Closing the osteon: Do osteocytes sense strain rate rather than fluid flow?

Area of Science:

• Bone Biology
• Mechanobiology
• Skeletal Physiology

Background:

• Osteons are fundamental structural units of bone, formed by osteoclasts and osteoblasts.
• Osteocytes, embedded in bone matrix, are mechanosensitive cells thought to direct bone remodeling.
• Interstitial fluid flow, induced by bone loading, is a proposed mechanism for osteocyte mechanotransduction.

Purpose of the Study:

• To investigate the stimulation of osteocytes during osteon closure by osteoblasts.
• To determine the physical cues controlling osteocyte activity and bone deposition in forming osteons.

Main Methods:

• A conceptual finite element model was developed.
• Bone was modeled as a poro-elastic material.
• Locomotion-induced loading conditions were applied to the model.

Main Results:

• Interstitial fluid flow magnitude remained constant along the closing cone of the osteon.
• Shear strain rate in the bone matrix decreased linearly with ongoing bone deposition.
• A discrepancy was observed between fluid flow and shear strain rate during osteon formation.

Conclusions:

• Shear strain rate, rather than interstitial fluid flow, is likely the primary physical cue for osteocytes.
• This suggests shear strain rate controls osteocyte-mediated bone deposition in newly forming osteons.
• The findings offer new insights into the mechanobiology of bone remodeling and osteon development.