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:
Women are more likely to have an ACL tear than men.
An ACL injury can occur if you:
Basketball, football, soccer, and skiing are common sports linked to ACL tears.
ACL injuries often occur with other injuries. For example, an ACL tear often occurs along with tears to the MCL and the shock-absorbing cartilage in the knee (meniscus).
Most ACL tears occur 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.
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 provider and have been treated.
Your provider 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:
You also may need:
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. You are also less likely to return to the same level of sports without the ACL.
Call your provider right away if you have a serious knee injury.
Get immediate medical attention if the foot is cool and blue after a knee injury. This means that the knee joint may be dislocated, and blood vessels to the foot may be injured. This is a medical emergency.
Use proper techniques when playing sports or exercising. Some college sports programs teach athletes how to reduce stress placed on the ACL. This involves a series of warm up exercises and jumping drills.
The use of knee braces during vigorous athletic activity (such as football) is controversial. It has not been shown to reduce the number of knee injuries, but not specifically ACL injuries.
Reviewed By: C. Benjamin Ma, MD, Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery, San Francisco, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.