Passive ligament stability in natural knee: a cadaveric biomechanical study

Abstract

Objectives: Applying the correct amount of collateral ligaments tension in the knees during surgery is a prerequisite to restore normal kinematics after TKA. It is well known that a low value of ligament tension could lead to an instable joint while a higher tension could induce over-tensioning and problems at later follow-up. In this study, an experimental cadaveric activity was performed to measure the minimum tension required to achieve stability in the knee joint.Methods: 10 cadaveric knee specimens were investigated in this study. The femur and tibia were fixed with polyurethane foam in specific designed fixtures and clamped to a loading frame.Increasing displacement was applied to the femoral clamp and the relative force was measured by a loading-frame machine up to the stability of the joint, determined by a decrease in the derivate of the force/displacement trend followed by a plateau.The force span between the slack region and the plateau was considered as the tension required to stabilize the joint.This methodology was applied for joints with intact cruciate ligaments, after ACL resection and after further PCL resection, to simulate the knee behavior prior a CR and a PS implant.The test was performed at 0, 30, 60 and 90° of flexion. Each configuration was analyzed three times for the sake of repeatability.Results and Conclusion: Results demonstrated that an overall tension of 41.2N (range 30.0-48.0 N) is sufficient to reach stability in a native knee with intact cruciate ligaments. Similar values appear to be sufficient also in an ACL resected knee (average 45.6, range 41.2-50.0 N), while higher tension is required (average 58.6N, range 40.0-77.0 N) were necessary in the case of PCL retention. Moreover, in this configuration, the tension required for stabilization was slighter higher at 30 and 60° of flexion compared to the one required at 0 and 90° of flexion.The results are in agreement to the ones found by other recent experimental study [Manning et al 2018 (KSSTA)] and shown that the tension necessary to stabilize a knee joint in different ligament conditions is way lower than the ones usually applied via tensioners nowadays.To reach functional stability, surgeons need to consider such results intraoperatively to avoid laxity, mid-flexion instability or ligament over-tension.

Design of an Affordable, Modular Implant Device for Soft Tissue Tension Assessment and Range of Motion Tracking During Total Hip Arthroplasty

“…Sensors ranging from strain-gauges to force-sensitive resistors (FSR) and optical sensors were evaluated. Hall-effect sensors were chosen because of their simplicity in electrical circuit design, space constraints, cost and reliability, and because they were effectively used in a knee balancer unit before [5] . These Hall sensors use a magnetic flux to determine their relative position to the source.…”

“…Soft tissue balance of THA is less investigated than that of total knee arthroplasties (TKAs) [5] , [6] , even though the outcomes of THAs also rely on the surgeon’s experience to determine properly balanced soft tissues. Instability is the biggest cause of early implant failure, typically within five years of surgery [7] .…”