osteoporosis n : abnormal loss of bony tissue resulting in fragile porous bones attributable to a lack of calcium; most common in postmenopausal women
Osteoporosis is a disease of bone that leads to an increased risk of fracture. In osteoporosis the bone mineral density (BMD) is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered. Osteoporosis is defined by the World Health Organization (WHO) in women as a bone mineral density 2.5 standard deviations below peak bone mass (20-year-old healthy female average) as measured by DXA; the term "established osteoporosis" includes the presence of a fragility fracture. Osteoporosis is most common in women after menopause, when it is called postmenopausal osteoporosis, but may also develop in men, and may occur in anyone in the presence of particular hormonal disorders and other chronic diseases or as a result of medications, specifically glucocorticoids, when the disease is called steroid- or glucocorticoid-induced osteoporosis (SIOP or GIOP). Given its influence on the risk of fragility fracture, osteoporosis may significantly affect life expectancy and quality of life.
Osteoporosis can be prevented with lifestyle advice and sometimes medication, and in people with osteoporosis treatment may involve lifestyle advice, preventing falls and medication (calcium, vitamin D, bisphosphonates and several others).
Signs and symptomsOsteoporosis itself has no specific symptoms; its main consequence is the increased risk of bone fractures. Osteoporotic fractures are those that occur in situations where healthy people would not normally break a bone; they are therefore regarded as fragility fractures. Typical fragility fractures occur in the vertebral column, rib, hip and wrist.
FracturesThe symptoms of a vertebral collapse ("compression fracture") are sudden back pain, often with radiculopathic pain (shooting pain due to nerve compression ) and rarely with spinal cord compression or cauda equina syndrome. Multiple vertebral fractures lead to a stooped posture, loss of height, and chronic pain with resultant reduction in mobility.
Fractures of the long bones acutely impair mobility and may require surgery. Hip fracture, in particular, usually requires prompt surgery, as there are serious risks associated with a hip fracture, such as deep vein thrombosis and a pulmonary embolism, and increased mortality.
Falls riskThe increased risk of falling associated with aging leads to fractures of the wrist, spine and hip. The risk of falling, in turn, is increased by impaired eyesight due to any cause (e.g. glaucoma, macular degeneration), balance disorder, movement disorders (e.g. Parkinson's disease), dementia, and sarcopenia (age-related loss of skeletal muscle). Collapse (transient loss of postural tone with or without loss of consciousness) leads to a significant risk of falls; causes of syncope are manifold but may include cardiac arrhythmias (irregular heart beat), vasovagal syncope, orthostatic hypotension (abnormal drop in blood pressure on standing up) and seizures. Removal of obstacles and loose carpets in the living environment may substantially reduce falls. Those with previous falls, as well as those with a gait or balance disorder, are most at risk.
Risk factorsRisk factors for osteoporotic fracture can be split between non-modifiable and (potentially) modifiable. In addition, there are specific diseases and disorders in which osteoporosis is a recognized complication. Medication use is theoretically modifiable, although in many cases the use of medication that increases osteoporosis risk is unavoidable.
NonmodifiableThe most important risk factors for osteoporosis are advanced age (in both men and women) and female sex; estrogen deficiency following menopause is correlated with a rapid reduction in BMD, while in men a decrease in testosterone levels has a comparable (but less pronounced) effect. While osteoporosis occurs in people from all ethnic groups, European or Asian ancestry predisposes for osteoporosis. Those with a family history of fracture or osteoporosis are at an increased risk; the heritability of the fracture as well as low bone mineral density are relatively high, ranging from 25 to 80 percent. There are at least 30 genes associated with the development of osteoporosis.
- Excess alcohol - small amounts of alcohol do not increase osteoporosis risk and may even be beneficial, but chronic heavy drinking(Alcohol intake greather than ≥ 3 units/day), especially at a younger age, increases risk significantly.
