Introduction

Senile osteoporosis consists of a metabolic bone disease characterized by low bone mass and microarchitectural deterioration of the skeleton, leading to enhanced bone fragility and a consequent increase in fracture risk. It is estimated that 1.5 million fractures attributable to osteoporosis occur annually in the United States, incurring a total cost estimated at 13.8 billion dollars in 1995 alone (Ray et al., 1997). Hip fracture is the most costly and catastrophic of the osteoporotic complications; about 25% of these patients have a fatal outcome, half of the survivors are unable to walk unassisted, and a quarter become confined to a long-term care institution. However, other types of osteoporotic fractures can also cause considerable functional impairment (Ray et al., 1997).

Although osteoporosis is more common in women, men also sustain substantial bone loss with aging (Riggs & Melton, 1986), and elderly men have age-specific hip and vertebral fracture rates that are at least half those in women (Melton, 1995). Thus, senile osteoporosis has significant clinical and economic consequences in both men and women, and the seriousness of this problem is being further magnified by the aging of the postwar generation. This chapter describes the role played by bone resorption and its relationship to reduced levels of sex steroids in both male and female osteoporosis.