FAILURE MECHANISMS IN HUMAN VERTEBRAL CANCELLOUS BONE

Specimens of human vertebral cancellous bone were compressed to well p ast mechanical failure (15% strain) in the infero-superior direction. The mechanisms of failure were examined microscopically and histologic ally. The primary mechanism of failure was shown to be microscopic cra cking rather than overt failure of the trabecular elements. The morpho logy of the cracks was consistent with an hypothesis that they were th e result of shear stress (or strain) in the tissue. Complete fracture of trabeculae was confined to elements oriented transversely to the di rection of loading. The tissue's ultimate strength and residual streng th after compressive failure were both strongly correlated to tissue s tiffness (R(2) = 0.88 and R(2) = 0.71, respectively). It is proposed t hat cancellous bone strength may be a consequence of the adaptation of bone stiffness to applied stresses. With removal of the load, all spe cimens recovered at least 94% of their original height. Implications o f energy dissipation by microcracking for recovery and maintenance of overall trabecular architecture are discussed.