Author(s)

S. Syngellakis & M. A. Arnold

Abstract

An asymmetric Ankle Foot Orthosis (AFO) H model was generated from leg surface data and a number of design parameters through a versatile graphics routine. The effect of modelling parameters, geometry, loading and constraints on the AFO mechanical behaviour was assessed through finite element analyses. Moderate thickness non-uniformity was predicted to have a small effect on AFO stiffness although the extent of this effect may also depend on the trimline position. Variation of the heel constraints was found to have a significant effect on both the maximum stress and the moment required to produce a given rotation about the ankle axis. The magnitude and distribution of stresses in critical regions, as well as the ankle moment, were all found to depend on the distribution of imposed deformation. The results of the parametric studies point towards some possible strategies for design optimisation. Keywords: orthotics, biomechanics, design, modelling, finite elements. 1 Introduction An Ankle Foot Orthosis (AFO) is a device prescribed for the management of a wide range of disorders, including cerebral palsy, hemiplegia, stroke and drop foot. Its purpose is to support and stabilise the ankle and thus improve the gait pattern. The all-plastic AFO is manufactured by vacuum forming a sheet of thermoplastic material over a plaster cast of the patient’s limb; it is then trimmed to the desired shape. Computer Aided Design (CAD) and Computer Aided Manufacture (CAM) can be used in the fabrication of such, custom-made, orthotic devices [1]. Computer technology could improve the prescription service by allowing control over the variables inherent in the design of such

Keywords

orthotics, biomechanics, design, modelling, finite elements.