Effects of vertical motion of the centre of mass on walking efficiency in the early stages after total hip arthroplasty.

PURPOSE

The purpose of this study was to identify factors related to walking efficiency in the early postoperative period of total hip arthroplasty (THA).

METHODS

The subjects of this study were 18 women who had undergone unilateral THA 4 weeks before and 18 healthy women as control. Using a force plate and a 3-D motion analyser, we measured: 1) gait speed, stride length, cadence; 2) centre of mass displacement in the three directions; 3) asymmetry of the centre of mass movement in vertical direction; and 4) the total internal work per unit mass and distance walked (a negative index of walking efficiency).

RESULTS

Compared with healthy persons, THA patients showed significantly greater total internal work per unit mass and distance walked. The vertical centre of mass motion of the THA patients demonstrated an asymmetrical pattern. In THA patients, the stepwise multiple regression analysis selected the displacement and the asymmetrical vertical motion of centre of mass as the sole significant variable affecting walking efficiency (R2 = 0.81).

CONCLUSIONS

Our findings indicated that rehabilitation programs that control the vertical movement of the centre of mass during gait are important to improve walking ability in the early post-operative phase after THA.