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Brain changes after ACL tear may increase risk of re-injury

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The anterior cruciate ligament (ACL) is one of the key ligaments that help stabilise the knee joint. ACL injuries are common in sports such as skiing, tennis, squash, football and rugby, and after an ACL tear an athlete faces a greater risk of knee injuries in the future — even with intensive physical therapy.

To help understand why, researchers at the University of Michigan School of Kinesiology took MRI brain scans of 10 patients who had undergone ACL reconstruction.

The scans revealed atrophy of part of the corticospinal tract — the pathway that sends messages from both hemispheres of the brain to muscles. The side of the tract that controls the ACL-reconstructed knee was about 15% smaller than on the uninjured side, the researchers found.

“In essence, the brain not only alters the way it communicates with the rest of the body, joints, muscles, etc., but the structural makeup of the basic building blocks of the brain are also changed after ACL injury,” said Adam Lepley, clinical assistant professor of athletic training. “We think that this is a protective mechanism, in which our body is trying to limit unwanted movement around a joint injury… and can be applied to not just ACL injuries, but other musculoskeletal injuries as well.”

The researchers cited another recent study which showed that downstream neural activity in the quadriceps is impaired during sport-like movements after ACL surgery, suggesting that poor brain structure and communication can lead to reduced functioning.

“It means that during treatment, a systemic approach should be taken not just to improve range of motion or swelling at the injured joint, but also consider other impairments like poor movement patterns and muscle activation in order to get better outcomes,” explained Lindsey Lepley, assistant professor of athletic training. “There is evidence of using visual retraining, different motor learning modalities like external focus of attention and biofeedback, which can help ‘rewire’ the brain to help the body adapt to a new normal.”