Can a knee sleeve influence ground reaction forces and knee joint power during a step-down hop in participants following ACL reconstruction? An explanatory analysis

PurposeElastic knee sleeves are often worn following anterior cruciate ligament reconstruction but mechanisms underlying observed changes in movement patterns are still unclear. The aim of this study was to determine the immediate and 6-week effects of wearing a knee sleeve on ground reaction forces (GRF) and knee joint power during a step-down hop task. MethodsUsing a cross-over design, we estimated GRF and knee kinematics and kinetics during a step-down hop for 30 participants (age 26.1 [SD 6.7] years, 14 women) following ACL reconstruction (median 16 months post-surgery) with and without wearing a knee sleeve. In a subsequent randomised clinical trial, participants in the Sleeve Group (n=9) then wore the sleeve for 6 weeks at least 1 hour daily, while a Control Group (n=9) did not wear the sleeve. Statistical parametric mapping (SPM) was used to compare (1) GRF trajectories in the three planes as well as knee joint power between three conditions at baseline (uninjured side, unsleeved injured and sleeved injured side); (2) within-participant changes for GRF and knee joint power trajectories from baseline to follow-up between groups. We also compared discrete peak GRFs and power, rate of (vertical) force development, and mean knee joint power in the first 5% of stance phase. ResultsGRF did not differ for the (unsleeved) injured compared to the uninjured sides based on SPM analysis. Discrete variables showed lower peak anterior (propulsive) GRF for the injured side, and lower peak eccentric and concentric power, and mean power in the first 5% of stance. When wearing the sleeve on the injured side, mean power in the first 5% of stance increased significantly [mean difference (95% CIs) 1.3 (0.6, 2.0) N/BW*ht] from a concentric to an eccentric power when wearing the knee sleeve. After six weeks, the direction of change for vertical GRF differed between the groups: while the Control Group had slightly decreased forces, the Sleeve Group presented increased forces. ConclusionsIncreased knee power in the first 5% of landing when wearing the knee sleeve, combined with greater knee flexion, may indicate a protective response for ACL ruptures, most commonly occurring during that early phase of landing. The directional change of increased vertical GRF for the Sleeve group, combined with shorter stance duration at follow-up, may indicate enhanced performance when being prescribed such sleeve.