Validation of a model of gross motor function for children with cerebral palsy

Background and Purpose. Development of gross motor function in children wit h cerebral palsy (CP) has not been documented. The purposes of this study w ere to examine a model of gross motor function in children with CP and to a pply the model to construct gross motor function curves for each of the 5 l evels of the Gross Motor Function Classification System (GMFCS). Subjects. A stratified sample of 586 children with CP, 1 to 12 years of age, who resi de in Ontario, Canada, and are known to rehabilitation centers participated . Methods. Subjects were classified using the GMFCS, and gross motor functi on was measured with the Gross Motor Function Measure (GMFM). Four models w ere examined to construct curves that described the nonlinear relationship between age and gross motor function. Results. The model in which both the limit parameter (maximum GMFM score) and the rate parameter (rate at which the maximum GMFM score is approached) vary for each GMFCS level explained 8 3% of the variation in GMFM scores. The predicted maximum GMFM scores diffe red among the 5 curves (level I=96.8, level II=89.3, level III=61.3, level IV=36.1, and level V=12.9). The rate at which children at level II approach ed their maximum GMFM score was slower than the rates for levels I and III. The correlation between GMFCS levels and GMFM scores was -.91. Logistic re gression, used to estimate the probability that children with CP are able t o achieve gross motor milestones based on their GMFM total scores, suggests that distinctions between GMFCS levels are clinically meaningful. Conclusi on and Discussion. Classification of children with CP based on functional a bilities and limitations is predictive of gross motor function, whereas age alone is a poor predictor. Evaluation of gross motor function of children with CP by comparison with children of the same age and GMFCS level has imp lications for decision making and interpretation of intervention outcomes.