Intersite variations of the Gillette Gait Index

The Gillette Gait Index (GGI) is a tool used to measure pathologic gait severity and assess outcomes. The purpose of this study is to assess the variation in calculated GGI values with different sets of control data. Five able bodied control sets from four labs were used to establish the basis of the GGI. Gait data from three pediatric patients seen pre- and post-operatively at one lab and one adult control subject that visited each lab were input to calculate GGI values. Differences in underlying control data created large differences in computed GGI values for both pathologic and able bodied subjects. Initial pre-operative GGI values calculated for the three patients with cerebral palsy using different control data sets varied widely with differences as large as 1129 and had magnitudes of improvement differing by as much as 800 (or 21%). GGI value differences greater than 250 were determined from an able bodied control subject seen at each lab, both when examining a single trial with different control sets, and when examining different trials of the same individual collected from different labs using a single control set. These results highlight the importance of the underlying control set for establishing mean values and variance in the GGI and suggest that if GGI values are compared longitudinally or between sites these comparisons should be based on a single control dataset.