Motion analysis of the lower extremities usually requires determination of the location of the hip
joint center. The results of several recent studies have suggested that kinematic and kinetic variables calculated from motion analysis data are highly sensitive to errors in hip
joint center location. “Functional” methods in which the location of the hip
joint center is determined from the relative motion of the thigh and pelvis, rather than from the locations of bony landmarks, are promising but may be ineffective when motion is limited. The aims of the present study were to determine whether the accuracy of the functional method is compromised in young and elderly sub
jects when limitations on hip motion are imposed and to investigate the possibility of locating the hip
joint center using data collected during commonly studied motions (walking, sit-to-stand, stair ascent, stair descent) rather than using data from an ad hoc trial in which varied hip motions are performed. The results of the study suggested that functional methods would result in worst-case hip
joint center location errors of 26mm (comparable to the average errors previously reported for
joint center location based on bony landmarks) when available hip motion is substantially limited. Much larger errors (
70mm worst-case), however, resulted when hip
joint centers were located from data collected during commonly performed motions, perhaps because these motions are, for the most part, restricted to the sagittal plane. It appears that the functional method can be successfully implemented when range of motion is limited but still requires collection of a special motion trial in which hip motion in both the sagittal and frontal planes is recorded.