The Effects of Splitting an Above Elbow Cast: A biomechanical study.

Background: Forearm fractures are one of the top three most common fractures in children. Treatment often includes immobilizing the arm in a cast extending above the elbow to help maintain fracture reduction and alignment. Complications from circumferential casting can occur including swelling in the forearm that can lead to neurovascular complications. About 16% of children require splitting of the cast to relieve the increased pressure. Our study investigates the impact the location of the split has on cast bending stiffness in an above elbow cast model.

Methods: A Sawbones© pediatric forearm model was used for application of a hybrid plaster-fiberglass cast to simulate treatment of a pediatric forearm fracture. The plaster was allowed to set for 20 minutes followed by application of a single fiberglass layer. The casts set for at least 24 hours and were then left intact or split along one of their 4 axes. Once categorized, the casts were subjected to biomechanical testing using an Instron ElectroPlus 10000 with a 3-point bending set up. The casts were tested until failure, and the load versus displacement curves were analyzed. Each category of casts was tested five times from both a volar and dorsal direction.

Results: When loaded dorsal to volar, intact casts were significantly stiffer than those split along the dorsal, radial, or volar surfaces (p=0.0062, 0.0267, 0.0024 respectively). There was no significant difference when comparing one axis of longitudinal split to another. Intact casts showed a significantly higher load to failure than those split along the radial border (p=0.0168). When loaded volar to dorsal, intact casts were significantly stiffer than those split along any axis. Intact casts showed a significantly higher maximum load to failure than those split along the radial or ulnar border (p=0.0247, 0.0112 respectively).

Conclusion: Consideration should be given to splitting above elbow casts along the volar or dorsal surface, as those split along the radial or ulnar border tend to have lower maximum load to failure.

Clinical Relevance: To analyze the effect of splitting an above elbow cast on bending stiffness.