What is the ACL?

Diagram of knee joint showing ACL

Diagram of Knee Joint showing ACL

Anterior Cruciate Ligament

The anterior cruciate ligament (ACL) is one of four critical ligaments that connects the bones of the knee joint. Its function is to provide stability to the knee and minimize the amount of stress that impacts the knee joint. The ACL accomplishes this by restraining the amount of excessive forward movement of the lower leg bone (tibia) in relation to the thigh bone (femur), and by limiting rotational movements of the knee.

Two other major ligaments are located outside the knee joint, and these stabilize the knee’s sideways motion. The ligament on the inner side of the knee is the medial collateral ligament (MCL), while the ligament on the outer side of the knee is the lateral collateral ligament.