Pathogenesis of Osteoporosis

Abstract

There has been a remarkable increase in research on osteoporosis during the last 2 decades. Clinical studies have characterized the primary osteoporotic syndromes and have resulted in a new classification (Riggs and Melton 1986). Laboratory studies have demonstrated many local factors which regulate bone metabolism, and this has led to the concept that local as well as systemic factors are important in pathogenesis (Raisz 1988). The mechanisms of secondary forms of osteoporosis have been explored. Nevertheless, there is still considerable controversy concerning pathogenesis, and there are many gaps in our knowledge. There has also been confusion concerning terminology. For the purpose of this chapter we will define “primary osteoporosis” as the condition in which there is a decrease in bone mass and strength leading to an increased frequency of fracture and which is not due to an associated disorder. The term “secondary osteoporosis” will be used for those patients with certain specific diseases or drug therapies which can cause bone loss and fractures. The term “osteopenia” will be used to describe conditions in which decreased bone mass has been found without a clear-cut association with fractures. While this usage avoids the problem of deciding whether or not there is a “fracture threshold,” it does not resolve it. There is as yet no agreement as to whether one can make a diagnosis of osteoporosis before fracture occurs, yet it seems obvious that the disease must have been present just prior to as well as after the fracture.