Summary

Our cadaveric study shows that the MCL takes on the role of a primary restraint to internal torque after ACL rupture

Abstract

Introduction

The anterior cruciate ligament (ACL) is the most injured ligament in the knee and plays a significant role in multi-ligament knee injury. Previous studies have only focused on strain measurement of ligaments in isolation. To our knowledge, there are no studies examining the strain behaviours of the knee cruciate and collateral ligaments simultaneously. Our study aims to simultaneously measure the strain on the knee cruciate and collateral ligaments under a common force. We will investigate the strain distribution on the posterior cruciate (PCL), medial collateral (MCL) and lateral collateral ligaments (LCL) with an intact and cut ACL.

Methods

Six fresh frozen cadavers were used in this study. To capture simultaneous strain of the knee ligaments, uniaxial strain gauges were sutured into the anterior bundle of the ACL, posteromedial bundle of the PCL and in the mid-substance of the MCL and LCL. The specimens were flexed from 0° to 90° using a 6 degrees-of-freedom (DOF) robotic simulator. The specimens were first tested with the ACL intact. The ACL was subsequently resected, and the specimens were tested again with the same protocol.

Results

The strain measurements obtained from the LCL, MCL, and PCL revealed distinct patterns of strain distribution following ACL injury. Specifically, the maximum mean strain across all six specimens increased by approximately 0.86 times for the LCL. The MCL showed the most significant increase in strain, with readings increasing by 2.25 times, while the PCL had a smaller increase of 0.28 times. These findings indicate that the MCL experiences the most significant increase in strain after ACL rupture, suggesting it becomes the primary restraint to internal torque. The moderate increase in LCL and PCL strain suggests that while these ligaments also contribute to knee stability, their role is less pronounced compared to the MCL in the context of an ACL-deficient knee.

Conclusion

Our study suggests that the MCL takes on the role of a primary restraint to internal torque after ACL rupture.