Distribution of lamellae in human femoral shafts deformed by bending with inferences on mechanical properties

On the basis of previous investigations indicating that the distribution of osteonic and interstitial lamellae in a normal femur depends on its mechanical properties, a procedure has been devised to provide information on the distribution of lamellae in human femora diaphyses deformed by bending. To achieve this, exactly plane parallel cross sections, 100 μm thick, were prepared from the portion of maximum bending, using an annular blade microtome. An index of the distribution of longitudinal lamellae (whose fiber bundles and crystallites have a longitudinal course and withstand loading by tension) and transverse lamellae (whose fiber bundles and crystallites have a transverse course and withstand loading by compression) was determined using circularly polarized light as illuminating source and a Quantimet 720 image analyzing computer. The results show that, even in a pathologically deformed bone, both the microscopic structure of sections at the level of osteonic and interstitial lamellae, and their macroscopic shape may be governed by the distribution of the forces active in bone.