Biomechanical Strength of 3 Prototype Designs of Vented Long Arm Fiberglass Casts.

Abstract

BACKGROUND: The standard nonsurgical treatment of pediatric elbow fractures uses a long arm cast for immobilization. Casts are typically worn for 4 to 6 weeks, during which time they can retain moisture, causing discomfort and skin maceration, especially in warm weather. In this study, we evaluated the biomechanical strength of long arm casts with material gaps designed to improve ventilation. METHODS: Three modified long arm cast designs were evaluated for structural integrity compared with standard casts. We refer to these designs as (1) the "ellipse," featuring an elliptical gap at the posterior elbow; (2) the "posterior," featuring a circular hole at the posterior elbow; and (3) the "lateral," featuring a circular hole at the lateral elbow. Five standard casts and 6 casts of each prototype design were created, for a total of 23 casts. Casts were made with 3-inch fiberglass by 1 orthopaedic surgeon to ensure consistency. Each cast was loaded until failure using a materials testing system, simulating a patient falling on a casted arm. We recorded the peak force (in Newtons) that each cast withstood before it failed. Single-factor analysis-of-variance testing was performed to assess how vented casts performed compared with the standard cast. Alpha = 0.05. RESULTS: The posterior design had the highest mean peak force (348 N), followed by the lateral design (302 N), the standard cast (290 N), and ellipse design (258 N) (P = 0.021). The ellipse casts had the highest variance in peak force, indicating variability in performance. Post hoc testing revealed that only the posterior design demonstrated significantly greater peak force than the standard cast. The other vented casts showed no differences in mechanical performance compared with the standard cast. CONCLUSIONS: Vented long arm casts, particularly the lateral and posterior designs, had equal or superior mechanical strength to casts of a standard design. These findings support the feasibility of ventilation in long arm casts to enhance patient comfort and skin access without compromising structural integrity of the cast. LEVEL OF EVIDENCE: Level V.