Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Biomechanics

Three main mechanisms have been described that may result in a burner or stinger:

(a) nerve compression,

(b)nerve traction,

(c) or a direct blow to the brachial plexus,

resulting in upper trunk or cervical root symptoms, particularly involving C5 and C6. Lower cervical roots are less susceptible to damage, but injury can occur with the shoulder either abducted or fully extended.

Controversy remains regarding whether a burner is primarily a brachial plexus or a cervical root injury, a situation that is compounded by the lack of clear demarcation about where the cervical nerve root ends and the brachial plexus begins. Permanent nerve damage can result from recurrent brachial plexus injuries.

Narrowing of the intervertebral foramen occurs with neck extension and with lateral bending, especially when the two motions are combined. The narrowing is most pronounced at the C4–C5 and C5–C6 levels.

Published series suggest that the extension–lateral compression mechanism is predominately the cause of burners (83% to 85% of cases). It appears that compression injuries occur in adult populations, whereas traction injuries are more common in children.

Burners associated with these mechanisms are seen in athletes with pre-existing (though may be asymptomatic) cervical spine pathology, such as cervical disc disease or degenerative change.

A second mechanism of a burner is nerve traction as the shoulder is depressed and the nerves are fixed proximally. The traction forces are transmitted to the upper trunk of the brachial plexus, especially the upper cervical nerve roots (C5–C6), stretching and injuring these structures.

The shoulder can be driven downward, and the head and neck in the opposite direction, while blocking or tackling in football or while landing on the shoulder in wrestling, the second most common sport in which this injury occurs. This is suggested to be the most frequent mechanism in younger athletes without cervical stenosis or arthritic change.

Finally, the third mechanism is a direct blow to the Erb point, which lies superior and deep to the medial clavicle, just lateral to the sternocleidomastoid muscle. In football, the upper trunk of the brachial plexus can be compressed between the shoulder pad and the superior medial scapula following direct trauma.

Athletes with recurrent cervical nerve root neurapraxia were found to have disc disease and narrowing of the intervertebral foramen in 93% of cases. Several papers have identified an association between the incidence of burners and developmentally narrowed spinal canals.

In two series, 47% and 53%  of athletes had a Pavlov ratio of less than 0.8, and a significant difference was found between measurements among individuals with a previous history of a burner and controls.

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