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Health Answers

What causes ACL injuries?

Q. What causes ACL injuries?

A. The anterior cruciate ligament (ACL) is one of the four major ligaments that hold the knee joint together; it crosses the middle of the knee joint from the front of the shin bone to the back of the thigh bone. The ACL helps keep the shin from sliding in front of the thigh and provides stability in rotational movements.

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We hear a lot about ACL injuries in professional athletes, but they’re extremely common in many activities. Women and teenage girls are far more likely to tear their ACLs than men. About two-thirds of injuries happen during movements like twisting, pivoting, or moving sideways, while the rest are caused by direct contact with an object or another person.

“We don’t fully understand why people tear their ACLs,” says Paul Weitzel, an orthopedic surgeon at New England Baptist Hospital. Anatomical differences may explain why some people are more susceptible to tears than others, as well as how they move their legs as they jump and land. Weitzel says that neuromuscular training, which helps people learn to control these movements to better absorb forces, has been found to lower ACL injuries.

Athletes involved in sports that require lateral or twisting movements may get reconstructive surgery to repair a torn ACL. But Weitzel says physical therapy is often a better choice for others. The ACL is not actually needed for front-and-back motions like walking, running, or biking, he says, and with training many people learn to cope without an ACL.

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