Adaptive and Injury Response of Bone to Mechanical Loading.

Bone responds to supraphysiological mechanical loads by increasing bone formation. Depending on the applied strain magnitude (and other loading parameters) the response can be either adaptive (mostly lamellar bone) or injury (mostly woven bone). Seminal studies of Hert, Lanyon, and Rubin originally established the basic "rules" of bone mechanosensitivity. These were reinforced by subsequent studies using non-invasive rodent loading models, most notably by Turner et al. More recent work with these models have been able to explore the structural, transcriptional, and molecular mechanisms which distinguish the two responses (lamellar vs. woven). Wnt/Lrp signaling has emerged as a key mechanoresponsive pathway for lamellar bone. However, there is still much to study with regard to effects of ageing, osteocytes, other signaling pathways, and the molecular regulation that modulates lamellar vs. woven bone formation. This review summarizes not only the historical findings but also the current data for these topics.