Effects of mechanical forces on maintenance and adaptation of form in trabecular bone

The architecture of trabecular bone, the porous bone found in the spine and at articulating joints, provides the requirements for optimal load transfer, by pairing suitable strength and stiffness to minimal weight according to rules of mathematical design. But, as it is unlikely that the architecture is fully pre-programmed in the genes, how are the bone cells informed about these rules, which so obviously dictate architecture? A relationship exists between bone architecture and mechanical usage while strenuous exercise increases bone mass9, disuse, as in microgravity and inactivity, reduces it. Bone resorption cells (osteoclasts) and bone formation cells (osteoblasts) normally balance bone mass in a coupled homeostatic process of remodelling, which renews some 25% of trabecular bone volume per year. Here we present a computational model of the metabolic process in bone that confirms that cell coupling is governed by feedback from mechanical load transfer.This model can explain the emergence and maintenance of trabecular architecture as an optimal mechanical structure, as well as its adaptation to alternative external loads

Trabecular merging into cortical bone under the growth plate during growth is regulated by mechanical load transfer

Poster 0406

Mechanically induced osteocyte signals explain osteoclast resorption direction and coupling of formation to resorption in Basic Multi-cellular Units

(Poster ; 30 : 1642

Relating osteon diameter to strain

Osteon diameter is generally smaller in bone regions that experience larger strains. A mechanism relating osteon diameter to strain is as yet unknown. We propose that strain-induced osteocyte signals inhibit osteoclastic bone resorption. This mechanism was previously shown to produce load-aligned osteons in computer simulations. Now we find that it also predicts smaller osteon diameter for higher loads. Additionally, we find that our model predicts osteon development with two cutting cones, one moving up and one moving down the loading axis. Such ‘double-ended osteons’ were reported in literature as a common type of osteon development. Further, we find that a steep gradient in strain magnitude can result in an osteonal tunnel with continuous resorption along the less strained side, which corresponds to ‘drifting osteons’ reported in literature