Temporal bone dynamics, the hard way. Formation, growth, modeling, repair and quantum type bone remodeling in the otic capsule.

This review presents studies in which temporal bone dynamics were monitored in undecalcified human and animal materials by combined microradiography and osteofluorochromic time labeling. The results are interpreted in accordance with modern concepts of spatial and temporal organization of bone behavior in an attempt to contribute to a new basis for understanding the structure and function of the bony otic capsule. In postcartilaginous development, perilabyrinthine bone formed a separate functional unit in which growth and modeling were absent. Consequently, all drift movements bypassed the bone present inside a narrow perilabyrinthine zone, which in effect maintained a so-called drift barrier enclosing the entire inner ear. In baseline bone remodeling and repair-associated remodeling transients, secondary osteons were distributed centrifugally with respect to inner ear spaces, and the average osteonal size decreased towards the inner ear, suggesting a progressive inhibition of bone resorption towards inner ear spaces. No histological capsular component proved resistant to bone resorption during modeling and remodeling. Instead the dynamic behaviour of any moiety of capsular bone appeared to depend on its spatial relation to the membranous labyrinth rather than on histological characteristics. This spatial organization of perilabyrinthine bone development and turnover is responsible for the unique histology of capsular bone and may explain the accumulation of fatigue micro-cracks which can be found in human perila byrinthine bone. These findings suggests the role of inner ear tissues as a functional matrix in control of capsular bone dynamics even beyond fetal life.