- Vitamin D deficiency - low circulating Vitamin D is a common among the elderly world wide. Smoking also results in increased breakdown of exogenous oestrogen, lower body weight and earlier menopause, all of which contribute to lower bone mineral density.
- Malnutrition - low dietary calcium intake, low dietary intake of vitamins K and vitamin c
- Soft drinks - some studies indicate that soft drinks (many of which contain phosphoric acid) may increase risk of osteoporosis; others suggest soft drinks may displace calcium-containing drinks from the diet rather than directly causing osteoporosis.
Diseases and disordersMany diseases and disorders have been associated with osteoporosis. For some, the underlying mechanism influencing the bone metabolism is straight-forward, whereas for others the causes are multiple or unknown.
- In general, immobilization causes bone loss (following the 'use it or lose it' rule). For example, localized osteoporosis can occur after prolonged immobilization of a fractured limb in a cast. This is also more common in active patients with a high bone turn-over (for example, athletes). Other examples include bone loss during space flight or in people who are bedridden or wheelchair-bound for various reasons.
- Hypogonadal states can cause secondary osteoporosis. These include Turner syndrome, Klinefelter syndrome, Kallmann syndrome, anorexia nervosa, andropause acromegaly and adrenal insufficiency. In pregnancy and lactation, there can be a reversible bone loss. , systemic lupus erythematosus and polyarticular juvenile idiopathic arthritis are at increased risk of osteoporosis, either as part of their disease or because of other risk factors (notably corticosteroid therapy). Systemic diseases such as amyloidosis and sarcoidosis can also lead to osteoporosis.
- Renal insufficiency can lead to osteodystrophy.
- Hematologic disorders linked to osteoporosis are multiple myeloma Alternate day use may not prevent this complication.
- Barbiturates, phenytoin and some other enzyme-inducing antiepileptics - these probably accelerate the metabolism of vitamin D.
- L-Thyroxine over-replacement may contribute to osteoporosis, in a similar fashion as thyrotoxicosis does. and warfarin (and related coumarins) have been linked with an increased risk in osteoporotic fracture in long-term use.
- Proton pump inhibitors - these drugs inhibit the production of stomach acid; it is thought that this interferes with calcium absorption. Chronic phosphate binding may also occur with aluminum-containing antacids.
- Chronic lithium therapy has been associated with osteoporosis.
- T-score -1.0 or greater is "normal"
- T-score between -1.0 and -2.5 is "low bone mass" (or "osteopenia")
- T-score -2.5 or below is osteoporosis
When there has also been an osteoporotic fracture (also termed "low trauma-fracture" or "fragility fracture"), defined as one that occurs as a result of a fall from a standing height, the term "severe or established" osteoporosis is used.
ScreeningThe U.S. Preventive Services Task Force (USPSTF) recommended in 2002 that all women 65 years of age or older should be screened with bone densitometry. The Task Force recommends screening only those women ages 60 to 64 years of age who are at increased risk. The best risk factor for indicating increased risk is lower body weight (weight < 70 kg), with less evidence for smoking or family history. There was insufficient evidence to make recommendations about the optimal intervals for repeated screening and the appropriate age to stop screening. Clinical prediction rules are available to guide selection of women ages 60-64 for screening. The Osteoporosis Risk Assessment Instrument (ORAI) may be the most sensitive strategy
Regarding the screening of men, a cost-analysis study suggests that screening may be "cost-effective for men with a self-reported prior fracture beginning at age 65 years and for men 80 years and older with no prior fracture". Also cost-effective is the screening of adult men from middle age on to detect any significant decrease in testosterone levels, say, below 300.
PathogenesisThe underlying mechanism in all cases of osteoporosis is an imbalance between bone resorption and bone formation. In normal bone, there is constant matrix remodeling of bone; up to 10% of all bone mass may be undergoing remodeling at any point in time. The process takes place in bone multicellular units (BMUs) as first described by Frost in 1963. Bone is resorbed by osteoclast cells (which derive from the bone marrow), after which new bone is deposited by osteoblast cells.
