Chapter 3: Osteoporosis

INTRODUCTION

• Osteoporosis is a bone disorder characterized by low bone density, impaired bone architecture, and compromised bone strength predisposing to fracture.

PATHOPHYSIOLOGY

• Bone loss occurs when resorption exceeds formation, usually from high bone turnover when the number or depth of bone resorption sites greatly exceeds the ability of osteoblasts to form new bone. Accelerated bone turnover can increase the amount of immature bone that is not adequately mineralized.

• Men and women begin to lose bone mass starting in the third or fourth decade because of reduced bone formation. Estrogen deficiency during menopause increases osteoclast activity, increasing bone resorption more than formation. Men are at a lower risk for developing osteoporosis and osteoporotic fractures because of larger bone size, greater peak bone mass, increase in bone width with aging, fewer falls, and shorter life expectancy. Male osteoporosis results from aging or secondary causes.

• Age-related osteoporosis results from hormone, calcium, and vitamin D deficiencies leading to accelerated bone turnover and reduced osteoblast formation.

• Drug-induced osteoporosis may result from systemic corticosteroids, thyroid hormone replacement, antiepileptic drugs (eg, phenytoin and phenobarbital), depot medroxyprogesterone acetate, and other agents.

CLINICAL PRESENTATION

• Many patients are unaware that they have osteoporosis and only present after fracture. Fractures can occur after bending, lifting, or falling or independent of any activity.

• The most common fractures involve vertebrae, proximal femur, and distal radius (wrist or Colles fracture). Vertebral fractures may be asymptomatic or present with moderate to severe back pain that radiates down a leg. Pain usually subsides after 2 to 4 weeks, but residual back pain may persist. Multiple vertebral fractures decrease height and sometimes curve the spine (kyphosis or lordosis).

• Patients with a nonvertebral fracture frequently present with severe pain, swelling, and reduced function and mobility at the fracture site.

DIAGNOSIS

• The World Health Organization (WHO) created the FRAX tool, which uses these risk factors to predict the percent probability of fracture in the next 10 years: age, race/ethnicity, sex, previous fragility fracture, parent history of hip fracture, body mass index, glucocorticoid use, current smoking, alcohol (three or more drinks per day), rheumatoid arthritis, and select secondary causes with femoral neck or total hip bone mineral density (BMD) data optional.

• The Garvan calculator uses four risk factors (age, sex, low-trauma fracture, and falls) with the option to also use BMD. It calculates 5- and 10-year risk estimates of any major osteoporotic and hip fracture. This tool corrects some disadvantages of FRAX because it includes falls and number of previous fractures, but it does not use as many other risk factors.

• Physical examination findings: bone pain, postural changes (ie, kyphosis), and loss of height (>1.5 in [3.8 cm]).

• Laboratory testing: complete blood count, creatinine, blood urea nitrogen, calcium, phosphorus, electrolytes, alkaline phosphatase, albumin, thyroid-stimulating hormone, total testosterone (for men), 25-hydroxyvitamin D, and 24-hour urine concentrations of calcium and ...