The role of cruciate ligaments in maintaining knee joint stability.

The role of the cruciate ligaments in maintaining the stability of the knee joint is delineated by experimental studies on 21 fresh adult knee specimens in addition to the analysis of symptoms in 111 cases of cruciate ligament injuries. Cruciate ligaments maintain not only the anteroposterior stability, but also rotational and one-plane medial or lateral stability together with the medial and lateral structures. The anterior cruciate ligament (ACL) plays a part in maintaining anterior one-plane stability and rotational stability of the knee, while the posterior cruciate ligament plays a major part in maintaining both posterior one-plane stability and rotational stability of the knee. An isolated medial (or lateral) ligament (ML) tear can only result in medial or lateral one-plane instability and an increased rotation, but no shift of the axis of rotation occurs. It is not a genuine rotational instability. Both ACL and ML tears are present in one-plane medial, one-plane anterior, and anteromedial rotational instability, but the anterior drawer test or abduction stress test may be negative if the tear of the ACL or ML is partial.