Limb Symmetry Index: What is it and Is it important - Part IV

Last week we continued our discussion about limb symmetry index (LSI).  Specifically we looked at Melick et al Br J Sports Med 2016.  In this study the authors looked at which battery of tests that test LSI that could be used when determining an athlete’s ability to return to play.  This study brought up a lot of good points and also provided us some insight to what battery of tests we should consider when looking to return to play.  However, one question this may raise is how many tests should we use and when we use a “battery of tests” to determine readiness for return to play, what should be considered passing.  Clinically we all have in our minds what should be considered passing but what does the research tell us?

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Considering this question, we can look at the Tooleet al J Ortho Sports Phys Ther 2017 study to give us some insight. 

Hypothesis:  The hypothesis for this study is that a higher proportion of young athletes who meet the recommended cutoffs will maintain the same level of sports participation over the year following return to play clearance versus those who do not meet recommended cutoffs.

Methods: At the time of RTPlay, the IKDC (international knee documentation committee subjective knee evaluation form), quadriceps and hamstring limb symmetry index and single leg hop tests (single hop for distance, triple hop for distance, crossover hop for distance, and 6-meter timed hop) were assessed.  Proportions of participants who met individual and combined cutoffs were calculated.  Proportions of participants who continued at the same level of sports participation over the year following return to sport clearance were compared between groups.

 Results: Participants included 115 young athletes (88 female and 27 males).  The proportions meeting the individual cutoffs ranged from 34.5% to 78.3%.  The proportions meeting the cutoffs for all hop tests, all strength tests and all combined measures were 53%, 27.8% and 13.9% respectively.  A higher proportion of participants who met the cutoffs for both strength tests maintained a higher level of sports participation over the year following return to play clearance thank those who did not (81.3% versus 60.2%).

Discussion:  Obviously there are some interesting findings in this study.  The cutoff criteria for all the LSI measures (strength and hop measures) was 90% or 10% deficit.  This is interesting considering what previous research has indicated regarding normative values for LSI.  Rohman et al Am J Sports Med 2015 showed 93% of non-injured normal athletes had an LSI of 85% or better.  So one question this raises is if this 90% cutoff or 10% deficit is too high.  That said, those who met this criteria, 81.3% of them were still participating in sport at the same level one year post return to play.  The results of this current study also showed that only when it came to the individual tests, athletes had a higher pass rate but when evaluating multiple tests that the pass rate was only 13.9%.  One thing to consider with this is that all of the hop tests were done in a specific sequence (single hop for distance, triple hop for distance, crossover hop for distance, and 6-meter timed hop) and one right after the other.  Considering, is this lower pass of meeting the criteria with all these test the result of the athlete being fatigued?  Does fatigue have an impact on movement and results on these tests?  Intuitively, we might think this to be the case, but what does the research tell us. 

Philosophically, I personally struggle with what do these tests really tell us?  Most of these tests are scored visually or by some measure (distance or time).  What do these measures tell us about the biomechanical risk factors?  Does the fact that the athlete jumps the same distance bilaterally tell us that they do this with good biomechanical form?  For example, this athlete may jump equal distance and may do it in the same time bilaterally, but does this tell us she is doing this with good form?  Let’s assume she is at 90% LSI, does this mean that she is at a reduced risk of reinjury with RTPlay?  I think we would all say no.

In addition, are these athletes that pass the tests really passing?  Do athletes figure out what we are attempting to test and sand bag their results?  Meaning, could they limit performance on the non-involved side to make the involved side look better so they get a passing score?  Finally, what does the fact that they have RTPlay really mean?  Are they sitting on the bench or are they “performing” at the same level as previous?  We have touched on this fact in previous blogs.  According to the Maiet al Am J Sport Med 2017, we know NFL players performance is reduced up to 2 years “after” return to play.  So even though they are RTPlay, there is a reduction in all performance measures for up to 2 years and their professional career is reduced by 2 years.

Although this is a great study, I think we raised more questions than we may have actually answered.  So stay tuned next week as we continue to dive into this topic of LSI and try to answer some of these questions.  If you enjoy this blog, please share with your colleagues and associates.  You can also follow us on Instagram at bjjpt_acl_guy and on 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 Innovation for Select Medical, is Vice Chairman of Medical Services for USA Obstacle Racing and movement consultant for numerous colleges and professional teams.  Trent is also a competitive athlete and blue belt in Brazilian Jiu Jitsu.