Background: Thermal injuries caused by application of casts continue to occur despite the development of newer cast materials. We studied the risk of these injuries with contemporary methods of immobilization.

Methods: Using cylindrical and L-shaped limb models, we recorded the internal and external temperature changes that occurred during cast application. Variables that we assessed included the thickness of the cast or splint, dip-water temperature, limb diameter and shape, cast type (plaster, fiberglass, or composite), padding type, and placement of the curing cast on a pillow. These data were then plotted on known time-versus-temperature graphs to assess the potential for thermal injury.

Results: The external temperature of the plaster casts was an average (and standard deviation) of 2.7° ± 1.9°C cooler than the internal temperature. The external temperature of twenty-four-ply casts peaked at an average of 84 ± 42 seconds prior to the peak in the internal temperature. The average difference between the internal and external temperatures of the thicker (twenty-four-ply) casts (4.9° ± 1.3°C) was significantly larger than that of the thinner (six and twelve-ply) casts (1.5° ± 1°C) (p < 0.05). Use of dip water with a temperature of <24°C avoided cast temperatures that can cause thermal injury regardless of the thickness of the plaster cast. A dip-water temperature of 50°C combined with a twenty-four-ply cast thickness consistently yielded temperatures high enough to cause burns. Use of splinting material that was folded back on itself was associated with a significant risk of thermal injury. Likewise, placing a cast on a pillow during curing resulted in temperatures in the area of pillow contact that were high enough to cause thermal damage, as did overwrapping of a curing plaster cast with fiberglass. Attempts to decrease internal temperatures with the application of isopropyl alcohol to the exterior of the cast did not decrease the risk of thermal injury.

Conclusions: Excessively thick plaster and a dip-water temperature of >24°C should be avoided. Splints should be cut to a proper length and not folded over. Placing the limb on a pillow during the curing process puts the limb at risk. Overwrapping of plaster in fiberglass should be delayed until the plaster is fully cured and cooled.