SPINE AND FEMUR DENSITOMETRY AT THE MENOPAUSE - ARE BOTH SITES NECESSARY IN THE ASSESSMENT OF THE RISK OF OSTEOPOROSIS

The aim of our study was to compare the results provided by the measur ement of vertebral and femoral bone mineral density (BMD) for assessin g the individual risk of osteoporosis as defined by either low BMD and /or rapid bone loss. Vertebral and femoral BMD were measured twice at a mean interval of 21 months in 85 normal, early postmenopausal women who had passed a natural menopause 6 months to 3 years previously. Acc ording to the measurement site, 36% (spine), 29% (femoral neck), 35% ( Ward's triangle), and 25% (trochanter) fall in the ''at risk'' categor y, defined by a BMD value of 1 SD or more below the normal values for premenopausal women. Based on vertebral BMD, 39-48% of the women at ri sk had a normal femoral BMD. On the other hand, 24-37% of the women cl assified at risk based on femoral BMD maintained a low risk at the ver tebral level. The annual rate of bone loss was significantly greater f or the Ward's triangle (-2.7 +/- 3.8%) and femoral neck (-2.1 +/- 2.5% ) than for the spine (-1.5 +/- 2.1%) and trochanter (-1.5 +/- 3.4%). T here was a significant relationship between the rate of loss measured at the spine and femoral levels (r = 0.34-0.58). Among the 21 women wi th a rapid vertebral bone loss, 48-67% had a low bone loss at the femo ral level and vice versa. The ratio between mean rate of loss and the precision of the measurement sites was greater for the spine (1.6) com pared with the femur (1.1-0.71). Our results indicate that vertebral a nd femoral BMD measurements produce discordant results in assessing th e individual risk for osteoporosis.