A method to determine bone movement in the ankle joint complex in vitro

An experimental set-up has been developed to quantify motion of bone structures in the ankle joint complex of human cadaver specimens under conditions approximating physiological joint loading. The device allows to load the foot/leg specimen along the axis of the tibia, and muscle forces can be simulated by clamping the extrinsic tendons of the foot. Additionally, an axial moment can be applied to the tibia. A variety of foot movements can be induced by rotating a foot plate around an arbitrary axis in the horizontal plane. The input force which produces the movement at the foot is applied to the entire sole of the foot. A forefoot fixation allows for the natural adaptation of the midfoot and hindfoot which occurs during loading of the specimen. Bone pins were placed in the tibia, talus, calcaneus and navicular, and three reflective markers were attached to each pin in order to record the bone movements with a video system. Intersegmental rotations in the talo-crural, talo-calcaneal, and talo-navicular joints were calculated in three dimensions, compared for different loading and ligament integrity conditions, and related to a functionally/anatomically described foot position. Repeated measurements of relative bone orientations indicated a reproducibility better than 2 degrees; the slope of the curves, representing the kinematic coupling, was virtually identical between repetitions. It is proposed that this method simulates multidirectional AJC compression similar to loading situations during locomotion.