#Nerves divided in Amputation.#—­In the case of nerves divided in an amputation, there is an active, although necessarily abortive, attempt at regeneration, which results in the formation of bulbous swellings at the cut ends of the nerves.  When there has been suppuration, and especially if the nerves have been cut so as to be exposed in the wound, these bulbous swellings may attain an abnormal size, and are then known as “amputation” or “stump neuromas” (Fig. 84).

When the nerves in a stump have not been cut sufficiently short, they may become involved in the cicatrix, and it may be necessary, on account of pain, to free them from their adhesions, and to resect enough of the terminal portions to prevent them again becoming adherent.  When this is difficult, a portion may be resected from each of the nerve-trunks at a higher level; and if this fails to give relief, a fresh amputation may be performed.  When there is agonising pain dependent upon an ascending neuritis, it may be necessary to resect the corresponding posterior nerve roots within the vertebral canal.

[Illustration:  FIG. 84.—­Stump Neuromas of Sciatic Nerve, excised forty years after the original amputation by Mr. A. G. Miller.]

#Other Injuries of Nerves.#—­Contusion of a nerve-trunk is attended with extravasation of blood into the connective-tissue sheaths, and is followed by degeneration of the contused nerve fibres.  Function is usually restored, the conducting paths being re-established by the formation of new nerve fibres.

When a nerve is torn across or badly crushed—­as, for example, by a fractured bone—­the changes are similar to those in a divided nerve, and the ultimate result depends on the amount of separation between the ends and the possibility of the young axis cylinders bridging the gap.

Involvement of Nerves in Scar Tissue.—­Pressure or traction may be exerted upon a nerve by contracting scar tissue, or a process of neuritis or perineuritis may be induced.

When terminal filaments are involved in a scar, it is best to dissect out the scar, and along with it the ends of the nerves pressed upon.  When a nerve-trunk, such as the sciatic, is involved in cicatricial tissue, the nerve must be exposed and freed from its surroundings (neurolysis), and then stretched so as to tear any adhesions that may be present above or below the part exposed.  It may be advisable to displace the liberated nerve from its original position so as to minimise the risk of its incorporation in the scar of the original wound or in that resulting from the operation—­for example, the radial nerve may be buried in the substance of the triceps, or it may be surrounded by a segment of vein or portion of fat-bearing fascia.

Injuries of nerves resulting from #gun-shot wounds# include:  (1) those in which the nerve is directly damaged by the bullet, and (2) those in which the nerve-trunk is involved secondarily either by scar tissue in its vicinity or by callus following fracture of an adjacent bone.  The primary injuries include contusion, partial or complete division, and perforation of the nerve-trunk.  One of the most constant symptoms is the early occurrence of severe neuralgic pain, and this is usually associated with marked hyperaesthesia.