Q: I tore my left ACL during a downhill snowboard accident. I've heard that once the ACL has been injured, there's always an increased risk it could happen again. Is there any way to keep this from happening?

A: Reinjury after an anterior cruciate ligament (ACL) injury is always a niggling concern in the back of the mind of most people. This is especially true for athletes who are putting the knee to the test with their activities.

The actual incidence of reinjury varies depending on age, level and type of activity, and treatment approach (conservative or nonoperative versus surgery). But studies show that improvements in surgical technique and post-operative rehab programs has made a difference in improving outcomes. With the development of tendon grafts and better fixation methods, a faster, more aggressive rehab program is possible.

But predicting who will have a second injury (or even a first injury on the opposite side) can be much more difficult. Prevention is less likely without an understanding of what are the predictive risk factors.

A recent study may offer some help in this area. The researchers (a combined group of physical therapists, athletic trainers, and sports medicine physicians) tested two groups of athletes. One group had completed rehab after ACL surgery. The second group played the same sports and were matched by age and sex (male versus female) but were healthy and without knee injuries.

After testing athletes with nine different tests, they found that three of those tests were sensitive enough to really measure differences from one leg to the other. The tests were the single hop, crossover hop, and triple hop.

Athletes who can complete these three activities during the final phases of rehab are ready to safely return-to-play. They must be able to do so with a performance on the injured leg that is at a level at least 90 per cent of the uninvolved leg.

Being able to successfully hop on one leg shows that the athlete has the power, strength, and agility needed for those vertical jumps, quick turns, and sudden changes in direction on the court or field.

Equalizing strength from side-to-side may not be the only way to prevent future injuries but it at least gives us a place to start. Future studies are needed to provide other predictive factors and insights for injury prevention.

Reference: Deydre S. Teyhen, PT, PhD. Return to Sport: When Should an Athlete Return to Sport After an ACL Surgery? In Journal of Orthopaedic & Sports Physical Therapy. June 2011. Vol. 41. No. 6. Pp. 388.