Genetics and ACL Tears

January 29, 2015
By Kenny Berkowitz

What role do genetics play in ACL injuries? Tim Hewett, PhD, Director of the Sports Medicine Biodynamics Center at Cincinnati Children's Hospital, is working hard to find the answer.
As part of a larger ongoing study to discover risk factors for anterior cruciate ligament injuries, he decided to focus on a set of fraternal twin girls. On their visit to the lab, the girls were videotaped wearing reflective markers while going through landing and cutting maneuvers. At the time, both girls' knees appeared perfectly healthy. But within a year, each had torn an ACL, as had their older sister.

Returning to the videotapes, Hewett and his team measured and analyzed the angles of the girls' knees as they progressed through the drills. The results, which were published last month in the British Journal of Sports Medicine, showed increased abduction angles at initial contact and maximum displacement during landing.

The twins had what Hewett calls "Gumby knees," with unusually loose, flexible joints, and each angled at least one knee outward during landings. Compared to the control subjects, who have remain uninjured, the pre-injury twins showed greater joint laxity, decreased hamstring-to-quadriceps torque ratios, and narrower femoral intercondylar notches where the ACL attaches to the bone.

In previous studies, all these conditions had been shown as risk factors--but this was the first time they had been seen clustered within a family.
"It appears that the propensity to be at high risk for an ACL tear is definitely heritable," Hewett told the New York Times. "If you have a first-generation relative, a sibling, or parent who has torn an ACL, you are likely to be at above-average risk."

Hewett is not alone. At the University of Cape Town in South Africa, researchers are using different methods to reach the same conclusions about a genetic predisposition for ACL injuries. In a new set of papers in the British Journal of Sports Medicine, scientists at the Research Unit for Exercise Science and Sports Medicine have identified two genes associated with ACL tears.

The two genes, COL1A1 and COL5A1, control the production of collagen, which is the primary ingredient of tendons and ligaments. Variations in the two genes affect the suppleness of collagen, and were more commonly found in women who had ruptured their ACLs than in women who hadn't. (COL5A1 has also been associated with Achilles tendon injuries.)

"For the first time, researchers have identified a genetic risk factor for ACL ruptures in female athletes," wrote Jay Williams, Professor of Exercise Science in the Department of Human Nutrition, Foods, and Exercise at Virginia Tech, commenting on the Cape Town studies. "While more research is needed to confirm these preliminary results, it may soon be possible to identify at risk individuals and design programs to counter this risk."

If the research is right, Hewett can foresee a time "in the not-so-distant future [when] we might be able to screen" the DNA of student-athletes to find those with the highest risk. But even then, questions will remain: Should all female student-athletes be tested, or only some? Once you administer the test, what do you tell a young woman with a higher-than-average genetic risk of ACL injury? And is there a similar genetic predictor for men?

"There's so much we still have to learn and think about," says Hewett. "But this field does give us another piece of the puzzle."

For more Training & Conditioning coverage of Hewett's work and its applications, see By Leaps and Bounds by RJ Anderson and Motivating and Building Champions by Rich Jacobs, MS, SCCC, CSCS.

Kenny Berkowitz is an Assistant Editor at
Training & Conditioning.
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