The Role of the Medial Collateral Ligament and Posteromedial Capsule in Controlling Knee Laxity

BackgroundThe medial aspect of the knee has a complex capsular structure; the biomechanical roles of specific structures are not well understood.HypothesisThe 3 strong stabilizing structures, the superficial and deep medial collateral ligaments and the posteromedial capsule, make distinct contributions to controlling tibiofemoral laxity.Study DesignControlled laboratory study.MethodsChanges in knee laxity under anterior-posterior drawer, valgus, and internal-external rotation loads were found by sequential cutting in 18 cadaveric knees. Three cutting sequences allowed the roles of the 3 structures to be seen in isolation and in combination. Some force contributions were also calculated.ResultsThe posteromedial capsule controlled valgus, internal rotation, and posterior drawer in extension, resisting 42% of a 150-N drawer force when the tibia was in internal rotation. The superficial collateral ligament controlled valgus at all angles and was dominant from 30° to 90° of flexion, plus internal rotation in f...