Surgical Technique

Surgery is performed with the patient in the supine position. The operating table may be manual or electrical, but must rotate from side to side, as well as Trendelenburg. The surgeon sits at the head of the operating table with the operating nurse sitting on the opposite side of the table. An audiologist monitors the facial nerve in patients with known anomalies of the facial nerve and in patients with a congenital hearing loss. The anesthesia equipment and anesthesiologist sit at the foot of the table.

General anesthesia or local anesthesia supplemented with intravenous sedation is employed, depending on the patient preference. The ear is cleaned with povidone-iodine solution and sterile self-adhering drapes are applied. The skin of the external auditory canal is injected with a solution of 1% lido-caine with 1:100,000 epinephrine. The injections are placed in the four quadrants of the external auditory canal at 1 to 2 mm lateral to the bony-cartilaginous junction.

While waiting for the vasoconstriction effect of the epinephrine, a vein graft is harvested. In men, a distal superficial vein from the dorsum of the hand provides a graft of proper thickness. In women, a more proximal vein, such as the cephalic vein or a vein from the volar surface of the wrist proximal to the flexor crease, may be chosen. The incision is closed with an absorbable subcuticular suture. The loose adventitia of the vein is removed by running a wire (or a Barbara needle) through the vein, grasping the adventitia with forceps and running a No. 15 scalpel blade along the sulcus between the vein and the adventitia. The vein is incised lengthwise, trimmed to a 5 X 5-mm square, and set aside in saline. If the vein graft is too thick, it may be placed in a Gelfoam press until used.

Speculums of increasing sizes are used to dilate and compress the skin of the ear canal, thus improving exposure and reducing bleeding at the incision. The speculums used are relatively soft and malleable, made of nickel-silver alloy. Only the posterior half of the tympanic membrane needs to be visualized.

The ear canal incision is made parallel to the annulus at the end of the speculum, not perpendicular or tangential to the annulus. This incision avoids tearing the tympanic membrane and reduces bleeding. The incision must not be made with the laser, which would result in a several millimeter shrinkage of the flap. The flap is elevated with a Merocel microsponge and the middle ear space is entered. The microsponge prevents direct trauma to the flap from the microsurgical instruments, aids in hemostasis, and prevents introduction of loose cotton fibers when cotton pledgets are used.

The bone over the chorda tympani is outfractured using a strong hook or is removed with a stapes curette. Adequate removal of the bony canal for the chorda tympani nerve is important to permit mobilization of this nerve inferior to the oval window The posterior scutum is removed with either a mallet and gouge or a stapes curette. The amount of the scutal bone that is removed is limited, but one needs to visualize the pyramidal eminence and the inferior aspect of the facial nerve clearly. Care is taken to maintain adequate scutal bone over the incus to avoid postoperative retraction of the tympanic membrane onto the incus and the prosthesis. The mobility of the lateral ossicular chain is tested for attic fixation.

Mesenchymal middle ear adhesions are removed with the laser (1.5 W X 0.1 s). The stapedius tendon is vaporized with three to five laser pulses. A No. 3 suction in the surgeon's nondominant hand aspirates the laser plume. Alternately, the stapedius tendon may be preserved and separated with a small hook from the stapes for later attachment to the stapes prosthesis.

With the suction stabilizing the incus, the incudostapedial joint is separated using a small, flat, right-angled hook or incudostapedial joint knife. The mobility of the malleus, incus, and stapes is checked again to rule out attic fixation or a mobile stapes. The posterior crus is vaporized (1.5 W X 0.1 s) as close as possible to its junction with the footplate. Care must be taken to avoid direct laser irradiation of the facial nerve and to aspirate the laser plume. Waiting 10 to 15 s for cooling between laser pulses lessens the risk of thermal injury to the facial nerve. Vaporization of the posterior crus is complete when bone turns to a white or gray char. The anterior crus is then vaporized at its junction to the footplate. In approximately one-fourth of cases, this step may be accomplished under direct vision. In the remaining cases, the junction of the anterior crus and the footplate cannot be seen. The fiberoptic tip is placed by palpation on the junction of the anterior crus and the footplate. Vaporization is complete after three to four pulses. The superstructure remnant is removed. The remnant of the posterior crus is removed to the level of the stapes footplate using a 0.7-mm diamond burr and microdrill.

The distance between the incus and the stapes is determined using a measuring instrument or by the use of "dummy" prostheses trimmed to a known length. A dummy prosthesis is placed on the posterior half of the stapes footplate and against the long process of the incus. With a Causse prosthesis, the proper size to select is one in which the lower portion of the ring sits approximately half above and half below the medial edge of the incus. This additional prosthesis length provides extension of the prosthesis 0.2 to 0.3 mm into the fenestra.

The fenestra is placed in the posterior half of the footplate. The tip of the optical fiber is placed directly on the footplate to create the laser rosette for the stapedotomy. A 0.8-mm rosette is made by connecting 0.2-mm laser spots (1.5 W X 0.1 s). Once again, care is taken to allow 10 to 15 s between pulses for cooling. The laser char of the rosette is gently brushed away with microdrill using a 0.7-mm diamond burr. Alternatively, the char may be removed with an oval window rasp.

The fenestra is placed in the posterior half of the footplate for several reasons. Placing the fenestra posteriorly minimizes the chance of damaging the saccule. Any adhesions between the saccule and footplate will be found at the level of the anterior annular ligament. Avoiding the anterior otosclerotic focus reduces the risk of releasing proteolytic enzymes into the inner ear and reduces the chance of bleeding. Finally, placing the fen-estra posteriorly allows reconstruction of the annular ligament with restoration of the proper acoustic impedance.

The prosthesis is trimmed 0.2 to 0.3 mm longer than the distance from the incus to the footplate. The ring of the prosthesis is opened by placing it between the thumb and index finger, placing a Barbara or Rosen needle instrument through the ring, and gently rolling the needle away from the shaft. Alternatively, the ring of the piston may be opened by placing the cup forceps within the ring of the piston and spreading the jaws of the instrument several times. With either method, the ring will remain open for several minutes because of the memory of the Teflon.

Before placing the vein graft in position, the surgeon notes the location of the fenestra relative to nearby landmarks. Alternatively, a single laser spot on the promontory may be used as a point of reference to the fenestra. The vein is placed over the tip of a No. 3 suction with the intimal surface facing the suction tip. With the suction in the surgeon's nondominant hand and a needle in the dominant hand, the vein is placed over the fenestra, and the edges are unfurled with the intimal surface facing the tympanic membrane and adventitial surface facing the vestibule.

Placement of the prosthesis into the vein-covered fenestra and over the incus may be accomplished with cup forceps, but for finer control, a suction to hold the prosthesis and needle to stabilize the incus are used. Alternatively, a Barbara needle is used to impale the prosthesis and a suction to stabilize the incus is used. With the prosthesis is in place, the vein graft puckers around the shaft of the prosthesis. The position of the prosthesis may be adjusted on the long process of the incus so that the shaft is perpendicular to the fenestra. The ring of the prosthesis is gently crimped over the incus with cup forceps. To ensure that the prosthesis is engaged into the fenestra, a small hook is used to apply lateral pressure to the shaft. If the prosthesis is not secure in the fenestra, it will swing out of position. If the prosthesis is properly positioned in the fenestra, the shaft will bend. The tympanomeatal flap is returned to the normal anatomic position and is held in place with a thin layer of Gelfoam that is covered with a Merocel otowick sponge expanded with saline. The expanded otowick applies gentle pressure to the flap and limits bleeding. The otowick also acts as aural protection for the immediate postoperative period.

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