Ankle power support of spring-like ankle foot orthoses and their effect on compensatory joint work.

Plantar flexor weakness reduces ankle push-off work during walking, causing inefficient proximal joint compensations to provide power for forward propulsion (1). To support ankle push-off work and reduce compensations, spring-like ankle foot orthoses (AFOs) can be applied (2). In people with plantarflexor weakness due to a neuromuscular disease, spring-like AFOs can increase push-off work, which is often accompanied by increases in walking speed (3). The higher walking speed likely also leads to higher proximal joint work demands. Consequently, it is unknown whether the higher push-off work leads to a reduction in compensatory joint work. Furthermore, not all patients increase push-off work with the AFO and understanding of who is able to increase push-off work is warranted for clinical decision-making. 1) Do spring-like AFOs redistribute lower limb joint work during walking in people with bilateral plantar flexor weakness compared to shoes-only? 2) Is ankle work when walking without AFO related with the effect of spring-like AFOs on ankle and hip work? In 18 people with bilateral plantar flexor weakness, we performed a 3D gait analysis at self-selected walking speed for walking without and with a spring-like AFO with individually tuned stiffness. We compared the relative joint work generated at the hip, knee and ankle between conditions. Furthermore, the association between ankle work without orthosis and joint work using the AFO were tested with Pearson's correlations. No difference in the relative contribution of ankle, knee and hip work to total joint work over the gait cycle was found between walking with and without AFO (p >0.499). Relative ankle work generated during pre-swing increased with the AFO (Shoes: 72.4±27.1% vs AFO: 85.3±9.1% of total ankle work, p =0.026). At the hip, relative less work was generated in pre-swing (Shoes: 34.1±10.4% vs AFO: 31.9±7.4% of total hip work, p =0.038) and more in loading response (Shoes: 11.9±9.8% vs AFO: 18.0±11.0%, p =0.022). Ankle work without AFO was inversely correlated with increased ankle work with the AFO (r=0.839, p <0.001) and this increase correlated with a larger reduction in hip work (r=-0.650, p =0.004). Although spring-like AFOs increased relative ankle work and reduced hip work during push-off, the relative hip and knee work did not reduce as hip extensor work in early stance increased. However, a higher ankle push-off deficit without AFO was related with more AFO support and higher reductions in compensatory hip work, which indicates that people with more severe push-off deficits benefit more from the energy storing-and-releasing capacity of spring-like AFOs. [ABSTRACT FROM AUTHOR]