Partial Stapedectomy

History

In 1958, Shea advocated total stapes footplate removal when using the polyethylene strut prosthesis and a vein graft to seal the oval window. Shortly thereafter, Schuknecht advocated the use of a wire and fat prosthesis, and House and Greenfield later advocated the use of a wire with absorbable gelatin sponge (Gelfoam) prosthesis. The use of a wire with Gelfoam or a wire-fat prosthesis necessitated total removal of the footplate for the wire prosthesis to function satisfactorily. Other methods that could be considered a partial stapedectomy technique included the shattered footplate procedure, with the use of a polyethylene strut, and the subluxated footplate procedure, both of which necessitated removal of the superstructure of the stapes. These two techniques were quickly rejected because of the associated sensorineural hearing loss resulting from either surgical trauma or a perilymphatic fistula.

In 1961, the piston concept was introduced, in which a cup-piston prosthesis was used with a connective tissue graft of vein to seal the oval window. The introduction of the piston prosthesis no longer required a total removal of the stapes footplate. The concept evolved of “removing only that part of the footplate which comes out easily.” Thus, this newly introduced surgical technique produced more successful hearing results and fewer inner ear complications. The same technique could be used for the thin blue footplate with minimal otosclerotic involvement, or for the obliterative footplate, in which only a stapedotomy opening (“drill-out”) could be created. In obliterated footplates, more footplate removal should occur because of a greater chance of regrowth. Measurement of the distance between the long process of the incus and stapes footplate was eliminated because a 4-mm prosthesis would protrude into the vestibule by 0.2 to 0.3 mm in virtually every patient. This slight protrusion would create a self-centering effect. With the interposition of a vein graft between the prosthesis and vestibule, regrowth of the otosclerotic bone, including the obliterative type, rarely occurs. In addition, because of this protrusion, migration of the piston in subsequent years was virtually unknown.

The unique design of the cup-piston prosthesis permitted the surgeon a choice of a total stapedectomy or partial stapedectomy or stapedotomy. The classic cup-piston prosthesis was fabricated of grade 316L stainless steel, an alloy that is inert in living tissue and is nonmagnetic. Since 2005, the stainless steel has been replaced with titanium because of the development of more powerful magnetic resonance imaging (MRI) scans and the theoretical possibility that they may affect a stainless steel prosthesis. The design enhanced the self-centering effect because of the cup attachment to the lenticular process of the incus (the true physiologic point of attachment) and because of the axially placed stem protruding minimally through the footplate opening. The four holes in the cup and the hole on the distal end of the piston encourage tissue and vascular ingrowth to secure the prosthesis and to allow capillaries to vascularize the lenticular process, eliminating the avascular necrosis that so frequently occurred with the polyethylene strut or a wire.

The 4-mm length is used in virtually every stapedectomy procedure, whether it is a drill-out stapedotomy, a partial footplate removal, or a total footplate removal. Any connective tissue can be used with this prosthesis, but one author (M.R.) uses a vein graft that outlines the oval window opening and ensures a complete, immediate seal of the oval window. Moon advocates the cup-piston prosthesis with areolar tissue. Alternate grafts could be a sensory nerve from the dorsum of the arm if a vein cannot be found, particularly in an obese patient. The subsequent numbness of the dorsum of the arm would take a few months to subside. Perichondrium is a possibility, especially if using a total ossicular prosthesis in a revision, but is likely too thick in a primary stapedectomy. The cup-piston prosthesis is radiopaque and easy to localize and identify on routine mastoid radiographic views. Comparison of impedance studies of various stapes prostheses has shown the stainless steel cup-piston to be the closest in compliance to that of a normal mobile stapes. Hearing results reported by otologic surgeons who have used this technique have consistently confirmed 96% air-bone gap closure of within 10 dB. Similarly, the complete closure (and overclosure) rate has been repeatedly confirmed at 80%, which the wire-tissue prosthesis and wire pistons have yet to attain.

Because the stapes does not increase in size with age, the 4-mm cup-piston prosthesis has been used in children aged 5 years, adults, and elderly individuals. All patients who demonstrate an air-bone gap, absent reflexes, and normal results on otologic examination are candidates for stapedectomy surgery if stapedial fixation is identified at the time of the middle ear exploration. Approximately 22% of patients with otosclerosis have a diminished cochlear reserve with a Shambaugh preoperative bone conduction classification of D or E. These patients have very severe mixed hearing losses, and in many, only a partial footplate removal can be obtained. These patients also most frequently demonstrate complete closure and overclosure of the air-bone gap. For these patients, the extra 10 dB of hearing gain is crucial because of their mixed hearing loss. Approximately 74% of the patients undergoing surgery have partial or total footplate removal that does not necessitate drilling. The remaining 26% require drilling to create a fenestra, 0.8 mm in diameter or larger, to accept the vein graft and cup-piston prosthesis.

In the last 20 years, the number of patients with otosclerosis requiring a drill-out has fallen to below 5%. In 1980, Austin compared the results of total stapedectomy and partial stapedectomy, tissue seal and no tissue seal, and the small fenestra of Smyth. His statistical analysis, using chi-square tables for success or failure, sensorineural hearing loss, fistula, and complete air-bone gap closure, was computed. He concluded that a tissue seal provides a better success rate, a significantly lower risk of fistula, and a better hearing result in terms of complete closure or overclosure of the air-bone gap. Austin noted that in addition to the increased risk of sensorineural complications and fistulas, the small-diameter pistons used in stapedotomies did not provide as good a hearing result.

