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Burners (stingers): Acute brachial plexus injury in the athlete
Geoffrey Kuhlman, MD, CAQSM Section Editor
Jeremy M Shefner, MD, PhD Deputy Editor
John F Dashe, MD, PhD
INTRODUCTION — Upper extremity nerve injury commonly results from impact to the neck and shoulder. One such injury, a burner (also called a stinger), generally results from traction or compression of the upper trunk of the brachial plexus or of cervical nerve roots 5 or 6. Burners are typically transient, but they can cause prolonged weakness resulting in time lost from athletic participation. They commonly recur, leading to further disability. Returning to sports activity requires restoration of pain free motion, complete recovery of strength, full functional status, and addressing predisposing factors.
THE INJURY — A burner is caused by trauma to the neck and shoulder, and is characterized by pain radiating down one upper extremity. Numbness, paresthesias, or weakness sometimes develop. The injury occurs most often in football, but has also been reported in wrestling, gymnastics, and hockey  .
A burner signifies peripheral nerve dysfunction or injury. In most cases, it is a brachial plexopathy involving the upper trunk (show figure 1). However, several authors also describe cervical nerve root lesions [2-6] . (See "Overview of upper extremity peripheral nerve syndromes", section on Brachial plexopathy.)
Burners are usually brief and self-limited, although recovery can take weeks or months in some cases. The injury often recurs and occasionally leads to a chronic syndrome  .
Although burners are common, the true incidence in each sport and at different levels of competition is unknown, primarily because of underreporting by athletes. One survey of college football players found that 65 percent of players had experienced at least one burner in their college careers; 70 percent did not report the injury to medical personnel  .
PATHOPHYSIOLOGY — Peripheral nerve injury is often graded using Seddon's classification:
Grade I is neurapraxia, a disruption of nerve function involving demyelinization [8,9] . Axonal integrity is preserved, and remyelinization follows within three weeks  . Electromyography (EMG) is typically normal.
Grade II is axontmesis, in which axonal damage  and Wallerian degeneration occur  . In contrast to grade I injuries, grade II injuries are associated with electroconduction changes on EMG within two to three weeks.
Grade III is complete nerve transection (neurontmesis), or permanent nerve damage.
Burners typically represent a grade I or II injury. Grade III peripheral nerve injuries are rare in sports and are not characteristic of burners  .
Three mechanisms of burners are known:
The first is traction injury to the brachial plexus, which occurs when the shoulder is depressed and the neck is forced laterally away from the involved side, stretching the brachial plexus [1,2,10] .
The second is a direct blow to the supraclavicular fossa, which causes a percussive injury to the upper trunk of the brachial plexus [5,6,10] .
The third is nerve compression by a combination of neck hyperextension and ipsilateral lateral flexion  . One author observed the most persistent and severe symptoms from burners developed with neck hyperextension and ipsilateral rotation  .
The role of abnormalities of the cervical neural foramina , canal, and discs is controversial. Cervical neural foramina narrow significantly with 20 to 30 degrees of neck extension. Cervical rotation further compromises this space  . Several studies have documented cervical stenosis (narrowing of the spinal canal) and disc abnormalities in collegiate or professional athletes with compressive burners [7,12,13] . One study found a statistically significant association of foraminal stenosis and/or canal stenosis among high school athletes with burners compared with controls  . However, asymptomatic individuals can have similar findings  . Thus, the significance of such radiographic findings is not always clear. Furthermore, the definition of cervical stenosis used in some of these studies has been questioned [16,17] . A causative role for these anatomic abnormalities awaits further study. Nonetheless, compared with the other two mechanisms of burner, the compression mechanism appears more common in higher levels of competition, such as collegiate and professional football, and more closely associated with a chronic course.
DIAGNOSIS — The diagnosis of burners can most commonly be made by the history and physical examination. Diagnostic studies are rarely necessary.
History and physical examination — Burners occur most often with tackling, which makes the injury common among linebackers and defensive backs. Immediately after contact the player classically feels burning pain in the supraclavicular area. It radiates down the arm, generally in a circumferential, nondermatomal pattern. The player might also note numbness, paresthesias, or weakness in the extremity. Frequently the discomfort resolves spontaneously in one to two minutes  .
Important questions for the athlete suspected to have a burner include detailed descriptions of immediate and residual symptoms. Pain quality, intensity, location, radiation, and duration provide clues, as does the presence of numbness, paresthesias, and weakness. Both the athlete and observers can describe the exact mechanism of injury. Because burners frequently recur, information on previous burners and their treatment is relevant to the chronicity of the disorder.
Physical examination begins with inspection. Acutely the player might shake the upper extremity or hold it against the body to reduce discomfort  . Atrophy or asymmetry in the neck, shoulder, or upper extremity suggests previous injury or a predisposition to injury. Shoulder depression and atrophy of the deltoid and supraspinatus commonly develop after burners because of weakness from nerve injury and subsequent maladaptive use of the shoulder  . Such changes usually take a few weeks to develop.
Palpation localizes tenderness and spasm, which are not specific for burners. Focal cervical vertebral tenderness should alert the clinician to the possibility of a serious cervical injury, such as fracture or disc herniation, and is not typical of burners. Provided cervical stability has been established, range of motion in the neck and the shoulder is evaluated since restricted mobility increases the risk of reinjury. Sensation and muscle stretch reflexes should also be examined.
Spurling's test and percussion of the supraclavicular fossa for tenderness or Tinel's sign may be positive. The Spurling or neck compression maneuver attempts to reproduce radicular pain (show picture 1). It is performed by applying downward pressure or tapping on top of the head in several positions. This maneuver is highly specific for the presence of cervical root compression, but the sensitivity is low  . Thus, a positive test is helpful, but a negative test does not rule out radiculopathy.
Deficits in burners usually involve muscles innervated by C5 or C6, the nerve fibers of which travel through the upper trunk of the brachial plexus (show figure 1) [8-10,19] . Each of these areas should be tested manually.
The deltoid is innervated by the axillary nerve (C5, C6) and is responsible for shoulder abduction.
The supraspinatus is innervated by the suprascapular nerve (C5, C6) and is responsible for "full can" abduction. This is performed with the shoulder abducted 90º, the arm in the plane of the scapula and the thumb directed upward, as if the patient could hold a full can of liquid without spilling. The examiner then resists abduction from this position.
The infraspinatus is innervated by the suprascapular nerve and is responsible for external rotation.