brachial plexus injury brachial plexus injury a brachial plexus injury (bpi), also known as brachial plexus lesion, is an injury to the brachial plexus, the network of nerves that conducts signals from the spinal cord to the shoulder, arm and hand. these nerves originate in the fifth, sixth, seventh and eighth cervical (c5–c8), and first thoracic (t1) spinal nerves, and innervate the muscles and skin of the chest, shoulder, arm and hand. brachial plexus injuryother namesbackpack palsy (bpp), rucksack palsy, rucksack paralysisthe right brachial plexus with its short branches, viewed from in frontspecialtyemergency medicine brachial plexus injuries can occur as a result of shoulder trauma (e.g. dislocation), tumours, or inflammation, or obstetric. obstetric injuries may occur from mechanical injury involving shoulder dystocia during difficult childbirth, with a prevalence of 1 in 1000 births. "the brachial plexus may be injured by falls from a height on to the side of the head and shoulder, whereby the nerves of the plexus are violently stretched. the brachial plexus may also be injured by direct violence or gunshot wounds, by violent traction on the arm, or by efforts at reducing a dislocation of the shoulder joint". the rare parsonage–turner syndrome causes brachial plexus inflammation without obvious injury, but with nevertheless disabling symptoms. signs and symptoms signs and symptoms may include a limp or paralyzed arm, lack of muscle control in the arm, hand, or wrist, and lack of feeling or sensation in the arm or hand. although several mechanisms account for brachial plexus injuries, the most common is nerve compression or stretch. infants, in particular, may experience brachial plexus injuries during delivery and these present with typical patterns of weakness, depending on which portion of the brachial plexus is involved. the most severe form of injury is nerve root avulsion, which usually accompanies high-velocity impacts that commonly occur during motor-vehicle collisions or bicycle accidents. disabilities based on the location of the nerve damage, brachial plexus injuries can affect part of or the entire arm. for example, musculocutaneous nerve damage weakens elbow flexors, median nerve damage causes proximal forearm pain, and paralysis of the ulnar nerve causes weak grip and finger numbness. in some cases, these injuries can cause total and irreversible paralysis. in less severe cases, these injuries limit use of these limbs and cause pain. the cardinal signs of brachial plexus injury then, are weakness in the arm, diminished reflexes, and corresponding sensory deficits. erb's palsy. "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". in klumpke's paralysis, a form of paralysis involving the muscles of the forearm and hand, a characteristic sign is the clawed hand, due to loss of function of the ulnar nerve and the intrinsic muscles of the hand it supplies. causes in most cases, the nerve roots are stretched or torn from their origin, since the meningeal covering of a nerve root is thinner than the sheath enclosing the nerve. the epineurium of the nerve is contiguous with the dura mater, providing extra support to the nerve. brachial plexus lesions typically result from excessive stretching; from rupture injury where the nerve is torn but not at the spinal cord; or from avulsion injuries, where the nerve is torn from its attachment at the spinal cord. a bony fragment, pseudoaneurysm, hematoma, or callus formation of fractured clavicle can also put pressure on the injured nerve, disrupting innervation of the muscles. a trauma directly on the shoulder and neck region can crush the brachial plexus between the clavicle and the first rib. although injuries can occur at any time, many brachial plexus injuries happen during birth: the baby's shoulders may become impacted during the birth process causing the brachial plexus nerves to stretch or tear. obstetric injuries may occur from mechanical injury involving shoulder dystocia during difficult childbirth, the most common of which result from injurious stretching of the child's brachial plexus during birth, most often during vaginal birth, but occasionally caesarean section. the excessive stretch results in incomplete sensory and/or motor function of the injured nerve. injuries to the brachial plexus result from excessive stretching or tearing of the c5-t1 nerve fibers. these injuries can be located in front of or behind the clavicle, nerve disruptions, or root avulsions from the spinal cord. these injuries are diagnosed based on clinical exams, axon reflex testing, and electrophysiological testing. brachial plexus injuries require quick treatment in order for the patient to make a full functional recovery (tung, 2003). these types of injuries are most common in young adult males. traumatic brachial plexus injuries may arise from several causes, including sports, high-velocity motor vehicle accidents, especially in motorcyclists, but also all-terrain-vehicle (atv) and other accidents. injury from a direct blow to the lateral side of the scapula is also possible. the severity of nerve injuries may vary from a mild stretch to the nerve root tearing away from the spinal cord (avulsion). "the brachial plexus may be injured by falls from a height on to the side of the head and shoulder, whereby the nerves of the plexus are violently stretched… the brachial plexus may also be injured by direct violence or gunshot wounds, by violent traction on the arm, or by efforts at reducing a dislocation of the shoulder joint". brachial plexus lesions can be divided into three types: an upper brachial plexus lesion, which occurs from excessive lateral neck flexion away from the shoulder. most commonly, improper use of forceps during delivery or falling on the neck at an angle causes upper plexus lesions leading to erb's palsy. this type of injury produces a very characteristic sign called waiter's tip deformity due to loss of the lateral rotators of the shoulder, arm flexors, and hand extensor muscles. less frequently, the whole brachial plexus lesion occurs; most infrequently, sudden upward pulling on an abducted arm (as when someone breaks a fall by grasping a tree branch) produces a lower brachial plexus lesion, in which the eighth cervical (c8) and first