Sports Medicine Research: In the Lab & In the Field: Limb Symmetry Indices…It May Not Be as Accurate as We Thought (Sports Med Res)
Wednesday, September 21, 2016

Limb Symmetry Indices…It May Not Be as Accurate as We Thought

The Utility of Limb Symmetry Indices in Return-to-Sport Assessment in Patients With Bilateral Anterior Cruciate Ligament Reconstruction

Zwolski C, Schmitt LC, Thomas S, Hewett TE, and Paterno MV. Am J Sports Med. 2016. [Epub Ahead of Print].

Take Home Message: Limb symmetry indices may not be sufficient to identify strength and performance deficits, particularly in patients who have a history of bilateral anterior cruciate ligament (ACL) reconstruction.

Clinicians commonly use limb symmetry indices to determine if a patient who sustained an ACL rupture is able to return to play. However, it is unclear if these indices are useful when an athlete has a history of bilateral ACL ruptures because both limbs may have strength deficits. Therefore, Zwolski and colleagues completed a cross-sectional study of 45 female athletes to evaluate limb symmetry indices among patients who had sustained bilateral or unilateral ACL ruptures. The authors recruited 15 patients with a unilateral ACL rupture, 15 patients with bilateral ACL ruptures, and 15 athletes with no history of ACL injury. These patients were all matched on age, sex and sport participation. The 30 female athletes with an ACL tear enrolled in the study when they were cleared for return to sport. All athletes performed 3 hop tests (single-leg hop for distance, triple-hop for distance, and triple-crossover hop for distance). The authors randomized the order of limbs being tested. Quadriceps strength was also assessed using 3 maximum contraction trials using a Biodex machine. Overall the authors found that both ACL groups had performance deficits and impaired limb symmetry indices with the single-leg hop for distance test compared with the healthy participants. However, the limb symmetry indices for the other two hop tests and quadriceps strength assessment were only different between the unilateral ACL group and control participants but not the ACL group with a history of bilateral tears. Despite the poor performance of limb symmetry indices among those with a history of bilateral ACL injuries it is noteworthy that the authors detected differences between left and right limbs with the triple-hop for distance and quadriceps strength tests.

The data presented in this study is concerning to clinicians who rely on limb symmetry indices to make return-to-play decisions. Patients who had a history of bilateral ACL reconstructions were less likely to show deficits than patients with a unilateral reconstruction. This may be attributed to the lack of a control limb in the bilateral ACL reconstruction group. This should also raise concern about using symmetry indices when patients have other contralateral injuries that may impair their performance. For example, what if a patient has chronic ankle instability? The other concerning finding from this study is that patients who were cleared to return to sport still had strength and performance deficits. We recently reported on a study where patients who failed to meet functional criteria for return-to-sport or who had a lower hamstring:quadriceps ratio were at greater risk for an ACL graft rupture. Hence, we need to ensure that our patients return to activity with the strength and performance they need to succeed but we also need to be cautious about how we define an acceptable level of performance. As these tests continue to be evaluated, clinicians can continue to use limb symmetry indices to aid in making return to play decisions, but should be increasingly cautious if the patient in question has a history of bilateral ACL reconstruction.


Questions for Discussion: Do you use limb symmetry indices to assess a patient’s capability of being return to play? If so, how you think this data might affect your decision making process now?

Written by: Kyle Harris
Reviewed by:  Jeffrey Driban

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Zwolski, C., Schmitt, L., Thomas, S., Hewett, T., & Paterno, M. (2016). The Utility of Limb Symmetry Indices in Return-to-Sport Assessment in Patients With Bilateral Anterior Cruciate Ligament Reconstruction The American Journal of Sports Medicine, 44 (8), 2030-2038 DOI: 10.1177/0363546516645084

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