The loss of stiffness as osteoporosis progresses.

The routine diagnosis of osteoporosis is based on radiological measurements of bone mineral content. An osteoporotic failure is influenced both by a loss of mineralized bone and internal bone structure. The structure cannot be estimated by bone reconstruction based on standard radiological equipment. To investigate the influence of structure on cancellous bone stiffness, a new finite element model of cancellous bone is developed. The model describes a cancellous bone unit as an open-celled structure. Trabecular length, trabecular thickness, diameter of trabecular connections, relative lattice disorder and relative bone loss determine the real architecture. Using this model, the loss of stiffness as a result of trabecular thinning and loss of trabecular connections is estimated. The volume fraction as a scalar value for a volume can not be a marker for orthotropic stiffness changes. A formula in the form Y = e(a *1 n(X) + b) can describe the correlation between cancellous bone stiffness and volume fraction. These formulas are appropriate for those cases, when the loss of bone mineral (decrease in trabecular thickness) is closely connected to a loss of structure (increasingly perforated trabecular network).