Causal relation between spasticity, strength, gross motor function, and functional outcome in children with cerebral palsy: a path analysis

Aim This study examined the causal relation between spasticity, weakness, gross motor function, and functional outcome (expressed as activity limitation) in children with cerebral palsy (CP) and tested models of functional outcome mediated by gross motor function. Method Eighty-one children (50 males, 31 females) with CP were recruited for this cross-sectional study. Their mean age was 10 years 4 months (SD 1y 9mo). Strength was assessed using the Manual Muscle Test. Spasticity was assessed by the Modified Ashworth Scale. The Gross Motor Function Measure assessed gross motor function. The Functional Skills domain of the Pediatric Evaluation of Disability Inventory assessed functional outcome. Twenty-eight children (34.6%) had quadriplegia, 44 children (54.3%) had diplegia, and nine children (11.1%) had hemiplegia. Children were classified using the Gross Motor Function Classification System with 14 (17.3%) in level I, 9 (11.1%) in level II, 13 (16.0%) in level III, 5 (6.2%) in level IV, and 40 (49.4%) in level V. Results The proposed path model showed good fit indices. The direct effects were significant between spasticity and gross motor function (beta=-0.339), between strength and gross motor function (beta=0.447), and between gross motor function and functional outcome (beta=0.708). Spasticity had a significant negative indirect effect (beta=-0.240) and strength had a significant positive indirect effect (beta=0.317) on functional outcome through effects on gross motor function. Interpretation Activity-based rather than impairment-based intervention is more important for reducing activity limitation in children with CP. The study established a base from which researchers can further develop a causal model between motor impairments and functional outcome.