#Subcutaneous Injuries of Nerves.#—­Several varieties of subcutaneous injuries of nerves are met with.  One of the best known is the compression paralysis of the nerves of the upper arm which results from sleeping with the arm resting on the back of a chair or the edge of a table—­the so-called “drunkard’s palsy”; and from the pressure of a crutch in the axilla—­“crutch paralysis.”  In some of these injuries, notably “drunkard’s palsy,” the disability appears to be due not to damage of the nerve, but to overstretching of the extensors of the wrist and fingers (Jones).  A similar form of paralysis is sometimes met with from the pressure of a tourniquet, from tight bandages or splints, from the pressure exerted by a dislocated bone or by excessive callus, and from hyper-extension of the arm during anaesthesia.

In all these forms there is impaired sensation, rarely amounting to anaesthesia, marked muscular wasting, and diminution or loss of voluntary motor power, while—­and this is a point of great importance—­the normal electrical reactions are preserved.  There may also develop trophic changes such as blisters, superficial ulcers, and clubbing of the tips of the fingers.  The prognosis is usually favourable, as recovery is the rule within from one to three months.  If, however, neuritis supervenes, the electrical reactions are altered, the muscles degenerate, and recovery may be retarded or may fail to take place.

Injuries which act abruptly or instantaneously are illustrated in the crushing of a nerve by the sudden displacement of a sharp-edged fragment of bone, as may occur in comminuted fractures of the humerus.  The symptoms include perversion or loss of sensation, motor paralysis, and atrophy of muscles, which show the reaction of degeneration from the eighth day onwards.  The presence of the reaction of degeneration influences both the prognosis and the treatment, for it implies a lesion which is probably incapable of spontaneous recovery, and which can only be remedied by operation.

The treatment varies with the cause and nature of the lesion.  When, for example, a displaced bone or a mass of callus is pressing upon the nerve, steps must be taken to relieve the pressure, by operation if necessary.  When there is reason to believe that the nerve is severely crushed or torn across, it should be exposed by incision, and, after removal of the damaged ends, should be united by sutures.  When it is impossible to make a definite diagnosis as to the state of the nerve, it is better to expose it by operation, and thus learn the exact state of affairs without delay; in the event of the nerve being torn, the ends should be united by sutures.

#Dislocation of Nerves.#—­This injury, which resembles the dislocation of tendons from their grooves, is seldom met with except in the ulnar nerve at the elbow, and is described with injuries of that nerve.

DISEASES OF NERVES