Osteoporosis

Osteoporosis is a systemic skeletal disorder characterized by decreased bone mass and deterioration of bony microarchitecture. The result is fragile bones and an increased risk for fracture with even minimal trauma. Osteoporosis is a chronic condition of multifactorial etiology and is usually clinically silent until a fracture occurs. Osteoporosis is a significant health problem in the United States and around the world.
Pathophysiology: Osteoporosis results from a combination of genetic and environmental factors that affect both peak bone mass and the rate of bone loss. These factors include medications, diet, race, sex, lifestyle, and physical activity. Osteoporosis may be either primary or secondary. Primary osteoporosis is subdivided into types 1 and 2. Secondary osteoporosis is also called type 3.
Type 1, or postmenopausal, osteoporosis is thought to result from gonadal (ie, estrogen, testosterone) deficiency. Estrogen or testosterone deficiency, regardless of age of occurrence, results in accelerated bone loss. The exact mechanisms of this bone loss potentially are numerous, but, ultimately, an increased recruitment and responsiveness of osteoclast precursors and an increase in bone resorption, which outpaces bone formation, occurs. After menopause, women experience an accelerated bone loss of 1-5% per year for the first 5-7 years. The end result is a decrease in trabecular bone and an increased risk of Colles and vertebral fractures.
Evidence indicates that estrogen deficiency causes bone to become more sensitive to the effects of parathyroid hormone (PTH), leading to an increase in calcium release from bone, a decrease in renal calcium excretion, and increased production of 1,25-dihydroxyvitamin D (1,25[OH]2 D3). Increased production of 1,25(OH)2 D3, in turn, causes increased calcium absorption from the gut, increased calcium resorption from bone, and increased renal tubular calcium resorption. PTH secretion then decreases via a negative feedback effect, causing the opposite effects. Osteoclasts are also influenced by cytokines, such as tumor necrosis factor-alpha and interleukins 1 and 6, whose production by mononuclear cells may be increased in the presence of gonadal deficiency.
Type 2, or senile, osteoporosis occurs in women and men because of decreased formation of bone and decreased renal production of 1,25(OH)2 D3 occurring late in life. The consequence is a loss of cortical and trabecular bone and increased risk for fractures of the hip, long bones, and vertebrae.
Type 3 osteoporosis occurs secondary to medications, especially glucocorticoids, or other conditions that cause increased bone loss by various mechanisms.
Frequency:
In the US: Approximately 10 million people have osteoporosis. Another 14-18 million have osteopenia (low bone mass).
Internationally: According to the International Osteoporosis Foundation, osteoporosis affects approximately 1 in 3 women and 1 in 8 men worldwide.
Mortality/Morbidity:
In Europe, an estimated 1 in 8 persons older than 50 years experiences a spinal fracture, and 1 in 3 women and 1 in 9 men older than 80 years experiences a hip fracture due to osteoporosis.
Approximately 1.5 million fractures per year in the United States are attributed to osteoporosis, and more than 37,000 people die from subsequent fracture-related complications. Among women who sustain a hip fracture, 50% spend time in a nursing home while recovering, and 14% of all patients with hip fractures remain in nursing homes 1 year later.
Only one third of patients return to their prefracture level of function. Patients incur a diminished quality of life and decreased independence in daily living.
Race: Whites, especially of northern European descent, and Asians are at increased risk for osteoporosis.
Sex: In type 1 and type 2 osteoporosis, women are affected more often than men, with female-to-male ratios of 6:2 and 2:1, respectively. In type 3, both sexes are equally affected.
Age: The peak incidence of type 1 osteoporosis is in people aged 50-70 years, and the peak incidence for type 2 is in people aged 70 years or older. Type 3 can occur in persons of any age.

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