Effects of isolated hip abductor fatigue on frontal plane knee mechanics.

PURPOSE Anterior cruciate ligament injuries and patellofemoral pain syndrome are both common and significant injuries to the knee that have been associated with hip weakness. Prospective studies have linked the risk of experiencing either injury to alterations in the frontal plane knee angle and moment during activity. These components of knee mechanics are theorized to be affected by hip abductor weakness. The purpose of this study was to identify the effects of isolated hip abductor fatigue-induced weakness on lower extremity kinematics and kinetics in recreationally active women. METHODS Twenty participants performed cut, jump, and run tasks off a raised platform while three-dimensional motion analysis data were collected.Participants then performed an isolated hip abductor fatigue protocol in side lying against isokinetic resistance, followed immediately by repeated biomechanical data collection. Separate repeated-measures ANOVA (P G 0.05) were used for each dependent variable. RESULTS After the hip fatigue protocol, regardless of task, the knee angle at initial ground contact was more adducted (pre = 0.7 degrees +/- 3.4 degrees, post = 1.2 degrees +/- 3.9 degrees, F(1,19) = 5.3, P = 0.032), the knee underwent greater range of motion into abduction (pre = 0.7 degrees +/- 1.5 degrees, post = 2.1 degrees +/- 1.6 degrees, F(1,19) = 73.2, P < 0.001), and there was a greater internal knee adductor moment (pre = -2.6 +/- 13.3 N x m, post = 4.7 +/- 14.1 N x m, F(1,19) = 41.0, P < 0.001) during the weight acceptance phase of stance. CONCLUSIONS This study demonstrates that simulated hip abductor weakness causes small alterations of frontal plane knee mechanics. Although some of these alterations occurred in directions associated with increased risk of knee injury, changes were small in magnitude, and the effect of these small changes on knee injury risk is unknown.