The long thoracic nerve (also: external respiratory nerve of Bell or posterior thoracic nerve) is a branch of the brachial plexus derived from cervical nerves C5-C7 that innervates the serratus anterior muscle.

Structure

Origin

The long thoracic nerve arises from the anterior rami of cervical spinal nerves C5, C6, and C7. The root from C7 may occasionally be absent. The roots from C5 and C6 pierce through the scalenus medius, while the C7 root passes in front of the muscle.

Course and relations

The long thoracic nerve descends through the cervicoaxillary canal. It is posterior to the brachial plexus, and the axillary artery and vein. This takes it deep to the clavicle. It rests on the outer surface of the serratus anterior muscle. It extends along the side of the thorax to the lower border of the serratus anterior muscle, supplying fibres to each of the muscle's digitations.

Function

The long thoracic nerve innervates the serratus anterior muscle. It supplies filaments to each of its digitations (finger-like projections).

Clinical significance

Due to its long, relatively superficial course, the long thoracic nerve is susceptible to injury, either through direct trauma or stretch. Mechanisms of injury include: Symptoms are often minimal – if symptomatic, a posterior shoulder or scapular burning type of pain may be reported. Some injuries, particularly lesions, can paralyse the serratus anterior muscle to produce a winged scapula. This is most prominent when the arm is lifted forward or when the patient pushes the outstretched arm against a wall. However, even winging may not be evident until the trapezius stretches enough to reveal an injury several weeks later.

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