Erb's palsy is a paralysis of the arm caused by injury to the upper group of the arm's main nerves, specifically the severing of the upper trunk C5–C6 nerves. These form part of the brachial plexus, comprising the ventral rami of spinal nerves C5–C8 and thoracic nerve T1. These injuries arise most commonly, but not exclusively, from shoulder dystocia during a difficult birth. Depending on the nature of the damage, the paralysis can either resolve on its own over a period of months, necessitate rehabilitative therapy, or require surgery. Presentation The paralysis can be partial or complete; the damage to each nerve can range from bruising to tearing. The most commonly involved root is C5 (aka Erb's point: the union of C5 & C6 roots) as this is mechanically the furthest point from the force of traction, therefore, the first/most affected. Erb–Duchenne palsy presents as a lower motor neuron syndrome associated with sensibility disturbance and vegetative phenomena. The most commonly involved nerves are the suprascapular nerve, musculocutaneous nerve, and the axillary nerve. The signs of Erb's palsy include loss of sensation in the arm and paralysis and atrophy of the deltoid, biceps, and brachialis muscles. "The position of the limb, under such conditions, is characteristic: the arm hangs by the side and is rotated medially; the forearm is extended and pronated. The arm cannot be raised from the side; all power of flexion of the elbow is lost, as is also supination of the forearm". The resulting biceps damage is the main cause of this classic physical position commonly called "waiter's tip". If the injury occurs at age early enough to affect development (e.g. as a neonate or infant), it often leaves the patient with stunted growth in the affected arm with everything from the shoulder through to the fingertips smaller than the unaffected arm. This also leaves the patient with impaired muscular, nervous and circulatory development. The lack of muscular development leads to the arm being much weaker than the unaffected one, and less articulate, with many patients unable to lift the arm above shoulder height unaided, as well as leaving many with an elbow contracture. The lack of development to the circulatory system can leave the arm with almost no ability to regulate its temperature, which often proves problematic during winter months when it would need to be closely monitored to ensure that the temperature of the arm