Surgical Technique: Local Anesthesia With Intravenous Sedation, Except In Young Children

Stapedectomy footplate surgery follows a very basic principle— be as atraumatic as possible in removing the footplate of the stapes . This principle is contingent on removal of “only that part of the footplate which comes out easily.”

Routine stapedectomy is divided into three stages: (1) exposure of the middle ear, incus, stapes, and footplate area; (2) removal of the stapes superstructure; and (3) removal of the stapes footplate. If the opening is 0.8 mm or larger, the piston can function satisfactorily. The new fenestra must be sealed with a tissue graft; a self-centering 4-mm cup-piston bridges the gap from the oval window membrane to the incus ( Figs. 23.1–23.5 ).

Footplate surgery can be classified as follows:

• • Total footplate removal , in which a blue footplate with all oval window margins is visualized

  • Partial footplate removal , in which absent margins are in part of the circumference of the footplate, but where there is a blue area for perforating

  • Total footplate removal with drilling , in which a thick footplate with margins and without a blue center exists for perforating the footplate (biscuit footplate)

  • Partial footplate removal with drilling , in which absent margins are in part of the circumference of the footplate, and there is no blue area for perforating the footplate

  • Drill-out for obliterative otosclerosis , in which no margins of the oval window and thick-mounding otosclerotic bone exist

The technique used in this method involves the use of the cup-piston stainless steel stapes prosthesis and a vein graft to seal the recreated oval window. The vein graft is usually taken from the dorsum of the opposite hand by an assistant surgeon at the same time the ear is being operated on. A surgeon may take the vein from the same side before exploring the ear. After the vein is opened, it is thinned and as much of the adventitia is removed as possible. It is trimmed to a final size of 4 × 8 mm. The graft is placed in a small bowl of intravenous saline until it is ready for insertion. The vein is folded over the tip of a smooth-jawed microalligator forceps, umbrella-style, and is inserted into the middle ear, avoiding contamination by not touching the ear speculum or the wall of the external auditory canal. The vein is placed over the oval window opening with its adventitial surface facing the vestibule. It is indented slightly into the vestibule with a fine, curved needle or a No. 26 suction so that the exact location of the oval window is visualized.

Measurement of the distance between the long process of the incus and the oval window is unnecessary because the 4-mm-long prosthesis is used in virtually every patient. If there is a drill-out, a 4.5-mm prosthesis may optionally be used to ensure the self-centering effect by protruding 0.7 mm into the vestibule; this also retards the formation of new otosclerotic bone. The prosthesis is grasped at its cup end with a small, smooth alligator forceps and targeted into the dimpled portion of the vein graft. It is engaged on the lenticular process of the incus by slightly depressing the socket with the curved needle, and then allowing the prosthesis to rise up and lock onto the lenticular process. One may use a two-hand technique using an incus hook in one hand and a strut guide in the other, simultaneously raising the incus and depressing the prosthesis into the dimpled graft. The wire loop is rotated over the long process of the incus. The wire is not crimped because the fit is precise. If the wire does not easily slip over the incus, it is not necessary to use it. Mucosa grows over the wire loop and secures its position.

Before the middle ear is closed, the malleus is gently palpated to ensure that there is mechanical transmission of vibration from the malleolar handle to the prosthesis. The vein graft is inspected to ensure that its edges overlap the entire oval window area and that there is no inversion of any of the edges toward the vestibule; otherwise this problem may predispose the patient to a perilymphatic fistula. The tympanomeatal flap is replaced and the ear canal packed with bacitracin-soaked Gelfoam that is removed after 1 month if it has not dissolved. Prophylactic antibiotics are used before and after surgery for 3 days, and glycerin and peroxide for 1 week prior to the 1-month postoperative visit.

This prosthesis or modifications thereof, because of the unique design, is a “smart” prosthesis—it can be fitted to the incus under many circumstances. It can fit an angled lenticular process; an extra-large lenticular process; an extra-long process; a short long process; or a fractured, atrophic, or necrotic long process. When a narrow oval window niche or prolapsed facial nerve is present, the prosthesis easily self-centers into the vein graft. When there is only partial footplate removal or drill-out for obliterative otosclerosis, the vein graft and prosthesis align perfectly because of the self-centering feature.

Modifications of The Cup-Piston Stapes Prosthesis

Infrequently, an anatomical variation in the middle ear may result in a prosthesis with suboptimal performance. For these infrequent situations, a cup-piston prosthesis with an offset shaft compensates for a short long process of the incus, a prolapsed facial nerve, and an abnormally high rise of the promontory.

When the lenticular process of the incus is absent or there is erosion of the long process of the incus, the modified Robinson-Moon-Lippy stapes prosthesis compensates for the absent lenticular process. A cutout is in the cup of the prosthesis to accept the eroded long process of the incus, and the shaft is offset in a way similar to the Moon modification. The length of this prosthesis should be 4.5 mm, to compensate for the fact that the long process is in the socket rather than above it.

The standard dimensions of the cup are 0.875 mm (inside diameter) and 0.6 mm (stem diameter), with a 4-mm length. The cup-piston prosthesis is available with a large well (1 mm) and a narrow stem (0.4 mm) for a large lenticular process or narrow oval window niche.