The high risk of second ACL injuries after return-to-sport highlights the importance of return-to-sport decision-making. Objective return-to-sport criteria frequently use LSI’s to quantify quadriceps strength and hop scores. Whether using the uninvolved limb in LSI’s is optimal is unknown.
To evaluate the uninvolved limb as a reference standard for limb symmetry indexes (LSI’s) utilized in return-to-sport testing and its relationship with second ACL injury rates.
Seventy athletes completed quadriceps strength and 4 single-legged hop tests before ACL reconstruction (ACLR) and 6 months after ACLR. LSI’s for each test compared involved limb measures at 6 months to uninvolved measures at 6 months. Estimated pre-injury capacity (EPIC) levels for each test compared involved measures at 6 months to uninvolved measures before ACLR. Second ACL injuries were tracked for a minimum 2-year follow-up after ACLR.
Forty (57.1%) patients achieved 90% LSI’s for quadriceps strength and all hop tests. Only 20 (28.6%) patients met 90% EPIC levels (comparing involved limb at 6 months after ACLR to uninvolved limb before ACLR) for quadriceps strength and all hop tests. Twenty-four (34.4%) patients who achieved 90% LSI’s for all measures 6 months after ACLR did not achieve 90% EPIC levels for all measures. EPIC levels were more sensitive to LSI’s in predicting second ACL injuries (LSI’s: 0.273 (95% CI: 0.010–0.566); EPIC: 0.818 (95% CI: 0.523–0.949)).