Bone mineral density (BMD): A risk factor for fractures. By DXA, BMD is expressed as the amount of mineralized tissue in the area scanned (g/[cm.sup.2]); with some technologies, BMD is expressed as the amount per volume of bone (g/[cm.sup.3]). Hip BMD by DXA is considered the best predictor of hip fracture; it appears to predict other types of fractures as well as measurements made at other skeletal sites. Spine BMD may be preferable to assess changes early in menopause and after bilateral ovariectomy.
Calcitonin (Miacalcin[R] or Fortical[R]): A polypeptide hormone that inhibits the resorptive activity of osteoclasts.
Calcitriol: A synthetic form of 1,25-dihydroxyvitamin [D.sub.3], a hormone that aids calcium absorption and mineralization of the skeleton. Its effectiveness as a treatment for osteoporosis is still uncertain.
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.
Cancellous bone: The spongy, or trabecular, tissue in the middle of bone (e.g., vertebrae) and at the end of the long bones.
Cortical bone: The dense outer layer of bone.
Cost-effectiveness analysis: As utilized in this Guide, a quantitative analysis that considers the value of treatment by comparing average costs and average health outcomes (quality-adjusted life expectancy) for patients who are treated for osteoporosis relative to untreated patients.
Dual-energy x-ray absorptiometry (DXA): A diagnostic test used to assess bone density at various skeletal sites using radiation exposure about one-tenth that of a standard chest x-ray. Central DXA (spine, hip) is the preferred measurement for definitive diagnosis of osteoporosis and for monitoring the effects of therapy.
Estrogen: One of a group of steroid hormones that control female sexual development; directly affects bone mass through estrogen receptors in bone, reducing bone turnover and bone loss. Indirectly increases intestinal calcium absorption and renal calcium conservation and, therefore, improves calcium balance. See hormone therapy.
Estrogen agonists/antagonists: A group of compounds that are selective estrogen receptor modulators, formerly known as SERMs.
Exercise: An intervention long associated with healthy bones, despite limited evidence for significant beneficial effect on bone mineral density or fracture risk reductions. Studies evaluating exercise are ongoing; however, enough is known about the positive effect of exercise on fall prevention to support its inclusion in a comprehensive fracture prevention program.
Fluoride: A compound that stimulates the formation of new bone by enhancing the recruitment and differentiation of osteoblasts. Studies show varying effects on BMD depending upon the preparation, dose, measurement site and outcomes assessed.
Fracture: Breakage of a bone, either complete or incomplete. Most studies of osteoporosis focus on hip, vertebra and/or distal forearm fractures. Vertebral fractures include morphometric as well as clinical fractures.
FRAX[TM]: The World Health Organization Fracture Risk Assessment Tool. www.NOF.org and www.shef.ac.uk/FRAX
Hormone/estrogen therapy (HT/ET) (HT--Activella[R], Femhrt[R], Premphase[R], Prempro[R] ; ET--Climara[R], Estrace[R], Estraderm[R], Estratab[R], Ogen[R], Ortho-Est[R], Premarin[R] , Vivelle[R]): HT is a general term for all types of estrogen replacement therapy when given along with progestin, cyclically or continuously. HT is generally prescribed for women after natural menopause or bilateral ovariectomy. ET is prescribed for postmenopausal women who have had a hysterectomy. Studies indicate that five years of HT may decrease vertebral fractures by 35 to 50 percent and non-vertebral fractures by about 25 percent. Ten or more years of use might be expected to decrease the rate of all fractures by about 50 percent.
Ibandronate (Boniva[R]): A bisphosphonate approved by the FDA for the prevention and treatment of postmenopausal osteoporosis. Ibandronate reduces the incidence of vertebral fractures by about 50 percent over three years.
Low bone mass (osteopenia): The designation for bone density between 1.0 and 2.5 standard deviations below the mean for young normal adults (T-score between -1.0 and -2.5).
Modeling: The term for skeletal processes that occur during growth (e.g., linear growth, cortical apposition and cancellous modification) and increase bone mass.
Non-vertebral fractures: Fractures of the hip, wrist, forearm, leg, ankle, foot and other sites.
