Optimizing ankle foot orthosis stiffness in calf muscle weakness

In people with neuromuscular diseases, non-spastic calf muscle weakness is common. This results in an impaired gait pattern, characterized by an excessive ankle dorsiflexion angle and reduced ankle push-off which increases walking energy cost and reduces walking speed. To improve gait, an ankle foot orthosis (AFO) is often prescribed. The effect of AFOs depend on its mechanical properties like ankle stiffness, but evidence about how AFO ankle stiffness affects gait is scarce.
Therefore, the aim of this thesis was 1) to quantify the effect of AFO ankle stiffness on gait, and 2) study whether AFO ankle stiffness optimization improves treatment outcomes beyond current usual care.
Results demonstrate that increasing AFO ankle stiffness reduces the knee and ankle angle, but also reduces ankle push-off power. Consequently, the AFO stiffness that best improves gait is a trade-off between normalizing joint angles and maintaining ankle power, which differs between individuals. In usual orthotic care the provided orthotic stiffness is usually too low. Individually optimizing the AFO ankle stiffness therefore improves walking energy cost, walking speed and fatigue beyond current usual care. Based on this thesis, it is advised to individually optimize the AFO ankle stiffness in people with calf muscle weakness.