Three-dimensional analysis of the gap space under forearm casts

Secondary displacement represents a frequent complication of conservative treatment of fractures, particularly of the distal radius. The gap space between skin and cast may lead to a certain degree movements and this increased mobility might favor redisplacement. The aim of this study was to develop a new 3D method, to measure the gap space in all 3 geometrical planes, and to validate this new technique in a clinical setting of distal radius fractures. This study applies 3D imaging to measure the space between plaster and skin as a potential factor of secondary displacement and therefore the failure of conservative treatment. We developed and validated a new methodology to analyze and compare different forearm casts made of plaster of Paris and fiberglass. An unpaired t-test was performed to document differences between the investigated parameters between plaster of Paris and fiberglass casts. The significance level was set at p < 0.05. In a series of 15 cases, we found the width of the gap space to average 4 mm, being slightly inferior on the radial side. Comparing the two different casting materials, plaster of Paris and fiberglass, we found a significantly larger variance of space under casts made of the first material (p=0.39). A roughness analysis showed also a markedly significantly higher irregularity of the undersurface of plaster of Paris as compared with fiberglass. This study allows for a better understanding of the nature of the “gap space” between cast and skin and will contribute to develop and improve new immobilization techniques and materials.