In favour of the galvano-cautery is the fact that the perforation does not tend to close so rapidly. On the other hand, considerable damage may be done unless it is applied with extreme care. For this reason it is wiser to operate under a general anæsthetic, such as gas and oxygen.
If the paracentesis knife be used it is not sufficient to make a simple incision; a small triangular flap must be excised. The operation should be performed under good illumination. The paracentesis knife is inserted boldly through the membrane a little behind and above the umbo. The membrane is incised in an upward and slightly backward direction towards its margin; then downwards parallel to its posterior border; then horizontally forward, meeting the original point of the incision. The excised portion of the membrane is removed by seizing it with a fine pair of crocodile forceps, or by means of a fine snare, if it has not been completely detached.
The galvano-cautery is applied cold; when it is in contact with the drum, the circuit is closed so that the point of the cautery becomes red-hot. After the membrane has been burnt through it is withdrawn rapidly so as not to scorch the surrounding tissues. In using the cautery care must be taken to push it only just through the membrane for fear of injuring the inner wall of the tympanic cavity.
After-treatment. The after-treatment consists in protecting the ear by a strip of gauze, which is changed as often as may be necessary.
DIVISION OF THE ANTERIOR LIGAMENT
Indication. It is advised by Politzer in those cases of marked retraction of the drum in which inflation causes an immediate improvement in hearing, which, however, only lasts a short time. In several cases Politzer found the cause of this to be due to tension of the anterior ligament causing retraction of the malleus.
Operation. The anterior fold is divided with the paracentesis knife just in front of the processus brevis of the malleus. The knife is then introduced 2 millimetres inwards through the incision and made to cut in an upward direction as far as Shrapnell’s membrane (Fig. 190, C). This should divide the ligament.
If the operation be successful, improvement in hearing and also diminution of the subjective noises should take place.