Injury to the cruciate ligaments is sometimes referred to as a "sprain." The ACL is most often stretched or torn (or both) by a sudden twisting motion (for example, when the feet are planted one way and the knees are turned another).

The PCL is most often injured by a direct impact, such as in an automobile accident or football tackle.

Symptoms and Diagnosis

Injury to a cruciate ligament may not cause pain. Rather, the person may hear a popping sound, and leg may buckle when he or she tries to stand on it. The doctor may perform several tests to see whether the parts of the knee stay in proper position when pressure is applied in different directions. A thorough examination is essential. An MRI is very accurate in detecting a tear, but often is not possible to differentiate a complete tear from partial. Arthroscopy may be the only reliable means of making a correct diagnosis.

Treatment

For an incomplete tear, the doctor may recommend that the patient begin an exercise program to strengthen surrounding muscles. The doctor may also prescribe a brace to protect the knee during activity. For a completely torn ACL in an active athlete and motivated person, the doctor is likely to recommend surgery. The surgeon may reattach the torn ends of the ligament or reconstruct the torn ligament by using a piece (graft) of healthy ligament from the patient (autograft) or from a cadaver (allograft). Although artificial ligaments have been tried in experiments, the results have not been as good as with human tissue. One of the most important elements in patient's successful recovery after cruciate ligament surgery is a 4 to 6 month exercise and rehabilitation program that may involve using special exercise equipment at a rehabilitation or sports center.