The anterior cruciate ligament (ACL) is an important stabilizer of the knee. It is critical to athletes involved in start-stop, explosive, di-rection change sports.

These include soccer, basketball, football, gymnastics, and volleyball to name a few. The ACL is the most common seri-ously injured ligament in the knee. It is estimated that more than 350,000 ACL injuries occur in the United States yearly, resulting in at least 150,000 ACL reconstructions.


The ACL is a tough, fibrous band of tissue and attaches the tibia to the femur.

Mechanism of Injury

It is estimated that 75 to 80% of ACL tears are the result of non-contact forces. The typical mechanism is a planted foot following a sudden stop or change in direction. The lower leg “sticks” and the body weight pivots through the knee. Contact injuries most often happen in colli-sion sports such as football when force is applied to the knee with the foot planted.

Manifestations of the Injury

The classic description of the injury is the feeling of a pop in the knee with the sense of the knee shifting inward. Pain can be sudden and severe or moderate. Often, the dis-comfort improves within a matter of minutes. Some athletes can “walk it off”, but the knee “just doesn’t feel right.” Swelling usually develops slowly over the course of several hours resulting in a stiff and painful knee by the next morning.

Associated Injuries

Approximately 60% of ACL injuries are accompanied by damage to me-nisci, other ligaments, and/or articular cartilage. Increased swelling and worse pain often signifies these addi-tional injuries.

Initial Treatment

Discontinuation of the activity should occur immediately. This should be followed by ice, elevation, compres-sion, and protected ambulation with crutches. Anti-inflammatory medication such as ibuprofen helps to de-crease pain and swelling. A trip to the orthopedic surgeon should occur within 7 to 10 days.


The orthopedic surgeon will obtain a history of the injury and perform a careful physical exam of the knee in the office. Most ACL tears can be diagnosed at the initial visit. An MRI (magnetic resonance imaging) is usu-ally ordered for confirmation and identification of additional injuries. Bone bruises and meniscal tears are readily seen on MRI studies along with the ACL tear The next step in treatment involves reduction in the inflammation in the knee and the regaining of function. This stage is aimed at eliminating pain/swelling and regaining full knee motion. Maintenance of quadriceps muscle function is emphasized.