Identification of elastic properties of human patellae using micro-finite element analysis

Current homogenized finite element (hFE) models of the patella lack a validated material law and mostly overlook trabecular anisotropy. The objective of this study was to identify the elastic constants of patellar trabecular bone. Using μCT scans of 20 fresh-frozen cadaveric patellae, we virtually extracted 200 trabecular cubes (5.3mm side length). Bone volume fraction and fabric tensor were measured. The elastic constants were identified from six independent load cases using micro finite element (μFE) analyses. Both anisotropic and isotropic material laws were considered. The elastic constants were validated by comparing stiffness, strain and stress between hFE and μFE predictions of 18 patellar sections and six load cases. The hFE section models were built from μCT (anisotropic law) and CT (isotropic law) scans. The homogenized anisotropic model induced less error (13±5%) in the global stiffness prediction than the isotropic one (18±6%), and less error in the prediction of local apparent strain, stress, and strain energy, compared to the isotropic one. This validated hFE model could be used for future applications, either with the anisotropic constants, or with the isotropic ones when the trabecular fabric is unavailable.