New Metric for Quantifying Stiffness of Intact Human Vertebrae

Accurately quantifying the compressive stiffness of whole human vertebrae is important in the development of new treatment regimes for osteoporotic fracture repair and vertebral height restoration. Historically, whole bone stiffness has been measured from in vitro load-deformation behavior of isolated vertebrae using two different methods: 1) maximum slope of the load-deflection curve over a 0.2% strain window (“Method #1) [1, 2], and 2) slope of the best-fit line to the load-deflection curve over a specified loading range (most commonly 100–250 lbs, “Method #2”) [3, 4]. Because the whole bone load-displacement response is non-linear, these two measurement systems may yield different stiffness values for the same set of experimental data. Furthermore, both measurement systems are arbitrary, and there has been no investigation of the sensitivity of the whole bone stiffness metric to its method of measurement. The goal of this study is to develop and validate a standard method for calculating whole bone stiffness based on basic principles. In developing this method, we will also evaluate the robustness of existing stiffness calculation methods.