What injuries does the anterior cruciate ligament prevent?

Knee instability: The anterior cruciate ligament (acl) is one of four major ligaments in the knee to help maintain knee stability (the others include the posterior cruciate ligament - pcl, lateral collateral ligament - lcl, and the medial collateral ligament - mcl). The ACL is the most significant of the four and helps prevent the lower leg from sliding forward from the upper leg.

Medial meniscus tear: Absence of an anterior cruciate ligament (acl) allows rotation and sliding of the knee. This sliding squeezes and stresses the medial meniscus (which attemps to prevent this sliding and rotating motion). Each time an acl deficient person twists the knee and tears the medial meniscus, swelling from the damage occurs. Over time, this can also contribute to arthritis resulting in loss of the meniscus.