Suffering torn ACL causes harmful changes in brain structure, surprising study finds

ANN ARBOR, Mich. — An ACL (anterior cruciate ligament) tear is a devastating injury. While reconstructive surgery can usually restore most of an individual’s range of movement, it’s very common for some joint function to be permanently gone. Moreover, once someone suffers a torn ACL, their chances of experiencing another increases considerably, regardless of a dedicated and thorough physical therapy regiment. Up until now, doctors and researchers have been puzzled as to why ACL tears tend to re-occur, but a new study has provided some much needed and surprising answers.

The University of Michigan School of Kinesiology has discovered that patients who have undergone ACL reconstruction surgery display noticeable structural changes in their brains. These changes appear to impede their recovery and even contribute to poor subsequent athletic performance and re-injury.

The research team took MRI brain scans of 10 patients who had undergone ACL-reconstruction. All of the patients’ corticospinal tracts had atrophied. The corticospinal tract runs through both hemispheres of the brain and serves as a pathway that sends messages from the brain to muscles. In all studied patients, the side of the tract responsible for the knee that had the torn ACL was 15% smaller than on the uninjured side.

The research team illustrated these findings by comparing the narrowed corticospinal tract to a traffic tunnel undergoing construction that allows fewer and fewer cars to pass through. In patients who have received ACL reconstructive surgery, their muscles near the injured knee aren’t receiving as much “information” or signals as they once did before the injury.

“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,” comments Adam Lepley, clinical assistant professor of athletic training at U-M, in a release. “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.”

These findings are supported by another recent research project that found downstream neural activity in the quadriceps muscles is often deluded during physical activities following surgery for a torn ACL.

In light of these revelations, this study’s authors believe both ACL patients and the doctors treating them should be aware that knee injuries often lead to adverse effects in other regions of the body.

“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,” concludes Lindsey Lepley, a study co-author and U-M 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.”

The study is published in NeuroImage: Clinical Volume.