The Impact of Quadriceps Femoris Strength Asymmetry on Functional Performance at Return to Sport Following Anterior Cruciate Ligament Reconstruction

STUDY DESIGN: Cross-sectional study. OBJECTIVES: To investigate the impact of quadriceps femoris (QF) muscle strength asymmetry at the time of return to sport on self-reported function and functional performance of individuals following anterior cruciate ligament reconstruction (ACLR). BACKGROUND: Evidence-based QF strength guidelines for return-to-sport decision making are lacking. Objective guidelines necessitate understanding the impact of QF strength deficits at the time of return to sport on function and performance. METHODS: Fifty-five individuals (mean age, 17.3 years) who were cleared for return to sport following primary ACLR (ACLR group) and 35 uninjured individuals (mean age, 17.0 years) in a control group participated in the study. QF strength (maximum voluntary isometric contraction) was assessed, and the quadriceps index (QI) was calculated [(involved strength/uninvolved strength) x 100%]. The ACLR group was further subdivided into 2 groups, based on the QI: high quadriceps (QI of 90% or greater) and low quadriceps (QI of less than 85%). The International Knee Documentation Committee Subjective Knee Evaluation Form score was used to assess self-reported function, and hop tests were used to assess functional performance. Multivariate analysis of variance and hierarchical regression analyses were performed. RESULTS: The individuals in the ACLR group were weaker, reported worse function, and performed worse on hop tests compared to those in the control group (P<.05). The low-quadriceps group demonstrated worse performance on the hop tests compared to the high-quadriceps group and the control group (P <=.016). Hop test performance did not differ between the high-quadriceps and control groups (P >=.14). QF strength predicted performance on the hop tests beyond graft type, presence of meniscus injury, knee pain, and knee symptoms. CONCLUSION: At the time of return to sport, individuals post-ACLR who had weaker QF (QI of less than 85%) demonstrated decreased function, whereas those with minimal QF strength deficits (QI of 90% or greater) demonstrated functional performance similar to uninjured individuals. QF strength deficits predicted hop test performance beyond the influences of graft type, presence of meniscus injury, knee pain, and knee symptoms. J Orthop Sports Phys Ther 2012;42(9):750-759, Epub 19 July 2012. doi:10.2519/jospt.2012.4194