Longitudinal development of gross motor function among Dutch children and young adults with cerebral palsy: an investigation of motor growth curves

AIM: The aim of this study was to describe patterns for gross motor development by level of severity in a Dutch population of individuals with cerebral palsy (CP). METHOD: This longitudinal study included 423 individuals (260 males, 163 females) with CP. The mean age at baseline was 9 years 6 months (SD 6y 2mo, range 1-22y). The level of severity of CP among participants, according to the Gross Motor Function Classification System (GMFCS), was 50% level I, 13% level II, 14% level III, 13% level IV, and 10% level V. Participants had been assessed up to four times with the Gross Motor Function Measure (GMFM-66) at 1- or 2-year intervals between 2002 and 2009. Data were analysed using non-linear mixed effects modelling. For each GMFCS level, patterns were created by contrasting a stable limit model (SLM) with a peak and decline model (PDM), followed by estimating limits and rates of gross motor development. RESULTS: The SLM showed a better fit for all GMFCS levels than the PDM. Within the SLM, significant differences between GMFCS levels were found for both the limits (higher values for lower GMFCS levels) and the rates (higher values for GMFCS levels I-II vs level IV and for GMFCS levels I-IV vs level V) of gross motor development. INTERPRETATION: The results validate the existence of five distinct patterns for gross motor development by level of severity of CP.