Determination of loads carried by polypropylene ankle-foot orthoses: a preliminary study

Ankle-foot orthoses (AFOs) are prescribed for the management of gait-related problems. Prescription of AFOs is based on empirical techniques due to the low level of evidence-based research on their efficacy, but primarily poor understanding of their mechanical characteristics. This study aimed to establish a method that would allow the quantification of the contribution of AFOs in the control of the ankle joint during gait. A possible way of achieving this aim would be to measure strain on the AFO during walking by the use of strain gauges. Following successful experimentation with the application of strain gauges to polypropylene tensile specimens, an AFO was instrumented by attaching strain gauges to it so as to allow the moment generated on the AFO in the sagittal plane about the ankle to be measured. Walking trials using this AFO on an able-bodied subject indicated good step-to-step repeatability. The use of an instrumented AFO in conjunction with kinematic and kinetic data acquisition would allow the contribution of the AFO and the residual anatomical loads to be determined. The advantage of such procedure over previously reported ones resides on the use of the actual orthosis being worn by patients thereby conducting tests under real-life situations. It is believed that such analysis of the load actions of an orthosis, which may in future be carried out in three dimensions, would allow a better understanding of the interaction between the leg and the orthosis. This should ultimately enhance AFO prescription criteria and help in optimising patient/device matching.