Rapid and reliable biomechanical screening of injectable bone cements for autonomous augmentation of osteoporotic vertebral bodies: appropriate values of elastic constants for finite element models.

We performed finite element analysis studies on 3 three-dimensional representations of a single vertebral body: a regular cube, made of low-density polyurethane foam (foam cube analog); a regular cube considered composed of cancellous bone only (bone cube analog)); and the body of the L2 vertebra (full anatomical body model). Each finite element model was subjected to a compressive load of 2300 N, uniformly distributed over its superior surface. The cancellous and cortical bones were assigned anisotropic elastic properties, while the foam and the endplate material were considered to have isotropic properties. In each representation, the elastic properties of the material(s) were adjusted (from the initial values that were used) to give a stiffness of the representation that was equal to that of the mean result for fresh cadaveric osteoporotic single vertebral bodies, as obtained from ex vivo experimental studies reported in the literature (1226 +/- 996 N mm(-1)). Thus, any one of these representations, when used with the final adjusted value(s) of the elastic constants and modified to include a cylindrical hole filled with a specific volume of bolus of an injected bone cement, may be utilized in the rapid and reliable experimental ex vivo and/or numerical screening of these cements for use in autonomous vertebral body augmentation. This approach has many advantages over those that are currently being used, which are either characterization of the cement in isolation from the vertebral body or use of cadaveric vertebral bodies.