LAUSR

Summary This study reported that the transitional zones in older adults were enlarged at the expense of the compact-appearing cortex with a greater porosity in all cortical sub-compartments. The magnitude of differences in areal and volumetric bone mineral density (aBMD, vBMD) between older and younger groups was similar. Introduction Aging is strongly associated with bone loss, but little is known about magnitudes of differences in bone microarchitectures, aBMD, and vBMD from peak bone mass (PBM) to senescence. We aimed to describe differences in aBMD, vBMD, and bone microarchitecture parameters at the distal radius between older and young adults. Methods We compared 201 participants, aged 62–89 years (female 47%) and 196 participants, aged 24–28 years (female 38%). Bone microarchitecture parameters at distal radius were measured using high-resolution peripheral computed tomography (HRpQCT). aBMD was measured using dual-energy X-ray absorptiometry (DXA). Unpaired t tests and chi-square tests were used to compare differences in means and proportions as appropriate. Results Older adults had thinner compact-appearing cortices with larger (cross-sectional area: outer 30.96 mm 2 vs. 28.38 mm 2 , inner 36.34 mm 2 vs. 32.93 mm 2 ) and thicker (outer 0.57 mm vs. 0.54 mm, inner 0.71 mm vs. 0.65 mm) transitional zones compared with young adults (all p  < 0.05). Cortical porosity was modestly higher in older adults than in young adults (54% vs. 49%, p  < 0.001). The magnitude of the difference in hip aBMD between older and young adults was slightly lower than of total radial vBMD (− 0.51 SD vs. − 0.78 SD). Conclusion Compared with young adults at the time of PBM, the transitional zones in older adults were enlarged at the expense of the compact-appearing cortex with a greater porosity in all cortical sub-compartments. The similar SD differences in aBMD and vBMD between older and younger groups suggest that the differences in bone area are not leading to major artefactual change in aBMD.