Anterior cruciate ligament

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Sagittal view of the knee joint showing the patellofemoral and tibiofemoral joints.

The anterior cruciate ligament (ACL), is the weaker of two cruciate ligaments of the knee, the other being the posterior cruciate ligament. These intracapsular ligaments are so named due to the fact that they cross each other, creating an imaginary cross (the word cruciate comes from the latin word crux that means cross).

The anterior cruciate ligament originates from the anterior intercondylar area of the tibia, close to the attachment of the medial meniscus. From here, it extends superoposteriorly, and laterally to insert on to the posteromedial side of the lateral femoral condyle. It measures roughly 38 mm in length and like its counterpart has no synovial covering although it sits inside the joint capsule. As it traverses the intercondylar region, the anterior cruciate ligament crosses lateral to the posterior cruciate ligament.

The primary function of the ACL is to prevent posterior displacement of the femur on a fixed tibia or anterior displacement of the tibia on the femur. Additionally, during flexion, the ACL limits posterior rolling of the femoral condyles on the tibial plateau. The ACL also serves to restrict hyperextension of the knee joint.