Determining the Sagittal Plane Function for a Model Prosthetic Foot

While it is generally believed that the choice of prosthetic components affects amputee gait, systematically quantifying the effects of prosthetic design on amputee walking is difficult [1]. A simulation model capable of predicting human amputee gait could allow for quantitative, systematic investigations. Existing models of amputee gait are either too complex for a predictive study (e.g. [2]) or do not provide any validation that the models can accurately predict amputee walking (e.g. [3]). One successful strategy to limit the complexity of predictive models for healthy human gait is to model the function, not the form, of the foot and ankle complex using a rigid curved foot and revolute ankle joint [4]. The curved foot captures the control of the center of pressure location [5], and the ankle joint helps to capture the change in the whole-body center of mass (CoM) velocity during the step-to-step transition [6]. Without ankle joints, the model exhibits excessively short step durations and large joint angle oscillations [4], both of which are uncharacteristic of healthy human walking. Whether an ankle joint is likewise required to capture the function of a passive prosthetic foot in an analogous model of amputee walking is unclear. Similar to human feet, prosthetic feet help to control the center of pressure location [7], but since passive prostheses cannot generate net positive ankle work, it appears they provide far less control of the CoM velocity than intact ankle joints [2]. Thus, a model prosthetic ankle joint may not be required. Prosthetic feet can, however, store and subsequently release