Analysis and Design of a Paediatric Ankle-Foot Orthosis

Approximately 100,000 ankle-foot orthoses (AFOs) are prescribed for children and adolescents with neuromuscular disorders such as spina bifida and cerebral palsy in North America annually in order to limit unwanted movement and maximize functional activities. The current AFO fabrication process is a lengthy and labour intensive process, and requires at least two client visits. There is a need for the development of an AFO that can be prescribed in a single visit at a lower cost. Through finite element analysis (FEA) new materials and design modifications of orthotic devices can be investigated in order to decrease their cost and time of fabrication. To accurately model these complex systems a knowledge of the loads that an orthosis undergoes during functional activities is required.

The interface pressures between an AFO and a subject with spina bifida were measured for trials of walking, running and hopping activities. Sensors based on force sensitive resistive technology were placed under the toe, heel, metatarsal heads, plantar arch, medial and lateral ankle, lower posterior calf, and top calf. Foil strain gauges were fixed to the exterior surface of the AFO opposite locations of pressure measurement. Results will be used to model the loading pattern in FEA in order to compare predicted strains to strains obtained during gait analysis.

Subject AFO testing.

AFO model.