FRIDAY, March 6, 2020 (HealthDay News) -- Your knee might never be the same after undergoing surgery for a torn anterior cruciate ligament (ACL), and the reason is in your head, a small, new study suggests.

It turns out ACL reconstruction causes changes in the structure of your brain, a University of Michigan (U-M) team found. That's why even after ACL reconstruction and physical therapy, your joint function might never get back to normal.

U-M School of Kinesiology colleagues Lindsey and Adam Lepley, and their team, took MRI brain scans of 10 patients who had ACL reconstruction surgery. The scans showed deterioration in part of the corticospinal tract, which is the pathway that relays messages from the brain to muscles.

The changes may slow recovery and may be responsible for performance deficits and re-injury, the researchers said in a university news release.

The scans showed that the side of the corticospinal tract responsible for the ACL-reconstructed knee was 15% smaller than the other side. With a smaller pathway, less information can travel from brain to muscle.

"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," Adam Lepley said. "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 team said the takeaway is that injuries aren't always isolated.

Lindsey Lepley said the findings suggest that treatment needs to look beyond improving range of motion or swelling at the injured joint.

"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," she noted.

Lindsey Lepley is director of the Orthopaedic Rehabilitation and Biomechanics Laboratory, and Adam Lepley is a clinical assistant professor of athletic training at the school.

The study was published online recently in the journal NeuroImage: Clinical.

More information

The American Academy of Orthopaedic Surgeons has more on ACL injuries.