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New Evidence on Underlying Causes of ACL Injuries

December 8, 2004 09:54 AM

By Jim Brown, Ph.D., Executive Editor, Sports Performance Journal (athletesperformance.com)

A study published in August issue of the Journal of Bone and Joint Surgery has provided new evidence on when gender differences begin to occur that result in injured anterior cruciate ligaments. We have known for some time that female athletes sustain anterior cruciate ligament (ACL) injuries at alarmingly higher rates than males.

“We now know that the neuromuscular imbalances that underlie anterior cruciate ligament injury risk begin at puberty,” said Tim Hewett, Ph.D., of the Sports Medicine Biodynamics Center at the University of Cincinnati. Hewett and three colleagues studied 181 middle school and high school athletes (male and female) to determine if and when poor neuromuscular control of the knee joint in female athletes happens at the same time as the maturation process.

The researchers measured control of the knee during various movements that have been known to cause ACL tears, as well as the angle of the knees in relation to the hips, and lower extremity bone length. Specifically, they were looking for the amount of inward collapse of knee during running, change of direction, and jumping activities. Then they compared the measurements of males to that of females.

They found that after the onset of puberty, the females landed (after jumps) with greater total inward motion of the knees and with a greater inward angle of the lower extremities than did the male athletes. While both boys and girls go through a growth spurt at puberty, boys also experience an increased testosterone boost that helps them develop muscles supporting the knee joint. Females go through a period of increased body mass, but the muscles do not naturally get stronger at the same time. Hewett explains that, while boys’ knees move in one direction much like a hinge, girls’ knees move in several directions. This puts added stress on the ACL and can lead to injuries. Landing off-balance after a jump shot and quick changes of direction in tennis are classic scenarios that lead to ACL tears among young women athletes.

The good news is that starting at the ages of 10-11, girls and women can reduce the risk of ACL injury by participating in a strength training program that include balance, core performance, and hamstring exercises. They can also develop landing and change of direction techniques in which the knees do not point inward. Hewett concludes, “We need to start neuromuscular training either right at or just prior to puberty for prevention strategies to be most effective.”

© 2004 HMS Publishing, Inc.
Jim Brown will be contributing new content to this site on a monthly basis. If you have a question for Dr. Brown please feel free to email him at




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