Snapshot A G1P1 woman gives birth to a boy at 41 weeks gestational age via vaginal delivery. Labor was prolonged due to shoulder dystocia which required a forceps delivery. The child's APGAR scores were 8 and 9 at 1 and 5 minutes, respectively. The child's weight at birth is 9 pounds 8 ounces. On exam, the baby's left upper extremity is notable for arm adduction, elbow extension, and forearm pronation. Introduction Clinical definition lesion in the upper trunk (C5-C6) of the brachial plexus leading to the characteristic "waiter's tip" deformity Epidemiology incidence most common neonatal brachial plexus palsy approximately 1 per 1000 live births risk factors obstetric large for gestational age shoulder dystocia forceps delivery breech presentation prolonged labor Etiology excess traction on head away from the ipsilateral shoulder this motion puts tension on the upper trunk of the brachial plexus common clinical scenarios obstetric complication traction on head away from the shoulder during a difficult delivery (e.g., shoulder dystocia) trauma falling on the shoulder with head bent away from the affected shoulder Pathoanatomy normal anatomy brachial plexus diagram upper trunk of brachial plexus C5 and C6 nerve roots important nerve branches and the muscles they innervate axillary nerve deltoid teres minor musculocutaneous nerve biceps brachialis brachialis coracobrachialis suprascapular nerve infraspinatus supraspinatus injury anatomy lesion in the upper trunk will weaken muscles innervated by the axillary, musculocutaneous, and suprascapular nerves resulting in weak arm abduction deltoid supraspinatus arm external rotation teres minor infraspinatus forearm supination biceps brachialis forearm flexion biceps brachialis brachialis Associated conditions clavicle fracture humerus fracture shoulder dislocation Prognosis unfavorable concomitant Horner syndrome C7 involvement cord avulsion Presentation Symptoms infant unable to move affected upper extremity Physical exam "waiter's tip" deformity arm is adducted abductor weakness deltoid and supraspinatous are strong abductors at the shoulder arm is internally rotated external rotator weakness infraspinatus and teres minor are external rotators forearm is pronated supination weakness biceps brachialis is a strong supinator of the forearm elbow is extended flexion weakness biceps brachialis and brachialis are strong flexors at the elbow Imaging Radiographs indication radiographs are not routinely performed unless another diagnosis is being considered fracture dislocation Magnetic resonance imaging (MRI) indication MRI is not routinely performed unless another diagnosis is being considered preferred modality to fully characterize the lesion preoperative planning Differential Klumpke palsy distinguishing factors lesion in C8-T1 nerve roots (lower trunk) caused by upward traction of arm presents with "claw hand" due to impaired lumbrical muscles extension of metacarpophalangeal (MCP) joints flexion of proximal and distal interphalangeal joints Radial head subluxation distinguishing factors subluxation of the radial head relative to the radiocapitellar joint occurs in children 2-5 years of age due to excess traction on the arm elbow held in slight flexion and pronation Treatment Nonoperative observation and daily passive exercises indications most cases of Erb-Duchenne palsy will resolve with conservative management complete recovery may take up to 2 years Complications Joint contracture Hemidiaphragm concomitant injury to the phrenic nerve