Page 54 - Maximizing the efficacy of ankle foot orthoses in children with cerebral palsy

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Chapter III
Measurements
Subjects walked on the GRAIL system (Motek Medical BV, Amsterdam, the Netherlands), consisting of a split-belt instrumented treadmill (ForceLink©, Culemborg, the Netherlands) and a passive marker motion capture system (Vicon, Oxford, UK), collecting marker trajectories. Ground reaction forces were captured from force sensors mounted underneath both treadmill belts, and synchronized with kinematic data at 120 Hz.
Reflective markers were placed at anatomical landmarks according to the Human Body Model[18,19] (see Figure 3.2). The SVA was calculated as it is defined in clinical practice[13], i.e. using the line over the anterior surface of the tibia, representing the long axis of the shank, and calculated as the angle between this line and the vertical in the global sagittal plane (see Figure 3.1). In order to do so, additional markers were added to the Human Body Model (see Figure 3.2): at the tibial tuberosity (#12 and #21) and at a distal point on the tibia (#13 and #22, i.e. at 75% of the lower leg, measured from the tibial tuberosity (#12 and #21) to the floor and vertically in line with the marker at tibial tuberosity in the frontal plane). Other additional markers were placed at the dorsal shell of each AFO (#14 and #23), which were horizontally aligned with the tibial tuberosity marker (#12 and #21) in the sagittal plane and vertically aligned to the calcaneus marker (#16 and #25) in the sagittal plane. These markers were used to determine movements of the shank in the AFO, therewith evaluating the immobilization of the ankle. This was done for interpretation of the results, as inadequate immobilization is expected to affect joint flexion-extension angles and moments. The Human Body Model foot markers (#16- 18 and #25-27) and the markers at the lateral malleoli (#15 and #24) were positioned on the shoe. None of the markers were replaced between different trials.
Procedure
After being provided with the AFO-FC, the subject accommodated to walking on a treadmill until he/she felt comfortable. Subsequently, the subject’s comfortable walking speed was determined following a standardized protocol. Following this protocol, the participant started walking at an initial speed of 0.8 m·s-1. Treadmill speed was then gradually increased with 0.1 m·s-1 until the participant indicated the speed as comfortable. From thereon, speed was further increased until comfortable speed +0.3 m·s-1 and gradually decreased until the participant indicated the speed as comfortable again. The mean of both self-selected speeds represented the subject’s comfortable