The stiffness of cylindrical casts enforced with splint laminations: biomechanical considerations

Splint lamination is often used to strengthen a plaster cast while minimizing its thickness and weight. We evaluated the following lamination configurations to determine the effectiveness of each relative to a 3-mm-thick short leg cast: anterior-posterior splints, medial-lateral splints, and an anteriorly placed fin. Theoretical stiffness was calculated as a function of the area moment of inertia, and then the actual casts were tested in three-point bending on a servohydraulic apparatus. The experimental results were correlated with the calculated data, and finite element studies were performed to correlate the experimental results with the geometries of the casts. The theoretical and experimental data indicate that anterior-posterior splint lamination reinforcement stiffens a cylindrical cast to flexion-extension bending moments more effectively than does medial-lateral splint placement. An anterior fin can stiffen the cast as effectively as a splint can. However, the fin must be relatively large, which may cause it to accentuate problems with clothing and be difficult to apply.