Principles in bone physiology.

The view that nonmechanical agents dominate control of osteoblasts and osteoclasts and thus postnatal changes in bone strength and mass (agent --> effector cells --> disease) is obsolete. Nonmechanical agents include hormones, calcium, vitamin D, cytokines, gender, genetics, etc. This paradigm overlooks all tissue level features, biomechanics and relationships found after 1960. This more recent information led to the Utah paradigm of skeletal physiology, proposed by Harold Frost in 1995. The Utah paradigm's view is that mechanical factors dominate control of the biologic mechanisms that control changes in postnatal bone and mass. Nonmechanical agents could help or hinder the influence of the mechanical factors but could not replace them. The simplified scheme is as follows: [reaction: see text] New evidence supports the Utah paradigm which we view as a supplement to many former views, not as a negation of them.