Compensatory stepping thresholds in children with and without cerebral palsy
Date
2017
Authors
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Publisher
University of Delaware
Abstract
Cerebral palsy (CP) is a non-progressive neurological disorder that arises from injury, typically at infancy, to the brain, resulting in permanent effects on muscle coordination, movement, and balance. These impairments to movement and balance likely underly the high incidence of falls reported for adults with CP. Investigations of the effects of CP on balance have been primarily limited to quasi-static measures of postural sway and functional assessments, both of which are limited as predictors of falls in the free-living environment. The ability to arrest a fall in response to external balance perturbations has been shown to be prospectively related to falls in older adults. We can quantify this fall-recovery ability with single-stepping thresholds, or the disturbance magnitudes that consistently elicit anterior and posterior compensatory steps. To date, the effects of CP on the fall-recovery response have been inconclusive. The purpose of this study was to 1) determine whether children with CP have an impaired ability to respond to external postural disturbances, as evident by lower stepping thresholds, and 2) determine whether children with CP have altered neuromuscular responses and dynamic stability maintenance after an external postural disturbance. ☐ Three children with spastic CP between the ages of five and twelve, and gross motor function classification I – II, participated in the study. Fourteen typically developing children in the same age range also participated. Participants attempted to prevent steps in response to a progressive series of rapid, precise treadmill belt accelerations delivered by a computer-controlled treadmill. Each participant’s anterior and posterior single-stepping thresholds were determined, as represented by the disturbance magnitudes that consistently elicited a step in each direction. The neuromuscular response about the ankle was assessed, and the resulting dynamic stability was quantified in an attempt to identify underlying mechanisms of anticipated group differences. These mechanisms were assessed for the successful, non-stepping trials at disturbance magnitudes immediately below threshold values. ☐ Children with CP had significantly lower single-stepping thresholds in both the anterior (Cohen’s d (d) = 2.579, p = 0.003) and posterior (d = 1.556, p = 0.047) directions. These differences were associated with moderate to large differences in the minimum margin of stability for the anterior (d = 0.808, p = 0.300) and posterior (d = 1.049, p = 0.032) direction, indicating a greater ability to recover from dynamic instability without a step in children with typical development. Analyses of the neuromuscular response revealed longer muscle onset latencies for both the medial gastrocnemius (dominant: d = 2.565, p = 0.033; non-dominant: d = 2.188, p = 0.019) and tibialis anterior (dominant: d = 2.528, p = 0.033; non-dominant: d = 2.018, p = 0.033) when their role was the agonist muscle. In addition, the activation amplitude of the tibialis anterior as an agonist was lower in children with CP than controls (dominant: d = 1.596, p = 0.067; non-dominant: d = 1.763, p = 0.017). The results from this study indicate that children with CP have a compromised fall-recovery, as represented by the ability to prevent a step in response to external balance perturbations. These differences may be due to a delayed, insufficient neuromuscular response and an inability or unwillingness to recover from dynamic instability.
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Keywords
Biological sciences, Health and environmental sciences, Balance, Cerebral, Compensatory stepping, Falls, Palsy