Sports Medicine Research: In the Lab & In the Field: ACL Symmetry Comparison – Timing Could Be Everything (Sports Med Res)
Wednesday, April 26, 2017

ACL Symmetry Comparison – Timing Could Be Everything

Limb Symmetry Indexes Can Overestimate Knee Function After ACL Injury

Wellsandt E, Failla MJ, & Snyder-Mackler L. J Ortho Sport Phys Ther. 2017; Published online ahead of print

Take Home Message: If we compare a post-surgical knee to the uninvolved limb it may be ideal to test the uninvolved limb before surgery rather than later.

A patient trying to return to their previous level of activity after an anterior cruciate ligament (ACL) reconstruction must work hard to improve strength and function.  Upon return, they are still at a high risk for another ACL tear and long-term complications from their injury.  Clinicians commonly use limb symmetry indexes to assess what is “normal” for a patient during hop and strength tests.  However, the uninvolved limb might be a poor standard to hold a patient to.  The authors of this study compared limb symmetry indexes and estimated pre-injury capacity among 70 ACL reconstruction patients.  Each participant completed an evaluation prior to an ACL reconstruction and again at 6-months post ACL reconstruction. The evaluation included quadriceps strength and 4 single-legged hop tests. At 2 years after the ACL reconstruction, participants reported if they experienced a new ACL injury in the prior 2 years. The authors estimated pre-injury capacity by using a participant’s involved limb at 6 months post surgery in comparison to their uninvolved limb at the initial evaluation. This differs from the limb symmetry index, which relies on the uninvolved limb’s performance at the 6 month follow-up.  The table below demonstrates that less people passed a 90% criteria on all tests with the estimated preinjury capacity index (20 people) compared with the limb symmetry index (40 people). During the two year follow up, 11 participants reported a second ACL injury and 8 of these participants passed the recommended 90% limb symmetry index cut off.  However, only 2 of the 11 participants passed the 90% estimated preinjury capacity cut off. 

Table. Disagreement between limb symmetry index and estimated preinjury capacity.

Failed 90% estimated preinjury capacity index on all tests (50 people)
Passed 90% estimated preinjury capacity index on all tests (20 people)
Failed 90% limb symmetry index on all tests (30 people)
26 people
(3 suffered another injury)
4 people

Passed 90% limb symmetry index on all tests (40 people)
24 people
(6 suffered another injury)
16 people
(2 suffered another injury)

These authors found that using the strength and functional performance of the uninvolved limb at the initial evaluation for comparative norms was better than assessing and comparing both limbs at 6 months after surgery.  This is very interesting because there may be adaptations that occur due to decreased physical activity levels during the post-surgical period.  So comparing the limbs after this relative deconditioning may underestimate where the healthy limb usually is.  It would also be interesting to see how the injured limb performed prior to injury (for example, during preseason screening) and how those measurements compare to the non-injured limb at the time of injury. This presurgery assessment strategy, however, is still vulnerable to arguments that the healthy limb may not be a good reference point at all because there may have been predisposing reason as to why the person got injured in the first place that affected both limbs.  Regardless, these findings support the use of the estimated preinjury capacity index instead of the limb symmetry index. This would be appealing because it is using a snapshot of where they were closest to their competitive physically active state.  It would not take much longer to do these assessments on the healthy limb at your initial evaluation during pre-surgical rehabilitation.  It would be interesting to continue to follow these patients out and not only compare their injury rates, but also monitor their patient-reported outcomes and risk for osteoarthritis.

Questions for Discussion:  What criteria do you use for return to play?  Do you establish any pre-injury or pre-surgery norms for the lower extremity in your initial screenings?

Written by: Nicole Cattano
Reviewed by: Jeffrey Driban

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2 comments:

Haley said...

Great article. Do you think baseline testing would occur during PPEs? If so, would you retest individuals each year because LSI may differ each year depending on training effects and adaptations of sport. I think these questions are important to consider because fitness levels and strength are always changing in sport. Also, soccer players have pre-established low symmetry measures due to the nature of the sport, so should different sports have different expectations for LSI?

I still believe LSI is important for returning an athlete back to sport. However, I think LSI needs to be tested before and after fatigue to determine how the ACL-R limb is responding to fatigue, which is when the athlete would be at greatest risk for sustaining a secondary ACL injury. After a clinician determines an athlete is ready to return to activity around 6 months using standard hop testing and isokinetic strength measures, testing under fatigue should be done.

Jeffrey Driban said...

Hi Haley:
I think baseline testing could occur during the PPE each season and shortly after an injury. I think you raise a great point about the fact that we probably shouldn't hold every athlete to the same standard cut-off. We also need to keep in mind that these athletes are often at risk of injuring the contralateral limb - so is the contralateral limb really the best comparison? I think more and more data is supporting your idea that whatever strategy we use to assess an athlete for RTP it should likely be both before and after fatigue. It would be interesting to replicate a study like this one to test that idea further.

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