Optimal Timing for Safe Bivalving of Fiberglass Casts Is Before the Exothermic Peak

Cast saw injury is a notable source of medicolegal risk. Previous work with plaster casts demonstrated that cast saw injury was minimized by waiting 12 minutes before removal. In this study, we evaluate the safety parameters of fiberglass casting materials.

Eight-ply plaster and fiberglass casts were applied to a pediatric forearm model at variable dip-water temperatures, and the mean time to reach their exothermic peak was determined. Fiberglass casts were then maintained at the manufacturer's recommended dip-water temperature and removed at intervals of 2 (before exothermic peak), 6 (approximately fiberglass's exothermic peak), or 12 (after exothermic peak) minutes. All casts were removed by a pediatric orthopaedic surgeon blinded to the cast set time. Cast/blade temperature, saw force, blade-to-skin contact, bivalve time, cast spreading force, and cut completeness were assessed individually and as short (<6-minutes) or long (≥6-minutes) set times.

Fiberglass casts exothermically peaked markedly earlier (5.2 [IQR = 5-5.4] minutes) than plaster (14.8 [IQR = 13.7-15.3] minutes), P < 0.0001, at maximum temperatures, which did not markedly differ. Downward force applied during fiberglass cast removal was markedly lower in the short versus long set time groups [average forces of 8.3 (IQR = 6.4-10.4) versus 12.9 (IQR = 11.1-14.5) Newtons, P < 0.0001, as were maximum forces: 23.2 (IQR = 18.9-26.6) versus 43.8 (IQR = 38.6-48.5) Newtons, P < 0.0001]. Bivalve time and maximum cast spreading force were decreased in short set times with 40.5 (IQR = 39.2-44.7) versus 44.4 (IQR = 40.6-47.3) seconds ( P = 0.06) and 15.5 (IQR = 14-18.5) versus 21.5 (IQR = 18-26.5) N ( P = 0.07), respectively. Maximum saw blade temperature was markedly lower in the short (99.6°C [IQR = 98.2-105.6°C]) versus long (130.6°C [IQR = 121.9-141°C]) set times ( P = 0.04). No notable differences in blade-to-skin touches or touch duration were detected.

Unlike plaster, fiberglass casts cut before exothermically peaking were associated with less downward force, faster bivalve times, and decreased spread force without increased blade temperature or skin contacts. This suggests that fiberglass casts can be bivalved markedly earlier without increased risk of injury.