Predilection of otosclerotic foci related to the bone turnover in the otic capsule.

Using multiple fluorochrome tagging of eight mongrel dogs and a newly established methodology of measuring bone turnover (BTO) in the otic capsule, it has previously been demonstrated that BTO in the canine otic capsule is highly reduced close to the perilymphatic spaces (PLS) compared to the normal level of BTO in the periphery. Reanalysis of these data shows that this inhibition of BTO is far more pronounced around the cochlea and vestibule than around the semicircular canals. Similar tendencies are seen for the numerical density and mean label area of the bone remodelling units. With increasing distance to the PLS, these patterns are weakened, but still recognizable. In otosclerosis, foci of abnormal bone deposition are particularly frequent around the oval and round windows and in the cochlear capsule, i.e. where inhibition of bone remodelling is most prominent. A surpassing (or failure) of this pronounced inhibition must precede the tumultuous but delimited osteogenesis of otosclerosis. Otosclerosis may be a deviation of the normal BTO process in an osteometabolically abnormal site, perhaps initiated as an osteogenetic response to abnormal stress exposure.