Monday, May 11, 2015
Where Are We Now - Part II
Last week we concluded with a study by Howell et al that looked at the impact that concussion has on gait balance deficits in youth athletics. We concluded with the question, what does this mean? First and foremost this demonstrates that the impact of a concussion has on a young athlete can last for several months. We need to manage these better! This is critical since most are returned to sport way too early and, from what this study indicates, you may be putting them at greater risk for additional injuries. Why? The ability of an athlete to control COM medial/lateral displacement is critical. Not only is this an indication of control of balance, but it also has a huge impact on injury risk and performance. We know from the research that if you have bad balance, that you are at increased risk for non-contact ankle sprains. But looking further at injury risk, the larger the displacement that occurs medial to lateral, the greater the load is to the medial and lateral structures of the body (spine, hip, knee and ankle). This means that tissues and joints are being loaded in a suboptimal way and often will create shearing stresses to the articular cartilage. In this diagram, we can see how this motion would stress the SI joint in the back, the hip joint/labrum of the hip, the meniscus and ankle. In most cases, the athlete will also be unable to control the knee which will result in valgus and internal rotation stress at the knee in combination with the lateral displacement. It is this suboptimal loading and shearing stresses that cause tissue breakdown and injury.
Looking at performance, think about your athlete. If you had an athlete that was running and had an excessive amount of medial to lateral movement of their upper body during a run, would you expect them to have optimal performance? What we do know is the larger the magnitude of medial to lateral displacement means loss of kinetic energy and decreased force production. This medial and lateral displacement also results in decreased efficiency of movement. This loss of maximal force production, loss of kinetic energy transfer across the system and decreased efficiency of movement will result in decreased power output and decreased endurance over time.
Keep in mind that this study looked at athletes “walking”. So, the question becomes does this get worse with running and what does single limb performance look like? Well first look at running. We know for a fact that what we see in walking gait will be magnified when observed in running due to the increased force demands. So, if you are seeing this in walking, you can be assured that this will be even worse in running gait.
But what about single limb performance. Well, that is where we get back to the previous study I mentioned that is ongoing. Ironically, they are seeing very similar results with the post concussed athlete. Not only are they seeing a much higher percentage of non-contact lower kinetic chain injuries being reported post concussion, they are also seeing dramatic changes in single limb performance. Specifically, when concussed athletes’ single limb performance is compared to controls, you see a significant difference in ability to control medial/lateral displacement of the lower limb (adduction toward midline) in athletes with a concussion history. Knowing that single limb performance has a better predictive value for what performance will be like in sport and that single limb performance has a better predictive value for non-contact ACL injury risk, then what we are seeing is an increased risk for non-contact ACL injuries post concussion.
Concussion and ACL risk. Now that is new. But only the beginning of what we can and will learn if we use technology to its fullest capability. Because, through all the assessments in sports and military, there are some common themes. Whether you label it COM medial to lateral displacement, lateral trunk lean or retro-trendelenbury (all which mean essentially the same), the ability to control the core is essential to prevent injuries to the upper and lower extremity. Upper extremity? Yes, upper extremity.
To examine this point, let’s look at a recent paper from the March 2015 issue of the American Journal of Sports Medicine by Solomito et al. In this study, the authors looked at the impact of lateral trunk lean on ball velocity and upper extremity joint moments.
Methods: 99 Division I and Division III pitchers underwent a pitching analysis using 3 dimensional motion analysis techniques and 12 camera vicon motion system. Each player was assessed for contralateral trunk lean, ball velocity as well as elbow varus and glenohumeral internal rotation moments.
Results: What the study found was that the greatest magnitude of lateral trunk lean occurred around the time of the peak elbow varus moment. The results also indicate for every 10° increase in contralateral trunk lean, there was a corresponding increase of .5 m/s in ball velocity. The results also showed that for every 10° increase in contralateral lean, there was a corresponding elbow varus moment of 3.7 Nm and a glenohumeral internal rotation moment increase of 2.5 Nm.
Unfortunately what some will take away from this is that to increase ball velocity, we should instruct in contralateral trunk lean. But that could be the furthest thing from the truth. Contralateral trunk lean is a compensatory strategy for poor mechanics and poor throwing velocity. The lateral trunk lean is a way to compensate to increase the velocity and maximize velocity on already bad throwing mechanics. Because one thing that is clear from this study is that pitchers who throw with contralateral trunk lean have a limited athletic career ahead of them. With the increased varus moment at the elbow and the increased internal rotation moment, this means that, if continued, this will eventually lead to a ulnar collateral ligament tear (Tommy John), labral tear or rotator cuff tear. If you look further in the results section of this study what you find is that the Division I pitchers had less contralateral trunk lean when compared to the Division III athletes and an overall higher pitching velocity than the Division III athletes.
In looking at that, it makes sense that the Division I athlete would have better throwing mechanics and better velocity and hence why they are Division I athletes. One thing that comes abundantly apparent when assessing Division I and III athletes is that you see a signficant difference in skill acquisition and athleticism between these two levels of athletes. That considered, it makes sense they would have better throwing mechanics and increased throwing velocity.
One thing that movement analysis has taught us is that you can see this contralateral trunk lean in pitch but also in single limb performance. So whether you call it retrotrendelenburg or contralateral trunk lean, it has an impact on upper extremity injury risk as well as lower extremity injury risk. If you like what you see, SHARE THE PASSION! It is the biggest compliment you can give. Follow us on Twitter @ACL_prevention and tweet about it. #MovingToChangeMovement and help us spread the passion.