A three-dimensional simulation of age-related remodeling in trabecular bone

After peak bone mass has been reached, the bone remodeling process results in a decrease in bone mass and strength. The formation deficit, the deficit of bone formation compared with previous resorption, results in bone loss. Moreover, trabeculae disconnected by resorption cavities probably are not repaired. The contributions of these mechanisms to the total bone loss are unclear. To investigate these contributions and the concomitant changes in trabecular architecture and mechanical properties, we made a computer simul ation model of bone remodeling using microcomputed tomography (micro-CT) sc ans of human vertebral trabecular bone specimens. Up to 50 years of physiol ogical remodeling were simulated. Resorption cavities mere created and refi lled 3 months later. These cavities were not refilled completely, to simula te the formation deficit. Disconnected trabeculae were not repaired; lease fragments generated during the simulation were removed. Resorption depth, f ormation deficit, and remodeling space were based on biological data. The r ate of bone loss varied between 0.3% and 1.1% per year. Stiffness anisotrop y increased, and morphological anisotropy (mean intercept length [MIL]) was almost unaffected. Connectivity density increased or decreased, depending on the remodeling parameters. The formation deficit accounted for 69-95%, d isconnected trabeculae for 1-21%, and loose fragments for 1-17% of the bone loss. Increasing format ion deficit from 1.8% to 5.4% tripled bone loss bu t only doubled the decrease in stiffness. Increasing resorption depth from 28 to 56 mum slightly increased bone loss but drastically decreased stiffne ss. Decreasing the formation deficit helps to prevent bone loss,but reducin g resorption depth is more effective in preventing loss of mechanical stiff ness.