Page 51 - Maximizing the efficacy of ankle foot orthoses in children with cerebral palsy

IntrodUctIon
Ankle foot orthoses (AFOs) are frequently applied in patients with neurological disorders, aiming to normalize joint kinematics and joint kinetics during walking[1-4]. Although it has been shown that AFOs can significantly improve sagittal joint kinematics and kinetics[2,3,5-7], inadequate alignment of ground reaction force (i.e. distant from the joint rotation centers) during walking negatively impacts the effectiveness[4,8,9].
Tuning of the AFO optimizes the alignment of the ground reaction force with respect to the joint rotation centers, enhancing normalization of the joint kinematics and kinetics[8-12]. Such tuning can be described as the process in which the properties of an AFO-footwear combination (AFO-FC) are manipulated. Commonly used adjustments comprise changing the footplate stiffness to affect the point of application of the ground reaction force, and altering the heel-sole differential (i.e. the difference in height between the heel and forefoot of the shoe), which affects shank orientation[8]. The combined effect of the AFO-FC’s ankle angle and heel-sole differential can be described in terms of the shank-to-vertical angle (SVA). The SVA, i.e. tibia inclination, is the angle between the anterior surface of the tibia and the vertical in the global sagittal plane[8,13]. It is clinically often measured using sagittal video recordings[13]. The SVA is considered inclined, when the shank is tilted forward, or reclined, when it is tilted backward with respect to the vertical. Owen[13] suggested that an appropriate shank orientation at midstance aligns the ground reaction force to the joint rotation centers, which contributes to stability, facilitates adequate switching from flexion to extension moments at the knee and hip, and lowers vertical center of mass excursion. Accordingly, the SVA at midstance may be an important and relatively simple parameter to evaluate the effects of adjustments to the AFO-FC during its tuning process[8,13], also because information on the ground reaction force and calculations of joint moments are not always available in clinical practice.
Several studies in patients with neurological disorders report the SVA, and describe a normalization of gait parameters following changes of the heel-sole differential[11,12,14,15]. However, in all available studies, the SVA was measured while the patient was in a static position, whereas there is no evidence showing that the SVA in this position represents the SVA at midstance[8]. Evidence on the effects of changing the footplate stiffness on the SVA, as well as on joint kinematics and kinetics is also lacking. Yet, in clinical practice, such manipulations of footplate stiffness, in addition to changing the heel-sole differential are commonly applied. Since tuning of these AFO-FC properties is generally guided by monitoring the SVA at midstance, insight is needed in how the SVA responds to changes
III
The shank-to-vertical angle
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