Tears of the anterior cruciate ligament in the knee are common in many sports – particularly basketball, soccer, football and skiing. As one of the four main ligaments within the knee, the ACL is crucial for its stability, so a tear will not only cause substantial pain but also a loss of stability in the affected knee. Full ACL tears will not heal on their own and must be repaired via surgery in order to restore the knee to its full range of function. However, a partially torn ACL may or may not require surgery, depending upon whether instability remains after a full course of progressive physical therapy with follow-up medical evaluation. Approximately 50 percent of these tears occur alongside an injury to the meniscus or other parts of the knee. Repair of a ruptured ACL involves replacing the ligament with a substitute graft comprised of a tendon from elsewhere in the patient’s body or from a cadaver. Most patients who undergo this surgery and the full course of prescribed rehabilitation following it have very good long-term outcomes with regard to knee function and stability.