Sutherland et al. (22) and Murray et al. (15) utilized
the coordinates of key anatomical points, obtained
from a cine film system, to compute joint
angle motion using planar definitions. A nonorthogonal
joint coordinate system with the associated
Cardan angles was proposed by Grood and Suntay
(7) and Suntay et al. (21) for describing the motion
of knee joint. Euler angle definitions were used by
Chao (5) for the measurement of knee joint motion
using a triaxial goniometer. Tylkowski et al. (25)
also utilized Euler angle definitions to compute hip
joint motion from trajectories of body surface markers
derived from cine film. Cappozzo (4) developed
a system to compute joint angle motion based on
the concept of Cardan angles. Antonsson (2), using
the concept of a screw axis (helical axis) of motion,
devised a method to compute limb rotations from
limb orientation data recorded using an optoelectronic
system. The concept of helical axis was also
utilized by Shiavi et al. (19) in the measurement and
analysis of knee joint motion using a six degrees of
freedom goniometer.