Neuroplasticity & ACLR

Neuroplasticity is not typically a term we think of when we think about knee injuries. However, we now know there are changes that occur in the brain following an ACLR.  Can we change that?  Is there training we could employ that would improve?  Would this training have an impact on performance as well?  Before we get into that, let's look at what we know.

In a study by Kapreli et al Am J Sport Med 2009, the authors showed that there were changes that occurred in the higher centers in the brain following an ACL injury.  In this study, the authors performed functional MRIs on 17 ACL deficient males and compared that to functional MRIs of 18 ACL in-tack males.  What they found was there were distinctive changes in the presupplementary motor area, posterior secondary somatosensory area, and posterior inferior temporal gyrus.  This suggest that such an injury might be regarded as a neurophysiologic dysfunction, not a simple peripheral musculoskeletal injury.  Should this be something we consider as a part of our training and if so, how do we do?

In a study by Monfort et al Am J Sports Med 2019 the authors found that these changes in the brain result in visual spacial deficits.  Meaning the athlete has a challenging time knowing where their knee is in space.  Further, the authors found that if these deficits are not addressed, this could lead to the increase in the valgus angle that occurs with sport specific cutting movements.  It is these neurological adaptations that appear to be associated with clinical deficits that may contribute to poor long-term outcomes and reinjury rates among athletes returning to play. 

As a result of the loss of the ligamentous structure and the associated mechanoreceptors, the system must compensate to regain neuromuscular control. As a result, after an ACLR, the brain begins to rely more on a visual-motor strategy (using visual input to visualize limb placement) as opposed to a sensory motor strategy (mechanoreceptors and proprioceptors) to engage in knee movement. It is believed that these compensatory strategies may put the athlete at greater risk of injury upon return to sport, result in a decrease in athletic performance and lead to poor long-term outcomes. 

The changes in the brain associated with ACL injury and reconstruction are not be sufficiently targeted with current rehabilitation approaches. WE must employ using the principles of motor learning that have the potential to support neuroplastic changes, reduce the risk for a second ACL injury and early onset of osteoarthritis.  If mechanoreceptors at the injury location are affected, it's important to integrate training techniques that target the afferent pathways from the point of injury. Current ACL research has suggested utilizing visual-training technologies and techniques can improve results when combined with already-established neuromuscular training methods.

Motor learning research has shown that externally focusing on the outcome of a movement (implicit strategies) is more likely to transfer to other tasks compared to internally focused movements (explicit strategies). An example of an implicit strategy is seeing a target on a screen in front of you and touching to that target with your foot without looking.  Explicit would be seeing the target and looking at it while you touch it.  Implicit requires more higher center input and is closer to how we must move in athletic situations.

ACL injury prevention programs addressing explicit rules regarding desired landing positions by emphasizing proper alignment of the hip, knee and ankle are reported in the literature.  This may  be a sensible way and effective way, but the use of explicit strategies may be less suitable for the acquisition of the control of the complex motor skills required in sports.  Additionally, this may be one reason re-injury rates remain high. 

These prevention programs may be further enhanced by integration of training which emphasizes implicit strategies. From a practical and scalable standpoint, how can we implement these strategies? This may be one of the most challenging questions providers are left to answer. Establishing new strategies, standardizing the strategies, tracking the outcomes and implementation may lead to paralysis by analysis.  

Next week, we will discuss one method we use to accomplish this.  If you did enjoy, please share with your colleagues, athletes and training partners and please be sure to follow us on instagrm @ bjjpt_acl_guy and twitter @acl_prevention.  Train hard and stay well.  #ViPerformAMI #ACLPlayItSafe

Dr. Nessler is a practicing physical therapist with over 20 years sports medicine clinical experience and a nationally recognized expert in the area of athletic movement assessment and ACL injury prevention.  He is the founder | developer of the ViPerform AMI,  ViPerform AMI RTPlay, the ACL Play It Safe Program, Run Safe Program and author of a college textbook on this subject.  Trent has performed >5000 athletic movement assessments in the US and abroad.  He serves as the National Director of Sports Medicine Innovation for Select Medical, is Vice Chairman of Medical Services for USA Obstacle Racing and movement consultant for numerous colleges and professional teams.  Trent has also been training in Brazilian Jiu Jitsu for 5 years and complete BJJ junkie.