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Knee News

The Mystery of Noncontact ACL Tear Continues

Something needs to be done to prevent injuries to the anterior cruciate ligament (ACL) in the knee. About 100,000 people injure their ACL in the United States each year. One billion dollars is spent every year to surgically treat torn ACLs.

Scientists agree that the first step is to find risk factors for ACL tears. It would be best to find factors that can be tested for easily. The next step is to reduce the risk. The hope is to find risk factors that can be changed. These are called modifiable risk factors.

Physical therapists at West Point have some information to offer. They studied 859 West Point cadets over a period of four years. The study included 739 men and 120 women. Researchers were particularly interested in noncontact ACL injuries. During the four years of this study, there were 24 noncontact ACL tears in 16 men and 8 women.

Doctors, physical therapists, and athletic trainers tested each freshman cadet. They looked at knee stability and ligament laxity. They also measured joint motion, muscle strength, and muscle flexibility. Measurements from X-rays showed ligament size in relation to the bone. The space or notch inside the joint for the ligament was also measured. Previous studies have shown a link between small notch width and ACL tears. There are some researchers who think smaller ACLs are more likely to be torn in noncontact injuries.

Therapists conducting this study were unable to find the cause of noncontact ACL injury in men. Notch width, ACL size, and joint laxity predicted some, but not all, injuries in men. It's likely there are many factors at work.

Risk factors for women were easier to find. The authors report that weight and body mass index (BMI) were the only modifiable risk factors. The risk of injury increased in women who also had a greater than normal joint laxity and a narrow femoral notch. These risk factors didn't account for all injuries. The authors conclude there are other factors at work as well. Future studies may be able to identify them.


John M. Uhorchak, COL, MC, USA, et al. Risk Factors Associated with Noncontact Injury of the Anterior Cruciate Ligament. A Prospective Four-Year Evaluation of 859 West Point Cadets. In The American Journal of Sports Medicine. November/December 2003. Vol. 31. No. 6. Pp. 831-842.

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