Patient having an MRI scan

An ACL tear is a serious injury and the road to recovery can be long. But a new study suggests that the damage isn’t only confined to the knee. It can cause harmful changes in our brain structure too.

Something strange happens when you rupture your anterior cruciate ligament (ACL). We know that some joint function can be permanently lost following ACL reconstruction, despite the procedure appearing to be entirely successful. We know reinjury is relatively common despite there being no obvious physical explanation for this. We even know that rupturing the ACL in one leg increases the risk of suffering an ACL injury in the other leg. Again, physically, there should be no reason for this.

‘Dimmer switch’

One possible explanation lies in the ‘dimmer switch’ theory. The idea goes that everyone’s muscular control operates on some sort of protective dimmer switch. Injure your ACL and the switch is ‘turned down’, downgrading your muscular control and reaction times while you’re undergoing surgery or rehab. It sounds rather far-fetched, but a recent study from the University of Michigan School of Kinesiology has identified neurological changes during ACL injury that may support some form of the theory.

The study used MRI scans of 10 ACL reconstructed patients. Each of the scans “showed that part of the corticospinal tract — the pathway that scuttles messages from brain to muscles — had atrophied in the patients”.

If you think of the tract as a motorway between brain and knee, this effectively means a lane is closed, reducing the amount of information that reaches the knee. The study also identified changes in the basic structural makeup of the brain after ACL injury. This, co-author Adam Lepley suggested to Michigan News, “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.”

New approaches to recovery

The study is interesting, not least because it provides a clear reason for the anomalies I mention at the start of this piece. There’s clearly more to be explored here, but the study does indicate that future ACL reconstruction treatments may need to incorporate a neurological element that helps rewire the brain in addition to existing procedures for managing the physical elements of the injury.

Until then, if you have suffered a knee injury that has left your leg feeling as though it might give way, or which gives you pain particularly when you twist, you could have damaged your ACL. For swift diagnosis and treatment, talk to us.

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