Three experimental designs testing orthopedic casting material strength.

Three methods for testing the comparative strength of orthopedic casts have been considered. Two of the tests, three-point-beam-bending and diametral compression, were expected to yield information about "material" strength, and a third simulated an actual cast yielding information about "structural" strength. In one study using these three methods, differences in strength were detected in the material tests, but not in the structural test. Thus, the authors believe that tests of material strength alone are insufficient to establish clinically relevant differences between the strength of orthopedic casts. Adequate testing must include structural tests like the cast-cylinder test described in this article if meaningful and clinically relevant conclusions are to be drawn regarding the comparative strength of the actual cast. Since both the three-point-beam-bending and diametral compression tests produced essentially the same results, both tests are probably not necessary. However, each of these two tests does serve to substantiate the results of the other.