THE BRACHIAL PLEXUS 99 



The whole plexus may be injured, but unless the nerves 

 are torn close to the intervertebral foramina, the rhomboids 

 and the serratus anterior escape. Sometimes all the trunks 

 of the plexus are torn, and when this occurs distal to the origin 

 of the supra-scapular nerve, the supra- and the infra-spinatus 

 escape paralysis. The examination of these muscles and of the 

 condition of the pupil (pp. 98, 125) helps to determine the site 

 of all such extensive lesions. 



In these injuries, epicritic and protopathic sensibility are lost 

 over the whole arm, except in the areas supplied by the descend- 

 ing branches of the cervical plexus (C. 3 and 4) on the lateral side 

 of the arm, and by the intercosto-brachial nerve on the medial 

 side of the arm (Fig. 13). The full area of supply of these 

 nerves is demonstrated as the overlapping nerves are all 

 paralysed. 



It is important to remember that limited haemorrhage into 

 the spinal medulla, from disease or accident, or the onset of 

 acute anterior poliomyelitis may give rise to clinical signs similar 

 to those produced by injuries of the plexus. It is necessary, 

 therefore, to examine the lower limbs for signs of motor and 

 sensory disturbance in order to determine whether the plexus 

 or the spinal medulla is the site of the lesion. 



Erb-Duchenne or Upper Arm Type of Paralysis. This 

 condition results usually from downward traction of the shoulder 

 during complicated labour. The upper trunk is torn proximal 

 to the origin of the supra-scapular nerve, but distal to the origins 

 of the long thoracic nerve (of Bell) and the dorsalis scapulce nerve 

 (to the rhomboids). The serratus anterior and the rhomboids 

 consequently escape, but all the other muscles innervated by 

 C. 5 and C. 6 are paralysed (p. 106). The deltoid, teres minor, 

 and infra-spinatus are all affected, and the arm is rotated medially 

 by the latissimus dorsi (C. 6, 7, and 8) and the sternal head of the 

 pectoralis major, the latter owing to its supply from the medial 

 anterior thoracic nerve (C. 8 and T. i). The biceps and the 

 brachio-radialis are paralysed and the brachialis (C. 5, 6, and 7) 

 is greatly weakened. The elbow is generally extended owing 

 to the action of the triceps (C. 7 and 8), which usually escapes. 

 The supinators are all paralysed and the forearm is pronated 

 by the pronator quadratus (C. 7, 8, and T. i) alone, the pronator 

 teres being supplied by C. 6. The radial extensors of the wrist 

 being affected, the hand is deviated to the ulnar side, but all the 

 other movements of the wrist and fingers are unchanged. 



7a 



