The role of periosteum : a neglected aspect of osteoporosis

Most current studies on the pathogenesis of osteoporosis emphasize the bone metabolic activities occurring on endosteal surfaces, whereas the periosteal aspect is somewhat neglected. In terms of bone physiology, periosteum plays a determining role in de novo cortical bone formation and cortical bone expansion through periosteum is the most efficient way of increasing bone strength against fractures. Despite the important role of periosteum in the pathogenesis and treatment of osteoporosis, little is known about the structural and cellular features of periosteum in osteoporosis. This chapter will focus on the major changes occurring in the periosteum of osteoporosis and possible implications of these changes in the pathogenesis of osteoporosis. The changes identified in the periosteum of osteoporosis are mainly located in the metaphyseal compartment, which include: (a) much thicker and more cellular cambial layer; (b) increased number of TRAP (tartrate resistant acid phosphatase), VEGF (vascular endothelial growth factor) cells and the degree of vascularization; and (c) enhanced expression of sympathetic nerve fibers. The structural and cellular changes of osteoporotic periosteum indicate that periosteum plays an important role in the cortical bone resorption in metaphyseal areas and this pathological process may be regulated by the sympathetic nervous system.