Oral Presentation 1st Asia Pacific Herbert Fleisch Workshop 2025

Cortical bone in older women has greater collagen compaction and less osteocyte connectivity at the time of deposition (#25)

Haniyeh Hemmatian 1 2 3 , Mary Louise Fac 1 2 3 , Anaïs Ledent 4 , Gordon Wu 2 5 , Blessing Crimeen-Irwin 5 , Rita Hardiman 6 , Stéphane Blouin 7 , Markus Hartmann 7 , Davide Ruffoni 4 , Richard Weinkamer 8 , Natalie A Sims 2 5 9
  1. St Vincent's Institute, Fitzroy, VIC, Australia
  2. Department of Medicine at St. Vincent's Hospital, The University of Melbourne, Melbourne, VIC, Australia
  3. contributed equally
  4. Mechanics of Biological and Bioinspired Materials Laboratory, Department of Aerospace and Mechanical Engineering, University of Liège, Liège, Belgium
  5. St. Vincent's Institute of Medical Research, Melbourne
  6. Melbourne Dental School, The University of Melbourne, Parkville
  7. Ludwig Boltzmann Institute of Osteology at Hanusch, Hospital of OEGK and AUVA Trauma Centre Meidling, Medical Department Hanusch Hospital, Vienna, Austria
  8. Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
  9. Australian Catholic University, Melbourne

Bone fragility increases with age and fractures are common even with normal bone mineral density. Poor bone composition, including reduced osteocyte connectivity, may contribute, but whether it occurs by gradual degradation of pre-existing bone or by deposition of compromised bone during remodelling is not known. Here, we tested the hypothesis that older women have an intrinsic defect in bone production.

Osteons from mid-diaphyseal femoral cortex of healthy younger (19–40 years) and older (77–95 years) women (10 women / group, Melbourne Femur Collection) were imaged by synchrotron-based Fourier-Transform Infrared Microspectroscopy (FTIRM), quantitative backscattered electron imaging (qBEI), and 3D confocal microscopy of the osteocyte canalicular network. Since these archived samples lacked fluorochrome labels, we developed a method to identify four stages of osteonal bone maturation (early, mid, late, and stable) based on histology (complete osteons uninterrupted by more recent remodelling), calcium content (qBEI), and phosphate:amide I gradient across the osteon wall (FTIRM).

The mineralisation process did not differ between the two age groups; older and younger women showed similar increases in phosphate, calcium, and carbonate from the Haversian canal to the cement line at all osteon maturation stages. However, in mid, late, and stable osteons from older women, collagen was more compact than in younger women: amide I:II ratio was ~5% lower (mean ratios ±SEM: 1.72±0.14 vs 1.63±0.06; p<0.001). While osteocyte lacunar density (osteocyte cell number) did not differ, osteocyte connectivity (canalicular density) was ~40% lower in new osteons of older women (0.088±0.011 vs 0.053±0.009; p<0.0001, µm/µm3). This indicates that the disconnected network originates during new bone formation.

Our classification method enables stage-specific identification of unlabelled osteons and suggests that bone fragility in older women originates as it forms during cortical remodelling. The more compact collagen and poorly connected osteocyte network may be bone mass-independent contributors to age-related bone fragility in women.