Introduction: Bone mineral density decreases before menopause and is held to be due to trabecular, not cortical, bone loss. Yet neither a negative bone balance, nor accelerated remodelling occurs before 45 years of age. We hypothesized that bone loss will first appear after 45 years and will be cortical (as 80% of bone is cortical).
Methods/design: Images of distal tibia acquired using high-resolution peripheral quantitative computed tomography (Scanco Medical) were analyzed using StrAx1.0 in 212 pre-, 42 peri- and 91 postmenopausal women aged 4061 years, and in 28 premenopausal women during 3.4 years follow-up, in Melbourne, Australia.
Results: In premenopausal women ≥45 years (not younger), medullary and total CSA were larger across age (P<0.05) so their ratio, an index of cortical thickness and total vBMD were unchanged. However, for each SD higher age, porosity of the compact cortex and outer transitional zone were 0.28 SD and 0.27 SD higher (both P≤0.001). Trabecular vBMD was unchanged. Between 40 and 61 years the diminution in bone mass was 75% cortical and 25% trabecular but only 4% preceded menopause and this was cortical. The prospective data in premenopausal women were similar; porosity increased by 0.20.3 SD, trabecular and total vBMD decreased by 0.050.11 SD (P<0.001), each correlated with remodeling markers.
Conclusion: Intracortical and endocortical remodeling cause cortical bone loss shortly before menopause, but net bone loss is modest because periosteal apposition occurs.
18 May 2013 - 22 May 2013