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B. Patterson1, K. Crossley1, L. Perraton2, A. Kumar1, M. King1, J. Heerey1, C. Barton1, A. Culvenor1
1La Trobe University, La Trobe Sport and Exercise Medicine Research Centre, Melbourne, Australia, 2Monash University, Physiotherapy, Melbourne, Australia
Background: A limb symmetry index (LSI) >90% on hop tests is a widely advocated benchmark for functional recovery and return-to-sport clearance after ACL injury. Yet, the LSI assumes the contralateral limb is the “gold standard” and immune to decline. Due to the bilateral functional deficits evident after ACL injury and ACLR, other assessment methods such as comparing performance of both limbs to age, sex and activity-level matched uninjured peers may be required.
Purpose: Our primary aim was to describe the functional performance changes in the ACL-injured and contralateral limbs 1- to 5-years post-ACL reconstruction (ACLR) to determine the influence on LSI. Our secondary aim was to compare the ACLR group results to uninjured healthy controls.
Methods: 59 participants (38 men) aged 29±16 years completed three hop-tests and a one-leg rise 1- and 5-years post-ACLR. Mean(±SD) scores for the ACLR and contralateral limbs, and LSI at 1- and 5-years were reported. Linear mixed-effects models evaluated the difference in change between the ACLR and contralateral limbs. Participants were classified with stable, improving or worsening function relative to previously published minimal detectable change thresholds. Healthy controls completed the hop-tests (n=41) and one-leg rise (n=31) at a single time-point to provide reference data. Linear regression models (adjusted for age and body mass index), assessed the differences in functional performance at 1- and 5-years between the ACLR group and the healthy control group.
Results: The contralateral limb had a significantly (p<0.05) greater decrease in functional performance between 1- and 5-years for the three hop-tests, compared to the ACLR limb. Worsening was more common in the contralateral limb than the ACLR limb; resulting in significant improvements in the LSI for the single-hop (mean 87% at 1-year to 95% at 5-years), side hop (77% to 86%) and one-leg rise (76% to 85%). Only one-in-five passed (>90% LSI on all four tests) the test battery at 1-year post-ACLR. The LSI on all four tests at 1-year post-ACLR was significantly lower than healthy controls, but did not generally differ between groups at 5-years.
Conclusion(s): Although the LSI significantly improved between 1- and 5-years post-ACLR, this was mostly due to worsening function in the contralateral limb. The LSI should be used and interpreted with caution, as it assumes the contralateral limb is immune to decline or the acceptable standard. Exercise-based interventions may need to continue beyond the typical rehabilitation period of 6-12 months to improve or maintain function in both limbs, considering the persistent deficits at 1-year post-ACLR compared to healthy controls, and minimal improvement over the proceeding 4-years.
Implications: The LSI should not be used in isolation when evaluating functional performance changes after ACLR as it may overestimate functional ability. Clinicians may consider alternatives such as pre-operative or early post-operative testing of the contralateral limb, or comparing ACLR limb performance to age, sex and activity-level matched normative data.
Funding, acknowledgements: Brooke Patterson, Adam Culvenor and Christian Barton are recipients of National Health and Medical Research Council awards
Keywords: anterior cruciate ligament, functional performance, limb symmetry index
Topic: Sport & sports injuries
Did this work require ethics approval? Yes
Institution: La Trobe University
Committee: La Trobe University Human Ethics Committee
Ethics number: HEC15-100, HEC16-045
All authors, affiliations and abstracts have been published as submitted.
