3-DIMENSIONAL, 6-DEGREES-OF-FREEDOM KINEMATICS OF THE HUMAN HINDFOOT DURING THE STANCE PHASE OF LEVEL WALKING

The goal of this study was to develop a technique to measure the uncon strained, six-degrees-of-freedom motion of the hindfoot during level w alking and to apply this technique to characterize this motion in a yo ung healthy population. The motion was described using a joint coordin ate system which provided a description of motion in terms of three an gular displacements and three linear displacements. The accuracy of th e technique was first determined using a six-degrees-of-freedom linkag e, The motion of the hindfoot was then measured during level walking o n ten young healthy volunteers. For this purpose, a motion analysis sy stem was used to record the motion of eight reflective skin markers at tached over bony landmarks on the tibia-fibula and calcaneus. The resu lts indicate that the baseline accuracy of the technique (not includin g skin motion) was 1 degree for rotations and 1.4 mm for translations. From the gait data it was concluded that the patterns of hindfoot mot ion are similar amongst individuals in some joint parameters but not i n others. Specifically, dorsiflexion/plantarflexion had a very consist ent pattern, followed by inversion/eversion and to a lesser extent by compression/distraction. The other parameters (axial rotation, anterio r/posterior displacement and medial/lateral displacement) demonstrated a highly variable pattern amongst the individuals tested. In terms of the range of motion of the six joint parameters it was found that ang ular excursions were smaller than 20 degrees and that linear displacem ents in both anterior/posterior direction and medial/lateral direction was smaller than 3.5 mm.