Redefining the Cast Index: The Optimum Technique to Reduce Redisplacement in Pediatric Distal Forearm Fractures

Background: The aim of this study was to identify the optimal cast index (CI) level that reduces the risk of fracture redisplacement. The CI is the ratio of sagittal to coronal width from the inside edges of the cast at the fracture site. Previous studies have used 0.7 as the standard. Methods: Case records and radiographs of 1001 children who underwent a manipulation under anesthesia for a displaced fracture of the distal forearm were studied. Redisplacement was defined as > 15 degrees of angulation and/or > 80% of translational displacement on check radiographs at 2 weeks. Angulation (degrees) and translational displacement (%) were measured on the initial and check radiographs. The CI was measured on the check radiographs. The CI has previously been validated in an experimental study. Results: The adequacy of reduction after manipulation was determined by translation and angulation of the radius and ulna in anteroposterior and lateral plain film radiographs. From the 1001 patients who qualified for the study, fracture redisplacement was seen in 107 (10.6%) cases at the 2-week follow-up. A total of 752 (75%) patients had CIs of <= 0.8, whereas 249 (25%) had casting indices of >= 0.81. In patients with CIs of <= 0.8, the displacement rate was only 5.58%. However, in patients with CIs of >= 0.81, the displacement rate was 26%. A high CI was the sole factor that was significantly higher in the redisplacement group. No statistically significant difference was seen for age, sex, or surgeon seniority. Statistical differences were not noted in initial angular deformity or initial displacement. Discussion: The CI 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. High CIs are associated with redisplacement of fractures and should be avoided when molding casts in distal forearm fractures.