Comments on "Femoral surface strain in intact composite femurs: A custom computer analysis of the photoelastic coating technique" [with reply]

Cristofolini and Viceconti read with great interest the title paper by Grecula et al. (see ibid., vol. 47, p. 926-33, 2000). Cristofolini and Viceconti were pleased to see an increasing interest toward new tools to improve in vitro investigations in orthopedics. In fact there still a strong need to improve the way hip prostheses are tested. The work Grecula et al. presented definitely gives a positive contribution in this direction, since they developed a new approach to assess the state of strains in the femur. In fact Grecula et al. proposed to use a novel indicator, the average strain areas, rather than looking at local information only. However, Cristofolini and Viceconti feel that Grecula et al. might have overlooked some methodological details that can possibly undermine the validity of the actual results they present, introducing both a significant bias, and a large scatter of the results. In reply Grecula et al. say that the goal of the project reported in the original paper was to improve on the methods available for measuring the surface strains in the proximal femur. Visualizing the complete topography of surface strains with the photoelastic coating technique is appealing but frustrating due to limits in its quantitative utility. Grecula et al. incorporated the advantages of computer imaging and software interpretation to improve the quantitative results of this technique. As with any new technique, Grecula et al. designed the protocol to be as simple as possible to reduce possible errors and variability. While the loading configuration was not necessarily physiologic and possibly over-constrained, it did allow the repeatable load transfer through the femur that was necessary for validating the computer techniques that Grecula et al. were testing.