Osteon classification in human fibular shaft by circularly polarized light

Pattern of osteonal classification referred to collagen fiber orientation in a human fibula was studied. Along the length of the whole bone, serial 100-microm parallel cross sections were obtained and analyzed by circularly polarized light microscopy. The distribution of 3 different kinds of osteons (transversal, alternated and longitudinal-hooped) depending on their collagen fiber orientation were analyzed to determine the effect of length, anatomical quadrant and cortical thickness. Referring to length, the 3 types of osteons appeared with approximately the same relative frequency, but when the symmetry of the fibula was considered and the length was expressed as distance from the bone mid-section, the alternated osteons are predominant in the mid-section. On the contrary, moving toward the epiphyses, the balance is inverted, and transversal together with longitudinal-hooped types become more frequent than the alternated type. Osteonal pattern distribution was not significantly affected by the anatomical quadrant of each section or by the thickness of the cortex. This observation seems to confirm that along the fibula shaft the orientation of collagen fibers within the osteons is consistent with the loading conditions which the bone undergoes.