Material properties of the inner and outer cortical tables of the human parietal bone

Even though the cranial vault functions as protection for the brain and as a support structure for facial and masticatory functions little is known about its mechanical properties or their variations The cranial vault bone is interesting because of its maintenance in spite of low functional strains and because calvarial bone cells are often used in cell culture studies We measured thickness density and ash weight and ultrasonically deter mined elastic properties throughout the cortices of 10 human parietal bones The results are unique for studies of the cranial vault because 1) measurements focused specifically on the cortical components 2) the orientations of the axes of maximum stiffness were determined before measurement of elastic properties and 3) two related measurements (bone density and percent ash weight) were compared Results showed that the periosteal cortical plate (outer table) and the endosteal cortical plate (inner table) had significant differences in material properties The outer table was on aver age thicker denser and stiffer than the inner table which had a higher ash weight percentage Within each table there were significant differences in thicknesses ash weight percentages and E-2/E-3 anisotropies among sites Few sites on either table had significant orientations of the axes of maxi mum stiffness Despite this apparent randomness in orientation almost all sites exhibited anisotropies equivalent to other parts of the skeleton.