Prediction of the optimal ankle foot-orthosis stiffness based on the peak ankle moment during walking in neuromuscular disorders.

Abstract

To maximize treatment outcomes with ankle-foot orthosis (AFO) in individuals with plantarflexor weakness, the AFO stiffness needs to be individualized. Peak ankle moment during walking may be used to predict the optimal stiffness. (1) Assess the effects of AFO stiffness on ankle moment, AFO-generated moment, and muscle-generated moment; (2) evaluate the accuracy of predicting optimal AFO stiffness using peak ankle moment during walking without AFO. A retrospective analysis was conducted on 18 individuals with neuromuscular disorders with reduced ankle moments during shoes-only walking. AFO stiffness was experimentally optimized to minimize energy cost. Using repeated measures ANOVA we evaluated the effects of AFO stiffness on ankle moment parameters. A quadratic relationship between AFO stiffness and net ankle moment (<i>p</i> < 0.001), a positive linear relationship with AFO-generated moment (<i>p</i> < 0.001), and a negative linear relationship with muscle-generated moment (<i>p</i> < 0.001) was found. The predicted optimal AFO stiffness, based on the difference between the healthy peak ankle moment (1.2 Nm/kg) and moment without AFO, differed on average 0.53 ± 0.46 Nm/degree (13.7%) from the experimentally optimized stiffness. Predicting AFO stiffness based on peak ankle moment during shoes-only walking is a promising method for determining optimal stiffness or guidance of experimental optimization.