Long Thoracic Nerve Anatomy

The long thoracic nerve is the tidiest nerve in the upper-limb syllabus: one nerve, one muscle, one sign. It is purely motor, from C5-C7, supplies only serratus anterior, and its failure produces the unmistakable medial scapular winging that examiners love as a spot diagnosis. The topic hangs on three linked ideas: the anatomy that explains why the nerve is so easily injured (a long, superficial course down the chest wall), the sign and how it is elicited and told apart from trapezius winging, and a staged management in which most palsies recover and surgery is reserved.

Origin. A pure motor nerve from the anterior (ventral) rami of C5, C6 and C7. The C5 and C6 contributions typically pierce scalenus medius; the C7 contribution usually joins distal to the muscle. "C5, 6, 7 raise your arms to heaven" is the mnemonic worth keeping, because serratus anterior upward-rotates the scapula to allow overhead elevation.

Root level. The nerve arises from the roots of the brachial plexus, proximal to the trunks, which is why it can be spared or selectively involved independently of the rest of the plexus.

Course. After forming, the nerve passes behind the brachial plexus and the axillary vessels and enters the axilla. It then descends on the superficial (outer) surface of serratus anterior along the mid-axillary line of the lateral chest wall, giving a branch to each digitation of the muscle.

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Why it is vulnerable. The course is long and relatively superficial, with little soft-tissue protection, and that is the anatomical basis of the injuries that follow:

• Traction or stretch - sudden shoulder depression, repetitive overhead activity, carrying loads
• Iatrogenic injury - axillary lymph node dissection, first-rib resection, chest-tube placement and thoracic procedures
• Direct blunt trauma to the lateral chest wall
• Neuralgic amyotrophy (Parsonage-Turner syndrome) and viral or post-immune causes, which have a predilection for this nerve

The muscle. Serratus anterior is the only muscle the long thoracic nerve supplies. It originates from the upper ribs and inserts along the costal surface of the medial border of the scapula, and its actions are essential for overhead function.

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What it does. Three actions:

• Protraction - draws the scapula forward around the chest wall, the "boxer's punch"
• Upward rotation - with trapezius as a force couple, swings the glenoid upward to permit full arm elevation above 90 degrees
• Scapulothoracic stabilisation - holds the medial border and inferior angle flat against the chest wall

What failure looks like. When serratus anterior fails the scapula loses its anchor and its upward-rotation contribution, and the result is both medial winging and loss of full overhead elevation.

Presentation. The patient has a prominent inferomedial scapula, accentuated by forward elevation or pushing against a wall, difficulty elevating the arm overhead, and a feeling of shoulder-girdle fatigue or weakness. Periscapular pain and aching are common, particularly early. The palsy may follow trauma, surgery such as axillary dissection, heavy or repetitive activity, or a viral or neuralgic-amyotrophy prodrome.

Neuralgic amyotrophy, the commonest atraumatic cause. The classic spontaneous long thoracic palsy is neuralgic amyotrophy (Parsonage-Turner syndrome, idiopathic brachial plexus neuritis), and examiners expect its pattern, not just the name. It begins abruptly with severe neuropathic shoulder or arm pain for days to a few weeks, and as the pain subsides patchy flaccid weakness and wasting appears. It is frequently multifocal in an upper-trunk distribution, the long thoracic, suprascapular, axillary and anterior interosseous nerves being characteristically involved, so look beyond the serratus.

Triggers and imaging. Many cases follow an antecedent viral infection, immunisation, recent surgery or strenuous exercise, and it can be familial (hereditary neuralgic amyotrophy). High-resolution MRI or ultrasound may show hourglass-like nerve constrictions or torsion, relevant because these sometimes need surgery if recovery stalls.

Treatment and recovery. Management is largely supportive, with analgesia and physiotherapy; early oral corticosteroids may shorten the painful phase. Recovery is usually good but slow, often 1-3 years, and incomplete in a minority, which is why this group is observed before any nerve surgery.

