The upper-arm type—­Erb-Duchenne paralysis—­is that most frequently met with, and it is due to a lesion of the fifth anterior branch, or, it may be, also of the sixth.  The position of the upper limb is typical:  the arm and forearm hang close to the side, with the forearm extended and pronated; the deltoid, spinati, biceps, brachialis, and supinators are paralysed, and in some cases the radial extensors of the wrist and the pronator teres are also affected.  The patient is unable to supinate the forearm or to abduct the arm, and in most cases to flex the forearm.  He may, however, regain some power of flexing the forearm when it is fully pronated, the extensors of the wrist becoming feeble flexors of the elbow.  There is, as a rule, no loss of sensibility, but complaint may be made of tickling and of pins-and-needles over the lateral aspect of the arm.  The abnormal position of the limb may persist although the muscles regain the power of voluntary movement, and as the condition frequently follows a fall on the shoulder, great care is necessary in diagnosis, as the condition is apt to be attributed to an injury to the axillary (circumflex) nerve.

The lower-arm type of paralysis, associated with the name of Klumpke, is usually due to over-stretching of the plexus, and especially affects the anterior branch of the first dorsal nerve.  In typical cases all the intrinsic muscles of the hand are affected, and the hand assumes the claw shape.  Sensibility is usually altered over the medial side of the arm and forearm, and there is paralysis of the sympathetic.

Infra-clavicular injuries, as already stated, are most often produced by a sub-coracoid dislocation of the humerus; the medial cord is that most frequently injured, and the muscles paralysed are those supplied by the ulnar nerve, with, in addition, those intrinsic muscles of the hand supplied by the median.  Sensibility is affected over the medial surface of the forearm and ulnar area of the hand.  Injury of the lateral and posterior cords is very rare.

Treatment is carried out on the lines already laid down for nerve injuries in general.  It is impossible to diagnose between complete and incomplete rupture of the nerve cords, until sufficient time has elapsed to allow of the establishment of the reaction of degeneration.  If this is present at the end of fourteen days, operation should not be delayed.  Access to the cords of the plexus is obtained by a dissection similar to that employed for the subclavian artery, and the nerves are sought for as they emerge from under cover of the scalenus anterior, and are then traced until the seat of injury is found.  In the case of the first dorsal nerve, it may be necessary temporarily to resect the clavicle.  The usual after-treatment must be persisted in until recovery ensues, and care must be taken that the paralysed muscles do not become over-stretched.  The prognosis is less favourable in the supra-clavicular lesions than in those below the clavicle, which nearly always recover without surgical intervention.