The relationship between maximal hip abductor strength and resultant loading at the knee during walking

The peak external knee adduction moment (KAM) is implicated in progression of knee osteoarthritis (OA). Recently, hip abductor weakness has also been found in patients with knee OA; however, it remains unknown as to how or if this weakness is a consequence of OA, or a predisposing factor. If it is the latter, a direct relationship between hip strength and KAM magnitude would be expected. The purpose of this study was to evaluate the relationship between hip abductor strength and KAM magnitude during walking. In fourteen adults, maximal isometric hip abductor strength was measured, and the KAM was quantified during gait. Additionally, internal hip abductor moments, vertical and medial ground-reaction-forces (GRFs), and GRF to knee joint center lever-arms were quantified during gait. The relationship between hip strength and GRFs, lever-arms and KAM were assessed using correlation. Internal hip abductor moments were compared to maximum hip strength by paired samples t-test. Correlations between hip strength and the vertical GRF (r = -0.05, p = 0.87), medial GRF (r = -0.24, p = 0.41), lever arm (r = -0.01, p = 0.97), and KAM (r = -0.24, p = 0.41) were not statistically significant. Peak internal hip abductor moments during gait (1.1 ± 0.2 Nm/kg) were significantly lower than maximal hip abductor strength (1.8 ± 0.3 Nm/kg, p < 0.001). It is concluded that hip abductor strength is not related to KAM magnitude. It seems more likely that hip abductor weakness is a consequence of OA rather than a predisposing factor.