Journal
BONE
Volume 117, Issue -, Pages 70-82Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.bone.2018.09.011
Keywords
Cortical bone; Remodeling balance; Reversal-resorption phase; Bone resorption; Bone formation; Aging
Categories
Funding
- Velux Foundation [VELUX34368]
- Danish Southern Region Research Grant [15/24851]
- Aase and Ejnar Danielsen Foundation [10-001584]
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Cortical bone is remodeled by intracortical basic multicellular units (BMUs), whose end result can be observed as quiescent osteons in histological sections. These osteons offer a unique opportunity to investigate the BMU balance between the magnitude of bone resorption and subsequent bone formation at the BMU level. Our main objective was to investigate whether the latter parameters change between defined categories of osteons and with age, and to which extend these changes contribute to age-induced cortical porosity. Cortices of iliac bone specimens from 35 women (aged 16-78 years) with a higher porosity with age were investigated. A total of 3084 quiescent osteons reflecting 75% of the intracortical pores were histological examined. The osteons diameter, pore diameter, wall thickness, prevalence and contribution to the porosity were highly variable, but unchanged with age. Next, the osteons were categorized according to whether they reflected the remodeling of existing canals (type 2Q osteons) or the generation of new canals (type 1Q osteons). Type 2Q osteons versus type 1Q osteons: (i) had more frequently a pore diameter > 75 mu m (7.4 vs. 1.3%;p < 0.001); (ii) had a larger mean pore diameter (40 10 vs. 25 4 m; p < 0.001), osteon diameter (120 +/- 21 vs. 94 +/- 21 mu m; p < 0.001) and wall thickness (40 +/- 10 vs. 35 +/- 9; p < 0.05); (iii) had a larger contribution to the cortical porosity (29 +/- 18 vs. 8 +/- 8%; p < 0.001); (iv) were more prevalent (44 +/- 10 vs. 31 +/- 11%; p < 0.001); and (v) were more prevalent with age. Collectively, this study demonstrates that quiescent osteons with age more frequently result from remodeling of existing canals, which in some cases had a more negative BMU balance. Still, the osteons showed no overall age -related change in their pore diameter i.e. BMU balance. In contrast to conventional wisdom, these data show that non -quiescent pores, not pores of quiescent osteons, were the main contributor to a higher cortical porosity.
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