medial bushing, 8.5 ± 1.0 vs. 13.9 mg for the lateral humeral bushing, and 34.1 ± 0.7 vs. 36.9 mg for the ulnar bushings, respectively. Model predicted contact stresses on the surfaces of bushings were substantially higher than the yield limit of conventional UHMWPE (87 MPa for the humeral bushings and 83 MPa for the ulnar bushing). CONCLUSIONS: Our study discovered that unintended wear at UHMWPE-UHMWPE contact surfaces, "fed" by excessive plastic flow may, in fact, be of more concern than wear that occurs at the intended metal-UHMWPE contact interfaces. Furthermore, formation of high localized contact stresses much above the yield limit of UHMWPE is another likely contributor to bushing failure for this implant.

Comparing damage on retrieved total elbow replacement bushings with lab worn specimens subjected to varied loading conditions.

Complication rates following total elbow replacement (TER) with conventional implants are relatively high due to mechanical failure involving the UHMWPE bushings. Unfortunately, there are no standardized pre-clinical durability testing protocols for assessing the durability of TER components. This study examines the damage observed on retrieved humeral bushings, and then uses in vitro durability testing with two different loading protocols to compare resulting damage. Damage on 25 pairs of retrieved humeral bushings was characterized using micro-computed tomographic imaging techniques. The damage was compared with that of in vitro test specimens which were subjected to 200 K cycles of either high joint reaction force (high JRF) or high varus moment (high VM) loading. Material removal (mass loss) from bushing components was measured using gravimetric techniques. Thinning was less for retrieved bushings which were still assembled in their humeral component, versus bushings which were loose (0.3 ± 0.3 mm vs. 0.6 ± 0.3 mm, p = 0.02). Comparing in vitro test specimens, thinning due to high VM loading was 0.9 ± 0.3 mm, versus 0.2 ± 0.0 mm for high JRF loading (p = 0.08); however, the actual material removal rates from the humeral bushings were not different between the two protocols (48 ± 5 mm3 /Mc vs. 43 ± 2 mm3 /Mc, p = 1). Neither loading protocol could produce damage patterns fully representative of the spectrum of damage patterns observed on clinical retrievals. Pre-clinical testing should employ multiple loading protocols to characterize implant performance under a broader spectrum of usage. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1998-2006, 2018.

Arthrokinematics of the Distal Radioulnar Joint Measured Using Intercartilage Distance in an In Vitro Model.

PURPOSE: Current techniques used to measure joint contact rely on invasive procedures and are limited to statically loaded positions. We sought to examine native distal radioulnar joint (DRUJ) contact mechanics using nondestructive imaging methods during simulated active and passive forearm rotation. METHODS: Testing was performed using 8 fresh-frozen cadaveric specimens that were surgically prepared by isolating muscles involved in forearm rotation. A wrist simulator allowed for the evaluation of differences between active and passive forearm rotation. Three-dimensional cartilage surface reconstructions were created using volumetric data acquired from computed tomography. Using optically tracked motion data, the relative position of the cartilage models was rendered and used to measure DRUJ cartilage contact mechanics. The effects of forearm movement method and rotation angle on centroid coordinate data and DRUJ contact area were examined. RESULTS: The DRUJ contact area was maximal at 10° supination. There was more contact area in supination than pronation for both active and passive forearm rotation. The contact centroid moved volarly with supination, with magnitudes of 10.5 ± 2.6 mm volar for simulated active motion and 8.5 ± 2.6 mm volar for passive motion. Along the proximal-distal axis, the contact centroid moved 5.7 ± 2.4 mm proximal during simulated active motion. These findings were statistically significant. The contact centroid moved 0.2 ± 3.1 mm distal during passive motion (not significant). CONCLUSIONS: It is possible to examine cartilage contact mechanics of the DRUJ nondestructively while undergoing simulated, continuous active and passive forearm rotation. The contact centroid moved volarly and proximally with supination. There were higher contact area values in supination compared with pronation, with a peak value at 10° supination. CLINICAL RELEVANCE: This study documented normal DRUJ arthrokinematics using a nondestructive in vitro approach. It further reinforced the established biomechanical and clinical literature on contact patterns at the native DRUJ during forearm rotation.

An In Vitro Study of the Role of Implant Positioning on Ulnohumeral Articular Contact in Distal Humeral Hemiarthroplasty.

PURPOSE: To investigate the effect of implant positioning on ulnohumeral contact using patient-specific distal humeral (DH) implants. METHODS: Seven reverse-engineered DH implants were manufactured based on computed tomography scans of their osseous geometry. Native ulnae were paired with corresponding native humeri and custom DH implants in a loading apparatus. The ulna was set at 90° of flexion and the humeral component (either native bone or reverse-engineered implant) was positioned from 5° varus to 5° valgus in 2.5° increments under a 100-N compressive load. Contact with the ulna was measured with both the native distal humerus and the reverse-engineered DH implant at all varus-valgus (VV) angles, using a joint casting method. Contact patches were digitized and analyzed in 4 ulnar quadrants. Output variables were contact area and contact pattern. RESULTS: Mean contact area of the native articulation was significantly greater than with the distal humeral hemiarthroplasty (DHH) implants across all VV positions. Within the native condition, contact area did not significantly change owing to VV angulation. Within the DHH condition, contact area also did not significantly change owing to VV angulation. Conversely, in the DHH condition, contact pattern did significantly change. Medial ulnar contact pattern was significantly affected by VV angulation. Lateral ulnar contact was variably affected, but generally decreased as well. CONCLUSIONS: Ulnar contact patterns were changed as a result of VV implant positioning using reverse-engineered DH implants, most notably on the medial aspect of the joint. Implant positioning plays a crucial role in producing contact patterns more like those observed in the native joint. CLINICAL RELEVANCE: Recent clinical evidence reports nonsymmetrical ulnar wear after DHH. This work suggests that implant positioning is likely a contributing factor and that more exact implant positioning may lead to better clinical outcomes.