Quantification of pelvic rotation as a determinant of gait.

OBJECTIVE To evaluate the effect of pelvic rotation, originally described as the first determinant of gait, on reducing the vertical displacement of the center of mass (COM) during comfortable speed walking. DESIGN Pelvic and lower extremity kinematic data during walking were collected. A modified compass gait model incorporating measured inputs was used to estimate the effect of pelvic rotation on reducing the vertical displacement of the COM. The actual reduction in vertical displacement was also calculated. SETTING A gait laboratory. PARTICIPANTS Thirty able-bodied subjects. MAIN OUTCOME MEASURE The estimated reduction in COM vertical displacement caused by pelvic rotation was compared with the actual reduction in COM displacement. RESULTS The estimated effect of pelvic rotation in reducing COM displacement was 2.5 +/- 1.1mm, accounting for only 12% of the actual reduction. CONCLUSION During normal comfortable speed walking by able-bodied subjects, pelvic rotation contributes only a small portion of the actual reduction in the vertical displacement of the COM compared with a compass gait model. Other primary gait factors or determinants are needed to explain the actual reduction in vertical displacement of the COM.