The effectiveness of bivalving, cast spreading, and webril cutting to reduce cast pressure in a fiberglass short arm cast.

Background: A fiberglass short arm cast can be used to treat a distal radial fracture, but posttraumatic edema may lead to excessive cast tightness and resultant soft-tissue injury. We sought to quantify a simulated edema-induced pressure within a fiberglass short arm cast and to determine the effectiveness of different cast-cutting methods for pressure reduction. We hypothesized that cast cutting could eliminate all clinically relevant pressure and Ace wrap would insignificantly increase pressure.

Methods: Skin surface pressure under fiberglass short arm casts was measured on ninety wrists from forty-five volunteers randomly assigned to one cast-cutting method: single-cut (cast bivalve and Ace wrap), double-cut (cast bivalve, spread, and Ace wrap), or triple-cut (cast bivalve, spread, Webril cut, and Ace wrap). Each wrist was immobilized in a cast in the neutral position with one roll of 2-inch (5.1-cm) cotton Webril and one roll of 2-inch (5.1-cm) fiberglass. Each fiberglass short arm cast contained an empty intravenous fluid bag in which we infused air. This simulated edema, which generated a skin surface pressure, which was measured by a pressure transducer.

Results: Each cast-cutting method significantly reduced (p < 0.0001) the skin surface pressure from the average maximum of 92.5 mm Hg in a non-fracture setting. Prior to Ace wrapping, there was a reduction in skin surface pressure of 70.8% for the single-cut method, 85.1% for the double-cut method, and 99.9% for the triple-cut method. Ace wrap significantly increased skin surface pressure (p < 0.0001), lessening the effectiveness of cast cutting. There was an overall reduction in skin surface pressure of 55.9% for the single-cut method, 64.3% for the double-cut method, and 77.2% for the triple-cut method. Throughout our study, women had significantly higher skin surface pressure than men (p < 0.0001); the average maximum was 104.4 mm Hg for women and 81.1 mm Hg for men.

Conclusions: The single-cut method provides the greatest pressure reduction, but only the triple-cut method eliminated all relevant skin surface pressure. Ace wrapping a cut cast noticeably increased skin surface pressure.

Clinical Relevance: In volunteers without a fracture, only the triple-cut method is effective enough to eliminate clinically relevant skin surface pressure. Ace wrap should be applied with caution after the cast is cut. The specific effect on pressure reduction in a patient who requires some soft-tissue pressure to maintain fracture reduction was not studied.