Causal Effects Contributing to Elevated Metabolic Power During Walking in Children Diagnosed with Cerebral Palsy

Abstract

Metabolic power (net energy consumed while walking per unit time) is, on average, two-to-three times greater in children with cerebral palsy (CP) than their typically developing peers, contributing to greater physical fatigue, lower levels of physical activity and greater risk of cardiovascular disease. The goal of this project was to identify the total causal effects of clinical factors that may contribute to high metabolic power demand in children with CP. We included children who 1) visited Gillette Children's Specialty Healthcare for a quantitative gait assessment after the year 2000, 2) were formally diagnosed with CP, 3) were classified as level I-III under the Gross Motor Function Classification System and 4) were 18 years old or younger. We created a structural causal model that specified the assumed relationships of a child's gait pattern (i.e., gait deviation index, GDI) and common impairments (i.e., dynamic and selective motor control, strength, and spasticity) with metabolic power. We estimated causal effects using Bayesian additive regression trees, adjusting for factors identified by the causal model. There were 2157 children who met our criteria. We found that a child's gait pattern, as summarized by the GDI, affected metabolic power approximately twice as much as the next largest contributor. Selective motor control, dynamic motor control, and spasticity had the next largest effects. Among the factors we considered, strength had the smallest effect on metabolic power. Our results suggest that children with CP may benefit more from treatments that improve their gait pattern and motor control than treatments that improve spasticity or strength.

A model for understanding the causes and consequences of walking impairments

“…Common treatments show limited effectiveness to reduce net energy consumption. In a previous study, overall kinematic deviations were shown to contribute substantially to elevated net energy consumption [ 34 ]. By examining the effects of Gait Mechanics on net energy consumption we can determine which specific kinematic deviations are the most impactful.…”

A Model for Understanding the Causes and Consequences of Walking Impairments

“…Common treatments show limited effectiveness to reduce power demands. In a previous study, overall kinematic deviations were shown to contribute substantially to elevated power demands (32). We quantify Energy as net (walking -resting) dimensionless power expressed as a z-score with respect to speed matched controls (metabolic walking power) (25).…”