Bone Abstracts

Postmenopausal women with forearm fracture have higher cortical porosity and lower trabecular density perhaps due to excessive age-related bone loss¹. Remodelling becomes unbalanced and rapid only after ~45 years of age. We therefore proposed that bone fragility in premenopausal women with a forearm fracture originates during growth. At metaphyses, trabeculae emerging from the periphery of the growth plate form cortex by ‘corticalization’)². We speculated that fewer and/or thinner trabeculae from the growth plate may impair corticalization so the spacing between more separated trabeculae leave a higher porosity (forming wider transitional zone), reduced cortical area and a larger medullary area (by lack of adsorption of trabeculae upon the endocortical surface).

In a previously reported cohort of 40 premenopausal women (mean age 30±8 years) with forearm fractures³, and 80 controls, we assessed trabecular architecture and cortical porosity of the compact-appearing cortex (CC), outer- and inner transitional zones (OTZ and ITZ) at the ultradistal radius acquired using HR-pQCT and quantified using StrAx1.0⁴. Cortical cross-sectional area (CSA)/total CSA was used as a measure of the cortical area corrected for bone size.

Cases had 4% lower cortical CSA/total CSA, a reciprocally higher medullary CSA/total CSA (both P=0.067), 2–3% higher porosity of the OTZ and ITZ (both P<0.04), and 19% lower trabecular vBMD due to 8% fewer and 3% thinner trabeculae than controls (P<0.04). A SD increment in ITZ porosity and trabecular vBMD conferred odds ratios for fracture of 1.33 (1.12–1.60) and 1.03 (1.01–1.04) respectively.

Within the constraints of this cross-sectional study, we infer that reduced trabecular number and thickness and impaired corticalization contribute to thinner and more porous cortices, reduced trabecular density and so bone fragility.

References: 1. Bala et al. 2014 JBMR.

2. Wang et al. 2010 JBMR.

3. Rozental et al. 2013 JSBS.

4. Zebaze et al. 2013 Bone.