Medial Collateral Ligament

Anatomy

Traditionally, the medial side of the knee has been described as containing a superficial layer, a middle layer, and a deep layer. More recently, the work of LaPrade and associates has detailed the three most important stabilizers of the medial knee: the POL, the superficial medial collateral ligament (sMCL), and the deep medial collateral ligament (dMCL) ( Fig. 17.1 ). ^{, ,} The sMCL is the largest structure of the medial knee, measuring 10 to 12 cm in total length. The femoral attachment is described as 3.2 mm proximal and 4.8 mm posterior to the medial epicondyle. Two separate tibial attachment sites are identified. The distal attachment site is 6 cm distal to the joint line attaching to bone, and the proximal attachment site is to soft tissue located over the semimembranosus tendon. The dMCL is identified as a thickening of the medial joint capsule distinct from and deep to the sMCL. The dMCL is comprised of the meniscotibial and the meniscofemoral components. The POL is a separate structure from the sMCL, consisting of three fascial extensions off of the semimembranosus that merge with the posteromedial joint capsule. The central extension has been proposed to be the most important because it is the largest and thickest. ^{, ,} The femoral POL insertion site is described as attaching 7.7 mm distal and 2.9 mm anterior to the gastrocnemius tubercle. The tibial insertion site of the POL is described as fanlike, primarily attaching to the posteromedial aspect of the medial meniscus, the meniscotibial portion of the posteromedial capsule, and the posteromedial part of the tibia ( Fig. 17.2 ).

The biomechanics of the sMCL can be attributed to the distinct proximal and distal and divisions. The proximal division is the primary stabilizer to valgus motion at all knee flexion angles, whereas the distal division resists valgus loading at increased knee flexion angles. The sMCL is also an important restraint to external rotation, as well as a secondary stabilizer against anterior and posterior tibial translation in the cruciate-deficient knee. The dMCL has been reported to provide secondary valgus stability, which becomes significant during sMCL injuries. The POL provides restraint to valgus loads, as well as internal rotation with knee flexion angles between 0 and 30 degrees. Reconstruction techniques should aim at anatomic recreation of these structures to restore the important load sharing characteristics ( Fig. 17.3 ).