ACL Injury

An anterior cruciate ligament (ACL) injury is a partial or complete tear of the main restraint to anterior tibial translation, usually from a non-contact pivoting, cutting or landing movement in a young athlete.

It is most common in pivoting sports such as football, rugby, netball, basketball and skiing, and female athletes are at higher risk. Not every rupture needs surgery: the prime indication for reconstruction is symptomatic instability, and management depends on instability, functional demand and associated injuries.

The ACL runs from the posteromedial aspect of the lateral femoral condyle to the anterior intercondylar area of the tibia. Its anteromedial bundle is tight in flexion and resists anterior translation; its posterolateral bundle is tight in extension and resists rotation. It is intra-articular but extra-synovial. The anterolateral ligament adds to rotational control.

Mechanism: in one series of 100 knees, 72% were non-contact, from sudden deceleration before a change of direction or a landing, typically with the knee near extension and in dynamic valgus. Contact injuries usually follow a valgus blow to the knee.

Associated injuries are common:

• •Meniscal tears: the lateral meniscus is typically torn acutely, the medial meniscus in chronic ACL deficiency
• •Bone bruises on the lateral femoral condyle and posterolateral tibial plateau
• •MCL and posterolateral corner injury; a missed posterolateral corner injury is a cause of graft failure