The quantitative morphology of anisotropic trabecular bone

SUMMARY Dimensional measurements have been made on a small number of tracings of low magnification scanning electron micrographs of trabecular bone sections, using the Quantimet Image Analysing Computer, with a view to expressing the properties of the local bone pattern in a quantitative manner. Measurements of the orthogonally projected length of the boundary profile of the interface between bone and marrow were made as a function of the direction of projection, and these showed that the majority of the patterns were distinctly anisotropic. A formula is proposed for calculating the mean widths of the trabecular bands as they appear on the surfaces of the sections, from the mean area of bone and the boundary profile length. As the validity of this formula is not theoretically evident, the results have been compared with direct experimental measurements, and found to agree very well. The mean intercept lengths in the bone and in the marrow spaces have been calculated as a function of direction across the section. The polar diagrams of these lengths are found to have the shapes of ellipses, to an unexpected degree of accuracy. This makes it possible to express the departure from isotropy of the pattern by a single number, for instance by the ratio of the axes of the ellipse. The essential limitations of the methods used in these experiments are briefly discussed, in particular the impossibility of finding the exact symmetry properties of the surface patterns by experiments of this type.