The three main mechanisms by which osteoporosis develops are an inadequate peak bone mass (the skeleton develops insufficient mass and strength during growth), excessive bone resorption and inadequate formation of new bone during remodeling. An interplay of these three mechanisms underlies the development of fragile bone tissue.
Oral bisphosphonates are relatively poorly absorbed, and must therefore be taken on an empty stomach, with no food or drink to follow for the next 30 minutes. They are associated with esophagitis and are therefore sometimes poorly tolerated; weekly or monthly administration (depending on the preparation) decreases likelihood of esophagitis, and is now standard. Although intermittent dosing with the intravenous formulations such as zolendronate avoids oral tolerance problems, these agents are implicated at higher rates in a rare but unpleasant mouth disease called osteonecrosis of the jaw. For this reason, oral bisphosphonate therapy is probably to be preferred, and prescribing advice now recommends any remedial dental work to be carried out prior to commencing treatment. Recently, teriparatide (Forteo, recombinant parathyroid hormone residues 1–34) has been shown to be effective in osteoporosis. It acts like parathyroid hormone and stimulates osteoblasts, thus increasing their activity. It is used mostly for patients with established osteoporosis (who have already fractured), have particularly low BMD or several risk factors for fracture or cannot tolerate the oral bisphosphonates. It is given as a daily injection with the use of a pen-type injection device. Teriparatide is only licensed for treatment if bisphosphonates have failed or are contraindicated (however, this differs by country and is not required by the FDA in the USA. However, patients with previous radiation therapy, or Paget's disease, or young patients should avoid this medication). Oral strontium ranelate is an alternative oral treatment, belonging to a class of drugs called "dual action bone agents" (DABAs) by its manufacturer. It has proven efficacy, especially in the prevention of vertebral fracture. In laboratory experiments, strontium ranelate was noted to stimulate the proliferation of osteoblasts, as well as inhibiting the proliferation of osteoclasts.
Strontium ranelate is taken as a 2 g oral suspension daily, and is licenced for the treatment of osteoporosis to prevent vertebral and hip fracture. Strontium ranelate has side effect benefits over the bisphosphonates, as it does not cause any form of upper GI side effect, which is the most common cause for medication withdrawal in osteoporosis. In studies a small increase in the risk of venous thromboembolism was noted, the cause for which has not been determined. This suggests it may be less suitable in patients at risk for thrombosis for different reasons. The uptake of (heavier) strontium in place of calcium into bone matrix results in a substantial and disproportionate increase in bone mineral density as measured on DXA scanning, making further followup of bone density by this method harder to interpret for strontium treated patients. A correction algorithm has been devised.
Although strontium ranelate is effective, it's not approved for use in the United States yet. However, strontium citrate is available in the U.S. from several well-known vitamin manufacturers. Most researchers believe that strontium is safe and effective no matter what form it's used. The ranelate form is simply a device invented by the Servier company of France so that they could patent their version of strontium.
Strontium, no matter what the form, must be water-soluble and ionized in the stomach acid. Stontium is then protein-bound for transport from the intestinal tract into the blood stream. Unlike drugs like Fosamax, strontium doesn't inhibit bone recycling and, in fact, may produce stronger bones. Studies have shown that after five years alendronate may even cause bone loss, while strontium continues to build bone during lifetime use.
Strontium must not be taken with food or calcium-containing preparations as calcium competes with strontium during uptake. However, it's essential that calcium, magnesium, and vitamin D in theraputic amounts must be taken daily, but not at the same time as strontium. Strontium should be taken on an empty stomach at night. Estrogen replacement therapy remains a good treatment for prevention of osteoporosis but, at this time, is not recommended unless there are other indications for its use as well. There is uncertainty and controversy about whether estrogen should be recommended in women in the first decade after the menopause.
