Face and construct validity of the Gait Deviation Index in adults with spastic cerebral palsy.

OBJECTIVE To investigate face and construct validity of the Gait Deviation Index (GDI) in adults with spastic cerebral palsy. The International Classification of Functioning, Disability and Health (ICF) was used as a framework, defining gait and walking as the manner or style of walking ("body function"), and the execution of gait ("activity"), respectively. DESIGN A cross-sectional study. METHODS PARTICIPANTS 66 adults with spastic cerebral palsy, mean age 37 years, and previously collected data on 50 healthy adults (reference population). VARIABLES GDI from three-dimensional gait analysis, Gross Motor Function Classification System (GMFCS), 6-min walk test (6MWT), Timed Up and Go (TUG), and Physiological Cost Index (PCI). RESULTS Mean GDI was 74.3 in adults with cerebral palsy, and 101.1 in the reference population. A significant difference in GDI was found between the reference population and GMFCS level I (p < 0.001), between I and II (p < 0.001), but not between II and III (p = 0.633). The associations between GDI and 6MWT, TUG and PCI were r = 0.30, r = -0.30, and r = -0.56, respectively. CONCLUSION GDI demonstrated similar distributional properties as those reported in children with cerebral palsy, suggesting satisfactory face validity. Low correlations between GDI and 6MWT/TUG reflect that gait and functional walking/mobility are different constructs, implicating the importance of selecting outcomes in all ICF domains when evaluating walking ability in adults with spastic cerebral palsy.