Baseline age and time to major fracture in younger postmenopausal women

Abstract

Objective: This study aims to estimate the incidence of first hip or clinical vertebral fracture or major osteoporotic (hip, clinical vertebral, proximal humerus, or wrist) fracture in postmenopausal women undergoing their first bone mineral density (BMD) test before age 65 years.

Methods: We studied 4,068 postmenopausal women, aged 50 to 64 years without hip or clinical vertebral fracture or antifracture treatment at baseline, who were participating in the Women's Health Initiative BMD cohort study. BMD tests were performed between October 1993 and April 2005, with fracture follow-up through 2012. Outcomes were the time for 1% of women to sustain a hip or clinical vertebral fracture and the time for 3% of women to sustain a major osteoporotic fracture before initiating treatment, adjusting for clinical risk factors and accounting for competing risks. Women without osteoporosis and women with osteoporosis on their first BMD test were analyzed separately.

Results: During a maximum of 11.2 years of concurrent BMD and fracture follow-up, the adjusted estimated time for 1% of women to have a hip or clinical vertebral fracture was 12.8 years (95% CI, 8.0-20.4) for women aged 50 to 54 years without baseline osteoporosis, 7.6 years (95% CI, 4.8-12.1) for women aged 60 to 64 years without baseline osteoporosis, and 3.0 years (95% CI, 1.3-7.1) for all women aged 50 to 64 years with baseline osteoporosis. Results for major osteoporotic fracture were similar.

Conclusions: Because of very low rates of major osteoporotic fracture, postmenopausal women aged 50 to 64 years without osteoporosis on their first BMD test are unlikely to benefit from frequent rescreening before age 65 years.

Trial registration: ClinicalTrials.gov NCT00000611.

Figures

Figure 1. Study population for analyses of time to hip or clinical vertebral fracture

Of the 4527 women who had DXA bone mineral density (BMD) testing, 459 were excluded, including those who had a past hip or clinical vertebral fracture or osteoporosis treatment (bisphosphonate or calcitonin) at their first study examination, or who did not have BMD measurements at two or more examinations, or one BMD measurement and subsequent development of a competing risk. In the analytical cohort of 4068 women with adequate femoral neck, total hip, and lumbar spine BMD measurements prior to censoring, two transitions were studied: T-score >-2.50 to first hip or clinical vertebral fracture (N=3724), and T-score

Figure 2. Unadjusted cumulative incidence of hip or clinical vertebral fracture according to baseline age range

The proportion of women who had transitioned to first hip or clinical vertebral fracture is plotted as a function of time. The cumulative incidence curves are estimated by parametric cumulative incidence models for known fracture dates. The dotted horizontal line shows where 1% of women have transitioned to first hip or clinical vertebral fracture; where this line intersects with each cumulative incidence curve, a vertical line to the x-axis marks the estimated time interval.