The posterior cruciate ligament serves a complex purpose throughout the entire flexion arc, acting primarily to prevent posterior travel of the tibia, but also performing secondary varus, valgus and rotational stabilizing roles when the collateral ligaments are deficient. It also provides resistance to hyperextension when the posterior capsule is deficient. Because the posterior cruciate ligament is a medial structure attached to the medial femoral condyle, it often contracts in the varus knee and stretches in the valgus knee. When it is contracted it often can be released partially, and much of its function can be preserved. Even when it is insufficient to provide adequate posterior stability, it can provide rotational and varus-valgus stabilization.