Manual of Surgery Volume First: General Surgery. Sixth Edition.

by Alexis Thomson; Alexander Miles

Fig. 91.—To illustrate the Loss of Sensation produced by Division of the Median Nerve. The area of complete cutaneous insensibility is shaded black. The parts insensitive to light touch and to intermediate degrees of temperature are enclosed within the dotted line. (After Head and Sherren.)

The Median Nerve is most frequently injured in wounds made by broken glass in the region of the wrist. It may also be injured in fractures of the lower end of the humerus, in fractures of both bones of the forearm, and as a result of pressure by splints. After division at the elbow, there is impairment of mobility which affects the thumb, and to a less extent the index finger: the terminal phalanx of the thumb cannot be flexed owing to the paralysis of the flexor pollicis longus, and the index can only be flexed at its metacarpo-phalangeal joint by the interosseous muscles attached to it. Pronation of the forearm is feeble, and is completed by the weight of the hand. After division at the wrist, the abductor-opponens group of muscles and the two lateral lumbricals only are affected; the abduction of the thumb can be feebly imitated by the short extensor and the long abductor (ext. ossis metacarpi pollicis), while opposition may be simulated by contraction of the long flexor and the short abductor of the thumb; the paralysis of the two medial lumbricals produces no symptoms that can be recognised. It is important to remember that when the median nerve is divided at the wrist, deep touch can be appreciated over the whole of the area supplied by the nerve; the injury, therefore, is liable to be over looked. If, however, the tendons are divided as well as the nerve, there is insensibility to deep touch. The areas of epicritic and of protopathic insensibility are illustrated in [Fig. 91]. The division of the nerve at the elbow, or even at the axilla, does not increase the extent of the loss of epicritic or protopathic sensibility, but usually affects deep sensibility.

Fig. 92.—To illustrate Loss of Sensation produced by complete Division of Ulnar Nerve. Loss of all forms of cutaneous sensibility is represented by the shaded area. The parts insensitive to light touch and to intermediate degrees of heat and cold are enclosed within the dotted line. (Head and Sherren.)

The Ulnar Nerve.—The most common injury of this nerve is its division in transverse accidental wounds just above the wrist. In the arm it may be contused, along with the radial, in crutch paralysis; in the region of the elbow it may be injured in fractures or dislocations, or it may be accidentally divided in the operation for excising the elbow-joint.

When it is injured at or above the elbow, there is paralysis of the flexor carpi ulnaris, the ulnar half of the flexor digitorum profundus, all the interossei, the two medial lumbricals, and the adductors of the thumb. The hand assumes a characteristic attitude: the index and middle fingers are extended at the metacarpo-phalangeal joints owing to paralysis of the interosseous muscles attached to them; the little and ring fingers are hyper-extended at these joints in consequence of the paralysis of the lumbricals; all the fingers are flexed at the inter-phalangeal joints, the flexion being most marked in the little and ring fingers—claw-hand or main en griffe. On flexing the wrist, the hand is tilted to the radial side, but the paralysis of the flexor carpi ulnaris is often compensated for by the action of the palmaris longus. The little and ring fingers can be flexed to a slight degree by the slips of the flexor sublimis attached to them and supplied by the median nerve; flexion of the terminal phalanx of the little finger is almost impossible. Adduction and abduction movements of the fingers are lost. Adduction of the thumb is carried out, not by the paralysed adductor pollicis, but the movement may be simulated by the long flexor and extensor muscles of the thumb. Epicritic sensibility is lost over the little finger, the ulnar half of the ring finger, and that part of the palm and dorsum of the hand to the ulnar side of a line drawn longitudinally through the ring finger and continued upwards. Protopathic sensibility is lost over an area which varies in different cases. Deep sensibility is usually lost over an area almost as extensive as that of protopathic insensibility.

When the nerve is divided at the wrist, the adjacent tendons are also frequently severed. If divided below the point at which its dorsal branch is given off, the sensory paralysis is much less marked, and the injury is therefore liable to be overlooked until the wasting of muscles and typical main en griffe ensue. The loss of sensibility after division of the nerve before the dorsal branch is given off resembles that after division at the elbow, except that in uncomplicated cases deep sensibility is usually retained. If the tendons are divided as well, however, deep touch is also lost.

Care must be taken in all these injuries to prevent deformity; a splint must be worn, at least during the night, until the muscles regain their power of voluntary movement, and then exercises should be instituted.

Dislocation of the ulnar nerve at the elbow results from sudden and violent flexion of the joint, the muscular effort causing stretching or laceration of the fascia that holds the nerve in its groove; it is predisposed to if the groove is shallow as a result of imperfect development of the medial condyle of the humerus, and by cubitus valgus.