An instrumentation system for the measurement and display of the dynamic force distribution under the foot during locomotion

Master Thesis


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University of Cape Town

The clinical assessment of the weight bearing foot during locomotion is normally based on subjective judgement rather than on quantitative measurement. The techniques which have been proposed for recording the dynamic forces acting on the foot are either too complex for clinical practise or there is difficulty in relating the measured force distribution to the physical surface of the foot. The system that has been developed measures the vertical foot/ground forces during gait and immediately displays the data in a manner which can be readily assimilated. The instrumentation system consists of a segmented force plate constructed from 16 transparent beams mounted so that the total load as well as the centre of pressure on any beam can be ascertained. When the foot contacts the plate, its plantar surface is photographed through the transparent force plate by a television camera while a second television camera photographs a lateral aspect of the legs and feet. A composite video display is then generated consisting of (i) a lateral view of the legs and feet (ii) a view of the plantar surface of the planted foot with centre of pressure lines superimposed (iii) a bar chart display of the load carried by each beam. The system output is recorded on a video tape recorder which has a stop motion facility. This enables a frame by frame analysis to be made subsequently and selected stills to be photographed as a permanent record. Three series of photographs are presented which clearly show the differences between normal and abnormal gait.

Bibliography: pages 81-83.