Abstract
We aimed to assess a simple radiological method of predicting redisplacement of paediatric forearm fractures. The Cast Index (CI) is the ratio of sagittal to coronal width from the inside edges of the cast at the fracture site. CI of 0.7 was used as the benchmark in predicting fracture redisplacement. Case records and radiographs of 1001 children who underwent a manipulation under general anaesthesia for a displaced fracture of the distal forearm were studied. Redisplacement was defined as more than 15 degrees of angulation and/or more than 80 percent of translational displacement on check radiographs at 2 weeks. Angulation (in degrees) and translation displacement (in percentage) were measured on the initial and check radiographs. The Cast index was measured on the check radiographs. Good intra and inter observer reproducibility was observed for both these measurements. The cast index has been previously validated in an experimental study.
The adequacy of reduction after manipulation was estimated by the postreduction translation and angulation of the radius and ulna in anteroposterior and lateral plain film radiographs. The 1001 patients who qualified for the study, fracture redisplacement was seen in 107 cases at the all important two week follow up. Seven hundred and fifty-two patients had cast indices of 0.8 or less whilst 249 had casting indices of 0.81 or more. In patients with cast indices of 0.8 or less, the displacement rate was only 5.58%. However, in patients with cast indices of 0.81 or more, the displacement rate was 26%. Initial displacement, angulation and the post manipulation cast index were the three factors which were significantly higher in the redisplacement group.
No statistically significant difference was seen for age, sex or ethnicity. Nor were statistical differences noted in initial angular deformity, initial displacement and seniority of the surgeon. There was no statistical difference in patients with cast indices between 0.7 and 0.8.
Cast index is a simple reliable radiographic measurement to predict the redisplacement of forearm fractures in children. A plaster with a CI of > 0.81 is prone to redisplacement. A high cast index is associated with redisplacement of fractures and should therefore be considered when moulding casts is distal forearm fractures.
Correspondence should be addressed to Associate Professor N. Susan Stott, Orthopaedic Department, Starship Children’s Hospital, Private Bag 92024, Auckland, New Zealand.
