An anterior cruciate ligament injury is the over-stretching or tearing of the anterior cruciate ligament (ACL) in the knee. A tear may be partial or complete.
The knee joint is located where the end of the thigh bone (femur) meets the top of the shin bone (tibia).
Four main ligaments connect these two bones:
- Medial collateral ligament (MCL) runs along the inside of the knee and prevents the knee from bending in.
- Lateral collateral ligament (LCL) runs along the outside of the knee and prevents the knee from bending out.
- Anterior cruciate ligament (ACL) is in the middle of the knee. It prevents the shin bone from sliding out in front of the thigh bone.
- Posterior cruciate ligament (PCL) works with the ACL. It prevents the shin bone from sliding backwards under the femur.
Women are more likely to have an ACL tear than men.
An ACL injury can occur if you:
- Get hit very hard on the side of your knee, such as during a football tackle
- Overextend the knee joint
- Quickly stop moving and change direction while running, landing from a jump, or turning
Basketball, football, soccer, and skiing are common sports linked to ACL tears.
ACL injuries often occur with other injuries. For example, an ACL tear commonly occurs along with tears to the MCL and the shock-absorbing cartilage in the knee (lateral meniscus).
Most ACL tears are seen in the middle of the ligament, or the ligament is pulled off the thigh bone. These injuries form a gap between the torn edges, and do not heal on their own.
- A "popping" sound at the time of injury
- Knee swelling within 6 hours of injury
- Pain, especially when you try to put weight on the injured leg
Those who have only a mild injury may notice that the knee feels unstable or seems to "give way" when using it.
See your health care provider if you think you have an ACL injury. Do not play sports or other activities until you have seen a doctor and been treated.
Your doctor may send you for an MRI of the knee. This can confirm the diagnosis. It may also show other knee injuries.
First aid for an ACL injury may include:
- Raising your leg above the level of the heart
- Putting ice on the knee
- Pain relievers such as nonsteroidal anti-inflammatory drugs (such as ibuprofen)
You may need:
- Crutches to walk until the swelling and pain get better
- Physical therapy to help improve joint motion and leg strength
- Surgery to rebuild the ACL
Some people can live and function normally with a torn ACL. However, most people complain that their knee is unstable and may "give out" with physical activity. Unrepaired ACL tears can lead to further knee damage.
- Do NOT move your knee if you have had a serious injury.
- Use a splint to keep the knee straight until you see a doctor.
- Do NOT return to play or other activities until you have been treated.
When to Contact a Medical Professional
Anyone with a serious knee injury should seek medical attention for x-rays and evaluation.
If the foot is cool and blue after a knee injury, the knee joint may be dislocated, and blood vessels to the foot may be injured. This is a medical emergency that requires immediate professional help.
Use proper techniques when playing sports or exercising. Some college sports programs teach athletes how to reduce stress placed on the ACL.
The use of knee braces during aggressive athletic activity (such as football) is controversial, and has not been shown to reduce the number of knee injuries.
Cruciate ligament injury - anterior; ACL injury; Knee injury - anterior cruciate ligament (ACL)
Griffin LY, Armstrong A, DeMaio M. The female athlete. In: DeLee JC, Drez D Jr, Miller MD, eds.DeLee and Drez's Orthopaedic Sports Medicine.
Honkamp NJ, Shen W, Okeke N, Ferretti M, Fu FH. Anterior cruciate ligament injuries: 1. Anterior cruciate ligament injuries in the adult. In: DeLee JC, Drez D Jr, Miller MD, eds.DeLee and Drez's Orthopaedic Sports Medicine.
Update Date 8/14/2011
Updated by: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine, Seattle, WA; C. Benjamin Ma, MD, Assistant Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery, San Francisco, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.