Improvements in thigh strength symmetry are related to changes in self-reported function after anterior cruciate ligament reconstruction

Objectives: Loss of quadriceps strength after anterior cruciate ligament (ACL) injury and reconstruction (ACLR) is a common and debilitating complicating factor. The association between the recovery of quadriceps strength and functional outcomes after ACLR is a focus of current study, while evaluation of the recovery of hamstrings strength is limited despite use of hamstrings autografts. Decreased hamstrings activation increases risk of a primary ACL injury; however, the effect of hamstring strength on postoperative knee function is unknown. We hypothesized that improvement in quadriceps and hamstrings strength would correlate with improvements in self-reported outcome (SRO) measures in the first six months after ACLR. Methods: Thirty subjects (20 males/10 females) diagnosed with acute ACL rupture that underwent ACLR with hamstrings autograft were enrolled in the study. Subjects were between the ages of 14 and 44 who previously had participated in level I/II pivoting/cutting sports. Subjects underwent isokinetic quadriceps and hamstrings strength assessment at 60 degrees/second (Biodex System III, Shirley, NY) prior to surgery and at 12, and 24 weeks post-operatively. Quadriceps and hamstrings limb symmetry indexes [(involved strength/uninvolved strength) x 100] were calculated at each time point. The Knee Injury Osteoarthritis Outcome Score (KOOS subscales Pain, Symptoms, ADL, Quality of Life (QOL) and Sport) was administered at each time point. Pearson’s correlation was utilized to determine the relationships between changes in quadriceps index (QI), hamstrings index (HI), and SRO measures between each time point. Results: Mean QI pre-ACLR, 12 weeks and 24 weeks post-ACLR were 78.3%, 76.7%, and 83.7% respectively. Mean HI at the same time points were 78.5%, 71.6% and 82.8% respectively. Improvements in QI were correlated with improvement on the KOOS-Sport at each time point (pre-ACLR to 12 weeks post-ACLR: r= 0.65; pre-ACLR to 24 weeks post-ACLR: r= 0.66; 12 weeks post-ACLR to 24 weeks post- ACLR: r= 0.69; p < 0.001) as well as KOOS-QOL pre-operative to 12 weeks post-ACLR (r= 0.38, p < 0.05). Improvements in HI were correlated with KOOS-Pain from the pre-operative to 12 and 24 weeks post-ACLR (r = 0.47 and r= 0.44 respectively; p < 0.04). Improvements in HI and QI were related to improvements on KOOS-Symptoms from pre-operative to 24 weeks post-ACLR (r = 0.43 and r= 0.51 respectively; p < 0.05) while QI and KOOS-Symptoms also improved from pre-operative to 12 weeks post-ACLR (r = 0.39, p < 0.04). Conclusion: Positive correlations were seen between QI and multiple SRO measures over time. Associations between HI and KOOS-Symptoms and Pain subscales were found early in post-operative recovery; there was no association between changes in HI and KOOS-ADL, Sport or QOL subscales at any time point. Correlations between HI and KOOS-Pain and Symptoms may be representative of pain and inflammation associated with hamstrings graft harvest, which resolve over time. These results support current literature demonstrating the relationship between the recovery of quadriceps strength and self-reported function post-ACLR. Continued focus on restoration of quadriceps strength is imperative to maximize functional outcomes post-ACLR.