A computer aided design system has been developed to define the proper geometry of thermoplastic ankle-foot orthoses (AFO). The system is composed of two components: 1) a structural analysis computer program with pre and post processors customized for the distinctive geometry associated with orthoses; 2) and a patient test fixture to quantify patient load-response characteristics. A simple structural model of the biomechanical leg-AFO system was devised which incorporates the linear spring rate of the AFO, obtained from the structural analysis, and the spring rate of the patient's lower leg, ankle and foot, obtained from a patient test fixture. Design criteria were established by applying the system to the "best" designs produced by the current trial and error procedure in which several AFO's are manufactured and trial tested on the patient before an acceptable configuration is obtained. Future designs will reflect the "best" design criteria, with the first configuration manufactured the most acceptable configuration.
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