This physical therapy review is dedicated to the knee and the brain.  While this is not a common connection, there are direct implications in how any peripheral joint injury should be approached with physical therapy and strength training in a well-designed program.
​Neuroplasticity following anterior cruciate ligament injury: a framework for visual-motor training approaches in rehabilitation
Grooms D, Appelbaum G, Onate J. Neuroplasticity following anterior cruciate ligament injury: a framework for visual-motor training approaches in rehabilitation. J Orthop Sports Phys Ther. 2015;45(5):381-393.
Why is this important for physical therapy?
The control of our body is dependent on three systems: visual, vestibular, and somatosensory.  The visual system contribution is obvious – the eyes.  Due to changes in information coming from the body (somatosensory) due to the ACL tear, the motor control system becomes more reliant on the eyes.   If we focus on retraining the body without disrupting this natural progression to visual dominance, the athlete will be at risk for injury as they progress to more demanding activities.  Well designed return to play programs follow a task-based outline for progression. As the athlete progresses from a closed environment with simple tasks, the use of visual feedback is not a problem.  However, the move into an open environment with this strategy requires more motor planning on the part of the athlete. A complex open environment (like playing soccer or basketball against other players) leads to huge demands on the brain as it attempts to use vision and top-down approach to control the knee.  This is a large cognitive load that appears to eventually fail as seen by the injury rates.

Brain changes that impact physical therapy plan and motor control system.

The proposed process for changes in the motor control system leading to visual dominance.
What did the authors propose?
During treatment, athletes need to train the somatosensory while blocking the dominance of the visual system. The use of blindfolds and stroboscopic glasses can force the body to use the impaired somatosensory system. As the athlete progresses in rehab, the dominance of the visual system needs to be constantly assessed or visual dominance will develop. The significance of this problem will not be exposed until the athlete is under a large cognitive load (ex. reacting to an opponent while attempting to cut and maintaining control of the ball simultaneously). During the large cognitive load, using the visual system to maintain adequate control of the injury knee will be impaired leading to risky knee behavior.

The following exercises could be included in the physical therapy regimen of an athlete coming off an ACL surgery in the their task based progression.
Blindfold Single Leg Balance
Blindfold Step Down
My Thoughts
This was a well written and thought provoking article.  Since reading it, Smith Performance Center has now started to incorporate blindfolds and stroboscopic glasses with physical therapy and knee group.  The authors included a photo of exercises that included an athlete performing an exercise while going into knee valgus, which we consider a significant problem. Since this is one of the largest indicators of knee injury, I felt the inclusion of this without a comment was interesting.  Understanding the there is a tendency to develop visual dominance for motor control feedback and control of the injured knee could be a game changer. Due to the disruption of the ACL and damage to afferents in the system, it may be impossible to prevent this process from occurring but at the least we need to make changes in the overall plan to account for this problem.
Want More?  Check out the following articles:
Courtney C, Rine RM, Kroll P. Central somatosensory changes and altered muscle synergies in subjects with anterior cruciate ligament deficiency. Gait & Posture. 2005;22(1):69-74. 

Kapreli E, Athanasopoulos S. The anterior cruciate ligament deficiency as a model of brain plasticity. Medical Hypotheses. 2006;67(3):645-650. 

Kapreli E, Athanasopoulos S, Gliatis J, et al. Anterior cruciate ligament deficiency causes brain plasticity: a functional MRI study. Am J Sports Med. 2009;37(12):2419-2426. 

Ward S, Pearce AJ, Pietrosimone B, Bennell K, Clark R, Bryant AL. Neuromuscular deficits after peripheral joint injury: A neurophysiological hypothesis. Muscle Nerve. 2015;51(3):327-332. doi:10.1002/mus.24463.

Ageberg E, Björkman A, Rosén B, Roos EM. Principles of brain plasticity in improving sensorimotor function of the knee and leg in patients with anterior cruciate ligament injury: a double-blind randomized exploratory trial. BMC Musculoskelet Disord. 2012;13:68. 

Gokeler A, Benjaminse A, Hewett TE, et al. Feedback Techniques to Target Functional Deficits Following Anterior Cruciate Ligament Reconstruction: Implications for Motor Control and Reduction of Second Injury Risk. Sports Med. 2013;43(11):1065-1074. 

Grooms DR, Page SJ, Onate JA. Brain Activation for Knee Movement Measured Days Before Second Anterior Cruciate Ligament Injury: Neuroimaging in Musculoskeletal Medicine. J Athl Train. 2015;50(10):1005-1010. 

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