Figure 1.

Force displacement curve of a bone. (A) Treatment with an ideal osteoporosis drug improves bone fragility by increasing both of the force and displacement at failure (23). X denotes fracture. (B) The curve would consist of the pre-yield “elastic” deformation associated with mineral and the post-yield “plastic” deformation associated with collagen. Consequently, mechanical strain-related feedback control, the mechanostat, could work against mineral-related, but not collagen-related, impairment of bone quality. X denotes fracture. (C) The pre-yield “elastic” deformation can be modified by osteoporosis therapy that (i) directly enhances the response to mechanical loading and increases the slope of the curve (upper) or (ii) lowers mineral-related bone quality and results in compensatory bone gain by the mechanostat to maintain the slope of the curve (lower). Note that, in the latter case, the yield force can be increased if compensated efficiently.