Cast index in predicting outcome of proximal pediatric forearm fractures

Many pediatric forearm fractures can be treated in plaster following closed reduction. The cast index (CI, a ratio of anteroposterior to lateral internal diameters of the cast at the fracture site) is a simple, reliable marker of quality of molding and a CI of >0.8 correlates with increased risk of redisplacement. Previously, CI has been applied to all forearm fractures. We hypothesize that an acceptable CI is more difficult to achieve and does not predict outcome in fractures of the proximal forearm.

Seventynine cases of pediatric forearm fractures initially treated by manipulation alone over a year were included in this retrospective radiographic analysis. The CI was calculated from the post manipulation radiographs. All fractures were divided as either proximal or distal half forearm based on the location of the radius fracture. Subsequent radiographs were reviewed to assess redisplacement and reoperation.

The mean CI was 0.77. Remanipulation was required in five cases (6%), all distal half fractures - mean CI 0.79. CI was higher in proximal half forearm fractures (0.83 vs. 0.76, P = 0.006), nonetheless these fractures did not re-displace more than distal fractures.

Cast index is useful in predicting redisplacement of manipulated distal forearm fractures. We found that in proximal half forearm fractures it is difficult to achieve a CI of <0.8, but increased CI does not predict loss of position in these fractures. We therefore discourage the use of CI in proximal half forearm fractures.