Distribution of microcrack surface density in the human otic capsule

Spatiotemporal Characterization of Microstructure Morphology, Mechanical Properties and Bone Remodeling of Rat Tibia Under Uniaxial Compressive Overload Loading

Bone tissue is subjected to increased mechanical stress during high-intensity work. Inadequate bone remodeling reparability can result in the continuous accumulation of microdamage, leading to stress fractures. The aim of this work was to investigate the characteristics and repair mechanisms of tibial microdamage under several degrees of overload. Also, we aimed at better understanding the effects of overload on the multi-scale structure and mechanical properties of bone. Sixty 5-month female rats were divided into three groups with different time points. Micro-CT was used to evaluate the three-dimensional microstructure, and three-point bending, quasi-static fracture toughness and creep mechanical test were carried out to evaluate the mechanical properties. SEM was used to observe the morphological characteristics of fracture surfaces. Section staining was used to count the microdamage parameters and numbers of osteoblasts and osteoclasts. The microarchitectures of cancellous and cortical bones in the three overload groups showed different degrees of damage. Overload led to a messy crystal structure of cortical bone, with slender microcracks mixed in, and a large number of broken fibers of cancellous bone. The properties associated with the elastic plasticity, fracture toughness, and viscoelasticity of cortical bone reduced in three groups, with that corresponding to day 30 presenting the highest damage. The accumulation of microdamage mainly occurred in the first 14 days, that is, the crack density peaked on day 14. Peak-targeted bone remodeling of cortical and cancellous bones occurred mainly between days 14 and 30. The influence of overload mechanical environment on bone quality at different time points was deeply investigated, which is of great significance for the etiology and treatment of stress fractures.

Cellular voids in the pathogenesis of otosclerosis

BACKGROUND

Otosclerosis is a common ear disease that causes fixation of the stapes and conductive hearing impairment. However, the pathogenesis of otosclerosis is still unknown. Otosclerosis could be associated with the unique bony environment found in the otic capsule. Normal bone remodelling is almost completely absent around the inner ear after birth allowing degenerative changes and dead osteocytes to accumulate. High levels of inner ear anti resorptive osteoprotegerin (OPG) is most likely responsible for this capsular configuration. Studies have demonstrated how osteocyte lifespan variation creates occasional clusters of dead osteocytes, so-called cellular voids, at otosclerotic predilection sites in the human otic capsule. These cellular voids have been suggested as possible starting points of otosclerosis.

AIM

To describe the cellular viability in otosclerotic lesions and compare it to that of cellular voids.

MATERIALS AND METHODS

The study was based on unbiased stereological quantifications in undecalcified human temporal bones with otosclerosis.

RESULTS

Osteocyte viability was found to vary within the otosclerotic lesions. Furthermore, the results presented here illustrate that inactive otosclerotic lesions consist of mainly dead interstitial bone, much like cellular voids.

CONCLUSIONS AND SIGNIFICANCE

Focal degeneration in the otic capsule may play an important role in the pathogenesis of otosclerosis.

The Spatial Distribution of Cellular Voids in the Human Otic Capsule: An Unbiased Quantification of Osteocyte-Depleted Areas

OBJECTIVE

This study aimed to describe the spatial distribution of osteocyte-depleted areas, so-called cellular voids, in the human otic capsule and compare it with that of otosclerosis.

BACKGROUND

Systematic histological studies of the bony otic capsule have revealed an osteoprotegerin (OPG)-mediated inhibition of normal bone remodeling around the inner ear. The resulting accumulation of bony degeneration and dead osteocytes has been thoroughly documented, and the spatial distribution of dead osteocytes and matrix microcracks resembles that of the human ear disease otosclerosis. Clusters of dead osteocytes that may interfere with osteocyte connectivity and thereby the OPG signaling pathway have been described in human temporal bones. It is possible that these cellular voids create disruptions in the antiresorptive OPG signal that may give rise to local pathological remodeling.

METHODS

Recently, a method of detecting cellular voids was developed. This study uses unbiased stereology to document the spatial distribution of cellular voids in bulk-stained undecalcified human temporal bone.

RESULTS

Cellular voids accumulate around the inner ear and increase in number and size with age. Furthermore, cellular voids are more frequently found in the anterior and lateral regions of the otic capsule, which are known predilection sites of otosclerosis.

CONCLUSION

This colocalization of cellular voids and otosclerosis suggests a causal relationship between focal degeneration and otosclerotic remodeling.