In hypogonadal men testosterone has been shown to give improvement in bone quantity and quality, but, as of 2008, there are no studies of the effects on fractures or in men with a normal testosterone level. The role of calcium in preventing and treating osteoporosis is unclear - some populations with extremely low calcium intake also have extremely low rates of bone fracture, and others with high rates of calcium intake through milk and milk products have higher rates of bone fracture. Other factors, such as protein, salt and vitamin D intake, exercise and exposure to sunlight, can all influence bone mineralization, making calcium intake one factor among many in the development of osteoporosis.
A meta-analysis of randomized controlled trials involving calcium and calcium plus vitamin D supported the use of high levels of calcium (1,200 mg or more) and vitamin D (800 IU or more), though outcomes varied depending on which measure was used to assess bone health (rates of fracture versus rates of bone loss). The meta-analysis, along with another study, also supported much better outcomes for patients with high compliance to the treatment protocol. In contrast, despite earlier reports in improved high density lipoprotein (HDL, "good cholesterol") in calcium supplementation, a possible increase in the rate of myocardial infarction (heart attack) was found in a study in New Zealand in which 1471 women participated. If confirmed, this would indicate that calcium supplementation in women otherwise at low risk of fracture may cause more harm than good. Some studies have shown that a high intake of vitamin D reduces fractures in the elderly, though the Women's Health Initiative found that though calcium plus vitamin D did increase bone density, it did not affect hip fracture but did increase formation of kidney stones.
Mechanical stimulationMultiple studies have shown that aerobics, weight bearing, and resistance exercises can all maintain or increase BMD in postmenopausal women. Many researchers have attempted to pinpoint which types of exercise are most effective at improving BMD and other metrics of bone quality, however results have varied. One year of regular jumping exercises appears to increase the BMD and moment of inertia of the proximal tibia in normal postmenopausal women. Treadmill walking, gymnastic training, stepping, jumping, endurance, and strength exercises all resulted in significant increases of L2-L4 BMD in osteopenic postmenopausal women. Strength training elicited improvements specifically in distal radius and hip BMD. Exercise combined with other pharmacological treatments such as hormone replacement therapy (HRT) has been shown to increases BMD more than HRT alone.
Additional benefits for osteoporotic patients other than BMD increase include improvements in balance, gait, and a reduction in risk of falls. Low-level high-frequency mechanical signals have been studied as signals stimulating bone turnover. Studies in animals show that this form of 'passive exercise' results in increased bone strength. Preliminary studies in humans (using for example vibrating platforms to produce whole body vibration) indicate that they might prevent BMD loss.
PrognosisAlthough osteoporosis patients have an increased mortality rate due to the complications of fracture, most patients die with the disease rather than of it.
Hip fractures can lead to decreased mobility and an additional risk of numerous complications (such as deep venous thrombosis and/or pulmonary embolism, pneumonia). The 6-month mortality rate following hip fracture is approximately 13.5%, and a substantial proportion (almost 13%) of people who have suffered a hip fracture need total assistance to mobilize after a hip fracture.
Vertebral fractures, while having a smaller impact on mortality, can lead to severe chronic pain of neurogenic origin, which can be hard to control, as well as deformity. Though rare, multiple vertebral fractures can lead to such severe hunch back (kyphosis) that the resulting pressure on internal organs can impair one's ability to breathe.
Apart from risk of death and other complications, osteoporotic fractures are associated with a reduced health-related quality of life.
It is estimated that 1 in 3 women and 1 in 12 men over the age of 50 worldwide have osteoporosis. It is responsible for millions of fractures annually, mostly involving the lumbar vertebrae, hip, and wrist. Fragility fractures of ribs are also common in men.
Hip fractures are responsible for the most serious consequences of osteoporosis. In the United States, osteoporosis causes a predisposition to hip fractures -- more than 250,000 occur annually. It is estimated that a 50-year-old white woman has a 17.5% lifetime risk of fracture of the proximal femur. The incidence of hip fractures increases each decade from the sixth through the ninth for both women and men for all populations. The highest incidence is found among those men and women ages 80 or older.
