Page 18 - Maximizing the efficacy of ankle foot orthoses in children with cerebral palsy

18
Chapter I
IMproVInG GaIt In cereBraL paLSY Treatment with AFOs
An ankle foot orthosis (AFO) is a commonly applied rehabilitation intervention in children with CP to maintain muscle length (i.e. passive range of motion), as well as to maintain or improve stability, standing, and/or walking ability[35]. An AFO is a medical device that imposes a mechanical constraint to the ankle and foot, aiming to compensate for a loss of function (i.e. resisting forces that act upon the body), or to counteract an excess of function (i.e. resisting forces from within the body). As such, an AFO can directly affect movements of the ankle and foot, and, dependent on its design, it can also stabilize the knee and hip joints[36]. AFOs are available in various different designs, e.g. hinged or non-hinged, and with a ventral shell or dorsal shell. In addition, AFOs can be made of different materials like carbon fiber or polypropylene. Consequently, each AFO holds specific mechanical properties, such as stiffness around the ankle . When prescribing an AFO, its design and mechanical properties should counteract the patient’s underlying impairments, and be designed such that it counteracts the specific gait deviations as much as possible, aiming to effectively improve gait.
AFO efficacy in cerebral palsy
The efficacy of AFOs on gait can be described in terms of its mechanical effects (i.e. gait biomechanics), and/or in terms of the patient’s gain in walking ability (e.g. gait efficiency)[37]. In general, the effects of AFOs on gait have been widely investigated, with studies mainly evaluating the efficacy of AFOs on gait biomechanics. These studies generally report improvements in terms of spatio-temporal parameters[38-45] and joint kinematics[38,40-44,46] and kinetics[40,41,43,46]. Although improvement of gait biomechanics has been shown to be closely coupled to improvement of gait efficiency[17], also in the context of orthotic interventions[40,46,47], evidence for the efficacy of AFOs on gait efficiency remains inconclusive[48].
These ambiguous results within AFO research have been acknowledged in some reviews[48-50], where various gaps in current literature have been addressed. First, the AFO’s efficacy is expected to be largely dependent on the match between the AFO’s mechanical properties and patient’s specific underlying impairments. Sufficient description of participants, especially in terms of motor impairments and gait patterns is however mostly lacking. Also the AFOs used in studies are described with global reference to design and materials, and rarely described in terms of mechanical properties[48-50].