Page 21 - Maximizing the efficacy of ankle foot orthoses in children with cerebral palsy

parameter to evaluate the effects of adaptations to the heel-sole differential[54]. Although effects of such adjustments, as quantified by the SVA, have already reported in some studies[55], the response of the SVA to manipulations to the AFO-footwear combination and its relation to joint kinematics and kinetics have not been investigated so far.
AFO stiffness
Secondly, children walking with excessive knee flexion in stance are typically prescribed with a rigid ventral shell AFO that is manufactured with a rigid footplate[57]. This type of AFO aims to reduce knee flexion by shifting the ground reaction force anterior to the knee joint rotation center, to create an external knee extensor moment in stance, which is done through a force by muscular contraction of the ankle plantar flexors in normal gait. Literature shows that rigid AFOs can effectively reduce knee flexion during stance[43], which may contribute to walking energy cost improvement[46]. However, the rigid properties also impede walking by impairing the rocker functions. This especially accounts for the third rocker, as the rigid AFO obstructs plantar flexion, therewith reducing push-off power[42,58-61]. As ankle range of motion and push-off power are considered key features for efficient gait[29,31], this could negatively impact on the walking energy cost.
The AFO’s impeding effect on third rocker function could be reduced by using spring- like AFOs. Research has shown that spring-like AFOs (e.g. carbon fiber AFOs) can improve the gait pattern, while less constraining voluntary push-off[62,63], which might be beneficial in terms of the walking energy cost[29,31]. Model studies[64], as well as studies in healthy adults[65] and adult patient populations[66,67], already showed that both joint kinematics and kinetics, as well as the walking efficiency can be influenced by applying spring-like AFOs with different degrees of stiffness. As a result, gait efficiency could be maximized by choosing the appropriate AFO stiffness for each individual patient[66]. This individual approach of selecting an appropriate AFO stiffness may also apply to children with CP who walk with excessive knee flexion. It is thought that an optimal AFO stiffness, which is the stiffness that results in maximized gait efficiency, could be found. This optimum is expected to reflect the trade-off between a sufficient reduction of the knee flexion and minimal obstruction of third rocker function, although this hypothesis has not yet been investigated.
I
General introduction
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