Restore sound conduction in stapes ankylosis by partial removal of the posterior third of the footplate (stapedectomy) or occasionally the entire footplate, or by making a small perforation 0.6–0.8 mm in diameter (stapedotomy) or inserting a stapes prosthesis.
Deafness (approx. 1 % risk), lack of hearing improvement, deterioration of hearing—may be delayed due to slippage or loosening of the prosthesis, or may result from further progression of otosclerosis.
See under Tympanoplasty in Chapter 18 (p. 367). Also, reinforced 90° hook, very fine Fisch or Plester footplate hooks, perforator, McGee crimper, stapes prosthesis, measuring instrument (gauge). Some techniques require a microdrill (Skeeter) or laser (CO2 or Er:YAG).
Local anesthesia is advantageous as it allows for intraoperative auditory testing, and any vertigo due to an oversized prosthesis can be quickly detected and corrected. General anesthesia may also be used.
Exposure. Endaural incision (see Chapter 17, p. 359f) with a No.15 blade. The initial 1-cm incision is made laterally from the center of the bony roof of the ear canal through the inter-cartilaginous fissure and parallel to the anterior helical rim. The second incision is made circumferentially from the 6 o'clock to the 12 o'clock position about 0.5 cm inside the bony meatal entrance. The two incisions form a triangular flap that is raised, reflected outward, and secured with the self-retaining retractor. Small pieces of connective tissue are harvested from the endaural incision.
With a large ear canal, it may be possible to omit the meatal flap or even use a pure endomeatal (transcanal) approach without an endaural auxiliary incision (this requires a self-retaining aural speculum and angled instruments). The tympanomeatal flap is outlined by making additional incisions toward the tympanic membrane at 5 and 11 o'clock in the right ear or 1 and 7 o'clock in the left ear (see Fig. 17.3). The flap is elevated to the annulus with an angled round incision knife.
Opening the middle ear cavity. The annulus is elevated in the posterosuperior quadrant, and the middle ear cavity is entered by dividing the thin, tense mucoperiosteum with a sickle knife while sparing the chorda tympani. The tympanomeatal flap is further mobilized and reflected (Fig. 21.1).
Exposure of the oval window niche. The lateral attic wall is taken down with a House curette to expose the pyramidal eminence and facial nerve over the oval window niche (Fig. 21.2). The long process of the incus is gently probed with a needle or microhook; concomitant movement of the manubrium rules out malleus fixation. Stapes fixation is easily recognized by moving the incus from side to side.
Stapes dissection. The distance from the incus to the foot-plate (measured distance + 0.2–0.3 mm = necessary length of prosthesis) is measured with a gauge (Fig. 21.3). The incudostapedial joint is separated with a medium-sized 90° hook, and the stapedius tendon is divided with the sickle knife (Fig. 21.4).
First the posterior and then the anterior stapes crus is fractured with a medium-sized 90° or 45° hook that is applied close to the footplate and is twisted slightly toward the promontory to shear off each crus at its base (Fig. 21.5). The stapes arch is extracted with a microforceps (Fig. 21.6).
Opening the vestibule. The mucosa surrounding the foot-plate is scored and divided with a slightly curved needle. The mucosa may then be separated from the footplate, although this is not essential (fragments may remain attached to the mucosa during footplate extraction). Working under high magnification, the surgeon perforates the footplate at the junction of the middle and posterior thirds with the perforator, which is applied to the footplate with a slight twisting motion (Fig. 21.7). The hand should be securely braced to avoid exerting too much pressure.
Footplate extraction. The footplate (if still intact) is now split apart with fine 45° or 90° hooks inserted into the perforation. The posterior third of the footplate or the fragments are first elevated with a 45° hook and then extracted with a 90 ° hook (reinforced Fisch or Plester hook or pick, Fig. 21.8). High magnification is still used at this stage to avoid penetrating too deeply into the vestibule. Under no circumstances should these manipulations cause mobile portions of the footplate to sink into the vestibule.
