A SEM study of osteocyte orientation in alternately structured osteons.

Previous morphometric analyses, carried out by means of the light microscope under ordinary and polarized light, show the existence of a close correlation between collagen texture and shape, size, and spatial orientation of the osteocytes (Marotti, 1979, 1981). In woven bone the osteocyte lacunae show an irregular globous shape, whereas when the collagen fibers follow a preferential orientation, i.e., in parallel-fibered bone and in lamellar bone, the lacunae have an ellipsoid shape along three axes, an almondlike shape. Moreover, we found that the major axis of the ellipsoid is always parallel to the length of the collagen fibers, and in lamellar bone the intermediate and minor axes are respectively parallel and perpendicular to the surfaces of the lamellae. It must be noticed that our investigations in lamellar bone were only carried out on longitudinally structured osteons. Alternately structured osteons were not analyzed because in these systems the collagen fibers run at an angle of nearly 90 degrees in adjacent lamellae, and therefore it would be difficult to compare their orientation with that of the lacunae. In fact light microscopy does not appear to be a suitable technique to detect whether the lacunae are located in Iongitudinally or in transversely structured lamellae or between the lamellae as classically maintained by the light microscopists. For this reason, in the present investigation we used the scanning electron microscope, whose resolving power allows an accurate analysis of both the structure of lamellae and the site of osteocyte lacunae.