Is There A Secret Sauce - Part IV

Importance of Single Limb Testing

Over the course of the last several weeks, we have been talking about how to apply the research to how we assess and treat athletes.  Whether we are strength coach, athletic trainer or a physical therapist, there is a way to take the current knowledge and literature and apply it in a way that is much more effective than the way we have traditionally done or do today.  For this discussion we are going to talk about single limb performance.

One of the hottest topics right now in sports medicine is when do you make a return to sport call.  Why?  Clinicians and physicians are becoming more and more cautious because re-injury rates are high with those who return to sport to early and the outcome on the 2^nd surgery is never as good as the first.  Why is this risk so high?  In a study published by Stearns et al in the American Journal of Sports Medicine in 2013, they looked at female soccer players that were cleared to return to sport following an ACL reconstruction.  What they found was that they still demonstrated increased adduction angles in the frontal plane which is directly associated with the adduction moment & risk.  The bigger the angle, the higher the moment which means the higher the risk is for ACL injury.  But this is only becomes clear when doing a comparison to the contralateral limb in a closed kinetic full weight bearing test (as demonstrated here). 

So, when do you know is the right time to return an athlete to sport following an injury or surgery?  Frankly, no one really knows.  There is a lot of debate about this issue because, as of today, we still don’t have a standardized way or protocol that we use in which can aid us in making that call.  Hence why so many athletes fail to return to their prior level of performance and why over 20% re-rupture their ACL within the first 2 years of returning to sport.  We know from the literature that you should be somewhere within 80-85% of your non-involved limb.  But how do we test that.  Today, that is mostly done off of subjective findings, subjective observations and an objective open kinetic chain computerized test (Kin Com for example).  In this particular test, the subject is seated in a device that looks like a computerized leg extension machine.  The subject performs both leg extension and flexion under resistance.  At the conclusion the computer provides a report showing symmetry or asymmetry between the two extremities.

If we consider the exercise physiology concept of specificity, then it would make sense that whatever test or tests that we do, we want to make sure it is as specific to the actual activity as possible.  Now, in a controlled environment and under testing conditions, it is often hard to truly mimic the activity in such a way that we can also get an objective measure.  That said, in most sports you are not in a seated position when your lower kinetic chain has to respond to a load and resist the stress.  When looking at the seated position versus the standing positions, the differences are clear.  There is change in length tension relationships along the entire lower kinetic chain from the core to the foot.  At the same time, recruitment patterns are completely different.  In standing your core is much more active and in seated position it is much less active.  We know that the core has a direct influence on the lower kinetic chains ability to attenuate force, so it would make sense that whatever testing we do should be in the upright position.  Considering all this then testing performed in the upright position is going to be much better than seated or laying down and will provide you with more accurate assessment of how they actually function.

Take this particular case in point.  This 16 year old basketball player who was previously seen for knee pain and patellofemoral issues was returned to sport after  a thorough examination by both her physical therapist and physician.  Her examination consisted of a review of her exercise program she was doing in therapy, her manual muscle testing scores performed on the table, her self reported outcome and measured range of motion.  However, she was not evaluated in a closed kinetic chain nor was her movement assessed during functional closed kinetic chain exercises.  In this case, upon return to sport, she demonstrated the following motion on a lateral pivoting motion which resulted in her rupturing her ACL.  Would she have demonstrated this motion on a functional closed kinetic chain test?  It is unknown nor can we speculate one way or the other.  What we do know is if you do not access closed kinetic chain motion, then you will never know.

If we were again to look at most sports and especially those that require running you will see a significant portion of it is single limb in nature.  Just looking at the running cycle, you can clearly see how most (all) of that is single limb in nature.  If we look at the epidemiology studies associated with non-contact ACL injuries, you will also see that most of these occur in a single limb position or a position where it is predominately single limb.  If we consider this factor alone, then it would make sense that if the mechanism of injury is during upright, full weight bearing single limb activity, then this should be how we test.   That said, Grindem et al published a paper in 2011 that looked at single limb testing versus bilateral testing to see which of these two were a better predictor of the athlete’s self-reported function.  Knowing that self-reported knee function was a fair predictor of risk, then seeing which test had a higher correlation to this self-reported function made sense.  What this study showed was that measurement of symmetry in single leg hop was a much better predictor versus bilateral hop.  The problem with testing athletes is that they are often very good at compensating in a way that it is hard to see, especially in bilateral tests versus single limb tests.  The higher the level the athlete the better their compensatory strategies are and hence why they are able to compete at a high level.    In this instance here, this athlete may have compensated for her lack of stability on the right by shifting her weight to the left during bilateral performance.  This could account for some of the results that we see in the current studies looking at bilateral performance in comparison to adduction seen in single limb.  This is clearer when looking at Kristinaslund et al 2013 study in which they looked at the bilateral drop jump and compared that to the adduction moment seen in sidestep cutting.  What they found was that there was only a moderate correlation to the adduction moments seen with bilateral jump and the overall adduction moment in the bilateral performance was significantly less.  The conclusion of this is that the bilateral jump is only a fair predictor but there is probably a better way to see what true adduction moments are in single limb.  That might lead us to the realization that maybe we should test single limb. 

Next week, we will continue this discussion on single limb testing and correlation to injury risk. We hope that you found this blog insightful and useful.  As we stated previously, stay tuned and 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.  #ACLPlayItSafe and help us spread the passion.

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.  He is the developer of an athletic biomechanical analysis, is an author of a college textbook on this subject  and has performed >5000 athletic movement assessments.  He serves as the National Director of Sports Medicine Innovation for Select Medical, is Chairman of Medical Services for the International Obstacle Racing Federation and associate editor of the International Journal of Athletic Therapy and Training.