The choice of the operation depends principally on the existing anatomical and pathological conditions.
If the meatus be very narrow the intrameatal method may fail to bring the stapes into view. If, on the other hand, the meatus be wide and there be a large perforation, the result of previous middle-ear suppuration, the incudo-stapedial joint or the head of the stapes itself may be actually within the field of operation.
The intrameatal method. The patient should be fully anæsthetized and the operation performed under good illumination. A portion of the tympanic membrane in its upper posterior quadrant is excised in order to bring into view the incudo-stapedial joint. The incision is begun just behind the handle of the malleus and is carried upwards and backwards in a circular fashion through the tympanic membrane along the posterior fold, and then downwards for a little distance along its margin. The flap so made either falls downwards, or can be pressed downwards so as to expose to view the inner wall of the tympanic cavity. With a small knife, curved on the flat, the incudo-stapedial joint is cut through. With a fine hook the long leg of the incus is dislocated forwards or backwards from the stapes. The head of the stapes will now be seen, with the tendon of the stapedius muscle running horizontally backwards. With a paracentesis knife, the tendon is cut through close to its attachment to the stapes.
A fine, blunt-pointed hook is now inserted between the crura of the stapes. If the stapes be not firmly ankylosed it can usually be removed by slight traction. If, however, it be firmly fixed, its crura will probably be broken. To determine whether the stapes is ankylosed or not, direct pressure of the probe on the head of the stapes may be necessary. If the head of the stapes cannot be seen, it is advisable, as suggested by Dench of America, to punch out part of the upper posterior margin of the attic-wall with the attic forceps (see [p. 357]).
The post-aural method. The preliminary steps of the operation are the same as have been already described for removal of an exostosis (see [p. 318]).
After separating and reflecting forward the membranous from the bony portion, the upper posterior part of the tympanic ring is chiselled away until a view of the stapes can be obtained. The incus is then disarticulated from the stapes.
If the stapes be ankylosed by fibrous adhesions to the margins of the fenestra ovalis, an attempt may be made to free it by cutting through the adhesions with a fine bistoury. If this be impossible, a sharp hook may be fixed into the margin of the plate of the stapes in the hope of forcibly extracting it. Some authorities advise chiselling away of the margins of the fenestra ovalis. If an opening can be made into the vestibule by this means, it is hoped that the resulting scar tissue will form a membrane more resilient than the ankylosed stapes, and, in this way, permit vibrations of sound to enter the labyrinth. This operation, however, necessitates the complete mastoid operation in order to freely expose the region of the fenestra ovalis.
After-treatment. It is sufficient to protect the ear with a small gauze drain. Occasionally there may be considerable vomiting and vertigo as an immediate result of the operation; this usually passes off within two or three days. Meanwhile the patient should be kept in a recumbent position and, if necessary, given small subcutaneous injections of morphine.
Difficulties. The chief difficulty is to obtain a good view; even if this be obtained it is difficult to extract the stapes without fracture of its crura.