Which is the preferred site for bone mineral density monitoring as an indicator of treatment-related anti-fracture effect in routine clinical practice? A registry-based cohort study.

Change in total hip bone mineral density (BMD) provides a robust indication of anti-fracture effect during treatment monitoring in routine clinical practice, whereas spine BMD change is not independently associated with fracture risk. The role of monitoring bone mineral density (BMD) as an indicator of an anti-fracture effect is controversial. Discordance between the spine and hip BMD is common and creates uncertainty in clinical practice. Using a population-based BMD Registry for the Province of Manitoba, Canada, we compared change in the spine and hip BMD as an indicator of treatment-related fracture risk reduction. The study cohort included 6093 women age > 40 years initiating osteoporosis treatment with two consecutive dual-energy X-ray absorptiometry (DXA) scans (mean interval 4.7 years). We computed change in the spine, total hip, and femur neck BMD between the first and second DXA scans as categorical (categorized as stable, detectable decrease, or detectable increase) and continuous measures. We modeled time to first incident fracture, ascertained from health services data, using Cox regression adjusted for baseline fracture probability. During a mean follow-up of 12.1 years, 995 women developed incident major osteoporotic fractures (MOF) including 246 with hip fractures and 301 with clinical vertebral fractures. Women with a detectable decrease in total hip BMD compared with stable BMD experienced an increase in MOF (adjusted hazard ratio [aHR] 1.46, 95% confidence interval [CI] 1.25-1.70) while those with a detectable increase in total hip BMD experienced a decrease in MOF (aHR 0.71, 95% CI 0.61-0.83), and these results were not attenuated when adjusted for change in spine BMD. Similar results were seen for hip and clinical vertebral fracture outcomes, when BMD change was assessed as a continuous measure, and when femur neck BMD monitoring was used instead of total hip BMD monitoring. Treatment-related increases in total hip BMD are associated with lower MOF, hip, and clinical vertebral fracture risk compared with stable BMD, while BMD decreases are associated with higher fracture risk. In contrast, spine BMD change is not independently associated with fracture risk.