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

Smit, Theo H.

doi:10.1002/bies.202000327

Cited by 3 publications

(4 citation statements)

References 110 publications

(204 reference statements)

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“…It is known that dynamic loading leads to a weakening of materials by structural microdamage [ 25 ]. Bone is a living material, and thus, is capable of repairing MCKs through bone remodeling, a cellular process in which osteoclasts resorb damaged bone and osteoblasts subsequently produce new tissue [ 26 , 27 ].…”

Section: Discussionmentioning

confidence: 99%

“…From another perspective, osteons can be considered to indicate the area where microdamage is most likely to occur. As a self-organizing mechanobiological process, osteons form as a result of microdamage and therefore align along the principal stress [ 25 , 39 , 40 ]. This mechanism may also be considered as an advantage, because it allows the bone grain to reorient in order to improve its mechanical effectiveness [ 33 ].…”

Section: Discussionmentioning

confidence: 99%

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Osteonal Microcracking Pattern: A Potential Vitality Marker in Human Bone Trauma

Schwab

Galtés

Winter-Buchwalder

et al. 2023

Biology

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In forensic anthropology, the differential diagnosis between peri- and postmortem bone fractures is mainly based on macroscopic criteria. In contrast, studies focusing on bone histology are very scarce. In a recent publication, we showed that (perimortem) fractures in fresh human bones exhibit a different osteonal microcracking pattern than (postmortem) damage in dry bones. In the current work, we explored whether this osteonal microcracking pattern is distinctive of the vitality of (perimortem) fresh bone fractures. To this end, we compared the number, length and structural distribution of microcracks in vital humeral fractures from forensic autopsy cases with experimentally reproduced, three point-bending fractures in fresh and dry human humeri. Half of the fresh experimental bones were fractured whilst applying axial compression, i.e., attempting to simulate intra vitam conditions more accurately. The results showed a similar osteonal microcracking pattern between vital fractures and experimental fractures of fresh humeri subjected to axial compression. Interestingly, this pattern was significantly different from the one observed in the experimental fractures of fresh humeri without axial compression and dry humeri. This supports our hypothesis that the osteonal microcracking pattern can potentially be used as a marker for vital perimortem trauma, providing a histomorphometric tool for fracture timing.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Osteonal Microcracking Pattern: A Potential Vitality Marker in Human Bone Trauma

Schwab

Galtés

Winter-Buchwalder

et al. 2023

Biology

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show abstract

“…For the closing osteon, the picture is somewhat different. Bone apposition decreases as filling of the osteon proceeds [ 72 , 73 ], but the fluid flow under mechanical loading remains constant [ 74 ]. This suggests that fluid flow is unrelated to osteoblast activity.…”

Section: Homogenized Models Of Mechanical Bone Adaptationmentioning

confidence: 99%

“…Recent multiscale finite-element studies included interstitial fluid flow and reached similar conclusions: fluid flow is highest close to the Haversian canals, and close to zero at the cement line [ 125 , 136 , 137 ]. Thus, the fluid shear stress that an osteocyte perceives highly depends on its position, a conclusion that could also be drawn from homogenized Biot-type poro-elasticity models [ 69 , 74 ].…”

Section: Multiscale Models Of Cortical Bonementioning

confidence: 99%

Finite Element Models of Osteocytes and Their Load-Induced Activation

Smit

2022

Curr Osteoporos Rep

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Purpose of Review Osteocytes are the conductors of bone adaptation and remodelling. Buried inside the calcified matrix, they sense mechanical cues and signal osteoclasts in case of low activity, and osteoblasts when stresses are high. How do osteocytes detect mechanical stress? What physical signal do they perceive? Finite element analysis is a useful tool to address these questions as it allows calculating stresses, strains and fluid flow where they cannot be measured. The purpose of this review is to evaluate the capabilities and challenges of finite element models of bone, in particular the osteocytes and load-induced activation mechanisms. Recent Findings High-resolution imaging and increased computational power allow ever more detailed modelling of osteocytes, either in isolation or embedded within the mineralised matrix. Over the years, homogeneous models of bone and osteocytes got replaced by heterogeneous and microstructural models, including, e.g. the lacuno-canalicular network and the cytoskeleton. Summary The lacuno-canalicular network induces strain amplifications and the osteocyte protrusions seem to be stimulated much more than the cell body, both by strain and fluid flow. More realistic cell geometries, like minute constrictions of the canaliculi, increase this effect. Microstructural osteocyte models describe the transduction of external stimuli to the nucleus. Supracellular multiscale models (e.g. of a tunnelling osteon) allow to study differential loading of osteocytes and to distinguish between strain and fluid flow as the pivotal stimulatory cue. In the future, the finite element models may be enhanced by including chemical transport and intercellular communication between osteocytes, osteoclasts and osteoblasts.

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Rib remodelling changes with body size in fossil hippopotamuses from Cyprus and Greece

Miszkiewicz,

Athanassiou,

Lyras

et al. 2023

J Mammal Evol

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Large species that are isolated for thousands of years on islands often evolve extreme degrees of dwarfism. Very little is known about physiological processes that accompany such extreme transitions in extinct dwarf species. We tested whether physiological cycles of bone maintenance (remodelling) in dwarf adult hippopotamuses correlate with insularity-driven body mass shifts that may occur due to variables such as ecological release from predation pressure and change in access to resources. We hypothesised that hippopotamuses with the smallest body size should show higher values of osteocyte lacunae, proxies for osteoblast proliferation during cycles of remodelling, when compared to relatively larger dwarf forms, as well as much larger mainland common hippopotamuses. We examined 20 ribs from three extinct Pleistocene Hippopotamus species spanning a gradient in body size: H. minor (~132 kg, Cyprus), H. creutzburgi (~398 kg, Crete), and H. antiquus (~3200 kg, mainland Greece). Ribs were selected because they reflect bone metabolic rates that are not completely clouded by factors such as biomechanics. Densities of osteocyte lacunae (Ot.Dn) were examined in 864 individual secondary osteons observed in histology sections. We found the highest average Ot.Dn in the H. minor ribs, intermediate Ot.Dn in the H. creutzburgi ribs, and the lowest Ot.Dn in the H. antiquus ribs. It appears that Ot.Dn distinctly separated these three species, possibly signifying a gradient in bone remodelling such that bone tissue optimises maintenance in the face of insularity-driven reduction of body size. We discuss hippopotamus rib bone microstructure and the utility of Ot.Dn in palaeontological analyses for elucidating intricate biological processes occurring in bone of insular fossil mammals.

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

Cited by 3 publications

References 110 publications

Osteonal Microcracking Pattern: A Potential Vitality Marker in Human Bone Trauma

Osteonal Microcracking Pattern: A Potential Vitality Marker in Human Bone Trauma

Finite Element Models of Osteocytes and Their Load-Induced Activation

Rib remodelling changes with body size in fossil hippopotamuses from Cyprus and Greece

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