Page 16 - Maximizing the efficacy of ankle foot orthoses in children with cerebral palsy

Chapter I
Gait in cerebral palsy
Due to symptoms of impaired motor control, muscle weakness, abnormal joint position, decreased joint range of motion, and a decreased muscle length, gait is often hampered in CP[16]. The clinical representation of gait in CP is very heterogeneous, and therefore several efforts have been made to categorize these into gait patterns[19]. In the Netherlands, the classification of Becher[5,20] is generally used for gait in spastic CP. This classification describes five gait types, mainly based on the deviations of the knee and ankle joint angles at midstance (see Figure 1.2). Gait type 1 describes a gait pattern characterized by a normal stance phase, but insufficient foot lift during the swing phase. Gait types 2 and 3 show hyperextension of the knee, respectively with or without full foot contact. Gait types 4 and 5 describe a pattern with excessive knee flexion, either with ankle plantar flexion (type 4) or excessive dorsiflexion (type 5). This thesis only discusses children who walk in gait types 4 or 5.
The ankle and foot rocker functions are impaired in most CP walking types. Weakness of the dorsiflexor muscles, for example, commonly causes mid- or forefoot contact during the first rocker. Consequently, the tibia is positioned excessively inclined already in the beginning of stance, allowing no forward tibia progression during the second rocker, and an excessively flexed knee joint at this stage. This effect is frequently enhanced by weakness of the plantar flexor muscles. The abnormal second rocker function leads to the posterior alignment of the ground reaction force with respect to the knee joint rotation center, and accordingly, in an increased knee moment. The push-off power is also often impaired as a result of abnormal ankle joint moments in late stance. The rapid plantar flexion movement that is needed for an effective push-off is impeded by the persistent
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Figure 1.2. The gait types according to the classification of Becher. This thesis focusses on the gait that are characterized by excessive knee flexion, either without foot contact (type 4) or with full foot contact (type 5) at midstance.