The term osteoporosis was first introduced in the nineteenth century based on histological diagnosis (“porous bone”). Osteoporosis is a “disease characterized by low bone mass and microarchitectural deterioration of bone tissue leading to enhanced bone fragility and a consequent increase in fracture incidence.” Osteoporosis can be defined either by the presence of a fragility fracture or by bone mineral density (BMD) measurement. In defining BMD criteria for osteoporosis, the World Health Organization (WHO) used as the standard the BMD of young adult women who are at the age of peak bone mass. For each standard deviation below peak bone mass (or 1 unit decrease in T-score), a woman's risk of fracture approximately doubles. As seen in Table 117-1, a T-score <−2.5 defines osteoporosis; osteopenia (low bone mass) and normal bone mass are also defined. A BMD measurement allows early diagnosis of osteoporosis and intervention prior to fracture in older adults. In addition, women with osteopenia can be followed carefully for further bone loss. Although the original standards for definitions of osteoporosis were determined in white women, recent data indicate that the standards for men and Hispanic women are probably similar to those of white women. In addition, standards are now being developed for African-American women. However, defining osteoporosis solely by T-score does not effectively capture all patients at risk of a fracture. Greater than 50% of all hip fractures occur in those with T-scores that are better than −2.5. Failure to evaluate and treat such patients adds to the individual and societal cost and consequences of osteoporosis. Therefore, we are still faced with the challenge of improving the identification of the individual patient at risk of fracture and subsequently optimizing both prevention and treatment for the elderly.
Table 117-1 World Health Organization Criteria for Osteoporosis ||Download (.pdf)
Table 117-1 World Health Organization Criteria for Osteoporosis
≤1 but >−2.5
≤−2.5 + fragility fracture
Primary or idiopathic osteoporosis has been historically classified as postmenopausal or senile osteoporosis. Postmenopausal osteoporosis, formerly known as type I, occurs in women between 51 and 75 years of age and is related to estrogen deficiency seen with the menopausal transition. In contrast, senile osteoporosis typically occurs in persons older than 60 years of age. It affects both men and women and has a different pathophysiology, which involves reduced levels of bone turnover owing to a reduction in the numbers of bone-forming cells. Increasing evidence points to a progressive age-related alteration in stem cell physiology that favors adipogenesis and thereby reduces osteoblastogenesis and bone formation. Nevertheless, estrogen probably plays a role in the pathophysiology of senile osteoporosis as well. Secondary osteoporosis is the result of an underlying disease or medications that adversely affect bone. In this chapter, we will focus on the typical characteristics of senile osteoporosis from its pathophysiology to therapeutic approaches.