Bone mineral density of human ear ossicles: An assessment of structure in relation to function

Abstract

Human ear ossicles are essential for normal sound conduction from the external environment to the inner ear. These bones are subjected to high biomechanical loads due to the sustained vibrations which occur with reception of sound. It is expected that the bones would undergo a significant amount of remodeling and change in bone mineral density during the lifespan of an individual. Therefore, the aim of the study was to evaluate the possible changes in bone mineral density of regions of the ossicular chain during postnatal life. Forty four left and 36 right sets of human ear ossicles, ranging from a sub-adult age group to a mature adult age group, were sourced from the School of Anatomical Sciences, University of Witwatersrand. The ear ossicles were scanned using a micro-focus CT X-ray. A three-dimensional reconstruction of each ossicle was created from the CT scan. Bone mineral density was then determined at specific sites on the ossicles. There was no statistically significant variation found in the bone mineral density in relation to the age of the specimens. However, the handle of the malleus, the incudo-stapedial joint and the insertion site for the tendon of stapedius had lower bone mineral densities when compared to adjacent articulation and nonattachment sites on the ossicular chain. This is possibly due to biomechanical stress in response to sound conduction rather than ageing. Lower bone mineral density may be indicative of regions that experience the highest biomechanical force, thus, resulting in increased remodeling. Clin. Anat. 00:000-000, 2018. © 2018 Wiley Periodicals, Inc.

Characterizing Bone Density Pattern and Porosity in the Human Ossicular Chain using Synchrotron Microtomography

“…Thus, these sites are expected to have higher bone mineralization. The stapes footplate, which is in contact with the inner ear, has been found to have a higher density than other parts of the ossicles 4 . It is considered essential for effective sound transmission, as the higher density of the footplate allows an e cient coupling with the uid in the inner ear.…”

“…Density affects their stiffness and mass, which in turn affects the ability to transmit sound. Unlike long bones, human auditory bones complete ossi cation shortly after birth, and little ossicular bone remodeling has been observed after that [2][3][4][5] . Recent studies have shown that the overall mineralization is much higher than in long bones 3 and that the density distribution within the ossicles is not uniform 6 .…”

“…Recent studies have shown that the overall mineralization is much higher than in long bones 3 and that the density distribution within the ossicles is not uniform 6 . It has also been hypothesized that there is a variable degree of bone remodeling due to the different loads in this tiny biomechanical system 4,6 .…”

Assessing the morphology and bone mineral density of the immature pars lateralis as an indicator of age

“…Whilst some changes may be the result of general increases in size-associated growth, others may be the result of biomechanical influences. Assessments of bone density changes across various elements of the immature skeleton including the mandible [ 25 ] and ear ossicles [ 26 ] have proven useful in showing the potential effects of biomechanical influences on changes in the morphology of bones with growth. Hutchinson et al [ 25 ] in a sample of 45 mandibles aged between 30 gestational weeks and 5 years of age provided insights into the direction of growth of the mandible relative to dental eruption [ 25 ].…”

“…Hutchinson et al [ 25 ] in a sample of 45 mandibles aged between 30 gestational weeks and 5 years of age provided insights into the direction of growth of the mandible relative to dental eruption [ 25 ]. Morris et al [ 26 ] showing a pattern of change in bone density relative to function across the ear ossicles illustrated how bone density patterns could be used to reflect changes in the functional environment [ 26 ]. These relationships between changes in bone mineral density patterns and growth of immature skeletal elements have provided valuable insights into how the morphology of the bone is influenced with age.…”