Purpose

The purpose of this study was to define the length-change patterns of the superficial medial collateral ligament (sMCL), deep MCL (dMCL), and posterior oblique ligament (POL) across knee flexion and with applied anterior and rotational loads.
Material and methods

Ten cadaveric knees were mounted in a kinematics rig with loaded quadriceps and hamstrings muscles. Length change patterns of the anterior and posterior fibres of the sMCL, dMCL and POL were recorded from 0 to 100° flexion. Length changes were recorded while a 90 N anterior load and a 5 Nm internal and external rotational torque were applied. Length changes were normalized to lengths at 0° flexion.
Results

The anterior sMCL tightened as the knee was flexed (p < 0.01), and further tensioned under tibial external rotation (p < 0.001). Conversely, the posterior sMCL slackened with flexion (p < 0.001), while internal rotation tightened these fibers between 10 and 100° (p < 0.05). Tibial external rotation significantly lengthened the anterior dMCL fibres by 10% compared to the unloaded condition throughout flexion (p < 0.001). Release of the sMCL caused the dMCL fibres to become taut and increased valgus rotation (p < 0.01). The lengths of the anterior and posterior POL fibres decreased continuously with knee flexion (p < 0.001). Tibial internal rotation significantly increased the length of the POL (p < 0.001).
Conclusion

The structures of the medial ligament complex reacted differently to knee flexion and applied loads. Structures attaching proximal and posterior to the medial epicondyle were taut in extension, whereas the anterior sMCL tensioned during flexion. The anterior dMCL was extensively strained by tibial external rotation and after sMCL release.