The stapediovestibular joint is the fully-functional articulation between the stapes and the oval window. It has a key role in the transmission of sound vibrations in the middle ear to the fluid in the vestibule, and thence in the cochlea .
The annular ligament of the stapes, also known as the ligamentum anulare stapedis, attaches the rim of the footplate of the stapes to the rim of the oval window.
The annular ligament is formed from fibrous tissue. Recent measurements of cadaveric specimens using micro-CT show that the thickness of the annular ligament varied from 0.26 mm to 0.64 mm, with a mean of 0.38 mm . In clinical work the small size of these structures is below the spatial resolution of even high resolution CT of the petrous bone to resolve. However cone-beam CT might be able to in the future.
There is disagreement in the literature about what type of articulation the stapediovestibular joint is, it has been described variously as a syndesmosis, amphiarthrosis, a synarthrosis, or an incomplete diarthrosis .
The stapediovestibular joint shows the typical development of a syndesmosis. The annular ligament forms as a cartilaginous precursor from the adjacent footplate and the otic capsule. The joint attains its normal developed form by the 12 gestation week .