Arthroscopic identification of the anterior cruciate ligament posterolateral bundle: the figure-of-four position.

Anatomic double-bundle reconstruction in anterior cruciate ligament (ACL) tears has been developed during the last few years. Although anteromedial (AM) bundle reconstruction is routinely performed, finding the femoral attachment of the posterolateral (PL) bundle remains a problem. We describe how a classic arthroscopic position, the figure-of-4 position, allows the PL bundle to be easily recognized. During flexion, the femoral attachment of the PL bundle describes an arc around the AM femoral attachment. The femoral attachment of the AM bundle is the center of rotation of the ACL, which explains the isometric behavior of this bundle. After 45 degrees of flexion, the PL femoral attachment becomes anterior to the AM femoral attachment. The AM bundle is tight during flexion, whereas the PL bundle is under tension when the knee is extended and becomes lax with knee flexion. At 90 degrees of flexion, the PL bundle is difficult to identify because it is lax; only its femoral insertion lies anterior to the AM bundle close to the articular cartilage of the lateral condyle. The use of an additional tibial varus torque and internal rotation (i.e., the figure-of-4 position) tightens the PL bundle and enhances the visualization of its insertion, allowing for easy identification of this bundle.