MECHANOTRANSDUCTION IN BONE - ROLE OF STRAIN-RATE

Bone tissue can detect and respond to Its mechanical environment, but there is no consensus for how bone cells detect mechanical loads. Some think that cells sense tissue deformation (strain) and respond when s train is abnormally high. However, strains in bone tissue are usually very small, and it is questionable whether bone cells are sensitive en ough to detect them. Another theory suggests that mechanical loads are coupled to the bone cells by stress-generated fluid flow within the b one tissue, which is dependent on the rate of change of bone strain. W e applied bending loads to the tibiae of adult rats to create equivale nt peak strains in the bone tissue but with varied rates of strain. Bo ne formation was significantly increased in the two experimental group s when the highest strain rates were compared with lower strain rates (P < 0.01), and the amount of new bone formation was directly proporti onal to the rate of strain in the bone tissue. These results suggest t hat relatively large strains alone are not sufficient to activate bone cells. High strain rates and possibly stress-generated fluid flow are required to stimulate new bone formation.