Haversian osteons: longitudinal variation of internal structure

Previous studies have suggested that one general type of osteon exists, rather than the three types previously classified as light, intermediate, and dark. A method is presented that permits rapid, quantitative measurement of the percent transmission of osteons seen in thin section between crossed polarizers. In studies of osteon segments from human cortical bone, cut either 200 or 5 micrometers in length, a continuous variation of transmission is seen, both for the populations as a whole and for serial sections. These variations cannot be ascribed to angulation between the direction of observation and the axis of the osteonal segment. No correlation can be observed between the angle of the segment axis and the percent transmission. It is suggested that the collagen fiber orientation in osteonal segments must be considered to be continuous, as judged by scattering of polarized light.