Medial winging. With serratus anterior paralysed the whole scapula, especially the inferior angle and medial border, moves medially, toward the spine, and lifts off the chest. It is worse on forward elevation and the wall push-up, and it is the more common neurogenic winging.

The neurogenic differential. Three neurogenic types are described, and telling medial from lateral clinically is the classic exam task:

• Type I, medial - serratus anterior, long thoracic nerve: the pattern above
• Type II, lateral - trapezius, spinal accessory nerve (cranial nerve XI): the scapula translates laterally and downward with drooping of the shoulder, the wing is worse on arm abduction, and its surgery is the Eden-Lange transfer
• Type III, rhomboid - dorsal scapular nerve: a rarer, subtler lateral-type winging

Examination. Ask the patient to push against a wall: the wall push-up makes medial winging obvious. Forward flexion accentuates the wing, whereas in trapezius palsy abduction accentuates lateral winging. Assess active overhead elevation and scapulohumeral rhythm, and examine for the differential.

Electrodiagnostics. EMG and nerve conduction studies confirm serratus anterior denervation, localise the lesion to the long thoracic nerve, exclude a broader plexopathy and assess for reinnervation, which matters before any surgery is considered.

Not all winging is neurogenic. Before attributing winging to a nerve, exclude the static, structural and muscular causes. Imaging (radiographs and MRI) excludes bony or structural causes and traumatic muscular detachment, and EMG alone is not enough, so always get a scapular radiograph (± CT):

• Scapular osteochondroma is the classic trap: a benign exostosis on the ventral (costal) surface of the scapula produces a fixed pseudo-winging with a snapping or grinding scapula and a palpable prominence, typically in a younger patient, and it is cured by excision, not physiotherapy or nerve surgery
• Traumatic muscular avulsion or detachment of serratus, trapezius or the rhomboids gives a non-neurogenic winging, the under-recognised cause flagged by Didesch & Tang
• Voluntary or habitual (pseudo) winging, and glenohumeral or scapulothoracic pathology causing protective splinting, round out the differential

Algorithm

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The principle. Management is staged and depends on cause, duration and the electrodiagnostic findings. Most isolated long thoracic nerve palsies, especially neuralgic amyotrophy or traction injuries, recover spontaneously over months, so observation comes first and surgery is reserved for persistent palsy.

Observation and physiotherapy. Scapular stabilisation and range-of-motion physiotherapy are the mainstay, with recovery often awaited for up to two years.

Nerve surgery. For persistent palsy with no reinnervation, neurolysis of the long thoracic nerve can restore serratus function, with good or excellent results in the majority. Outcomes are best when it is performed within about 12 months, though in Roulet's series neurolysis remained useful beyond that and could avoid palliative surgery. Nerve transfers, for example a branch of the thoracodorsal nerve to the long thoracic nerve, are an option.

Salvage. For established, irreversible palsy, pectoralis major (sternal head) transfer to the inferior scapula gives dynamic stabilisation and is the classic reconstruction; scapulothoracic fusion is the salvage for refractory cases or generalised winging.

Ultrasound. Transverse ultrasound identifies the nerve on serratus anterior, and the labelled hydrodissection example below teaches the sonoanatomy; injection is an emerging case-report technique, not established treatment for motor palsy.

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Global Practice Picture

The diagnosis and staged management of long thoracic nerve palsy are consistent internationally and rest on clinical examination plus electrodiagnostics rather than registries. The universal principles are: recognise the medial-winging pattern, exclude trapezius (lateral) winging and traumatic muscular detachment, allow spontaneous recovery for isolated/neuralgic cases, and reserve surgery for persistent palsy.

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Practice Variation

Electrodiagnostic access varies, but the clinical distinction between medial and lateral winging can be made anywhere with a careful examination. Non-operative care is the universal first step; the choice and availability of nerve versus tendon-transfer surgery for persistent cases varies with local expertise.