Q: I heard a report that injuring the ACL of the nondominant leg puts athletes at increased risk of future injuries. Is that true? and what's the explanation for it?

A: There haven't been a lot of studies comparing long-term results following ACL injuries and in particular, what happens to the other leg. Comparing results of dominant versus non-dominant leg is another added dimension. And there are many other factors and variables to consider (e.g., age, gender, sport, type of treatment) that can make it difficult to tell cause and effect.

When the treatment approach is surgery, there are two different types of graft material that can be used. Results may vary depending on which leg is affected and which graft material is used.

There was a study done recently where surgeons from three large medical centers combined their efforts to investigate the rates of return-to-play and need for further surgery among just soccer players. Part of their research did report on the effects of injury based on whether the injury affected the dominant versus nondominant leg.

One-hundred (100) active soccer players (males and females) between the ages of 11 and 53 were included in the study. This was a retrospective study, which means the athletes were contacted after their surgery and rehab to see what kind of results they had. Two-thirds had a bone-patellar-bone graft to reconstruct the anterior cruciate ligament (ACL). The other one-third had a hamstring graft. Information about the type of graft used is always important in these studies to see if it makes a difference in results.

Final, long-term results were measured by looking at number of patients who went back to full sports participation, how many were still actively playing soccer years later, and how many people had to have another knee surgery (either on the injured side or the opposite side).

They found some interesting patterns. First, the graft type (hamstring versus patellar) did NOT make a measurable difference. Second, female soccer players were more likely to experience reinjury or future injuries. Any athlete who injured the nondominant leg was at increased risk for recurrent ACL injuries. That's because after the injury, they put even more stress and strain on the dominant side -- eventually leading to an overuse injury. Slightly more than half of all injuries (57 per cent) affected the dominant leg in these 100 patients.

The fact that women are actually more likely to experience future injuries (compared with men) may have to do with differences in muscular strength and joint laxity between the sexes. Women tend to have greater joint laxity or looseness. Men tend to have tighter and stronger muscles on either side of the joint to support and protect it.

The authors suggested greater emphasis on injury prevention for all soccer players (young and old, male and female). Studies reporting results of ACL injury prevention programs are favorable at this point. Future programs need to pay attention to those athletes at increased risk for ACL reinjuries or opposite leg ACL injuries. Females and athletes injuring the nondominant leg are the first groups to target with a prevention plan.

Reference: Robert H. Brophy, MD, et al. Return to Play and Future ACL Injury Risk After ACL Reconstruction in Soccer Athletes from the Multicenter Orthopaedic Outcomes Network (MOON) Group. In The American Journal of Sports Medicine. November 2012. Vol. 40. No. 11. Pp. 2517-2522.