Introduction - Video motion
analysis systems have been successfully employed in the study of whole body
gait and have proven their value in clinical applications. Similar usefulness
could be found in the study and diagnosis of many foot and ankle disorders.
In this study, a 4 segment rigid body model was developed to investigate isolated
foot and ankle kinematics. To obtain clinical data, the foot and ankle were
instrumented with 15 retroreflective markers. Once marker co-ordinates were
determined by using a video motion analysis system (Vicon, Oxford, England),
the model was employed to transform raw 3-D co-ordinate data into a more clinically
meaningful set of angular and translational relationships between distal and
proximal rigid body segments. Three 3-D reference methods were considered in
this work, the helical axis, Euler angles, and a set of three independent angles.