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Upper trunk

Trunks · C5 C6

C5 and C6 unite at Erb's point in the posterior triangle. Gives the suprascapular nerve and the nerve to subclavius before dividing.

Traced from the start

  1. C5 nerve rootC6 nerve root
  2. Upper trunk

Detail

Motor
Most of what C5 and C6 supply — abduction, external rotation, elbow flexion and supination. Not everything: the dorsal scapular and long thoracic nerves and the C5 fibres to the phrenic nerve leave the roots above the trunk, so rhomboids, serratus anterior and the diaphragm are spared — winging or a raised hemidiaphragm points to a root avulsion instead
Sensory
Lateral shoulder, lateral arm and lateral forearm

When it goes wrong

Erb–Duchenne palsy — shoulder dystocia at birth, or a fall forcing the head away from the shoulder

The waiter's tip posture: arm adducted and internally rotated, elbow extended, forearm pronated and the wrist flexed. Deltoid, supraspinatus, infraspinatus, biceps and brachialis are all weak.

Practise this structure

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