Muscle activity in children with spastic unilateral cerebral palsy when walking with ankle-foot orthoses: an explorative study

Background: A hinged ankle-foot orthosis is prescribed for children with spastic unilateral cerebral palsy to improve gait function by correcting spastic equinus. However, little is known about how orthotic management relates to muscle activity during walking in this population. Research question: Does muscle activity in medial gastrocnemius and tibialis anterior change in children with spastic unilateral cerebral palsy when walking with hinged ankle-foot orthoses featuring two different footplate designs? Methods: In this prospective, repeated-measures trial, electromyographic activity in medial gastrocnemius and tibialis anterior was recorded from 17 children (mean age: 8.4 years +/- 1.3 years) with spastic unilateral cerebral palsy walking barefoot and with two designs of hinged ankle-foot orthosis. The orthotic devices consisted of custom-made hinged ankle-foot orthoses with unmodified, flatter footplates and rectified, contoured footplates. Primary outcome measures were total muscle activity, quantified as the area under a linear envelope, and relative change in profiles of muscle activity, depicted by curves of mean difference with 95% confidence bands. Results: No statistical difference was found in total activity of either muscle for the ankle-foot orthosis with an unmodified footplate but a significant reduction in muscle activity of tibialis anterior was seen for the ankle-foot orthosis with a contoured footplate relative to barefoot walking. Profiles of change in muscle activity were significantly altered for both shank muscles between all walking conditions. The most pronounced differences were decreased activity in medial gastrocnemius during early stance phase and lower activity in tibialis anterior during swing phase with orthotic devices. Significance: Orthotic management with hinged ankle-foot orthoses may mitigate spastic activation of medial gastrocnemius in children with spastic unilateral cerebral palsy but also appears to functionally inactivate tibialis anterior during gait. The hinged ankle-foot orthosis with an unmodified footplate corresponded with better performance by facilitating more functional muscle activity while impeding spastic response.