MORPHOLOGY AND FRACTURE OF BONE

Abstract

An attempt has been made to correlate the brittle and ductile behaviour of bone to its micro structure. Neglecting the contribution of liquids, cortical bone may be considered as a composite material consisting of a mineral and an organic phase. A more sophisticated model should incorporate liquids as structural members and also consider an organic phase which in certain circumstances, may behave like a liquid. The latter model is more realistic and more applicable to the interpretation of crack propagation in bone. In this model, the lamellar structure of osteons includes concentric cylinders comprising a high volume fraction of a polycrystalline mineral separated by an organic-mineral aggregate. This interlamellar aggregate is the major contributer to the ductility of bone. With advancing age, this aggregate becomes radially bridged by calcified polycrystalline tissue rendering the bone brittle. Not all osteons, however, calcify: some of them become remodelled and form young osteons, with the same characteristics as in young bone. Thus the brittle or ductile behaviour of bone depends not so much on the age of an individual as on the ratio of old to young osteons in the bone.