Acromioclavicular joint reconstruction implants have differing ability to restore horizontal and vertical plane stability

Purpose Persistent acromioclavicular joint (ACJ) instability following high grade injuries causes significant symptoms. The importance of horizontal plane stability is increasingly recognised. There is little evidence of the ability of current implant methods to restore native ACJ stability in the vertical and horizontal planes. The purpose of this work was to measure the ability of three implant reconstructions to restore native ACJ stability. Methods Three groups of nine fresh-frozen shoulders each were mounted into a robotic testing system. The scapula was stationary and the robot displaced the clavicle to measure native anterior, posterior, superior and inferior (A, P, S, I) stability at 50 N force. The ACJ capsule, conoid and trapezoid ligaments were transected and the ACJ was reconstructed using one of three commercially available systems. Two systems (tape loop + screw and tape loop + button) wrapped a tape around the clavicle and coracoid, the third system (sutures + buttons) passed directly through tunnels in the clavicle and coracoid. The stabilities were remeasured. The data for A, P, S, I stability and ranges of A–P and S–I stability were analyzed by ANOVA and repeated-measures Student t tests with Bonferroni correction, to contrast each reconstruction stability versus the native ACJ data for that set of nine specimens, and examined contrasts among the reconstructions. Results All three reconstructions restored the range of A–P stability to that of the native ACJ. However, the coracoid loop devices shifted the clavicle anteriorly. For S–I stability, only the sutures + buttons reconstruction did not differ significantly from native ligament restraint. Conclusions Only the sutures + buttons reconstruction, that passed directly through tunnels in the clavicle and coracoid, restored all stability measures (A, P, S, I) to the native values, while the tape implants wrapped around the bones anteriorised the clavicle. These findings show differing abilities among reconstructions to restore native stability in horizontal and vertical planes. (300 words)

Enabling Performance Qualification of Additively Manufactured Parts Under Multiaxial Loading Emulating In-Service Conditions

The material imperfections generated by Additive Manufacturing (AM) processes across multiple scales can differ significantly from those arising by conventional manufacturing (CM) methods. To qualify these parts in a manner that accounts for all these imperfections without accounting explicitly for each of them, an outline of a rapid functional qualification methodology based on the concept of Performance Signature (PerSig) is presented first. The PerSigs are defined for both the prequalified CM parts and the AM-produced ones. Comparison measures are defined and enable the construction of differential PerSigs (dPerSig) in a manner that captures the differential performance of the AM part vs. the prequalified CM one. This approach is extended in this paper for the case of multiaxial loading conditions reflecting actual in-service loading. Application of the methodology is presented for a fitting bracket in the P-3C Orion aircraft platform and is based on synthetic data. The application of multiaxial loading emulating in-service loading conditions is proposed by the utilization of a custom-designed 6-DoF robotic testing system that will generate physical data.

Talar Motion is Constrained by Tricortical Screw Fixation of the Syndesmosis: A Cadaveric Robotic Study

Objectives: High ankle sprains are a common injury that occur in up to 11% of ankle sprains. Injury to the structures of the syndesmosis, the anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), and interosseous membrane (IOM), has been shown to be predictive of residual symptoms after ankle injury. When the syndesmosis is unstable, it is typically treated surgically with cortical screw fixation or suture button fixation. Studies have shown that a 1 mm lateral shift of the talus relative to the tibia significantly decreases the tibiotalar contact area by 42%. Thus, restoring the tibiotalar kinematics to those of the intact ankle with appropriate fixation is important to avoid accelerated tibiotalar arthritis. The objective of this study was to quantify tibiotalar joint motion after syndesmotic screw and suture button fixation compared to the intact ankle. Methods: Nine fresh-frozen human cadaveric specimens (mean age 60 yrs.; range 38-73 yrs.) were tested using a six degree-of-freedom robotic testing system. The subtalar joint was fused and the tibia and calcaneus were rigidly fixed to a robotic manipulator, while fibular length was maintained and fibular motion was unconstrained. Talar motion with respect to the tibia was measured using the robotic testing system. A 5 Nm external rotation moment and 5 Nm inversion moment were applied independently to the ankle at 0°, 15°, and 30° plantarflexion and 10° dorsiflexion. Outcome variables included talar medial-lateral (ML) translation, anterior-posterior (AP) translation, and internal/external rotation relative to the tibia in the following syndesmosis states: 1) intact, 2) AITFL transected, 3) AITFL, PITFL, and IOM transected, 4) 3.5 mm cannulated tricortical screw fixation, and 5) suture button fixation. An ANOVA with a post-hoc Tukey analysis was performed for statistical analysis. Statistical significance was set at p < 0.05. Results: There were significant differences in ML translation of the talus relative to the tibia between the tricortical screw fixation and the intact ankle. These significant changes were only present during states with no loads applied. Tricotical screw fixation resulted in a significant decrease in medial translation of the talus compared to the intact ankle at 30° plantarflexion and increased lateral translation at 0° flexion (p < 0.05) (Figure 1). The talus moved 1.1 mm less medially at 30° plantarflexion and 0.4 mm more laterally at 0° flexion in the tricortical screw fixation state compared to the intact ankle. The total medial translation of the talus relative to the tibia during plantarflexion decreased from 1.1 mm to only 0.4 mm. No significant difference in AP translation or external rotation of the talus existed between the tricortical screw fixation and the intact ankle. No significant differences existed in translation or rotation of the talus between the suture button fixation and intact ankle at any ankle positions. Conclusion: Suture button fixation restored tibiotalar motion in all planes, with no significant differences compared to the intact ankle. Tricortical screw fixation significantly increased lateral shift of the talus in a neutral ankle position and constrained motion during plantarflexion compared to the intact ankle, which can lead to accelerated tibiotalar arthritis. Thus, physicians should consider hardware removal after tricortical screw fixation for syndesmotic repair to avoid post-traumatic arthritis. [Figure: see text]

