Osteoporosis

Dual energy X-ray absorptiometry

noreply@blogger.com (health victorro) — Mon, 26 Jan 2009 14:02:00 +0000

Dual energy X-ray absorptiometry (DXA, formerly DEXA) is considered the gold standard for the diagnosis of osteoporosis. Osteoporosis is diagnosed when the bone mineral density is less than or equal to 2.5 standard deviations below that of a young adult reference population. This is translated as a T-score. The World Health Organization has established the following diagnostic guidelines:

* 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.

The International Society for Clinical Densitometry takes the position that a diagnosis of osteoporosis in men under 50 years of age should not be made on the basis of densitometric criteria alone. It also states that for pre-menopausal women, Z-scores (comparison with age group rather than peak bone mass) rather than T-scores should be used, and that the diagnosis of osteoporosis in such women also should not be made on the basis of densitometric criteria alone.

Screening

noreply@blogger.com (health victorro) — Mon, 26 Jan 2009 14:01:00 +0000

The 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.

Pathogenesis

noreply@blogger.com (health victorro) — Mon, 26 Jan 2009 13:58:00 +0000

The 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. Hormonal factors strongly determine the rate of bone resorption; lack of estrogen (e.g. as a result of menopause) increases bone resorption as well as decreasing the deposition of new bone that normally takes place in weight-bearing bones. The amount of estrogen needed to suppress this process is lower than that normally needed to stimulate the uterus and breast gland. The α-form of the estrogen receptor appears to be the most important in regulating bone turnover. In addition to estrogen, calcium metabolism plays a significant role in bone turnover, and deficiency of calcium and vitamin D leads to impaired bone deposition; in addition, the parathyroid glands react to low calcium levels by secreting parathyroid hormone (parathormone, PTH), which increases bone resorption to ensure sufficient calcium in the blood. The role of calcitonin, a hormone generated by the thyroid that increases bone deposition, is less clear and probably not as significant as that of PTH.

The activation of osteoclasts is regulated by various molecular signals, of which RANKL (receptor activator for nuclear factor κB ligand) is one of best studied. This molecule is produced by osteoblasts and other cells (e.g. lymphocytes), and stimulates RANK (receptor activator of nuclear factor κB). Osteoprotegerin (OPG) binds RANKL before it has an opportunity to bind to RANK, and hence suppresses its ability to increase bone resorption. RANKL, RANK and OPG are closely related to tumor necrosis factor and its receptors. The role of the wnt signalling pathway is recognized but less well understood. Local production of eicosanoids and interleukins is thought to participate in the regulation of bone turnover, and excess or reduced production of these mediators may underlie the development of osteoporosis.

Trabecular bone is the sponge-like bone in the ends of long bones and vertebrae. Cortical bone is the hard outer shell of bones and the middle of long bones. Because osteoblasts and osteoclasts inhabit the surface of bones, trabecular bone is more active, more subject to bone turnover, to remodeling. Not only is bone density decreased, but the microarchitecture of bone is disrupted. The weaker spicules of trabecular bone break ("microcracks"), and are replaced by weaker bone. Common osteoporotic fracture sites, the wrist, the hip and the spine, have a relatively high trabecular bone to cortical bone ratio. These areas rely on trabecular bone for strength, and therefore the intense remodeling causes these areas to degenerate most when the remodeling is imbalanced.[citation needed]

Nutrition

noreply@blogger.com (health victorro) — Mon, 26 Jan 2009 13:57:00 +0000

Calcium

Calcium is required to support bone growth, bone healing and maintain bone strength and is one aspect of treatment for osteoporosis. Recommendations for calcium intake vary depending country and age; for individuals at higher risk of osteoporosis (after fifty years of age) the amount recommended by US health agencies is 1,200 mg per day. Calcium supplements can be used to increase dietary intake, and absorption is optimized through taking in several small (500 mg or less) doses throughout the day. 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.In the report of WHO (World Health Organization) in 2007, because calcium is consumed by an acid load with food, it influences 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.

Vitamin D

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.

Exercise

noreply@blogger.com (health victorro) — Mon, 26 Jan 2009 13:54:00 +0000

Multiple 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.