Gap index: a good predictor of failure of plaster cast in distal third radius fractures

The aim of this study was to assess the usefulness of the cast index and an indigenously developed gap index as measures of poor moulding of plaster. Twenty cases of re-manipulation of distal third radius fractures in children excluding growth plate injuries were compared with a control of 80 patients. A significant difference (< 0.001) was observed in the cast index and the gap index of both the groups. The gap index was more sensitive than the cast index in predicting failure. At a level of cast index of more than 0.8 the relative risk of failure is 6.8 as compared with 35 when the sum of the gap index is more than 0.15. The gap index is a better predictor of failure than the cast index. A quick assessment of these indices is a good practice before accepting any plaster following a manipulation of distal radial fractures.