Use this feature to invite colleagues, clients, and associates to view this content item(s). Please supply your name and email address (for reply purposes) and the recipient's name and email address. To send the email, click the "Send" button. Fields marked with an asterisk are required. To return, click the "Cancel" button.
Anterior Cruciate Ligament (ACL)
Anterior Cruciate Ligament (ACL) Injury Pronounced: an-TEER-ee-or KROO-shee-ate ligament by Carrie Myers Smith Definition An anterior cruciate ligament (ACL) injury is a tear in the ACL ligament. The ACL is located in the middle of the knee joint and connects the lower leg bone to the thigh bone and prevents the leg bone from sliding too far forward at the knee, which would cause instability. Causes Most ACL tears occur during non-contact injuries, such as: Landing on a straight leg Making a sudden stop Pivoting Planting the foot and cutting The ACL can also be injured from a direct blow to the knee. Risk Factors A risk factor is something that increases your chance of getting a disease or condition. Incorrect technique for cutting, planting, pivoting or jumping Muscle imbalance between the quadriceps and hamstrings (weaker hamstrings) Playing sports that require sudden changes of direction and deceleration Sex: Female Weak quadriceps and hamstrings Symptoms When the ACL tears, you may hear a popping sound. When you stand, the knee will probably give-way immediately, and it will be difficult to walk on the affected leg. There is usually moderate pain and swelling of the knee joint, although in the first several hours, this may be minor. It will, however, worsen over the first two days, and then begin to subside. Diagnosis The doctor will ask about your symptoms and how you injured your knee, and perform a physical exam. Tests may include: MRI scan - a test that uses magnetic waves to show the structures inside the knee joint Arthroscopy - a thin, lighted tube inserted through a small incision in the knee to look at the structures inside the knee Treatment Treatments include: Knee brace You may need to wear a knee brace while recovering from your knee injury, as well as when you return to your sport. This may be needed regardless of whether or not you have surgery to reconstruct the ligament. Surgery Surgery may be needed to fully restore function of the knee, particularly in younger and athletic people. The decision to have surgery should be made after discussion with your doctor about your athletic needs, age, and associated factors. Physical therapy Range of motion exercises - The therapist will assist you with moving your knee through its full range of motion. Stretching is a part of this treatment. Strengthening exercises - Due to its lack of use, the affected leg muscles will atrophy (shrink) and lose strength. Therapy will help you regain strength in the thigh muscles, especially the quadriceps and hamstrings. Prevention Because ACL tears most often occur due to non-contact injuries, precautions can be taken to prevent them. Incorporate adequate warm-up exercises to prepare the knee for your sport. Keep the quadriceps and hamstrings flexible by stretching regularly. Plyometrics, a form of jumping exercises, can be used to train and strengthen the leg muscles for jumping and landing. However, this should only be done under professional supervision if your doctor has determined it is right for you. Strengthen both the quadriceps and the hamstrings. When jumping and landing, or turning and pivoting, your hips and knees should be bent, not straight. Last reviewed: January 2003 by Robert Leach, MD.