Polyplanar Hip Joint for Use in Lower Limb Bracing

Abstract

CHILDREN with nervous or muscular disorders affecting the movements of the trunk and lower limb sometimes have great difficulty in walking or learning to walk. External support may be provided by long callipers fitting into the heels of the boots and extending upwards to a padded metal strap around the waist. A simple hinge joint at the level of the hip (joint) allows the legs to swing in one vertical plane only. The complexity of normal walking is highlighted when a child attempts to move in such an apparatus, for the pelvis cannot rotate around a vertical axis through the hip joint of the supporting leg during the swinging phase of the other leg. The patient therefore progresses by pivoting his body around an axis passing through the ball of the supporting foot. This produces the abnormal foot positions relative to the line of march and the pelvis, which are shown in Fig. 1a and b. Fig. 1b shows that the foot bearing the weight (A) must pivot through an angle equal to that of the pelvic swing (BAC). In normal walking (Fig. 1a) the position of the foot remains unaltered relative to the line of march, because the necessary rotation of the lower limb has taken place at the hip joint.