thoracic (t1) nerves are injured "either before or after they have joined to form the lower trunk. the subsequent paralysis affects, principally, the intrinsic muscles of the hand and the flexors of the wrist and fingers". this results in a form of paralysis known as klumpke's paralysis. backpack palsy is caused by much use of a heavy backpack whose pack-straps chronically press on the brachial plexus. mechanism injury to the brachial plexus can happen in numerous environments. these may include contact sports, motor vehicle accidents, and birth. although these are but a common few events, there is one of two mechanisms of injury that remain constant during the point of injury. the two mechanisms that can occur are traction and heavy impact. traction, also known as stretch injury, is one of the mechanisms that cause brachial plexus injury. the nerves of the brachial plexus are damaged due to the forced pull by the widening of the shoulder and neck. this is a closer look at the traction mechanism at the cervical spine. the arrowed red line represents the stretch of the nerves. depending on the force, lesions may occur. anatomy this image shows the anterior view of the five brachial plexus nerves on the human arm. axillary, median, musculocutaneous, radial, ulnar. the brachial plexus is made up of spinal nerves that are part of the peripheral nervous system. it includes sensory and motor nerves that innervate the upper limbs. the brachial plexus includes the last four cervical nerves (c5-c8) and the 1st thoracic nerve (t1). each of those nerves splits into smaller trunks, divisions, and cords. the lateral cord includes the musculocutaneous nerve and lateral branch of the median nerve. the medial cord includes the medial branch of the median nerve and the ulnar nerve. the posterior cord includes the axillary nerve and radial nerve. traction traction occurs from severe movement and causes a pull or tension among the nerves. there are two types of traction: downward traction and upward traction. in downward traction there is tension of the arm which forces the angle of the neck and shoulder to become broader. this tension is forced and can cause lesions of the upper roots and trunk of the nerves of the brachial plexus. motorcycle accidents and sports injuries usually cause this type of injury to brachial plexus. upward traction also results in the broadening of the scapulo-humoral angle but this time the nerves of t1 and c8 are torn away. humeral fractures and shoulder dislocations can also cause this type of injury with high energy injuries. root avulsion or nerve rupture may occur during severe trauma, inappropriate surgical positioning, or inappropriate use of surgical retractors. there are two mechanisms for root avulsion injury: peripheral and central mechanism. in peripheral mechanism, traction is transmitted to the rootlet, however dura mater will be torn with the rootlet intact because the dura is less elastic when compared to the rootlet. pseudomeningocele can be shown on cervical myelography. on the other hand, through central mechanism, the head and neck is pushed along with the spinal roots of the brachial plexus to the opposite site of the body, leading to direct nerve root injury but the dura sheath remains intact. in this case, anterior roots are more prone than posterior roots for avulsion, thus the c8 and t1 nerve roots are more prone to injury. root avulsion injury can be further divided based on the location of the lesion: pre- and postganglionic lesions. in a preganglionic lesion, the sensory fibre remain attached to the cell body of the sensory ganglion, thus there is no wallerian degeneration of the sensory fibre, thus sensory action potential can still be detected at the distal end of the spinal nerve. however, those who get this type of lesion have sensory loss over the affected nerve roots. in this case, surgical repair of the lesion is not possible because the proximal nerve tissue is too short for stitching to be possible. for postganglionic lesions, the cell body of the sensory ganglion is detached from the spinal nerve, leading to wallerian degeneration of the sensory fibre. thus, no action potential detected at the distal end of spinal nerve. however, surgical repair is possible because proximal nerve tissue has enough length for stitching. impact heavy impact to the shoulder is the second common mechanism to causing injury to the brachial plexus. depending on the severity of the impact, lesions can occur at all nerves in the brachial plexus. the location of impact also affects the severity of the injury and depending on the location the nerves of the brachial plexus may be ruptured or avulsed. when passing through between the clavicle and first rib, the brachial plexus may be crushed in the costoclavicular space. this is usually due to direct trauma to the shoulder or neck region as a result of vehicular accidents, occupational injuries or sports injuries. the brachial plexus may also be compressed by surrounding damaged structures such as bone fragments or callus from the clavicular fracture, and hematoma or pseudoaneurysm from vascular injury. cervical rib, prominent transverse process, and congenital fibrous bands can also compress the brachial plexus and cause thoracic outlet syndrome. during the delivery of a baby, the shoulder of the baby may graze against the pelvic bone of the mother. during this process, the brachial plexus can receive damage resulting in injury. the incidence of this happening at birth is 1 in 1000. this is very low compared to the other identified brachial plexus injuries. diagnosis the most accurate test for diagnosing a brachial plexus injury is operative exploration of the potentially injured segments from the spinal roots to end-organs. nerves should be evaluated under an operative microscope, with or without intraoperative electrical studies (e.g. bipolar stimulation, seps or meps) to supplement. operative evaluation of the rootlets within the spinal canal and intraforaminal portion of the spinal roots proximal to the dorsal root ganglia (e.g. via hemilaminectomy or otherwise) is difficult and rarely clinically justifiable, so in the context of an apparently in-continuity root, preoperative imaging studies are the only method of evaluating this