Physical Therapy Evaluation Tool (PEAT) 4 Practice Exam

Erb's Palsy results from injury to the upper part of the brachial plexus, specifically the nerve roots C5 and C6. These roots feed the major shoulder and elbow flexors and rotators (such as deltoid, supraspinatus, infraspinatus, biceps, and brachialis). When C5-C6 are affected, there is weakness of shoulder abduction and external rotation, along with elbow flexion and forearm supination—producing the classic waiter's tip position: the arm adducted and internally rotated with the elbow extended and forearm pronated. This pattern distinguishes it from injuries of lower roots (C8-T1), which would impair hand and finger function (Klumpke palsy) rather than the proximal arm muscles.