Stapes surgery for otosclerosis
Results of Mr Hamilton's Stapes Surgery
Mr Hamilton has operated on over four hundred patients with otosclerosis. Mr Hamilton's results have been audited and presented for discussion twice.
- Hearing improved in 99% of patients in both studies.
- Hearing has been restored to normal in 97% of patients.
- 1% experienced loss of hearing in the operated ear.
Here is more information about otosclerosis and how Mr Hamilton performs the operation.
The cells in the cochlea which are responsible for converting the signal from one form to another are surrounded by fluid through which the acoustic waves travel. Sound waves do not pass from air into water particularly well. In fact, only one part in a thousand is transmitted and the rest is reflected. This means that a cochlea on its own is not a very sensitive detector.
To improve the transmission of sound into the cochlea we have an ear canal, and ear drum and three hearing bones. The innermost of the three hearing bones is named 'the stapes' and this inserts into the wall of the cochlea.
A simplified view of the hearing mechanism. Sound is passed from the ear canal to the cochlea by means of the ear drum and the three hearing bones. In the cochlea the signal is converted to nerve signals which are interpreted by the brain.Otosclerosis fixes the footplate of the stapes (stirrup) to the wall protecting the cochlea. This stops the stapes' movement so sound is no longer transmitted into the cochlea. The patient becomes aware that their hearing in the affected ear has deteriorated.
Doctors think of hearing loss due to changes in the cochlea and hearing loss due to changes in the structures transmitting sound to the cochlea as two separate categories.
Sensorineural loss: hearing loss due to changes in the cochlea or cochlear nerve. The mechanism of the cochlea and its nerve are so complicated that doctors do not know how to improve them with medicines or surgery, so hearing aids are used if they don't work well. Hearing aids are amplifiers.
Conductive loss: hearing loss due to changes in the structures that transmit sound to the cochlea. The structures are relatively simple and so their disorders can be treated with medicines or surgery.
Otosclerosis is a disease of the bony protective layer of the cochlea.
The footplate of the innermost of the three hearing bones (the stapes) sits in a window in this layer. Otosclerosis causes the stapes to fuse with the protective layer. This stops the stapes from moving, so it can no longer vibrate. This means that sound cannot reach the cochlea. A patient with an ear affected by otosclerosis notices hearing loss in that ear.
A microscopic section through the tissues of the cochlea, the stapes and the incus. Otosclerosis is a disease of the bone capsule of the cochlea which fixes the stapes footplate to the rest of the capsule. This means that the stapes is unable to vibrate and transmit sound into the cochlea.Part of the superstructure is outside the plane of the section and so appears to be absent.
It is usually possible to diagnose otosclerosis on the basis of a consultation alone. A patient who has conductive hearing loss with normal eardrums has usually got otosclerosis. Other features of otosclerosis which support the diagnosis are a positive family history, onset in the third or fourth decade and worsening of hearing during pregnancy. Hearing tests will confirm the presence of a conductive hearing loss as well as loss of the loss of mobility of the stapes. Sometimes a scan may be required to exclude other rare causes of a conductive hearing loss.
The aim of stapes surgery is to eliminate the conductive hearing loss due to otosclerosis. Provided that the patient has no sensorineural loss, surgery will restore the patient's hearing in the operated ear to normal.
The ear drum is lifted forward to reveal the fixed stapes, the arch of which is removed. The laser is used for this to minimise the risk of fracturing the stapes in the wrong place. In this image one limb of the stapes arch has already been lasered through; the other is hidden by the incus but the optical fibre can guide the laser energy around the corner to the stapes.
Once the stapes arch is removed, the remaining two hearing bones can move freely again.
A tiny (0.8mm) hole is made in the stapes footplate.
The hole through the stapes footplate is sealed with a tiny vein graft to ensure no leakage of inner ear fluid.
The replacement prosthesis is placed onto the vein graft and inserted into the fenestration, where it can move in and out freely, and is clipped to the mobile incus.
The position and mobility of the prosthesis is checked and then the ear drum is closed in its original position.