Anterior Cruciate Ligament ACL

The ACL is attached to the anteromedial aspect of the tibia and courses posteriorly, laterally, and proximally across the tibiofemoral joint and attaches to a fossa along the posterior aspect of the medial surace of the lateral femoral condyle.

The ACL consists of two primary bands or bundles, the anteromedial band and the posterolateral band. The AMB is taught with flexion and the PLB becomes relaxed. With extension the AMB relaxes and the PMB becomes taught. The PLB provides the greatest restraint to anterior translation in extension till about 20 degrees of flexion (Dodds & Arnoczky. Arthroscopy 10:132 1994; Bach et al J Biomech 30:281 1997). The AMB is preferentially tested when anterior translation tests are performed in flexed positions. When the AMB bundle is torn with an intact PLB, the anterior drawer test will still come up positive (Amis & Dawkins JBJS Br 73:260 1991).

The ACL resists anterior tibial translation on the femur. Butler et al (JBJS Am 62:259; 1980) determined that the ACL provides 85% of the resistance to anterior translation at 30 degrees and 90 degrees of knee flexion. It also resists hyperextension of the knee. The ACL is a secondary restraint to varus and valgus motion (Wascher et al JBJS Am 75:377 1993; Inoue et al Am J Sports Med 15:15 1987). During a valgus stress to the flexed knee, the ACL becomes a restraint to ER of the tibia (130). The ACL assissts the MCL in controlling tibial IR (65). Other functions include the screw-home mechanism (68) and a guiding function during tibiofemoral flexion and extension (68,116).

nerve branches of the posterior tibial nerve.

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