Anatomic variations of the anterior cruciate ligament (ACL) are very rare. The prevalence of congenital aplasia or hypoplasia of the ACL is 0.017 per 1,000 live births. The normal ACL consists of the anteromedial (AMB) and posterolateral bundles (PLB). Together, they attach to a fossa on the posteromedial aspect of the lateral femoral condyle. The PLB fibrils are smaller and shorter than those of the AMB. We report an ACL variation that had not been previously described, in which the PLB was attached to an intraarticular accessory ossicle, without causing knee instability. The large accessory ossicle caused pain. We reviewed the anatomy, anomalies, and variation in the ACL.
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