Normal bone mass: The designation for bone density within 1 standard deviation of the mean for young normal adults (T-score at -1.0 and above).
Osteopenia: See low bone mass.
Osteoporosis: A chronic, progressive disease characterized by low bone mass, microarchitectural deterioration of bone tissue and decreased bone strength, bone fragility and a consequent increase in fracture risk; bone density 2.5 or more standard deviations below the young normal mean (T-score at or below -2.5).
Peak bone mass: The maximum bone mass accumulated during young adult life.
Peripheral DXA: A DXA test used to assess bone density in the forearm, finger and heel.
Physiatrist: A physician who specializes in medicine and rehabilitation, or physiatry.
Previous fracture: A risk factor for future fractures, defined here as a history of a previous fracture after age 40.
PTH(1-34), teriparatide, (Forteo[R]): An anabolic therapy approved for the treatment of osteoporosis. The pivotal study indicates a 65 percent reduction in vertebral fractures and a 53 percent reduction in non-vertebral fractures after 18 months of therapy in patients with osteoporosis.
Quantitative computed tomography (QCT): A diagnostic test used to assess bone density; reflects three-dimensional BMD. Usually used to assess the lumbar spine, but has been adapted for other skeletal sites. It is also possible to measure trabecular and cortical bone density in the periphery by peripheral QCT (pQCT).
Quantitative ultrasound densitometry (QUS): A diagnostic test used to assess bone density at the calcaneus or patella. Ultrasound measurements correlate only modestly with other assessments of bone density in the same patient, yet some prospective studies indicate that ultrasound may predict fractures as well as other measures of bone density.
Raloxifene (Evista[R]): An estrogen agonist/antagonist (or selective estrogen receptor modulator) approved by the FDA for prevention and treatment of osteoporosis. It lowers the risk of vertebral fracture by about 30 percent in patients with and about 55 percent in patients without prior vertebral fracture.
Remodeling: The ongoing dual processes of bone formation and bone resorption after cessation of growth.
Resorption: The loss of substance (in this case, bone) through physiological or pathological means.
Risedronate (Actonel[R]): A bisphosphonate approved by the FDA for prevention and treatment of osteoporosis. It lowers the risk of vertebral fracture by about 41-49 percent and non-vertebral fractures by about 36 percent.
Risk factors: For osteoporotic fractures, includes low BMD, parental history of hip fracture, low body weight, previous fracture, smoking, excess alcohol intake, glucocorticoid use, secondary osteoporosis (e.g., rheumatoid arthritis) and history of falls. These readily accessible and commonplace factors are associated with the risk of hip fracture and, in most cases, with that of vertebral and other types of fracture as well.
Secondary osteoporosis: Osteoporosis that is drug-induced or caused by disorders such as hyperthyroidism, renal disease or chronic obstructive pulmonary disease.
Severe or "established" osteoporosis: Osteoporosis characterized by bone density that is 2.5 standard deviations or more below the young normal mean (T-score at or below -2.5), accompanied by the occurrence of at least one fragility-related fracture.
Standard deviation (SD): A measure of variation of a distribution.
T-score: In describing BMD, the number of standard deviations above or below the mean for young normal adults of the same sex.
Teriparatide: See PTH(1-34), teriparatide, (Forteo[R]).
Vitamin D: A group of fat-soluble sterol compounds that includes ergocalciferol (vitamin [D.sub.2]) and cholecalciferol (vitamin [D.sub.3]). These compounds are ingested from plant and animal sources; cholecalciferol is also formed in skin on exposure to ultraviolet light. When activated in the liver and then the kidney, vitamin D promotes calcium absorption and bone mass. Vitamin D replacement also increases muscle strength and lowers risk of falling. A 25(OH) D level of [greater than or equalto] 30 ng/ml (75 nmol/L) is considered by many to be optimal.
Zoledronic acid (Reclast[R]): A bisphosphonate approved by the FDA for treatment of postmenopausal osteoporosis. It lowers risk of vertebral fractures by about 70 percent, hip fractures by about 41 percent and non-vertebral fractures by about 25 percent.
Z-score: In describing BMD, the number of standard deviations above or below the mean for persons of the same age and sex.