Changes in bone mass and skeletal structure in the postmenopausal period

University dissertation from Annelie Norrby, Department of Orthopaedics, Malmö University Hospital, 20502 Malmö, Sweden

Abstract: The aim of this thesis was to evaluate long-term changes in bone mass and skeletal structure in the forearm in the peri- and postmenopausal period. 156 premenopausal women, at baseline aged 48 years, not taking medications and without disease processes known to interfere with bone metabolism, were followed through menopause by measurements of bone mass and skeletal structure at the cortical site of the distal radius by single photon absorptiometry, on average every second year until age 72. General health and life-style factors were reported, and the postmenopausal serum estradiol level and fragility fractures were noted. Menopause was determined according to the definition established by the World Health Organisation. The age-dependent reduction in bone mineral density accelerated after menopause, with the highest bone loss found during the first 5 years following menopause. Independent of age at menopause, premenopausal women with low, age-specific bone mineral density at age 48 years were likely to have low bone mineral density also at age 64 years. Furthermore, menopause was followed by structural geometrical changes such as endosteal resorption, increasing the medullary cavity, and periosteal apposition, increasing the bone size. Increased periosteal apposition was associated with both increased bone loss and low postmenopausal serum levels of estradiol. The periosteal apposition seemed to partly compensate for the decreased bone strength, caused by the decrease in tissue mineral content. A Strength Index, taking both bone density and skeletal geometry into account, predicted a future fracture of the distal radius. If the structural skeletal changes of the distal radius, with enlargement of the medullary cavity, are a general phenomenon of the diaphyseal bones, this theoretically could have implications for the long-term fixation of a hip prosthesis. Bone loss following menopause was less in physically active than in physically inactive women, so that physically active women had a higher bone mineral density at age 72 than physically inactive women. This suggests that moderate physical activity in the postmenopausal period could possibly be recommended as a strategy to prevent bone loss. Furthermore, the effect of hormone replacement therapy on bone loss after menopause was evaluated in an observational study with 28 women with and 196 women without hormone replacement therapy. Hormone replacement therapy seemed to reduce the rate of bone loss over a period of 23 years, and the longer the duration of the therapy, the less the bone loss.

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