A Biomechanical Evaluation of Casting Technique and Cast Core Size Effect

The goals of this study were to (1) compare the effect of casting technique on biomechanical function with different casting materials and different cast core diameters, and (2) compare the strength of a cast based on the number of layers in relation to the core diameter.

Two standardized cylindrical cast model sizes were used to simulate forearm and short leg casts (core diameter: 60 mm, 100 mm) with 2 different casting techniques (non-smoothing vs. smoothing with lamination), utilizing 2 casting materials [fiberglass and Plaster of Paris (POP)]. Each cast was created using 3 different layers (Fiberglass: 2 to 4 layers; POP: 3 to 5 layers). Ultimate load-to-failure and flexural rigidity were analyzed through cyclic 4-point bend testing.

The biomechanical comparison between forearm and short leg casts were significantly different regardless of the same number of layers for both casting materials and between 2 casting techniques. Increased cast thickness significantly increased the ultimate load-to-failure and bending strength. An increased core diameter size significantly decreased the cast's ultimate load-to-failure (fiberglass: 50% to 108%; POP: 10% to 93%) and bending strength (fiberglass: 17% to 35%; POP: 37% to 49%). Casting technique with smoothing with lamination technique had a negative biomechanical effect on POP and a minimal effect on fiberglass.

The number of layers to apply for a cast should be based on the size of the extremity. Smoothing and lamination technique did not significantly improve the cast mechanical behavior.

The findings of this study provide valuable evidence, analysis, and supplementary knowledge that helps guide physicians in proper casting technique.