SKIN SURFACE PRESSURE BENEATH AN ABOVE-THE-KNEE CAST - PLASTER CASTS COMPARED WITH FIBERGLASS CASTS

Complications related to immobilization in a cast after an injury or a n operation may be related to the materials used for the cast or to th e techniques of application, or to both, To evaluate the widely held c linical opinion that the use of a fiberglass cast is dangerous and ina ppropriate when subsequent swelling of the extremity is anticipated, w e studied the skin surface pressures that were generated beneath above -the-knee casts made with different materials and applied with differe nt techniques. A prosthetic model of the lower extremity was designed with an expandable calf compartment to simulate swelling after an inju ry or an operation, With use of this model, we measured the skin surfa ce pressure beneath a plaster-of-Paris cast, a fiberglass cast that ha d been applied with a standard technique, and a fiberglass cast that h ad been applied with a stretch-relax technique, The highest mean skin surface pressure after application of the cast (p < 0.001) and after s imulated swelling of the limb (p = 0.04) was generated by the fibergla ss cast that had been applied with a standard technique, The lowest me an skin surface pressure after application of the cast (p = 0.006), si mulated swelling of the limb (p < 0.001), and all subsequent steps of the experimental protocol (p < 0.001) was generated by the fiberglass cast that had been applied with the stretch-relax technique. The mean skin surface pressure generated by the plaster cast and by the fibergl ass cast applied with the standard technique did not return to the val ue before application of the cast until anterior and posterior longitu dinal cuts had been made in the cast and the cast had been spread at t hose cuts. When the fiberglass cast had been applied with the stretch- relax technique, the mean pressure returned to the baseline value afte r only an anterior longitudinal cut and spreading at that cut. The pri ncipal pitfall of the use of a fiberglass cast is related to the techn ique of application, When the fiberglass cast had been applied with th e standard technique, it generated a mean skin surface pressure that w as higher than that associated with the plaster cast and it accommodat ed simulated swelling poorly, When the fiberglass cast had been proper ly applied, with the stretch-relax technique, it generated a mean skin surface pressure that was significantly lower (p = 0.006) than that a ssociated with the plaster cast and it better accommodated simulated s welling without the need to sacrifice the structural integrity of the cast.