Scanning electron micrographs of cancellous bone from the human sternum.

Thick sections from the manubrium and the first and second sternabrae were polished and the marrow removed. Low magnification scanning electron micrographs show that the cancellous bone near the medial plane is lightly constructed, is not markedly anisotropic and does not vary greatly from place to place. In the lateral parts of the sternabrae the trabeculae are somewhat thicker and the spaces between them are larger. Measurements on the polished surface lead to numerical values of a number of parameters characteristic of the surface patterns, such as the relative surface occupied by bone, the mean widths of the trabecular sections, the mean path lengths through the bone or marrow, and a number representing the departure from isotropy of the pattern. Parameters characteristic of the three-dimensional trabecular structure can be deduced, viz., the relative volume of bone, the area of the interface between bone and marrow and the mean thickness of the trabeculae. The sternum is compared with other bones which have been investigated by the same methods. There is little resemblance to the rib or to the proximal femur. The cancellous bone in the sternum and in the lumbar vertebral body are similar in appearance but the former has slighter trabeculae and larger marrow spaces.