MRI Analysis of Anteroposterior Stability in the Normal Human Knee

During activities the knee experiences compressive forces caused by the weight of the body and muscle forces. However, there is also an anterior shear force pushing the femur forwards on the tibia. It is likely to be important to the feeling of stability that the shear force is resisted so as to limit the anterior femoral displacement. The dished bearing surface of the medial tibial compartment in combination with the medial meniscus may well perform this function. In contrast, the lateral tibial surface is convex in the sagittal plane and the meniscus is too mobile to offer any anteroposterior (AP) restraint. Therefore, we hypothesize that if an anterior or posterior force is applied to the femur relative to the tibia, AP stability is provided by the medial side, while the lateral side allows for femoral rollback to facilitate a high range of flexion. At any flexion angle, rotational laxity will occur about a point on the medial side.