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

172 Cerebral palsy (CP) is the most common cause of children's disability in Western Europe. Children with the spastic type of CP, which is the most common type of motor disorders, show impairments such as spasticity, muscle weakness, and a decreased selective motor control. These impairments lead to decreased motor function, and accordingly, these children experience gait-related problems. The gait pattern of children with spastic CP is frequently characterized by specific gait deviations, which can be categorized into different gait types according to the classification of Becher. This thesis focusses on the children presenting with gait types 4 and 5, i.e. a gait pattern that is characterized by excessive knee flexion in (mid) stance. The excessive knee flexion during walking is usually accompanied by abnormal hip and ankle kinematics and kinetics, implying impaired biomechanical function. The gait deviations in CP are associated with an increase of energy consumption during walking. This especially applies to children with CP who walk with excessive knee flexion in stance, as these gait patterns are particularly energy consuming. To minimize the increased energy consumption, patients often decrease their walking speed. This leads to an increased walking energy cost (i.e. energy consumption per distance), reflecting poor gait efficiency. Although the nature of the association between underlying biomechanical gait deviations and the increased energy consumption in children with CP is not yet unraveled, abnormal knee and ankle kinematics and kinetics are considered key features. To counteract the gait deviations, an ankle foot orthosis (AFO) is a commonly applied rehabilitation intervention in children with CP. AFOs apply a mechanical constraint to the ankle and foot, either to compensate for a loss of function, or to counteract an excess of function. As such, an AFO can directly control the ankle and knee joint motion, and dependent on its design, it may also affect the hip joint. Although the effects of AFOs on gait in CP have been frequently investigated, the results are inconclusive. Some studies report improvements of gait in terms of gait biomechanics, and/or efficiency, while other studies show that AFOs can have no effect or even detrimental effects in some children. Several factors may underlie the ambiguous results with regard to AFO efficacy, of which some are discussed in this thesis. The general aim of this thesis was to evaluate factors that enable an individual optimization of AFO prescription in order to maximize AFO efficacy in children …