[An experimental study on the stability of the knee joint. Special reference to the mechanisms of rotatory stability of the knee joint].

In order to evaluate the stabilizing mechanisms of the ligaments, menisci and the conformity of the condylar surface, six human knee joints and five dog's knee joints were tested by the rotatory stability testing machine devised by myself. The torque-rotation curve and the amount of the up hill movement were measured under various compressive loads. Internal and external rotation were applied to the knee joint with range of 0.2 radian respectively. During rotatory movement, various compressive loads (0 kgf, 20 kgf, 40 kgf, 60 kgf, 80 kgf) were applied on the tibio-femoral joint. The following results were obtained in this study. Within a range of 0.2 radian in internal and external rotation respectively, rotatory stability was almost unaffected by sectioning of the cruciate ligaments. Rotatory stability was affected significantly by sectioning the medial collateral ligament. Almost the same results were obtained by removal of the medial meniscus. The intrinsic factors, especially the medial collateral ligament and the medial meniscus, provided the stability of external rotation for the knee joint. The amount of the up hill movements were measured 0.5 mm in internal rotation, and 0.1-0.2 mm in external rotation respectively. Only after removal of the medial meniscus, the amount of the up hill movement were decreased obviously. This decreases of the up hill movement were observed in external rotation. So, it was concluded that medial meniscus has the stabilizing mechanism of external rotation by the up hill movement. The conformity of the condylar surface was an important factor in the stability of the knee joint under compressive load. Especially, it restricts internal rotation.