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.

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.