Between 35-50% of all women over 50 had at least one vertebral fracture. In the United States, 700,000 vertebral fractures occur annually, but only about a third are recognized. In a series of 9704 of women aged 68.8 on average studied for 15 years, 324 had already suffered a vertebral fracture at entry into the study; 18.2% developed a vertebral fracture, but that risk rose to 41.4% in women who had a previous vertebral fracture.
Distal radius fracturesDistal radius fractures, usually of the Colles type, are the third most common type of osteoporotic fractures. In the United States, the total annual number of Colles' fractures is about 250,000. The lifetime risk of sustaining a Colles' fracture is about 16% for white women. By the time women reach age 70, about 20% have had at least one wrist fracture.
Rib FracturesFragility fractures of the ribs are common in men as young as age thirty-five on. These are often overlooked as signs of osteoporosis as these men are often physically active and suffer the fracture in the course of physical activity. An example would be as a result of falling while water skiing or jet skiing. However, a quick test of the individual's testosterone level following the diagnosis of the fracture will readily reveal whether that individual might be at risk.
PreventionMethods to prevent osteoporosis include changes of lifestyle. However, there are medications that can be used for prevention as well. As a different concept there are osteoporosis ortheses which help to prevent spine fractions and support the building up of muscles. Fall prevention can help prevent osteoporosis complications.
LifestyleLifestyle prevention of osteoporosis is in many aspects inversions from potentially modifiable risk factors. As tobacco smoking and unsafe alcohol intake have been linked with osteoporosis, smoking cessation and moderation of alcohol intake are commonly recommended in the prevention of osteoporosis. Achieving a higher peak bone mass through exercise and proper nutrition during adolescence is important for the prevention of osteoporosis. Exercise and nutrition throughout the rest of the life delays bone degeneration. Jogging, walking, or stair climbing at 70-90% of maximum effort three times per week, along with 1,500 mg of calcium per day, increased bone density of the lumbar (lower) spine by 5% over 9 months. Individuals already diagnosed with osteopenia or osteoporosis should discuss their exercise program with their physician to avoid fractures. A proper nutrition is a diet sufficient in calcium and vitamin D. Patients at risk for osteoporosis (e.g. steroid use) are generally treated with vitamin D and calcium supplements and often with bisphosphonates. In renal disease, more active forms of Vitamin D such as paracalcitol or (1,25-dihydroxycholecalciferol or calcitriol which is the main biologically active form of vitamin D) is used, as the kidney cannot adequately generate calcitriol from calcidiol (25-hydroxycholecalciferol) which is the storage form of vitamin D.
High dietary protein intake increases calcium excretion in urine and has been linked to increased risk of fractures in research studies. Other investigations have shown that protein is required for calcium absorption, but that excessive protein consumption inhibits this process. No interventional trials have been performed on dietary protein in the prevention and treatment of osteoporosis.
MedicationJust as for treatment, bisphosphonate can be used in cases of very high risk. Other medicines prescribed for prevention of osteoporosis include raloxifene (Evista), a selective estrogen receptor modulator (SERM).
Estrogen replacement therapy remains a good treatment for prevention of osteoporosis but, at this time, is not recommended unless there are other indications for its use as well. There is uncertainty and controversy about whether estrogen should be recommended in women in the first decade after the menopause.
In hypogonadal men testosterone has been shown to give improvement in bone quantity and quality, but, as of 2008, there are no studies of the effects on fractures or in men with a normal testosterone level. The American endocrinolgist Fuller Albright linked osteoporosis with the postmenopausal state. Bisphosponates, which revolutionized the treatment of osteoporosis, were discovered in the 1960s.
- Osteoporosis risk assessment tools
- Diet, Nutrition and the prevention of osteoporosis the World Health Organization and Food and Agriculture Organization (2003)
- Bone Health and Osteoporosis: A Report of the Surgeon General distributed by the U.S. Department of Health and Human Services
- http://www.nof.org The National Osteoporosis Foundation
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