Summary: A simple external marker system and algorithms for computing
lower extremity joint angle motion during level walking were developed and
implemented on a computer-aided video motion analysis system (VICON).
The concept of embedded axes and Euler rotation angles was used to define the
three-dimensional joint angle motion based on a set of body surface markers.
Gait analysis was peformed on 40 normal young adults three times on three
different test days at least 1 week apart using the marker system. Angular
motion of the hip, knee, and ankle joints and of the pelvis were obtained
throughout a gait cycle utilizing the three-dimensional trajectories of markers.
The effect of uncertainties in defining the embedded axis on joint angles was
demonstrated using sensitivity analysis. The errors in the estimation of joint
angle motion were quantified with respect to the degree of error in the construction
of embedded axes. The limitations of the model and the marker
system in evaluating pathologic gait are discussed. The relatively small number
of body surface markers used in the system render it easy to implement for use
in routine clinical gait evaluations. Additionally, data presented in this paper
should be a useful reference for describing and comparing pathologic gait
patterns. Key Words: Gait analysis-Joint angles-Gait parameters-
Biomechanical model-Sensitivity analysis.