Distribution of microcrack surface density in the human otic capsule

The bony otic capsule is comprised of highly mineralized and dense compact bone. It is rarely remodelled and degenerative changes, therefore, accumulate around the inner ear. It is also a predilection site for the pathological remodelling seen in otosclerosis. Morphometric studies have documented increased numbers of dead osteocytes and microcracks in the human otic capsule. Microcracks may disrupt the lacuno-canalicular network and cause osteocyte apoptosis ultimately breaking up the perilabyrinthine bone signalling pathways and dynamics. This may be important to understand the pathogenesis of remodelling diseases like otosclerosis.

This study describes the spatial and regional distribution of microcrack surface density in relation to the inner ear and compares it to that previously recorded for otosclerosis.

Forty-two temporal bones and five ribs were used. All samples were undecalcified, bulk stained in basic fuchsin and plastic embedded. Unbiased stereology was used to estimate the true surface density of microcracks (mm²/mm³) in perilabyrinthine bone.

The surface density of microcracks accumulates around the inner ear spaces, particularly in the lateral window regions, and increases with age.

This study documents the spatial and temporal association between microfractures and otosclerosis in the otic capsule.