Brachial plexus injury
Brachial plexus injury | |
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Other names | Backpack palsy (BPP), rucksack palsy, rucksack paralysis |
The right brachial plexus with its short branches, viewed from in front | |
Specialty | Emergency medicine |
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.[1][2][3]
Brachial plexus injuries can occur as a result of shoulder trauma (e.g. dislocation
"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".[7]
The rare Parsonage–Turner syndrome causes brachial plexus inflammation without obvious injury, but with nevertheless disabling symptoms.[1][8]
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.[2]
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
The cardinal signs of brachial plexus injury then, are
- 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".[7]
- In Klumpke's paralysis, a form of paralysis involving the muscles of the forearm and hand,[12] 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.[13]
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.[citation needed]
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.[14]
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.[2][5]
Injuries to the brachial plexus result from excessive stretching or tearing of the C5-T1
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[18] or falling on the neck at an angle causes upper plexus lesions leading to Erb's palsy.[7] 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.[2][13]
- Less frequently, the whole brachial plexus lesion occurs;[19]
- 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 (
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.[21] 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.[22][23]
Anatomy
The
Traction
Traction occurs from severe movement and causes a pull or
Root avulsion or nerve rupture may occur during severe trauma, inappropriate surgical positioning, or inappropriate use of surgical retractors.[14][25] 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.[14]
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,
During the delivery of a baby, the shoulder of the baby may graze against the
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 section of nerve.[citation needed]
The best non-invasive test for BPI is magnetic resonance imaging (MRI). MRI aids in the assessment of the injuries and is used to provide information on the portion of the plexus which cannot be operatively explored (the rootlets and roots). In addition, assessment of the cervical cord, post-traumatic changes in soft tissues and associated injuries (e.g. fractures, cuff tears, etc.) may be appreciated. Although superior to nerve conduction studies, ultrasound and other tests, conventional MRI has a poor specificity (72%) meaning that the false-positive rate is high and surgeons can't rely upon the test to guide treatment.[27] Consequently, the future of peripheral nerve MR imaging (including imaging brachial plexus injuries) is likely to be based on diffusion-weighted imaging, such as diffusion tensor techniques, which are of significant potential clinical utility[28] and can enable the production of easily interpreted 3D reconstructions of the spinal cord and brachial plexus such as this.
Several weeks/months after BPI, EMG examination can provide additional information about whether the muscle is denervated. These examinations are painful, highly user-dependent and lack normal values so cannot be relied upon.[citation needed]
Classification
The severity of brachial plexus injury is determined by the type of nerve damage.
- Neurapraxia: The mildest form of nerve injury. It involves an interruption of the nerve conduction without loss of continuity of the axon. Recovery takes place without wallerian degeneration.[29][30]
- Axonotmesis: Involves axonal degeneration, with loss of the relative continuity of the axon and its covering of myelin, but preservation of the connective tissue framework of the nerve (the encapsulating tissue, the epineurium and perineurium, are preserved).[29][31]
- Neurotmesis: The most severe form of nerve injury, in which the nerve is completely disrupted by contusion, traction or laceration. Not only the axon, but the encapsulating connective tissue lose their continuity. The most extreme degree of neurotmesis is transsection, although most neurotmetic injuries do not produce gross loss of continuity of the nerve but rather, internal disruption of the nerve architecture sufficient to involve perineurium and endoneurium as well as axons and their covering. It requires surgery, with unpredictable recovery.[29][32]
A more recent and commonly used system described by the late Sir Sydney Sunderland,[33] divides nerve injuries into five degrees: first degree or neurapraxia, following on from Seddon, in which the insulation around the nerve called myelin is damaged but the nerve itself is spared, and second through fifth degree, which denotes increasing severity of injury. With fifth degree injuries, the nerve is completely divided.[29]
Treatment
Treatment for brachial plexus injuries includes orthosis/splinting, occupational or physical therapy and, in some cases, surgery. Some brachial plexus injuries may heal without treatment. Many infants improve or recover within 6 months, but those that do not, have a very poor outlook and will need further surgery to try to compensate for the nerve deficits.[1][5] The ability to bend the elbow (biceps function) by the third month of life is considered an indicator of probable recovery, with additional upward movement of the wrist, as well as straightening of thumb and fingers an even stronger indicator of excellent spontaneous improvement. Gentle range of motion exercises performed by parents, accompanied by repeated examinations by a physician, may be all that is necessary for patients with strong indicators of recovery.[2] Furthermore, in a systematic review it has been noted that physical therapy interventions in children is able to improve range of motion, muscle strength, bone mineral density, and shoulder function; this can help children regain some or all the function they initially lost.[34]
The exercises mentioned above can be done to help rehabilitate from mild cases of the injury. However, in more serious brachial plexus injuries surgical interventions can be used.
Rehabilitation
There are many treatments to facilitate the process of recovery in people who have brachial plexus injuries. Improvements occur slowly and the rehabilitation process can take up to many years. Many factors should be considered when estimating recovery time, such as initial diagnosis of the injury, severity of the injury, and type of treatments used.[38] Some forms of treatment include nerve grafts, medication, surgical decompression, nerve transfer, physical therapy, and occupational therapy.[38]
Therapy
Physical and occupational therapy is important when dealing with a brachial plexus injuries. One of the main goals of rehabilitation is to prevent muscle atrophy until the nerves regain function.
A study has also shown that a sensory-motor deficit in the upper limbs after a brachial plexus injury can affect the corporal balance in the vertical positioning. Examined patients had a lower score in the Berg balance scale, a greater difficulty in maintaining in the unipodal stance during one minute and leaned the body weight distribution to the side affected by the lesion. Patients also exhibited a greater variability in the postural oscillation, evaluated by the directional stability index. The results alert the clinical community about the necessity to prevent and treat secondary effects of this condition.[40]
In studies about the effectiveness of additional effect of modified constraint induced movement therapy (MCIMT), it was found that MCIMT helped improved the range of motion, shoulder function and it has the potential to promote functional gains for children with BPBI. [41]
Epidemiology
Brachial plexus injury is found in both children and adults, but there is a difference between children and adults with BPI.[42]
Adults
The prevalence of brachial plexus injuries in North American adults in the 1900s was about 1.2%.[42] BPI is most commonly found in young healthy adults, from ages 14 to 63 years old, with 50% of patients between 19 and 34 years old. 89% of BPI patients are male.[42] The rate of brachial plexus injury has been increasing.[when?][43]
Children
OBPP, also known as obstetrical brachial plexus palsy, occurs primarily in young children at a rate of 0.38 to 1.56 per 1000 live births depending on the type of care and the average birth weight of infants in different regions of the world.
Traumatic injuries
BPI has shown to occur in 44% to 70% of traumatic
Prognosis
The site and type of brachial plexus injury determine the prognosis. Avulsion and rupture injuries require timely surgical intervention for any chance of recovery. Equally, reconstruction of elbow flexion in patients with pan-plexus injuries should be performed as soon as possible, because delays lead to worse motor outcomes.[47] Most closed infra-clavicular injuries due to shoulder dislocation are managed non-operatively initially and data shows that most fail to recover sensory function but recover some motor function.[48] For milder injuries involving buildup of scar tissue and for neurapraxia, the potential for improvement varies, but there is a fair prognosis for spontaneous recovery, with a 90–100% return of function.[1][2]
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