A method for the measurement of three-dimensional geometry of casts used for the manufacture of ankle foot orthoses

Objective. To develop a method to measure the geometry of casts for the manufacture of ankle foot orthosis. Design. A measurement study in which the feasibility of the technique, and its reliability were studied, using statistics based upon the analysis of variance. Background. Studies have shown that the effectiveness of ankle foot orthoses is influenced by small changes in geometry and, particularly, by the amount of dorsiflexion. This study is concerned with a technique to identify the variations between nominally identical casts. Methods. A measuring technique was used to determine the coordinates of grids drawn on the surface of the casts. Repeatability studies involved the measurement of six casts of the same leg produced by one orthotist. The influence of rectification, in which the technician makes modifications prior to moulding, was also studied. Results. The measurement technique was reliable, and there were no significant differences in grid dimensions among the casts. There were significant differences in dorsiflexion (up to 11 degrees) which were not influenced by rectification. Conclusions. This technique has been shown to be suitable to study the geometry of casts for the manufacture of ankle foot orthoses, and has demonstrated that relatively large variations may occur between nominally identical casts. There is a need to apply this procedure to study the influence of orthotic technique on geometry and function.