Page 36 - Maximizing the efficacy of ankle foot orthoses in children with cerebral palsy

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Chapter II
Study information will be provided to potential participants in the form of a patient information letter and a brochure. Patients and parents willing to participate will be con- tacted by the primary investigator, who will verify inclusion and exclusion criteria (see Table 2.1). When a patient meets the inclusion criteria, oral and written informed consent will be obtained from both parents, and from children aged 12 years and older, in accor- dance with the declaration of Helsinki.
Sample size
The sample size will be based on a power analysis of the expected changes (i.e. T0 versus T2) in the primary outcome, walking energy cost (EC) [J·kg·m-1]. According to lit- erature, walking energy cost in children with CP may be 30-50% higher than in healthy children[10-12]. Spastic CP children with GMFCS levels I, II and III show a mean net EC of 5.02 (±1.70) J-1·kg-1·m1[26]. A reduction of 25% in this value (≈1.26 J-1·kg-1·m-1) is considered to be a clinically significant change[25,26]. Assuming a power of 80% and a significance level of 0.05, detecting a clinically significant change will require a sample size of 29 children[43]. Allowing for a dropout of approximately 10%, a sample size of 32 will be sufficient.
Investigational AFO
Investigational FROs will be composed of prepreg carbon, manufactured using the Mälmo-technique (Otto Bock HealthCare GmbH, Duderstadt, Germany). For fair evalua- tion of efficacy, the investigational FRO will be fabricated with a rigid footplate. To fur- ther ensure a fair comparison, tuning of the FRO-footwear combination following the Owen method will be carried out for each configuration[44].
Investigational FROs will be fabricated with an integrated Neuro Swing® system hinge (Fior & Gentz, Lüneberg, Germany), which is available in different sizes. The size of the hinge is dependent on the body weight and length of the patient. For this study, it is expected that only the 14mm and 16mm hinges will be used. The hinge holds an anterior and posterior shaft, and comes with a package of five springs, each with a different de- gree of stiffness. Ankle stiffness can be adjusted within the same orthosis, using different spring forces towards plantar and dorsal flexion. In this study, the hinge will be prepared in three configurations: rigid, stiff and flexible. The rigid configuration (i.e. ±4.3 Nm·deg-1) will entirely prevent dorsal or plantar flexion. For the stiff and flexible configurations, the spring force for dorsal flexion will be varied using the strongest spring (i.e. ±1.2 Nm·deg-1 [14mm] and ±2.4 Nm·deg-1 [16mm]) and the second strongest spring (i.e. ±0.5 Nm·deg-1