This surgical procedure is performed to treat deafness due to otosclerosis. Otosclerosis is caused by fixation of the foot plate of stapes which prevents efficient sound transmission to the oval window. The deafness caused is conductive in nature.
The surgical procedure is performed under local anesthesia. Advantages of performing this surgery under local anesthesia are:
1. Improvement in hearing can be ascertained on the table.
2. Bleeding is minimal under local anesthesia.
Indications for stapedectomy:
1. Conductive deafness due to fixation of stapes.
2. Air bone gap of atleast 40 dB.
3. Presence of Carhart's notch in the audiogram of a patient with conductive deafness.
4. Good cochlear reserve as assessed by the presence of good speech discrimination.
Contraindications for stapedectomy:
1. Poor general condition of the patient.
2. Only hearing ear.
3. Poor cochlear reserve as shown by poor speech discrimination scores
4. Patient with tinnitus and vertigo
5. Presence of active otosclerotic foci (otospongiosis) as evidenced by a positive flemmingo sign.
Since a patient with otosclerosis is also an ideal candidate for hearing aid and surgery, the patient must be properly counselled regarding the advantages and disadvantages of both.
Xylocaine with adrenaline mixed in concentration of 1:1000 is used to infiltrate the external auditory canal. 0.25 ml of the solution is infiltrated using a 27 gauge needle. Infiltration is given as illustrated in the diagram.
Image showing the areas where local anesthetic agent needs to be infiltrated
Exposure: A large speculum is used to straighten the external auditory canal. A curved or triangular incision is made in the external canal skin begining at 2mm away from the annulus. The incision extends from 11 o clock position to 6 o clock position as viewed in the right ear. The tympano meatal flap is elevated up to the annulus. Using a sharp pick the annulus is slowly lifted from its groove, the middle ear mucosa is exised and the middle ear proper is entered.
Diagram showing incision for elevating tympanomeatal flap in the right ear
In most patients the posterior superior bony overhang must be curetted using a curette (designed by House). The long process comes into view. Curetting is continued till the base of the pyramidal process is visualised. Oval window is visualised. At this point round window reflex is tested by moving the handle of malleus and looking for movement of round window membrane. In otosclerosis this reflex is absent.
Using a hand burr a small fenestra about 0.6mm in diameter is made over the foot plate. The stability of the incus is left intact because the stapedial tendon is not cut at this point. From now on the steps may vary according to the surgeon's viewpoint. Some surgeons would like to insert the piston at this stage without disturbing the stability of the incus. The distance between the long process of incus and the foot plate is measured using a measuring rod. Appropriate size teflon piston is introduced and humg over the long process of the incus and is crimped after ascertaining whether its lower end is inside the fenestra. The stapedial tendon is cut at this point and the supra structure of the stapes is disarticulated and removed. The Tympanomeatal flap is repositioned.
Complications of stapedectomy:
1. Facial palsy
2. Vertigo in the immediate post op period
4. Perilymph gush
5. Floating foot plate
6. Tympanic membrane tear
7. Dead labyrinth
8. Perilymph fistula