Analysis of bone remodelling in the otosclerotic stapes by means of tetracycline labelling

Pathology of otosclerosis: a review

Otosclerosis is a bone disorder of unknown etiology confined to the otic capsule. Failure of remodeling of newly formed vascular, woven bone (otospongiosis) results in sclerotic bone (otosclerosis) with abnormal osteons. Involvement of the oval window causes conductive hearing loss. Electron microscopic, histochemical, and biochemical studies identify normal cellular and matrix components of otosclerotic bone without providing clues to the abnormal bone formation and resorption. Plastic-embedded, nondecalcified histologic sections with in vivo tetracycline labels permit the study of mineralization rates to separate this disorder from other bone dyscrasias that have similar histopathologic appearances. Characterization of the cells, matrix, and their mediators can yield an understanding of abnormalities that disorder bone.

Quantitative evaluation of postnatal bone growth in the auditory ossicles of the dog

The postnatal bone growth (appositional and internal) in the auditory ossicles and in the tibia of three mongrel dogs was studied by means of tetracycline and alizarin labeling. The appositional growth is characterized by an increase in the external dimensions of the auditory ossicles within the first month of postnatal life. No trace of bone deposition was found after this period of time. The patterns of internal growth are: 1) the rate of primary osteon formation shows the same value in the incus and malleus; 2) these values are always less than those in the primary osteons of the diaphysis of the tibia of the same dog; 3) the time required for the formation of these osteons in the auditory ossicles, like in the other parts of the skeleton, increases significantly with age.

Otosclerotic stapes: morphological and microchemical correlates. An electron microscopic and x-ray analytical investigation

A total of 32 otosclerotic stapes is thin-sectioned without decalcification and examined using transmission and scanning electron microscopes, with a nondispersive x-ray analyzer attached to the latter. These otosclerotic stapes are classified as spongiotic, sclerotic, or preotosclerotic, accoring to their pathologic characteristics and state of mineralization. Either diffuse or patchy demineralization in the ground substance appears to be the initial stage of otosclerosis, and this area coincides with preotosclerotic lesions (also known as blue mantle) in light microscopy. Therefore, it is interpreted that demineralization precedes the destruction of ground substance in the preotosclerotic lesion. Bone mineral deposits in new otosclerotic bone appear to be related to the collagen fibrils that are embedded in the ground substance. No mineral deposit could be seen without the ground substance deposition; therefore, it is suggested that this ground substance is the single most important factor in the poor mineralization of the otosclerosis. The sclerotic lesions are well mineralized and show a typical pattern of hydroxyapatite by x-ray diffraction study. We could not confirm the notion that the sclerotic lesion is hypermineralized as compared to the normal stapes. The spongiotic lesions are poorly mineralized, with low calcium salt. Using the Ca/P ratio and x-ray diffraction pattern as criteria, it was determined that spongiotic lesions belong to unstable, immature bone.

A topographic quantitative analysis of the post-natal bone formation in the auditory ossicles of the dog

The amount and distribution of the post-natal bone deposition in the auditory ossicles and in the left tibia of dogs of varying ages were studied by means of alizarin labelling. The relative amount of fluorescent new-formed bone was expressed as a percentage ratio NB/(NB+PB) of new bone (NB) on the pre-existing bone (PB). The result was that the post-natal bone deposition (1) was larger in the tibia than in the incus, malleus and stapes; (2) significantly decreased with age both in the ossicles and in the tibia; (3) in the stapes it stopped at 3 months, while it was present in the tibia, incus and malleus even at 12 months. In the ossicles the post-natal bone deposition takes place both on the periosteal surfaces of the ossicles and on the internal surfaces of the haversian systems. The first process produces an appositional growth that stops in all three ossicles within the 1st month of post-natal life, the second one produces an internal growth that continues until the age of three months in the stapes, while in the incus and malleus it occurs in small amounts, even in the 12th month of life. In the ossicles all the new-formed bone tissue, periosteal and osteonic, is built up by primary bone (addition bone). In the tibia from 50 days of age the primary bone is gradually replaced by secondary haversian systems as a consequence of remodelling processes.

Active otosclerotic foci in the stapes. An electron microscopic study

A total of 12 undecalcified and decalcified otosclerotic stapes containing active spongiotic lesions were examined using an electron microscope. Evidence of osteolytic osteolysis was seen in all specimens, but osteoclasts were observed in only four. The advancing front in the spongiotic lesion was 'moth-eaten' due to the demineralization of canaliculi and lacunae. The demineralizing process appeared to be initiated by degranulation of lysosomes by the degenerating osteocytes. As bone resorption continued, poorly mineralized new bone was laid down by osteoblasts which showed mitochondrial swelling. The possible implication of this mitochondrial swelling is discussed in relation to the pathology of the otosclerosis.