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How Knee Injuries Damage the Brain

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A fascinating study has revealed brain damage occurring when other parts of the body are injured.  Focusing on ACL (anterior cruciate ligament) injuries to the knee, which are often treated with surgical repair, the University of Michigan School of Kinesiology analyzed the brain scans of ten adults who had ACL injuries treated with surgical reconstruction.  The participants were asked to perform an isometric extension of their repaired knee during their scans.

                Each of the post-surgical patients showed atrophied (weakened) corticospinal tracts. The brain uses the corticospinal tract to send messages to muscles and is present in both the left and the right hemispheres of the brain.  The damage was seen on the MRIs in the hemisphere respective to the side of the body which was injured, and the corticospinal tract in the affected hemisphere was diminished in size by 15% when compared to the other side.

                While successful, ACL reconstructive surgery is one of the most common injuries to re-occur, despite physical rehabilitation.  Patients with ACL injuries may also lose functionality of the joint permanently.  The team at the University of Michigan believe that the high incidence of re-injury is due to the smaller, weaker corticospinal tract which is unable to send the same quantity and quality of messages to the muscles on the injured side of the body.

                The poor communication between the brain and the injured side of the body shows that the brain is affected by structural injury to other parts of the body.  The study’s participants were between 66.6-96.5 months (about 6 years) post-surgical repair. The research team hypothesizes that the atrophy occurring to the corticospinal tract is a protective mechanism, where the body tries to reduce any painful movement which isn’t truly necessary.

                Adopting  a systemic approach to the healing after structural injuries will now need to account for the knowledge that injury to the body causes damage to the brain.  Future rehabilitation plans may be able to work on “brain rehab” during routine physical therapy treatments to help the brain re-wire itself through biofeedback and other motor skill therapies.


Lepley, Adam S., et al. “Corticospinal Tract Structure and Excitability in Patients with Anterior Cruciate Ligament Reconstruction: A DTI and TMS Study.” NeuroImage: Clinical, vol. 25, no. 102157, 2020, doi:https://doi.org/10.1016/j.nicl.2019.102157.


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