## INTRODUCTION

Osteoporosis, a condition characterized by decreased bone strength, is prevalent among postmenopausal women but also occurs in both women and men as a function of age and with underlying conditions or major risk factors associated with loss of bone mass. Its chief clinical manifestations are vertebral and hip fractures, although fractures can occur at almost any skeletal site. Osteoporosis affects >10 million individuals in the United States, but only a proportion are diagnosed and treated.

## DEFINITION

Osteoporosis is defined as a reduction in the strength of bone that leads to an increased risk of fractures. Loss of bone tissue causes deterioration in skeletal microarchitecture, and thus, the process of bone loss causes a greater detriment to bone strength than might be appreciated from the simple measure of bone “density.” The World Health Organization (WHO) operationally defined osteoporosis as a bone density that falls 2.5 standard deviations (SDs) or more below the mean for young healthy adults of the same sex and race—also referred to as a T-score of –2.5. Postmenopausal women at the lower end of the young normal range (a T-score <–1.0) are defined as having low bone density and may be at increased risk of osteoporosis. Although fracture risk is lower in this group, >50% of fractures among postmenopausal women, including hip fractures, occur in those with low bone density as the numerical size of that population is larger than the group with bone density osteoporosis. As a consequence, clinical assessment has evolved to include an estimate of the risk of fracture, incorporating bone mineral density (BMD) with age, gender, and other clinical risk factors to allow a calculated 10-year risk of hip or major osteoporosis-related fracture. This has evolved into a second definition of osteoporosis with cut points for intervention that are variable across different geographies.

Osteoporosis-related fractures are defined as fractures of any bone in adults that occur in the setting of trauma less than or equal to a fall from standing height, with the exceptions of fingers, toes, face, and skull. However, in individuals thought to be at risk of osteoporosis, any traumatic fracture must be regarded as possibly indicative of an underlying skeletal problem, raising consideration of further evaluation.

## EPIDEMIOLOGY

In the United States, as many as 10.8 million women and 2.5 million men have osteoporosis (BMD T-score <–2.5 at lumbar spine, total hip, or femoral neck). This does not include additional people who present with an osteoporosis-related fracture but with low bone mass (T-score <–1 to –2.5). It is estimated that 2 million osteoporosis-related fractures occur each year in the United States at a cost of $19 billion, a problem that will increase as the population ages with an estimate of 3 million fractures and$25 billion in costs by 2025. The failure to identify the first fracture and intervene is estimated to cost \$6 ...

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