Quantifying the regional variations in the mechanical properties of cancellous bone of the tibia using indentation testing and quantitative computed tomographic imaging

Finite element models apply material properties using experimentally derived density-modulus equations and computed tomographic image data, yet numerous different equations exist in the literature. The purpose of this study was to experimentally evaluate the distribution of mechanical properties through the proximal tibia and compare with those predicted using existing density-modulus equations. Indentation testing was performed on five cadaveric tibiae, with four slices removed from the proximal epiphysis and metaphysis of each. Elastic modulus and yield strength were identified for each test and grouped into nine transverse regions. These regions were identified on computed tomographic scans, and four density-modulus equations from the literature applied. Errors between measured and predicted modulus were then calculated. Elastic modulus and yield strength varied regionally, with the bone located closest to the joint and in the condyles being strongest and the intercondylar region the weakest. The optimal relationship for predicting modulus varied depending on anatomical region, but generally was best predicted by the Goulet equation. The regions of high strength identified in this study (condyles and proximal regions) can serve as improved sites of attachment for orthopedic devices and should be preserved during surgery, if possible. The substantial regional variations observed herein (almost a threefold change in modulus across different regions) should be incorporated into finite element models and applied using the Goulet density-modulus equation.