Trabecular eccentricity and bone adaptation

It is well established that bones functionally adapt by mechanisms that con trol tissue density, whole bone geometry, and trabecular orientation. In th is study, we propose the existence of another such powerful mechanism, name ly, trabecular eccentricity, i.e. non-central placement of trabecular bone within a cortical envelope. In the human femoral neck, trabecular eccentric ity results in a thicker cortical shell on the inferior than superior aspec t. In an overall context of expanding understanding of bone adaptation, the goal of this study was to demonstrate the biomechanical significance of, a nd provide a mechanistic explanation for, the relationship between trabecul ar eccentricity and stresses in the human femoral neck. Using composite bea m theory, we showed that the biomechanical effects of eccentricity during a habitual loading situation were to increase the stress at the superior asp ect of the neck and decrease the stress at the inferior aspect, resulting i n an overall protective effect. Further, increasing eccentricity had a stre ss-reducing effect equivalent to that of increasing cortical thickness or i ncreasing trabecular modulus. We conclude that an asymmetric placement of t rabecular bone within a cortical bone envelope represents yet another mecha nism by which whole bones can adapt to mechanical demands. (C) 2001 Academi c Press.