Clinical Features.—­Immediately after the injury it is impossible to tell whether the nerve is torn across or merely compressed.  The patient may complain of numbness and tingling in the distribution of the superficial branch of the nerve, but it is a striking fact, that so long as the nerve is divided below the level at which it gives off the dorsal cutaneous nerve of the forearm (external cutaneous branch), there is no loss of sensation.  When it is divided above the origin of the dorsal cutaneous branch, or when the dorsal branch of the musculo-cutaneous nerve is also divided, there is a loss of sensibility on the dorsum of the hand.

The motor symptoms predominate, the muscles affected being the extensors of the wrist and fingers, and the supinators.  There is a characteristic “drop-wrist”; the wrist is flexed and pronated, and the patient is unable to dorsiflex the wrist or fingers (Fig. 90).  If the hand and proximal phalanges are supported, the second and third phalanges may be partly extended by the interossei and lumbricals.  There is also considerable impairment of power in the muscles which antagonise those that are paralysed, so that the grasp of the hand is feeble, and the patient almost loses the use of it; in some cases this would appear to be due to the median nerve having been injured at the same time.

[Illustration:  FIG. 90.—­Drop-wrist following Fracture of Shaft of Humerus.]

If the lesion is high up, as it is, for example, in crutch paralysis, the triceps and anconeus may also suffer.

Treatment.—­The slighter forms of injury by compression recover under massage, douching, and electricity.  If there is drop-wrist, the hand and forearm are placed on a palmar splint, with the hand dorsiflexed to nearly a right angle, and this position is maintained until voluntary dorsiflexion at the wrist returns to the normal.  Recovery is sometimes delayed for several months.

In the more severe injuries associated with fracture of the humerus and attended with the reaction of degeneration, it is necessary to cut down upon the nerve and free it from the pressure of a fragment of bone or from callus or adhesions.  If the nerve is torn across, the ends must be sutured, and if this is impossible owing to loss of tissue, the gap may be bridged by a graft taken from the superficial branch of the radial nerve, or the ends may be implanted into the median.

Finally, in cases in which the paralysis is permanent and incurable, the disability may be relieved by operation.  A fascial graft can be employed to act as a ligament permanently extending the wrist; it is attached to the third and fourth metacarpal bones distally and to the radius or ulna proximally.  The flexor carpi radialis can then be joined up with the extensor digitorum communis by passing its tendon through an aperture in the interosseous membrane, or better still, through the pronator quadratus, as there is less likelihood