The internationally agreed upon definition of osteoporosis is “a progressive systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture.”<sup>12 Consensus development conference Diagnosis, prophylaxis and treatment of osteoporosis Am J Med 1991 ;  90 : 107-110

Cliccare qui per andare alla sezione Riferimenti</sup> Osteoporosis is one of the most prevalent diseases associated with aging, and, because of its cost, it is viewed as a major health problem. Common fractures include vertebral compression fractures and fractures of the distal radius and the proximal femur (hip fracture). In addition, when the skeleton is osteoporotic, fractures occur more commonly at many other sites including the pelvis, proximal humerus, distal femur, and ribs. Osteoporotic fractures occurring at the spine and the forearm are associated with significant morbidity; however, the most serious consequences arise in patients with hip fracture, which is associated with a significant increase in mortality (15% to 20%), particularly in elderly men and women. In white women, the lifetime risk for hip fracture is 19%; for vertebral fracture, 15.6%; and for distal forearm fracture 16%. The lifetime risk for any fracture of the hip, spine, and forearm is almost 40% in white women aged 50 years or more (Table 1). Age-related bone loss is more pronounced in women than in men and in cancellous (trabecular) bone than in cortical (compact) bone. In women, uncertainty remains in regards to the age at which peak bone mass is achieved and starts to decline and concerning the magnitude of premenopausal bone loss according to skeletal site. The menopause is followed by an accelerated loss of the peripheral and axial bone mass that can be prevented by antiresorptive therapy including hormone replacement therapy and bisphosphonate. Screening for osteoporosis is therefore most efficiently performed at the time of menopause. Currently, there is no way to predict bone mass at the time of menopause. In some cases, the clinician may be able to identify risk factors such as chronic corticosteroid therapy, subtle estrogen or progesterone deficiency or both during premenopausal life, or prolonged immobilization resulting in significant premenopausal bone loss. However, in most cases, bone mass at the time of the menopause is largely determined by the peak bone mass achieved two decades or more earlier. This, in turn, is mainly related to genetic determinants. Well-known risk factors that have been identified by epidemiologic studies (e.g., low body weight, low calcium intake, smoking, alcohol consumption, lack of exercise) may have relatively minor roles in determining individual bone mass.

The definition of osteoporosis captures the notion that low bone mass is by far the most important risk factor for osteoporotic fractures, although other factors must also be taken into account, including age, per se; familial and personal history of fracture; ill-defined structural parameters that influence the fragility of bone architecture; hip axis length; and factors unrelated to bone, such as the propensity to fall in the elderly. Nevertheless, bone mass measured as bone mineral forms the basis for the diagnosis of osteoporosis. The prognostic assessment of fracture risk is important to optimize therapeutic strategies. Several components can be identified, including the quantification of bone mass, previous fracture, and the rate of bone loss, which can be assessed indirectly by the measurement of biochemical markers of bone turnover. Repeated bone mass and turnover measurements are also useful to assess the efficacy of antiresorptive therapy such as hormone replacement therapy, bisphosphonate, and calcitonin. Bone mass measurements and biochemical markers of bone turnover are key methods to diagnose osteoporosis, predict future fracture, and monitor therapeutic regimens. Both methods for measuring bone mass (Table 2) and bone turnover (Table 3) have improved greatly in recent years.<sup>32 Garnero P., Delmas P.D. Assessment of the serum levels of bone alkaline phosphatase with a new immunoradiometric assay in patients with metabolic bone disease J Clin Endocrinol Metab 1993 ;  77 : 1046-1053  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti, 54 Mazess R.B., Wahner H.W. Nuclear medicine and densitometry Osteoporosis: Etiology, Diagnosis and Management New York: Raven Press (1988). 

Cliccare qui per andare alla sezione Riferimenti</sup> This article reviews their clinical use in osteoporosis.