Knee muscle strength in runners who have had knee surgery: differences between limbs and associations with functional performance

Abstract

Introduction: Knee muscle weakness has been associated with an increased risk of various overuse injuries in runners and incident knee osteoarthritis; however, little is known about knee strength in runners, particularly those who are at high risk of osteoarthritis who have previously had knee surgery. The aim of this study was to explore differences in knee extensor and flexor strength between surgical and non-surgical limbs in runners with a history of knee surgery, and to explore if knee strength is associated with functional performance. Methods: A convenience sample of 38 runners (run ≥10km/week, ≥3 sessions/week) who had unilateral knee surgery (45% anterior cruciate ligament reconstruction) were recruited (33.2±6.8 years, 11 women). Three maximal voluntary isometric contractions of the knee extensors and flexors were performed at 60° knee flexion (Biodex dynamometer). The highest torque value (Nm) for the knee extensors and flexors for each leg was used for analysis. Functional performance was assessed via three trials of the hop for distance test, with the furthest distance hopped for each leg recorded. Paired t-tests were used to explore differences in knee strength between limbs (whole group and stratified by sex) and partial correlations were used to explore associations between knee strength and hop for distance, controlling for mass, age, and sex. Results: There was no significant difference in knee extensor strength between the surgical and non-surgical limbs (surgical=205.9±53.4Nm, non-surgical=215.5±57.9Nm; p=0.087, Cohen’s d=0.285). A significant difference was observed between limbs for knee flexor strength (surgical=103.6±24.1Nm, non-surgical=112.3±28.6Nm; p=0.001, Cohen’s d=0.576). When examining men only, the same results were found, but there were no significant differences between limbs for women. Small to moderate non-significant associations were observed between knee strength and hop for distance on both the surgical (knee extensor r=0.321, p=0.060; knee flexor r=0.333, p=0.051) and non-surgical limbs (knee extensor r=0.286, p=0.095; knee flexor r=0.093, p=0.596). Discussion: Runners who have had unilateral knee surgery demonstrate knee flexor weakness in the surgical limb, but not knee extensors, although differences may be sex specific. Small to moderate non-significant associations between knee strength and hop for distance indicate that factors other than knee strength may influence functional performance in runners who have had knee surgery. Conflict of interest statement: My co-authors and I acknowledge that we have no conflict of interest of relevance to the submission of this abstract.