Related Info
Glossary
- Accuracy:
- the ability of measurements to reflect the true bone density value.
- Activities of daily living (ADL):
- basic activities, such as dressing, washing, and using the toilet.
- Alendronate:
- a bisphosphonate approved by the U.S. Food and Drug Administration for treatment and prevention of osteoporosis; accumulates and persists in the bone. Studies indicate about a 50 percent reduction in fractures of the vertebra, hip, and wrist. Proprietary name: Fosamax (Merck and Company, Inc.)
back to top- Bisphosphonates:
- analogues of pyrophosphate (P-O-P) in which the oxygen of the pyrophosphate is replaced with carbon (P-C-P); include etidronate, alendronate and risedronate. Bind to hydroxyapatite crystals in bone, inhibiting crystal's dissolution, aggregation, and formation. Can inhibit both resorption and mineralization of bone. Studies indicate some bisphosphonates stabilize or increase bone mineral density, decreasing vertebral fractures by about 50 percent.
- Bone mineral density (BMD):
- usually the amount of mineralized tissue in the area scanned (grams/cm2), but with some technologies the amount per volume of bone (grams/cm3); a risk factor for fractures. Hip BMD is considered the best predictor of hip fracture and appears to predict other types of fractures as well as measurements made at other skeletal sites do. Spine BMD may be preferable to assess changes early in menopause and after bilateral oophorectomy.
back to top- Calcitonin:
- a polypeptide hormone that inhibits the resorptive activity of osteoclasts. Because of its analgesic effect, it is frequently used with a patient with an acute vertebral fracture that is symptomatic. Because of its analgesic effect, it is frequently used with a patient with an acute vertebral fracture that is symptomatic. Studies indicate that calcitonin might decrease vertebral fractures by about two-thirds. Proprietary names: Miacalcin (Sandoz Pharmacuticals), Calcimar (Rhone-Poulenc Rorer/Aventis).
- Calcitriol:
- a synthetic form of 1,25-dihydroxyvitamin D3, a hormone that aids calcium absorption and mineralization of the skeleton.
- Calcium:
- a mineral that plays an essential role in development and maintenance of a healthy skeleton. If intake is inadequate, calcium is mobilized from the skeleton to maintain a normal blood calcium level. In addition to being a substrate for bone mineralization, calcium has an inhibitory effect on bone remodeling through suppression of circulating parathyroid hormone. It is probable that calcium reduces fracture rates by at least 10 percent.
- Cancellous bone:
- the spongy or trabecular tissue in the middle of bones and at the end of the long bones.
- Cortical bone:
- the dense outer layer of tissue in bones.
back to top- Dual photon absorptiometry (DPA):
- a diagnostic test used to assess bone density; has been mostly replaced by dual X-ray absorptiometry. Cannot distinguish between cortical and cancellous bone. Measures all calcified tissue in the path of the scan. In dealing with the lumbar spine. Extraneous calcification might artificially increase bone density values.
- Dual X-ray absorptiometry (DXA):
- a diagnostic test used to assess bone density. Permits faster scans than dual photon absorptiometry with improved precision; source size and collimation also are smaller, and spatial resolution is better as a result. Measures all calcified tissue in the path of the scan. In dealing with the lumbar spine. Extraneous calcification might artificially increase bone density values.
back to top- Estrogen:
- one of a group of steroid hormones that control female sexual development; has a direct effect on bone mass through estrogen receptors in bone, reducing bone turnover and bone loss. Indirectly increases intestinal calcium absorption and renal calcium conservation and, therefore, calcium balance. See hormone replacement therapy.
- Estrogen replacement therapy (ERT):
- See hormone replacement therapy.
- Etidronate:
- a bisphosphonate not approved by the U.S. Food and Drug Administration for treatment of osteoporosis; fracture area considered weak. . Proprietary name: Didronel (Proctor and Gamble).
- Exercise:
- a treatment long associated with strong bones, but actual evidence that it has an important effect on bone mineral density or reduces fractures is meager.
back to top- Family history:
- defined here as a maternal and/or paternal history of a hip, wrist, or spine fracture when the parent was 50 years old or older; a risk factor for fractures.
back to top- Hormone replacement therapy (HRT):
- a general term for all types of estrogen replacement therapy when given along with progestin, cyclically or continuously. HRT generally is prescribed for women who have gone through a natural menopause. Studies indicate that 5 years of HRT might decrease vertebral fractures by 50 to 80 percent and non-vertebral fractures by 25 percent; 10 or more years of use might be expected to decrease the rates of all fractures by 50 to 75 percent.
- Hydroxyapatite:
- a complex crystal of calcium, phosphate, and water that gives bone its hardness, rigidity, and resistance to compression. Includes more than 90 percent of total body calcium. See bisphosphonates.
- Hypercalcemia:
- the presence in the blood of an abnormally high concentration of calcium.
- Hypercalciuria:
- the presence in the urine of an abnormally high concentration of calcium.
- Hypocalcemia:
- the presence in the blood of an abnormally low concentration of calcium.
back to top- Kyphosis:
- excessive outward curvature of the spine, causing hunching of the back.
back to top- Low body weight (thin):
- defined here as being in the lowest quartile in weight, less than or equal to 57.8 kg; a risk factor for fractures.
