Fig. 398
Various incisions for reaching different branches of the trifacial nerve: a, supra-orbital; b, external nasal; c, Bruns’ incision; d, inf. dent. at mental foramen; e, internal nasal; f, infra-orbital; g, Carnochan’s incision. (Marion.)
Operations upon nerves, then, include suture, grafting, stretching, division, and resection. After any operation upon a nerve trunk the parts pertaining to it should be placed in a position of rest; and, furthermore, such position as will prevent stretching and favor relaxation of the sutured trunk should be maintained. The writer is credited with the first primary suture of the sciatic nerve, which was done immediately after its accidental division, during the course of an extensive operation. Recovery was prompt and complete. The limb was immobilized in the extended position and physiological rest thus maintained.
Nerves can be stretched, it has been found, to one-twentieth of their length. Nerve trunks have much more strength than has been generally appreciated. The sciatic trunk of a full-grown individual will bear a stress of more than eighty pounds, while even six pounds’ pull are necessary to tear the supra-orbital nerve. The benefit which follows nerve elongation is ascribed to the improvement in its nutrition produced by the damage done to its substance, and the consequently enhanced blood supply, as well as to the severing of adhesions between the sheath and its surroundings and between the nerve bundles within the sheath.
The operation of nerve stretching consists simply in exposing the nerve at a site of election, detaching it from its surroundings, and then hooking either the finger or some smaller instrument beneath it and pulling firmly, yet gently, in both directions; in the case of the sciatic, for instance, the entire limb should be lifted from the table, and even this does not entail upon the nerve trunk anywhere near a breaking force.
The cranial nerves are sought, found, and treated as follows, in their respective cases:
The supra-orbital nerve is attacked at its exit from the supra-orbital notch, which can usually be felt, or foramen, when such exists, either by a straight incision made directly over it, where it can be felt, or by a curved incision through the region of the eyebrow, which should have been shaved for the purpose, the resulting scar being hidden by the hair as it grows again.
The infra-orbital nerve is similarly treated at the infra-orbital foramen, where it lies under the levator labii superioris. It may be exposed by either a curved incision, parallel to the orbital margin, or by a vertical incision, which will leave a more disfiguring scar.
The second branch of the fifth nerve may be attacked from the front by Chavasse’s modification of Carnochan’s original method, consisting of a T-shaped incision from one corner of the eye to the other, the vertical branch extending from its middle well down to the mouth. After the infra-orbital nerve is identified it is secured with a piece of silk. The anterior wall of the antrum is then removed, the cavity opened, and a small trephine applied to its posterior wall. The nerve, being exposed in its canal or groove, is divided anteriorly, pulled down into the cavity by means of a ligature previously applied to it, and now made to serve as a guide into the sphenomaxillary fossa. Here it may be followed directly into its connection with Meckel’s ganglion, which may also be extirpated. The nerve trunk is forcibly pulled out of the foramen rotundum, through which it escapes from the Gasserian ganglion.