<Tr> <Td> ulnar nerve </Td> <Td> Skin of palm and medial side of hand and digits 3 - 5 </Td> <Td> Hypothenar eminence, some forearm flexors, thumb adductor, lumbricals 3 - 4, interosseous muscles </Td> </Tr> <P> Lesions can lead to severe functional impairment . </P> <P> Brachial plexus injury affects cutaneous sensations and movements in the upper limb . They can be caused by stretching, diseases, and wounds to the lateral cervical region (posterior triangle) of the neck or the axilla . Depending on the location of the injury, the signs and symptoms can range from complete paralysis to anesthesia . Testing the patient's ability to perform movements and comparing it to their normal side is a method to assess the degree of paralysis . A common brachial plexus injury is from a hard landing where the shoulder widely separates from the neck (such as in the case of motorcycle accidents or falling from a tree). These stretches can cause ruptures to the superior portions of the brachial plexus or avulse the roots from the spinal cord . Upper brachial plexus injuries are frequent in newborns when excessive stretching of the neck occurs during delivery . Studies have shown a relationship between birth weight and brachial plexus injuries; however, the number of cesarean deliveries necessary to prevent a single injury is high at most birth weights . For the upper brachial plexus injuries, paralysis occurs in those muscles supplied by C5 and C6 like the deltoid, biceps, brachialis, and brachioradialis . A loss of sensation in the lateral aspect of the upper limb is also common with such injuries . An inferior brachial plexus injury is far less common, but can occur when a person grasps something to break a fall or a baby's upper limb is pulled excessively during delivery . In this case, the short muscles of the hand would be affected and cause the inability to form a full fist position . </P> <P> To differentiate between pre ganglionic and post ganglionic injury, clinical examination requires that the physician keep the following points in mind . Pre ganglionic injuries cause loss of sensation above the level of the clavicle, pain in an otherwise insensate hand, ipsilateral Horner's syndrome, and loss of function of muscles supplied by branches arising directly from roots--i.e., long thoracic nerve palsy leading to winging of scapula and elevation of ipsilateral diaphragm due to phrenic nerve palsy . </P>

The brachial plexus is formed from components of spinal nerves c5–t1