Causal factors affecting gross motor function in children diagnosed with cerebral palsy

Abstract

AbstractCerebral palsy (CP) is a complex neuromuscular condition which may negatively impact gross motor function. Children diagnosed with CP often exhibit spasticity, weakness, reduced motor control, contracture, and bony malalignment. Despite many previous association studies, the causal impact of these impairments on motor function is unknown. In this study, we propose a causal model for motor function as measured by the 66-item Gross Motor Function Measure (GMFM-66), and estimate the direct and total effect sizes of these common impairments using linear regression based on covariate adjustment sets implied by the causal model. We evaluated 300/314 consecutive subjects with cerebral palsy who underwent routine clinical gait analysis. The largest effect sizes, as measured by standardized regression coefficients (standard error), were for static motor control (direct = 0.35 (0.04), total = = 0.40 (0.04)) and dynamic motor control (direct = 0.26 (0.04), total = 0.31 (0.04)), followed by strength (direct = 0.23 (0.04), total = 0.26 (0.04)). The next largest effect was found for gait deviations (direct = total = 0.15 (0.04)). In contrast, common treatment targets, such as spasticity (direct = 0.05 (0.03), total = 0.08 (0.03)) and orthopedic deformity (direct = 0.00 (0.03) to 0.08 (0.03), total = −0.01 (0.03) to 0.11 (0.03)), had relatively small effects. We also show that effect sizes estimated from bivariate models, which fail to appropriately adjust for other causal factors dramatically overestimate the total effect of spasticity (510%), strength (271%), and orthopedic deformity (192% to -2017%). Understanding the relative influences of impairments on gross motor function will allow clinicians to direct treatments at those impairments with the greatest influence on gross motor function and provide realistic expectations of the anticipated functional changes.