axis. This procedure was used in this study to obtain
a consistent definition of the neutral axis of
rotation in the transverse plane. While this procedure
yielded reasonable results for normal subjects,
it may not be practical in a disabled group, particularly
children with cerebral palsy.
The hip joint center estimation is another area
that needs further analysis. How well do the empirical equations reflect the location of the true joint
center? What happens to the joint angle patterns if
there is an error in the location of the hip joint center?
To answer some of the questions, the estimated
hip center was perturbed in all three directions up to
1 cm and the resulting joint angle patterns were
computed. For a 1 cm displacement, a maximum
constant offset of 2" in the angle patterns was ob-