On the clinical interpretation of overground gait stability indices in children with cerebral palsy.

Several indices have been devised to quantify a person's stability from its gait pattern during overground walking. However, clinical interpretation of the indices is difficult because the link between being stable and adopting a mechanically stable gait pattern may not be straightforward. This is particularly true for one of these indices, the margin of stability, for which opposite interpretations are available in the literature. We collected overground walking data in two groups of 20 children, with unilateral cerebral palsy (CP) and typically developing (TD), for two conditions, on flat and on uneven grounds (UG). We postulated that TD children were more stable during gait than children with CP and that both groups were more stable on flat compared to UG. We explored the coherent association between several indices and the two postulates to clarify clinical interpretation. Our results showed that increased margin of stability, increased amplitude of the whole-body angular momentum, decreased duration of single limb support, increased variability (gait kinematics, step length, and step width) were associated with reduced stability for both postulates. However, results for the margin of stability were paradoxical between the sides in the CP group where small margin of stability was indicative of a fall forward strategy on the affected side rather than improved stability. Whole-body angular momentum and duration of single limb support appeared as the most sensitive indices. However, walking speed influenced these and would need to be considered when comparing groups of different walking speed.