Page 52 - Maximizing the efficacy of ankle foot orthoses in children with cerebral palsy

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Chapter III
of the heel-sole differential and footplate stiffness, in order to assess its potential as a parameter to evaluate the effects of such manipulations.
To this end, we evaluated in healthy young adults i) whether the SVA at midstance can be influenced during walking with an AFO-FC by applying commonly used manipulations within the process of tuning (i.e. changing AFO-FC heel-sole differential and footplate stiffness), and ii) how changes in the SVA, as a result of the manipulations, are reflected in ankle, knee and hip flexion-extension angles and net internal joint moments at midstance. We hypothesized that the SVA would be responsive to changes in AFO-FC heel height and that this would be reflected by increased knee and hip flexion angles and net internal joint extension moments at midstance. As a stiff footplate mainly aims to shift the ground reaction force forward without affecting joint flexion-extension angles, we expected no response of the SVA to changes in footplate stiffness, while it was expected to affect internal net joint moments.
MethodS Participants
Ten healthy young adults (3 male; mean (SD) age: 24 (3) years; mean (SD) body mass index: 22.8 (2.2)) participated. All subjects provided written informed consent in accordance with the procedures of the Institutional Review Board of the VU University.
Materials
For this study, two pairs of prepeg carbon AFOs were manufactured (European shoe size: 39 and 43) (see Figure 3.1A). Each participant chose the best fitting pair. The stiffness of the AFOs at the ankle and metatarsal joints was measured using BRUCE[16], which is an instrument to define AFO mechanical properties. The AFOs were rigid at the ankle (7.9 Nm·deg-1), aiming to immobilize the ankle joint at 0°.
According to Owen[13], important kinematic characteristics at midstance (e.g. thigh inclination) can only be preserved with an SVA ranging from 7°-15°, while an SVA of 10°-12° is suggested to be optimal. In the current study, AFO-FC heel-sole differential was varied using three heel heights by applying insole wedges, aiming to impose an SVA of 5°, 11° and 20° in static position. As such, the effects of SVA manipulations near the presumed optimum and outside the suggested optimal range were investigated. The height of the wedges was pre-defined for both AFO-FCs, using a dedicated instrument to measure heel height and heel-sole differential of an AFO-FC when doffed (Vertical Inclinometer