Background: Control of the mediolateral displacement of the center of gravity (COG) is considered to be important for efficient walking. Few studies have been published on the relation between walking efficiency and the lateral displacement of the trunk, pelvis, or COG in patients soon after total hip arthroplasty (THA). The present study was undertaken to examine the effects of lateral displacement on walking efficiency after THA.
Methods: The subjects of this study were 15 women who had undergone unilateral THA 4 weeks before and 14 healthy women as controls. Using a force plate and a three-dimensional motion analyzer, we measured (1) gait speed, stride length, cadence; (2) lateral trunk displacement (LTD) and lateral pelvis displacement (LPD); (3) lateral displacement of the center of gravity; and (4) the total internal work done per unit mass and distance walked (a negative index of walking efficiency) (WE(-1)).
Results: Compared with healthy persons, THA patients showed significantly increased amplitude of LTD and greater WE(-1) (P < 0.01). The WE(-1) value of the THA group was 21.4% higher than that of the control group. The results suggest that the patients need more energy to progress their body forward in a gait cycle, indicating reduced walking efficiency. In THA patients, the stepwise multiple regression analysis selected LTD as the sole significant variable affecting WE(-1) (R(2) = 0.72, P < 0.01).
Conclusions: These results suggest that trunk compensation strategy for hip abductor weakness in patients soon after THA can lead to increased energy expenditure.