Osteoporosis is a silent disease that causes no symptoms until a fracture occurs. It is a major public health concern, with about 44 million American men and women, or 55% of the population age 50 and over, having osteoporosis or low bone density that can lead to fractures. About 80% of osteoporosis occurs in women and 20% in men. The prevalence is increasing, with over 61 million expected to have osteoporosis or low bone density by 2020.
Bone density and bone strength
Osteoporosis is defined as “a skeletal disease characterized by compromised bone strength predisposing a person to an increased risk of fracture. Bone strength primarily reflects the integration of bone density and quality.” Bone mineral density (BMD) correlates very well with fracture risk, with the relative risk of fracture approximately doubling (range 1.6–2.6) for every standard deviation decrease in BMD, depending on the skeletal site measured and the type of fracture . Many devices and technologies are available for measuring BMD. Dual-energy X-ray absorptiometry (DXA) is the method used to diagnose osteoporosis according to criteria established by the World Health Organization.
Classification of Bone Mineral Density (World Health Organization)
|Normal||-1.0 or greater|
|Osteopenia||Between -1.0 and -2.5|
|Osteoporosis||-2.5 or less|
|Severe Osteoporosis||-2.5 or less with a fragility fracture|
The WHO classification is founded on epidemiological data in postmenopausal Caucasian women with BMD measured at the spine, hip, and forearm. The prevalence of osteoporosis in this group is approximately 30%, which roughly corresponds to the lifetime risk of fragility fracture.
Non-BMD factors that may alter bone strength include bone turnover, architecture (size and shape, or bone geometry), microarchitecture, damage accumulation, matrix properties, mineralization, and mineral properties.
Bone density testing
The preferable method of diagnosing osteoporosis is by bone density testing, before the first fracture has occurred. The WHO criteria may be used to classify BMD, expressed as T-score, as normal, osteopenia, or osteoporosis.
A T-score is the standard deviation (SD) variance of the patient’s BMD compared to a healthy young-adult reference population. It is calculated according to the following formula, with BMD and SD expressed as g/cm2:
Who should be tested?
Bone density testing should be considered in anyone at risk for osteoporosis, or being monitored for treatment of osteoporosis, provided that the results of the test are likely to play a role in patient management decisions. Of all the published guidelines of indications for bone density testing, the most comprehensive are those of the International Society for Clinical Densitometry (ISCD) , listed in Table.
Evaluation of low bone density
It is prudent to have a high index of suspicion for contributing factors in every patient with low density. A T-score of -2.5 or below is not always osteoporosis. It could be metabolic bone disease, such as osteomalacia, or a localized bone disorder, such as a bone cyst in the measured skeletal site. A postmenopausal woman with osteoporosis does not always have postmenopausal osteoporosis. She could have malabsorption due to undiagnosed celiac disease, or possibly multiple myeloma. Table lists diseases, conditions, and medications commonly associated with low bone density.
Prevention and treatment
Nonpharmacologic therapy can be divided into the categories of nutrition, lifestyle, and fall prevention. These represent the foundation for the management of osteoporosis, without which patients are unlikely to achieve the full benefit of pharmacologic therapy. Calcium and vitamin D supplementation have been shown to increase BMD and reduce the risk of fractures in prospective trials.
Indications for Pharmacologic Therapy.
|National Osteoporosis Foundation|
|Initiate therapy to reduce fracture risk in women with:|
|1. BMD T-scores below -2.0 by central DXA with no risk factors|
|2. BMD T-scores below -1.5 by central DXA with one or more risk factors|
|3. A prior vertebral or hip fracture|
|The following women may benefit from pharmacologic treatment of osteoporosis:|
|1. Women with postmenopausal osteoporosis (Women with low-trauma fractures and low BMD and women with BMD T-scores of -2.5 and below)|
|2. Women with borderline low BMD (e.g., T-scores of -1.5 and below) if risk factors are present|
|3. Women in whom nonpharmacologic preventive measures are ineffective (bone loss continues or low trauma fractures occur)|
These recommendations are very similar, with the main difference being the T-score cut-off for treatment in patients with no other risk factors.
The medications that are FDA-approved for the management of osteoporosis may be divided into antiresorptive agents (estrogen, alendronate, risedronate, and calcitonin) and anabolic agents, of which there is now only one-teriparatide. These agents can be expected to stabilize or increase BMD and reduce fracture risk by approximately 50% in most patients. All of the FDA-approved medications have been shown to reduce the risk of vertebral fractures, while only estrogen, alendronate, and risedronate have reduced the risk of hip fractures in prospective clinical trials.
Teriparatide, human recombinant 1–34 parathyroid hormone, is approved for use in women and men at high risk for fracture. Despite its greater expense and the inconvenience of daily subcutaneous injections for a 2-year course of therapy, this agent is a welcome addition to the pharmacologic armamentarium for selected patients. Current evidence suggests that there is no added benefit to combining teriparatide with alendronate, but giving a bisphosphonate following a course of treatment with teriparatide may serve to preserve the bone mass previously gained.