RELATING TKA TISSUE RELEASE TO JOINT RESPONSE USING AN INSTRUMENTED TRIAL IMPLANT

Introduction Improper soft-tissue balancing can result in postoperative complications after total knee arthroplasty (TKA) and may lead to early revision. A single-use tibial insert trial with embedded sensor technology (VERASENSE from OrthoSensor Inc., Dania Beach, FL) was designed to provide feedback to the surgeon intraoperatively, with the goal to achieve a “well-balanced” knee throughout the range of motion (Roche et al. 2014). The purpose of this study was to quantify the effects of common soft-tissue releases as they related to sensor measured joint reactions and kinematics. Methods Robotic testing was performed using four fresh-frozen cadaveric knee specimens implanted with appropriately sized instrumented trial implants (geometry based on a currently available TKA system). Sensor outputs included the locations and magnitudes of medial and lateral reaction forces. As a measure of tibiofemoral joint kinematics, medial and lateral reaction locations were resolved to femoral anterior-posterior displacement and internal-external tibial rotation (Fig 1.). Laxity style joint loading included discrete applications of ± 100 N A-P, ± 3 N/m I-E and ± 5 N/m varus-valgus (V-V) loads, each applied at 10, 45, and 90° of flexion. All tests included 20 N of compressive force. Laxity tests were performed before and after a specified series of soft-tissue releases, which included complete transection of the posterior cruciate ligament (PCL), superficial medial collateral ligament (sMCL), and the popliteus ligament (Table 1). Sensor outputs were recorded for each quasi-static test. Statistical results were quantified using regression formulas that related sensor outputs (reaction loads and kinematics) as a function of tissue release across all loading conditions. Significance was set for p-values ≤ 0.05. Results Tissue releases, and in particular the sMCL and PCL, led to multiple findings, many of which were dependent on flexion (Table 2). For PCL resection, at 10° of flexion lateral and total joint loads decreased, whereas at 45 and 90° lateral load increased. In addition, there was a significant anterior shift of the femur that increased with flexion angle, while tibial rotation was only affected at 90°. sMCL release decreased the total load across all flexion angles, and impacted the medial load at 10° only. The only structure for which no significant relationship was discovered was the deep medial collateral ligament, as this variable was confounded on others. Discussion One critical aspect of TKA is achieving appropriate soft-tissue balance to maximize postoperative performance. In this study, the sensor provided a direct measurement of joint loading and kinematics, which were related to surgically relevant soft-tissue releases. Results showed the sMCL to decrease joint loads and flexion dependent changes after PCL release, likely an indication of bundle specific response. Future work should be performed to examine the roles of individual ligament bundles, as well as graded effects of tissue releases. Overall, the results corroborate previous findings and provide a new and direct look at the role of ligaments in TKA. Significance This study quantified relationships between surgically relevant tissue states and joint response in TKA. The data has the potential to be applied intraoperatively to guide soft-tissue releases. To view tables/figures, please contact authors directly.