- Low bone mass (osteopenia):
- bone density between -1.0 and -2.5 standard deviations below the mean for young-normal adults (T-score between 1 and 2.5).
back to top- Modeling:
- such processes as linear growth, cortical apposition, and cancellous modification that occur during growth, increasing bone mass.
back to top- NOF:
- the National Osteoporosis Foundation.
- Normal bone mass:
- bone density within 1 standard deviation of the mean for young-normal adult women (T-score above 1).
- Number needed to treat (NNT):
- the NNT is the number of patients one needs to treat to prevent one complication of their disease. It is the reciprocal of the absolute risk reduction and is a measure of the clinical impact of a treatment. All else being equal, the treatment with the lowest NNT is the most clinically effective.
back to top- Osteoblast:
- a cell responsible for the formation of bone.
- Osteoclast:
- a large multinucleate cell that resorbs calcified bone; found only when bone is being resorbed.
- Osteopenia:
- see low bone mass.
- Osteoporosis:
- a chronic, progressive disease characterized by low bone mass and microarchitectural deterioration of bone tissue, leading to enhanced bone fragility and a consequent increase in fracture risk. Bone density more than 2.5 standard deviations below the young-normal mean (T-score below -2.5).
back to top- Peak bone mass:
- maximum bone mass accumulated during youth.
- Peripheral fractures:
- fractures of the hip, wrist, forearm, leg, ankle, foot, rib, sternum, face, and other sites; i.e., not vertebral.
- Precision:
- reproducibility of a value upon repeat measurement.
- Prevention of osteoporosis:
- preventing bone mineral density from dropping lower than 2.5 standard deviations below the mean for young-normal adult women; colloquially used to describe the prevention of osteoporosis-related fractures.
- Previous fracture:
- defined here as a history of a previous fracture after age 50; a risk factor for fractures.
back to top- Quality-adjusted life-year (QUALY):
- the average quality of life lost over a year.
- Quantitative computed tomography (QCT):
- a diagnostic test used to assess bone density; reflects three-dimensional bone mineral density. Usually used to assess the lumbar spine, but can be adapted for other skeletal sites.
back to top- Radiogrammetry:
- a diagnostic test used to assess bone density; less well developed than others in clinical practice.
- Radiographic absorptiometry (RA):
- used to assess bone density at a peripheral site, usually the hand. Similar techniques are referred to as aluminum equivalence, photodensitometry, and radiographic densitometry.
- Raloxifene:
- an estrogen receptor modulator that selectively binds to estrogen receptors, inhibiting bone resorption and turnover. It is approved for treatment and prevention of osteoporosis. Proprietary name: Evista (Eli, Lilly and Company).
- Remodeling:
- after cessation of growth, a process coupling bone formation with bone resorption.
- Resorption:
- loss of substance--in this case, bone--through physiological or pathological means.
- Risedronate:
- a bisphosphonate approved by the U.S. Food and Drug Administration for treatment and prevention of osteoporosis. Proprietary name: Actonel (Aventis Pharmacuticals, Inc.)
- Risk factors:
- used here because they are easily accessible, relatively common, and associated with the risk of hip fracture and, in most cases, with the risk of vertebral or other types of fracture: bone mineral density, family history, low body weight, previous fracture, and smoking.
back to top- Secondary osteoporosis:
- can be drug-induced or caused by endocrine disorders or chroic medical disease (eg. chronic renal disease).
- Severe osteoporosis:
- bone density that is more than 2.5 standard deviations below the young-normal mean (T-score below -2.5), accompanied by the occurrence of at least one fracture.
- Single photon absorptiometry (SPA):
- a diagnostic test used to assess bone density; has been replaced by single X-ray absorptiometry.
- Single X-ray absorptiometry (SXA):
- a diagnostic test used to assess bone density. Limited to peripheral sites; it cannot measure bone density in the hip or spine nor can it discriminate between cortical and cancellous bone.
- Smoking:
- evidence is strong that smoking is an important risk factor for hip and vertebral fractures.
- SOF:
- the Study of Osteoporotic Fractures.
- Standard deviation (SD):
- a measure of the scatter of observations about their arithmetic mean, which is calculated from the square root of the variance of the readings in the series.
back to top- T-score:
- in describing bone mineral density, the number of standard deviations above or below the mean for young-normal adults.
- Three-dimensional bone mineral density:
- grams/cm3; theoretically superior to two-dimensional bone mineral density (grams/cm2), but advantage is slight in practice.
- Treatment of osteoporosis:
- therapy for women who already have osteoporosis; includes diet, vitamins, exercise, smoking cessation, and drugs.
- Two-dimensional bone mineral density:
- grams/cm2; theoretically inferior to three-dimensional bone mineral density (grams/cm3), but disadvantage is slight in practice.
back to top- Ultrasound densitometry:
- a diagnostic test used to assess bone density; measures speed (or apparent velocity) of ultrasound at the calcaneus or patella or broadband ultrasound attenuation, or an index of the two measures, at the calcaneus. Ultrasound measurements correlate only modestly with assessments of bone density in the same patients.
back to top- Vitamin D:
- a group of fat-soluble sterol vitamins that includes ergocalciferol and cholecalciferol; formed in the skin on exposure to ultraviolet light; also can be ingested from fortified foods (milk, cereal) or foods that naturally contain vitmain D (fatty fish, egg yolks).
back to top- Z-score:
- in describing bone mineral density, the number of standard deviations above or below the mean for persons of the same age (age-matched).
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