Impact of Concussion on Single Limb Stability

Over the course of the last couple of years, we have been seeing more and more research coming out highlighting the impact that concussion has on injury risk.  Specifically, the impact that there is on ACL and knee injury risk.  Since 2015, what we once hypothesized was true has in fact been well documented in the research.  Brooks et al Am J Sports Med 2016 was one of the first major papers published in this area that looked at the relationship of previously reported concussion and knee injury risk in college athletics.  What the authors found was that Division I athletes who had suffered a concussion where at 2.48xs greater risk of lower kinetic chain musculoskeletal injury than non-concussed athletes. 

Later that same year, Gilbert et al Sport Health 2016 published a paper that looked at the correlation of concussion to all lower kinetic chain musculoskeletal injuries and length of time since the concussion.  What the authors found here was that Division I athletes who suffered a concussion were at 1.6 to 2.9 times greater risk for a non-contact ankle and/or knee injury up to 2 years post concussion.  This is telling as we are not only seeing the impact on all lower kinetic chain injuries but also how long this impacts the athlete.  Further, McPherson et al Am J Sport Med 2018 performed a systematic review and meta-analysis looking at research from 2000 - 2017.  Based on the meta-analysis, the authors concluded that athletes with a concussion are at 2xs greater risk of lower kinetic chain musculoskeletal injury than non-concussed athletes.

If you are like me, you may be asking yourself, why is this the case.  We know that there are some vestibular and balance issues that can persist after a concussion, but how does that impact lower kinetic chain injuries?  Since 2016, we have been tracking concussion history and movement data with an inertial measurement unit (IMU via DorsaVi ViPerform AMI).  Since this time, we have collected movement data on over 11,200 athletes.  That means we have movement data on >930,000 reps, >33,000 minutes of core testing and over 11,200,000 variables.  With this level of data, it is allowing us to see movement trends prior to being published in the research.  Some current trends we have identified are:

1. Those with a history of concussion have a larger magnitude of frontal plane motion than non-concussed athletes.  This is measured in single limb activities, specifically a single leg squat, single leg hop and single leg hop plant.  During these activities, the magnitude of varus to valgus motion at landing is much greater in those with a history of concussion.
2. Those with a history of concussion have higher speeds of valgus than non-concussed athletes.  This is also measured in single limb activities, specifically a single leg squat, single leg hop and single leg hop plant.  During these activities, the speed at which the knee falls into valgus is much greater or faster in those with a history of concussion.  This is a huge risk factor for knee and ACL injury.
3. Those with a history of concussion have a greater time to stability than non-concussed athletes.  Time to stability is the amount of time that it takes for the athlete to be stable once they land.  Some athletes, once they land, they will have multiple hops before they become stable.  The longer they hop, the greater their time to stability.  What we do is time stamp the time they first land to the time it takes them to become stable.  This is measured in single limb hopping activities, specifically the single leg hop and single leg hop plant.  During these activities, the time that it takes for an athlete to become stable is much greater in those with a history of concussion.

The increase in magnitude of motion and the speed of motion we know, from current research, are associated with an increase risk for lower kinetic chain injury (specifically knee injury).  This may be something that is leading to the results that we are seeing in the previously mentioned research that is associating concussion in athletes with lower kinetic chain musculoskeletal injuries.  Just as importantly, this can also guide us on what additional interventions we may deploy with our concussed athletes. Currently, most of the concussion rehab protocols do not include single limb training, core training or single limb plyometric training.  Based on the above results, this might be advantageous to include as a part of the training.   We know that you can improve the stability in the frontal plane (speed and magnitude) in single limb performance and time to stability with training. We also know that when you include this type of training, that we record objective improvement in magnitude of motion (with less occurring), improvement in speed (with lower speeds recorded) and improved time to stability.

In addition to the above, something else that we see is an increase in center of mass (COM) displacement, especially in single limb activity.  We will look at this in more detail next week.  If you enjoy this blog, please share with your colleagues and follow us on instagram @ bjjpt_acl_guy and twitter at @acl_prevention.  #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, 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 and a competitive athlete in Brazilian Jiu Jitsu for 5 years.