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Alternative Names Return to topCruciate ligament injury - anterior; ACL injury; Knee injury - anterior cruciate ligament (ACL)
Definition Return to top
An anterior cruciate ligament injury is extreme stretching or tearing of the anterior cruciate ligament (ACL) in the knee. A tear may be partial or complete.
Considerations Return to top
The knee is essentially a modified hinge joint located where the end of the thigh bone (femur) meets the top of the shin bone (tibia). Four main ligaments connect these two bones:
The ACL and PCL cross each other inside the knee, forming an "X." This is why they are called the “cruciate” (cross-like) ligaments.
ACL injuries are often associated with other injuries. The classic example is when the ACL is torn at the same time as both the MCL and medial meniscus (one of the shock-absorbing cartilages in the knee). This type of injury often occurs in football players and skiers.
Women are more likely to have an ACL tear than men. The cause for this is not completely understood, but it may be due to differences in anatomy and muscle function.
Adults usually tear their ACL in the middle of the ligament or pull the ligament off the femur bone. These injuries do not heal by themselves. Children are more likely to pull off their ACL with a piece of bone still attached. These injuries may heal on their own, or they may require an operation to fix the bone.
When your doctor suspects an ACL tear, an MRI may help confirm the diagnosis. This test may also help evaluate other knee injuries, such as to the other ligaments or cartilage.
Some people are able to live and function normally with a torn ACL. However, most people complain that their knee is unstable and may "give out" with attempted physical activity. Unrepaired ACL tears may also lead to early arthritis in the affected knee.
Causes Return to top
ACL tears may be due to contact or non-contact injuries. A blow to the side of the knee, which can occur during a football tackle, may result in an ACL tear.
Coming to a quick stop, combined with a direction change while running, pivoting, landing from a jump, or overextending the knee joint (called hyperextended knee), also can cause injury to the ACL.
Basketball, football, soccer, and skiing are common causes of ACL tears.
Symptoms Return to top
First Aid Return to top
An ACL injury should be treated with:
Do not play again until you have been evaluated and treated.
Some people may need crutches to walk until the swelling and pain have improved. Physical therapy may help you regain joint motion and leg strength.
If you still have instability after your leg strength and knee motion have returned, your doctor may recommend a reconstruction of the ACL. The old ligament cannot be fixed, so a new one needs to be constructed. Common grafts used for reconstruction include:
DO NOT Return to top
When to Contact a Medical Professional Return to top
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 may be dislocated and blood vessels to the foot may be injured. This is a true medical emergency that requires immediate professional help.
Prevention Return to top
Use proper techniques when playing sports or exercising. Several women's college sports programs have reduced ACL tears through a training program that teaches athletes how to minimize the stress they place on their ACL.
Although the issue is controversial, the use of knee braces during aggressive athletic activity (such as football) has not been shown to decrease the incidence of knee injuries and may give the player a false sense of security.
References Return to top
Renstrom P, Ljungqvist A, Arendt E, Beynnon B, Fukubayashi T, Garrett W, et al. Non-contact ACL injuries in female athletes: an International Olympic Committee current concepts statement. Br J Sports Med. 2008;42:394-412.
Birmingham TB, Bryant DM, Giffin JR, Litchfield RB, Kramer JF, Donner A, Fowler PJ. A randomized controlled trial comparing the effectiveness of functional knee brace and neoprene sleeve use after anterior cruciate ligament reconstruction. Am J Sports Med. 2008;36:648-655.Update Date: 7/17/2008 Updated by: Andrew L. Chen, MD, MS, Orthopedist, The Alpine Clinic, Littleton, NH. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.