Improvements in Thigh Strength Symmetry Are Modestly Correlated With Changes in Self-Reported Function After Anterior Cruciate Ligament Reconstruction

BACKGROUND: The association between quadriceps strength and functional outcomes after anterior cruciate ligament reconstruction (ACLR) is a focus of current research, while evaluations of hamstring strength are limited, despite the frequent use of hamstring autografts. PURPOSE/HYPOTHESIS: The purpose of this study was to determine the relationship between changes in quadriceps and hamstring strength symmetry and self-reported outcomes before ACLR and at 12 and 24 weeks after surgery. We hypothesized that improvements in quadriceps and hamstring strength symmetry would be correlated with improvements in self-reported outcome measures within the first 6 months after ACLR. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: Thirty patients who underwent ACLR with a hamstring autograft were enrolled. Quadriceps and hamstring strength and Knee injury and Osteoarthritis Outcome Score (KOOS) values were assessed before and at 12 and 24 weeks after ACLR; limb symmetry indexes for strength were calculated at each time point. The Friedman and Wilcoxon signed-rank tests were used to analyze changes in KOOS values over time. Spearman rank-order correlations were used to test the relationship between changes in strength and KOOS values between each time point. RESULTS: Hamstring and quadriceps limb symmetry significantly increased with time (P ≤ .03). Fair correlations were observed between changes in the hamstring index and changes in the KOOS Symptoms subscore from before surgery to 12 weeks postoperatively (r = 0.48; P ≤ .05). Changes in the quadriceps index (QI) were moderately correlated with changes in the KOOS Sport/Recreation subscore (r = 0.60; P = .001), and fair correlations were seen between the QI and the KOOS Quality of Life subscore (r = 0.39; P ≤ .04) from preoperatively to 12 weeks after surgery. Moderate correlations were seen between the QI and the KOOS Sport/Recreation subscore (r = 0.57; P = .005) from 12 to 24 weeks after surgery. CONCLUSION: Improvements in quadriceps and hamstring strength symmetry were modestly associated with improvements in athletes’ perceived function in the first 6 months after ACLR. Specifically, improvements in hamstring symmetry were associated with improvements in knee symptoms within the first 12 weeks postoperatively, while improvements in quadriceps symmetry were associated with improvements in self-reported sport function throughout the first 6 months after ACLR. The restoration of strength symmetry within the first 6 months may be a critical component of rehabilitation aimed at maximizing function after ACLR. Further investigation is warranted to comprehensively evaluate whether the timing of strength gains predicts future function, including those who successfully return to their preinjury activity level after ACLR.