Repeatability and validation of gait deviation index in children: typically developing and cerebral palsy.

The Gait Deviation Index (GDI) is a dimensionless parameter that evaluates the deviation of kinematic gait from a control database. The GDI can be used to stratify gait pathology in children with cerebral palsy (CP). In this paper the repeatability and uncertainty of the GDI were evaluated. The Correlation between the GDI and the Gross Motor Function Classification System (GMFCS) was studied for different groups of children with CP (hemiplegia, diplegia, triplegia and quadriplegia). Forty-nine, typically developing children (TD) formed our database. A retrospective study was conducted on our 3D gait data and clinical exams and 134 spastic children were included. Sixteen TD children completed the gait analysis twice to evaluate the repeatability of the GDI (test-retest evaluation). Monte Carlo simulations were applied for all groups (TD and children with CP) in order to evaluate the propagation of errors stemming from kinematics. The repeatability coefficient (2SD of test-retest differences), obtained on the GDI for the 16 TD children (32 lower limbs) was ± 10. Monte Carlo simulations showed an uncertainty ranging between 0.8 and 1.3 for TD children and all groups with CP. The Spearman Rank correlation showed a moderate correlation between the GDI and the GMFCS (r=-0.44, p<0.0001).