Are Bad Knees In Our Genes? - NYTimes.com

Are fragile knees inherited? That intriguing question motivated a new study published earlier this month in The British Journal of Sports Medicine, during which researchers looked at one family's propensity for shredding anterior cruciate ligaments during sports. The report was part of a much larger, ongoing study of risk factors for A.C.L. injury, led by researchers affiliated with the Cincinnati Children's Hospital and Ohio State University, which involves thousands of young athletes. For this pocket version of the larger experiment, the scientists singled out a set of fraternal twin girls who already had been videotaped in the laboratory while wearing reflective markers. The angles of their knees during landing and cutting maneuvers had been analyzed, and the knees themselves measured. At the time of the taping, both girls' knees were healthy. But within a year, each had suffered a catastrophic A.C.L. tear during separate volleyball and basketball games, as had an older sister, who wasn't part of the original study.

"We thought this repeated incidence of A.C.L. tears within one family was important to look at," said Timothy Hewett, the director of sports-medicine research for Ohio State University and Cincinnati Children's Hospital and lead author of the new study. "In my lab, we have another set of twins, identical young women, who are post-docs. They both had torn their A.C.L.'s" as high school athletes. "Their father, who is one of a set of triplets, also had torn his A.C.L.," as had his two triplet brothers, Dr. Hewett said. "Those incidences," together with the injuries to the fraternal twins, "made us wonder, How much does familial predisposition influence your risk for an A.C.L. tear?"

The answer may be quite a bit. What Dr. Hewett and his colleagues found when they parsed the data about the fraternal twin girls' knees was that each had unusually loose, flexible knee joints, or "Gumby knees," as Dr. Hewett called them. Each also angled at least one knee outward during landings and had narrower-than-average notches in the knee bone, where the A.C.L. attaches to the bone. Each of these conditions previously had been identified as a risk factor for an A.C.L. tear, but they hadn't been shown to cluster within a family. "It appears that the propensity to be at high risk for an A.C.L. tear is definitely heritable," Dr. Hewett said.

Anyone who has an active daughter or who follows the sports pages knows that the incidence of non-contact-related A.C.L. tears among young female athletes is high and increasing. Many strength- and balance-training programs have been developed to try to reduce the number of these A.C.L. injuries. But part of the problem with the
training programs, Dr. Hewett said, "is that they'll only work if they reach the girls who actually are at risk," because of how their knees are built. "Otherwise it's like giving antibiotics to someone who doesn't have an infection. It won't work."

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