When the knee is twisted or falls, the ligaments that link the femur and tibia for stability may be torn. When the anterior cruciate ligament (ACL) ruptures and does not heal itself, it splits into a twist, severely affecting the stability of the knee joint. Fortunately, current reconstruction techniques can restore good function to the knee after an ACL rupture. ACL Rupture: Ligaments are tough, non-extending fibers that hold the bones together. The ACLs cross each other within the knee joint to provide stability to the joint. The ACL is often ruptured by sudden changes in direction while running, by stopping sharply or by landing from a height, and adolescents between the ages of 15 and 25 are particularly susceptible to injury in basketball or other sports that require rotation on the axis of the leg. A meniscus rupture is associated with a popping sound, knee dysfunction, and rapid onset of pain and swelling. Early management of the injury includes rest, ice, immobilization of the knee in an elevated brace, crutches and analgesics, and evaluation of the ligament injury by a physician who practices sports medicine. Evaluation: The physician determines the extent of the ACL injury by physical examination and radiographs and MRI. In most cases, ACL reconstruction is required, in which strong, normal tissue is taken from elsewhere near the knee to replace the damaged ACL, usually the patellar ligament or N-tendon. They are passed through the interior of the knee joint to reconstruct the ACL to restore knee stability and protect the knee cartilage. In some cases the ACL is treated with avulsed bone masses, which may be considered for repositioning and fixation. A non-surgical approach using muscle strengthening is not sufficient when the ACL injury severely endangers the knee stability, which would compromise the articular cartilage and cause irreversible cartilage damage. Prognosis: Successful ACL reconstruction can enhance knee stability, prevent further damage to the joint and allow the patient to return to sports. In the United States, 95,000 ACL injuries occur each year, with 50,000 reconstructive procedures performed, with a success rate of 85-92%. Patients need functional exercises to gradually restore knee flexibility and stability after ACL reconstruction, and leg strength exercises to protect the reconstructed structure. Knee braces are required and return to sports can be started after 4-6 months postoperatively.