The prescription of a passive dynamic ankle foot orthosis (PD-AFO), trademarked the Momentum, has improved functional outcome for many patients, though not all. The design features of the PD- AFO that account for this improvement, and the changes the PD-AFO introduces into gait, are not fully understood. This thesis aims to establish how the PD-AFO alters the external and internal loading of the foot during gait.
Gait analysis was used to evaluate changes in external loading of the foot when wearing the PD-AFO (possible offloading). It was demonstrated that the PD-AFO reduced loading in the foot when walking, with maximum offloading seen during early stance. A novel methodology, using strain gauges, demonstrated the struts’ energy storage and return (ESAR) characteristics and ability to provide propulsive power during late stance.
Finite element (FE) modelling was used to evaluate internal loading of the foot. A comprehensive development process was undertaken to build FE models of the foot and PD-AFO. By running multiple simulations of the FE model of the PD-AFO, design components whose mechanical characteristics may significantly alter gait were highlighted, such as the alignment of the posterior struts.
The FE models of the foot and PD-AFO were combined to model the loading at a point during early stance; comparable results with data recorded experimentally was achieved. Simulation results demonstrated greater relative reduction in contact stresses, compared to contact force, at the subtalar joint. This suggested that PD-AFO’s influence on the subtalar joint angle may be an important design feature in the PD-AFO’s success.
This research may help to predict who may be successfully aided by the PD-AFO, target research on design components that influence the mechanical response of the PD-AFO; and indicate potential long-term adverse effects of using the device as a result of changes to gait.