The trunks of the brachial plexus (upper, middle, and lower) emerge laterally between the anterior and middle scalene muscles and descend toward the clavicle (Figure 30-4A). The following nerves branch off the trunks of the brachial plexus:
Erb's palsy (brachial plexus birth injury)
is caused by a stretch injury of the brachial plexus that occurs during a difficult birth, specifically to nerve roots C5 and C6 and sometimes C7. The severity of the injury varies from a stretch to complete avulsion from the spinal cord. Depending on the severity of the injury, some infants experience complete recovery, while others may not recover. The suprascapular, musculocutaneous, axillary, upper and lower subscapular, long thoracic, and dorsal scapular nerves may be involved, resulting in notable loss or limited function of the supraspinatus, infraspinatus, biceps brachii, brachialis, deltoid, subscapularis, rhomboids, and serratus anterior musculature. In addition, the affected limb will be internally rotated as a result of the lack of muscle support.
Klumple's palsy results from the inferior trunk of the brachial plexus. The intrinsic muscles of the hand are affected and a “claw hand” may result.