The aims of this study were i) to see if there is an association between poorly applied plasters and redisplacement of paediatric forearm fractures, and ii) to define reliable radiographic measurements to predict redisplacement of these fractures. The two radiographic measurements which were assessed were Cast Index and Padding Index which are a guide to plaster moulding and padding respectively. The sum of these was termed as the Canterbury Index. Case records and radiographs of 142 children who underwent a manipulation for a displaced fracture of forearm were studied. Angulation, translation displacement, Cast index and Padding index were measured on radiographs. Redisplacement was seen in 44 cases (32.3%). The means and 95 % Confidence intervals for cast index and padding index were 0.87 (0.84, 0.90) and 0.42 (0.39, 0.62) in the redisplacement group whereas were 0.71 (0.69, 0.72) and 0.11 (0.09, 0.12) in the group with no redisplacement respectively. Initial displacement, Cast index, Padding index and Canterbury Index were significantly greater in the redisplacement group (p< 0.005). No statistically significant difference was seen for age, fracture location, initial angular deformity and seniority of the surgeon. We suggest that Cast Index > 0.8, Padding Index > 0.3 and Canterbury Index > 1.1 are significant risk factors for redisplacement of conservatively treated paediatric forearm fractures

We present an objective method for predicting the redisplacement of paediatric forearm and wrist fractures. Novel radiographic measurements were defined and their value assessed for clinical decision making. In Phase I of the study we defined the cast index and padding index and correlated these measurements with the incidence of fracture redisplacement. Phase II assessed these indices for their value in clinical decision making. Cast Index (a/b) is the ratio of cast width in lateral view (a) and the width of the cast in AP view (b). Padding Index (x/y) isthe ratio of padding thickness in the plane of maximum deformity correction (x) and the greatest interosseous distance (y) in AP view. The sum of cast index and padding index was defined as the Canterbury Index. In Phase I, 142 children's radiographs were analysed and a statistically significant difference was identified between redisplacement and initial complete off-ending of the bones, cast index > 0.8 and padding index of > 0.3. There was no significant association with age, fracture location, seniority of surgeon or angulation. In Phase II, radiographs of 5 randomly selected cases were presented to 40 surgeons (20 consultants & 20 registrars). Following an eyeball assessment they were asked to measure the cast index and padding index (after instruction). With eyeballing the consultants predicted 33% and registrars 25% of the cases that redisplaced. After learning to measure the indices the accuracy increased to 72% for consultants and 81% for registrars (p<0.001). We conclude that the cast index, padding index and Canterbury Index are validated tools to assess plaster cast quality and can be used to predict redisplacement of paediatric forearm fractures after manipulation. They can easily be taught to orthopaedic surgeons and are more accurate than eyeballing radiographs in the clinical setting. Redisplacement can be predicted if cast index > 0.8, padding index > 0.3 and Canterbury Index > 1.1

We assessed two simple radiological methods of predicting redisplacement of forearm fractures in children: a) Cast Index (ratio of sagittal to coronal cast width at the fracture site), and b) Padding Index (ratio of padding thickness at the fracture site in the plane of the deformity to the maximum interosseous width). Case records and radiographs of 100 children who underwent a manipulation under general anaesthesia for a displaced fracture of forearm or wrist were studied. Redisplacement was defined as more than 15 degrees of angulation and/or more than 50 percent of translational displacement on check radiographs at 1–2 weeks. Angulation (in degrees) and translation displacement (in percentage) were measured on the initial and check radiographs. Cast index and Padding index were measured on the check radiographs. Good intra and inter observer reproducibility was observed for both these measurements. The cast index was validated in an experimental study. Redisplacement was seen in 29 cases. Of these 21 cases underwent a secondary procedure for redisplacement. Initial displacement, cast index and padding index were the three factors which were significantly higher in the redisplacement group (p< 0.05). The means and 95% Confidence intervals for cast index and padding index were 0.88 (0.84, 0.90) and 0.48 (0.39, 0.62) in the redisplacement group whereas were 0.71 (0.69, 0.72) and 0.11 (0.09, 0.12) in the group with no redis-placement respectively. No statistically significant difference was seen for age, fracture location, initial angular deformity and seniority of the surgeon. Conclusion: cast index and padding index are simple and reliable radiographic measurements to predict the redisplacement of forearm fractures in children. A plaster with a cast index of> 0.9 and padding index of > 0.3 is prone to redisplacement