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

Research paper by Elizabeth E Wellsandt, Mathew J MJ Failla, Lynn L Snyder-Mackler

Indexed on: 31 Mar '17Published on: 31 Mar '17Published in: The Journal of orthopaedic and sports physical therapy


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 (LSI's) to quantify quadriceps strength and hop scores. Whether using the uninvolved limb in LSI's is optimal is unknown. Objectives To evaluate the uninvolved limb as a reference standard for LSI's utilized in return-to-sport testing and its relationship with second ACL injury rates. Methods 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. Results 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)). Conclusion LSI's frequently overestimate knee function after ACLR and may be related to second ACL injury risk. These findings raise concern 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 Therapy, level 2b. J Orthop Sports Phys Ther, Epub 29 Mar 2017. doi:10.2519/jospt.2017.7285.