Reconstruction. The stapes prosthesis (e. g., platinum band–Teflon or titanium model, properly sized, average length 4.5 mm, piston diameter 0.4–0.8 mm) is grasped with a fine alligator forceps and held so that the long axis of the prosthesis is at a slight angle to the forceps axis (Fig. 21.9). The eyelet of the prosthesis is threaded over the long process of the incus. The lower end of the piston should project only ca. 0.2–0.3 mm into the vestibule. The position of the prosthesis can still be adjusted at this stage with the 90° hook. When the piston is perfectly positioned, the eyelet is crimped onto the long process of the incus with a McGee forceps (Fig. 21.10), and the placement is again checked for accuracy. The small pieces of connective tissue harvested at the start of the operation are packed around the piston to seal the window (Fig. 21.11).
Concluding the operation. Blood clots are suctioned from the hypotympanum, and the tympanomeatal and meatal flaps are returned to their original positions. The ear canal is lined with silicone film and packed with ointment-impregnated strips. The wound is closed and a dressing is applied.
If the footplate is generally mobile during manipulations before the perforation has been made, the surgeon should attempt to separate the annular ligament at a small site with a needle, working toward the promontory, or drill a small hole directly adjacent to the annular ligament with a very fine, low-speed diamond burr to create a site where a hook can be passed beneath the footplate to elevate it. The oval window is then covered with a small piece of connective tissue that overlaps the window on all sides, creating a foundation on which the prosthesis is placed. With proper facilities, a better option is to convert to a laser stapedotomy, in which even a floating footplate can be perforated using a noncontact laser technique.
If cerebrospinal fluid (CSF) gushes from the opened vestibule because of a wide communication between the CSF space and perilymphatic space, the procedure should be halted at once. The head and upper body are elevated to lower the CSF pressure. The oval window niche is sealed with connective tissue or fibrin-coated collagen that extends to the long process of the incus. Lumbar puncture can be done for additional decompression. In a laser stapedotomy, it may be possible to seal the leak by inserting the piston and covering the site with fat or connective tissue during lumbar drainage of CSF. When this is successful, the procedure can be concluded in the usual way.
A facial nerve that dangles into the niche, usually exposed, or a vascular anomaly can make it impossible to dissect in the niche without jeopardizing the facial nerve. Although it is possible in principle to drill a hole in the promontory and insert a piston, treatment with a hearing aid provides a risk-free alternative.
If stapedectomy cannot be performed because the perforator will not penetrate the otosclerotic niche, a recommended alternative is stapedotomy with a Skeeter drill or laser. A hole is carefully drilled through the footplate with a 0.6-mm burr on a Skeeter microdrill operating at low speed. The upper part of the opening is then widened with a 1-mm diamond burr to prevent the piston jamming in the long, narrow hole.
Visualization of the oval window niche can often be improved by slightly adjusting the patient's head position relative to the surgeon. An overhanging promontory wall can be taken down with a low-speed diamond burr. This should be done carefully because of the risk of opening the cochlea.
Avoid trauma to the chorda tympani. It can be displaced anteriorly from the niche to improve visualization. The bony canal of the chorda tympani can be removed to ca. 3 mm with the House curette to minimize traction.
Optimum coupling of the prosthesis to the long process of the incus is important for a satisfactory hearing result (too loose: deficient sound conduction; too tight: eventual necrosis). Coupling of the prosthesis can be significantly improved by using pistons with a clip mechanism (see different types shown in Fig. 21.12).
Intraoperative sensorineural hearing loss or deafness. Hearing loss that starts on the second or third postoperative day and progresses rapidly to deafness, usually accompanied by nystagmus, is suspicious for early granuloma formation in the oval window niche. (Treat with high-dose corticosteroids, Stenvers infusion protocol, and intravenous antibiotics. If symptoms do not improve within 24 hours, revise by removing the prosthesis, connective tissue, and granulations without entering the vestibule. Then cover the oval window niche with fascia.)