Mineral density differences between femoral cortical bone and trabecular bone are not explained by turnover rate alone

Abstract We report on measurements of the bone mineral density distribution (BMDD) from human femoral cortical bone samples, which show that femoral cortical bone possesses a higher bone mineral density, but a similar mineral heterogeneity around the mean as trabecular bone. To understand why cortical and trabecular BMDDs differ, we propose a rigorous hypothesis-testing approach based on quantitative modelling, and test whether the difference in BMDD can be explained by (i) differences in turnover rate; (ii) differences in osteoclast resorption behaviour; and (iii) differences in mineralisation kinetics between the two bone types. We find that accounting only for differences in turnover rate is inconsistent with the fact that both BMDDs have a similar spread around the mean, and that accounting for differences in osteoclast resorption behaviour leads to biologically inconsistent bone remodelling patterns. We conclude that the kinetics of mineral accumulation in bone matrix must therefore be different in femoral cortical bone and trabecular bone. Although both cortical and trabecular bone are made up of lamellar bone, the different mineralisation kinetics in the two types of bone point towards more profound structural differences than usually assumed.