Limb Symmetry Index - What is it and Is It Important

Over the course of the last 5-10 years, there has been a lot of discussion in the literature about limb symmetry index or LSI.  So, what is LSI and what does it mean?  LSI or limb symmetry index is simply the variance between one limb (typically the involved or injured limb) and the other (uninvolved) limb.  This is usually represented as a % of the involved to the uninvolved (LSI = score involved/score uninvolved x 100).  LSI can be used to describe the variance between upper extremities or lower extremities.  However, most of the research done in this area is in relation to the lower extremity.  LSI is often used by physicians as one of the factors that is considered when determining an athletes ability to return to play. 

When looking at LSI for return to play, most physicians will tend to default to the conservative and shoot for an LSI of 90% to 95%.  The thought process here is that if there is greater than a 5-10% variance then this will put the athlete at greater risk.  Limb symmetry IS very important but, is this an accurate assumption?  And whether it is or not, how are we measuring LSI and is this truly an accurate measure of risk?  Let's first look at what does the research tell us about normative values for LSI.

In a study by Rohman et al Am J Sports Med 2015, the authors did a retrospective case series looking at LSI. 

Methods: Retrospective case series of 122 patients who underwent ACL reconstruction and rehabilitation.  Each subject received standard functional testing at 4 and 6 months post operatively.  The standard functional test (SFT) consisted of 12 exercises performed in the following order:

• Single leg anterolateral reach - Patient balances upright on the tested leg only, and reaches with the contralateral hand as far as possible along the floor, at a 45 degree angle anterolaterally. (I.e., standing on the right leg, the patient reaches with the left hand forward and to their right). The patient is not allowed to bear weight on the reaching arm.

• Single leg anteromedial reach -  Patient balances upright on the tested leg only, and reaches with the contralateral hand as far as possible along the floor, at a 45 degree angle anteromedially. (I.e., standing on the right leg, the patient reaches with the left hand forward and to their left). The patient is not allowed to bear weight on the reaching arm

• Stork stance with eyes open - Patient stands on the tested leg with arms crossed over chest, and must maintain their balance without using arms for balance or touching down with the opposite leg. The trial ends at 60 seconds unless the patient loses balance sooner.

• Stork stance with eyes closed - If patient is able to complete 60 seconds with eyes open, the test is repeated with eyes closed.

• Retro step up - The patient steps backwards with the tested leg onto a raised platform, and straightens to an upright position without pushing off with the front (untested) leg. The patient then must then reverse this motion, performing a controlled descent bringing the untested leg back down to the floor. This is repeated with platforms of increasing size until the patient cannot complete the step up. 3 trials allowed at each height.

• Single leg squat - Patient is standing on the tested leg without any support, and squats as deep as possible. Arms can be extended for balance. The opposite leg is not allowed to touch the floor or brace against the tested leg.

• Single leg hop - Patient begins standing on the tested leg only, and hops forward as far as possible. Patient must demonstrate a balanced and controlled landing, without touching the untested leg to the ground for support.

• Single leg triple hop - Patient starts balanced on the tested leg, and takes 3 consecutive hops forward on the tested leg only. Patient must demonstrate balanced and controlled landings, without touching the untested leg to the ground for support.

• Cross over triple hop - Patient starts standing on the tested leg only. The patient then takes 3 consecutive hops forward parallel to a line of tape placed on the floor. Each hop must land only on the tested leg, and must land on alternating sides of the line of tape. Patient must demonstrate balanced and controlled landings, without touching the untested leg to the ground for support.

• Timed hop - The patient starts balanced on the tested leg, and hops forward on that leg only as quickly as possible, over a distance of 6 meters. Patient must demonstrate balanced and controlled landings, without touching the untested leg to the ground for support.

• Core plank - Patient is positioned prone on their elbows and toes, with a neutral spine. They must then hold this position for 60 seconds. The test ends if patient gives up, or displays excessive arching/sagging through the lumbar spine.

• Single leg bridge - Patient is positioned supine with knees bent. They then straighten and elevate the untested leg, and with the tested leg extend through the hip, pushing down and lifting their core off of the ground until the hips are neutral. The patient is not allowed to touch the ground with the untested leg or brace against the tested leg.

The SFTs were performed at 4 and 6 months post operatively for both the involved and uninvolved leg.  Ten of the twelve SFTs were analyzed and compared for changes in LSI and absolute function in each limb.  

Results: In all patients with multiple SFTs, the involved limb performance increased in all tests with the exception of the stork stance with eyes closed.  Univolved limb performance increased in 5 SFTs and decreased in none.  5 tests showed initial LSI below 90% (single leg squat, retro-step up, single leg hop, cross over triple hop and timed hop.   

Conclusion:  During ACLR rehabilitation, the improvements seen in LSI indicated absolute increases and were not attributed to univolved limb deterioration.  The single leg squat, retro step up, single leg hop, crossover triple hop and timed hop are suggested as highly useful tests since showed initial LSI below 90% and had significant improvement with rehabilitation.  

So this study shows us that there are some good measures of LSI, but are they really telling us you are at risk and are we being too stringent on the thresholds?  Meaning is this 90%-95% LSI too restrictive and more importantly, does 95% or 100% LSI mean you are not at risk? 

In a study by Adams et al J Ortho Sports Phys Ther 2012 the authors showed that 93% of normal individuals (those without injury) had an LSI of 85% or greater.  So I ask again, is the current threshold of 90-95% too restrictive and if you don't meet that threshold, are you really at risk?

As we have seen over and over again, you can have 100% LSI of really bad movement.  I think we could all look at this athlete and despite having 100% LSI, we would agree she is at risk.  So, are we relying too much on LSI and what is it really telling us?  We will continue to dive into this question again next week. 

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 is also a competitive athlete in Brazilian Jiu Jitsu.