What question did this study set out to answer?

To assess the effectiveness of limb symmetry indexes in evaluating knee function post-ACL injury and their correlation with second injury rates.

March 30, 2017

Limb Symmetry Indexes Can Overestimate Knee Function After Anterior Cruciate Ligament Injury

Key Points

To assess the effectiveness of limb symmetry indexes in evaluating knee function post-ACL injury and their correlation with second injury rates.
Assessments involved quadriceps strength and single-leg hop tests before and 6 months after ACL reconstruction in 70 athletes.
Comparative analyses were conducted between involved and uninvolved limbs for strength and hop measures.
A minimum of 2 years follow-up tracked second ACL injuries in the cohort.
57.1% of patients achieved 90% LSIs post-reconstruction for quadriceps strength and hop tests.
Only 28.6% met 90% EPIC levels, indicating higher thresholds were not met by many.
EPIC levels showed greater sensitivity in predicting second ACL injuries compared to LSIs, with respective values of 0.818 and 0.273.

Abstract

Study Design Prospective cohort. Background The high risk of second anterior cruciate ligament (ACL) injuries after return to sport highlights the importance of return-to-sport decision making. Objective return-to-sport criteria frequently use limb symmetry indexes (LSIs) to quantify quadriceps strength and hop scores. Whether using the uninvolved limb in LSIs is optimal is unknown. Objectives To evaluate the uninvolved limb as a reference standard for LSIs utilized in return-to-sport testing and its relationship with second ACL injury rates. Methods Seventy athletes completed quadriceps strength and 4 single-leg hop tests before anterior cruciate ligament reconstruction (ACLR) and 6 months after ACLR. Limb symmetry indexes for each test compared involved-limb measures at 6 months to uninvolved-limb measures at 6 months. Estimated preinjury capacity (EPIC) levels for each test compared involved-limb measures at 6 months to uninvolved-limb measures before ACLR. Second ACL injuries were tracked for a minimum follow-up of 2 years after ACLR. Results Forty (57.1%) patients achieved 90% LSIs for quadriceps strength and all hop tests. Only 20 (28.6%) patients met 90% EPIC levels (comparing the involved limb at 6 months after ACLR to the uninvolved limb before ACLR) for quadriceps strength and all hop tests. Twenty-four (34.3%) patients who achieved 90% LSIs for all measures 6 months after ACLR did not achieve 90% EPIC levels for all measures. Estimated preinjury capacity levels were more sensitive than LSIs in predicting second ACL injuries (LSIs, 0.273; 95% confidence interval CI: 0.010, 0.566 and EPIC, 0.818; 95% CI: 0.523, 0.949). Conclusion Limb symmetry indexes frequently overestimate knee function after ACLR and may be related to second ACL injury risk. These findings raise concern about whether the variable ACL return-to-sport criteria utilized in current clinical practice are stringent enough to achieve safe and successful return to sport. Level of Evidence Prognosis, 2b. J Orthop Sports Phys Ther 2017;47(5):334-338. Epub 29 Mar 2017. doi:10.2519/jospt.2017.7285.

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