Effect of Meniscal Ramp Repair on Knee Kinematics, ACL In Situ Force and Bony Contact Forces - A Biomechanical Study

Objectives: While recent studies showed that all inside meniscal ramp repair is able to restore knee kinematics, the effects of ramp repairs on ACL in-situ forces (ISF) and bony contact forces is still unclear. Therefore, the purpose of this study is to determine the effect of ramp lesion repair on knee kinematics, the ACL-ISF and bony contact forces using a 6-degree-of-freedom (DOF) robotic testing system. It was hypothesized that ramp repair will restore kinematics, ACL-ISF and bony contact forces comparably to the forces of the intact knee. Methods: 5 fresh-frozen human cadaveric knee specimens were tested using a 6-DOF robotic testing system (FRS2010) to continuously flex the knee from 0° to 90° and apply continuous loading conditions: 134 N anterior load + 200 N compressive load (CL), 4 Nm internal torque + 200 N CL, 4 Nm external torque + 200 N CL. Loading conditions were applied to the: 1) Intact knee 2) Arthroscopically induced 25 mm ramp lesion via posteromedial portal 3) All inside ramp repair 4) ACL deficient knee + ramp repair 5) soft tissue removal 6) Transection of the lateral condyle. To mimic an ideal ACL reconstruction the native ACL was kept intact. By replaying kinematics, ACL-ISF and bony contact forces were determined. Repeated measure ANOVAs were performed to compare knee states at each flexion angle (p<0.05). Results: Ramp repair significantly reduced anterior translation compared to the ramp deficient knee in high flexion under anterior load and CL (mean diff. -0.8 mm, range 0.6-0.9 mm) and at all flexions angles while applying internal torque and CL (mean diff. -2.3 mm, range 1.8-3.3 mm). Increased medial translation and valgus position were observed in all loading conditions at all flexion angles. Both ACL-ISF and medial bony contact forces were not significantly altered by the ramp lesion and repair under any applied loading and flexion angle. In contrast, ramp repair significantly increased lateral bony contact forces by under external torque and CL at 60° and 70° flexion compared to the ramp deficient knee, 32 N and 37 N respectively. No significant differences between intact and ramp deficient knee were detected with respect to kinematics, ACL-ISF and bony contact forces. Conclusion: In this study ramp repair decreased anterior translation, increased valgus rotation, and increased bony contact forces in the lateral compartment, disproving the hypothesis under study. The data from this study puts into question potential overconstraint when repairing ramp lesions utilizing all inside devices in 10 degrees of knee flexion. Contrasting previous literature that showed the restoration of the intact state, the results might be attributable to added CL forces and missing influence of the ACL reconstructions. The findings of this study also imply that untreated ramp lesion might not affect ACL-ISF. Future research is needed to better understand the influence of different techniques for repair of ramp lesions and the effect of chronicity on ramp lesions in patients.

Validation of a High-Payload Robotic/UFS Testing System for Studying of Joint Motion

Robotic technology has been adopted for studying the biomechanics of the knee joint by our research center and others since 1993 to gain a fundamental understanding of the knee, as well as to provide orthopedic surgeons with scientific data on the efficacy of various reconstructive techniques [1–4]. A robotic testing system generally consists of a six degree-of-freedom (DOF) robotic manipulator with a universal force-moment sensor (UFS) attached to the end effector [5]. This testing system offers a wide range of motion with precision path and position repeatability.

An Intelligent Control Method Based on Fuzzy Logic for a Robotic Testing System for the Human Spine

In previous biomechanical studies of the human spine, we implemented a hybrid controller to investigate load-displacement characteristics. We found that measurement errors in both position and force caused the controller to be less accurate than predicted. As an alternative to hybrid control, a fuzzy logic controller (FLC) has been developed and implemented in a robotic testing system for the human spine. An FLC is a real-time expert system that can emulate part of a human operator’s knowledge by using a set of action rules. The FLC provides simple but robust solutions that cover a wide range of system parameters and can cope with significant disturbances. It can be viewed as a heuristic and modular way of defining a nonlinear, table-based control system. In this study, an FLC is developed which uses the force difference and the change in force difference as the input parameters, and the displacement as the output parameter. A rule-table based on these parameters is designed for the controller. Experiments on a physical model composed of springs demonstrate the improved performance of the proposed method.