There is no consensus on the behavior of the medial passive structures of the knee under motion and applied loads. Hence, current medial collateral ligament (MCL) reconstruction techniques differ fundamentally in attachment points, number of bundles and the tensioning protocol. The purpose was to define the length change patterns of the anterior and posterior fibers of the superficial MCL, deep MCL 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 6-DOF kinematics rig with loaded quadriceps and hamstrings muscles. Length change patterns of the anterior and posterior borders of the sMCL, dMCL and POL were recorded from 0° to 100° of knee flexion by use of linear variable displacement transducers. Length changes were also recorded while a 90 N anterior force, and 5 Nm internal and external rotational torques were applied. Length changes were normalized to lengths at 0° flexion. The statistical analysis used a two-factor analysis of variance (ANOVA) with repeated measures and statistical significance was defined as p < 0.05.
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 fibers by 10% compared to the unloaded condition throughout flexion (p < 0.001). In the intact knee dMCL fibers are slack but release of the sMCL caused the dMCL fibers to become taut and increased valgus rotation (p<0.01). The lengths of the anterior and posterior POL fibers decreased continuously with knee flexion (p < 0.001). Tibial internal rotation significantly increased the length of the POL (p < 0.001).
The three medial structures 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 isometric point was at the ME, at the center of the sMCL. The anterior dMCL, with its oblique orientation towards the anteromedial rim of the tibial plateau, was extensively strained by tibial external rotation and after sMCL release. These results provide fundamental knowledge of the native behavior of the sMCL, dMCL and POL and their response to externally applied loads. It therefore offers the basis for new MCL reconstruction techniques regarding graft positioning and tensioning.