The spinal accessory nerve powers the trapezius, a major muscle that stabilises the shoulder blade. When it’s injured, the shoulder droops, the shoulder blade wings out, and lifting the arm becomes difficult and painful. So what causes a spinal accessory nerve injury, and how is it treated?
What is the spinal accessory nerve?
The spinal accessory nerve is the eleventh cranial nerve (cranial nerve XI). It’s a pure motor nerve, and its main job is to supply the trapezius — the large muscle of the upper back and neck that shrugs the shoulder, stabilises the shoulder blade, and helps lift the arm overhead. It also supplies the sternocleidomastoid muscle in the neck.
The nerve runs a superficial course through the side of the neck (the posterior triangle), which is exactly why it’s vulnerable to injury there.
What causes a spinal accessory nerve injury?
The commonest cause is iatrogenic — injury during an operation in the neck, especially a lymph node biopsy or neck dissection, because the nerve lies so superficially in the posterior triangle. Other causes include:
- Blunt trauma to the side of the neck or shoulder (including contact sports, or a blow from a stick in hockey or lacrosse)
- A traction injury — a fall onto the shoulder, stretching the nerve
- Rarely, a tumour or a spontaneous neuritis
Symptoms of a spinal accessory nerve palsy
Trapezius weakness produces a characteristic picture:
- A drooping shoulder on the affected side, with an asymmetric neckline
- Aching shoulder and neck pain — often the main complaint, from the strain on other muscles compensating
- Difficulty lifting the arm out to the side and overhead
- Weakness of shoulder shrugging
- Winging of the shoulder blade — which, importantly, sticks out towards the side (lateral winging)
Many people don’t notice the winging itself and instead present with shoulder pain, weakness, and a droop.
Lateral vs medial winging: the key distinction
Scapular winging has two main causes, and telling them apart points to the nerve involved:
- Lateral winging — the shoulder blade drifts outwards; caused by trapezius weakness (spinal accessory nerve). It’s often accentuated by turning the arm outwards against resistance.
- Medial winging — the shoulder blade drifts inwards; caused by serratus anterior weakness (the long thoracic nerve), and it’s accentuated by pushing against a wall.
Getting this right is central to the diagnosis, because it distinguishes a spinal accessory nerve injury from a long thoracic nerve injury.
How is spinal accessory nerve damage diagnosed?
- Examination — the drooping shoulder, lateral scapular winging, and weakness of shrug and overhead lifting, with the winging tests above
- Nerve conduction studies and EMG — the key test, confirming the injury to the nerve and the denervation of the trapezius, and distinguishing it from other causes of winging
- MRI or ultrasound — to look at the nerve and the trapezius, and to exclude a mass
A history of recent neck surgery or trauma is an important clue.
How is a spinal accessory nerve damage treated?
Treatment depends on the cause and severity:
- Physiotherapy — maintaining shoulder movement, and strengthening the surrounding muscles to support the shoulder blade
- Pain management — for the shoulder and neck ache from compensating muscles
- Time — a stretch or minor injury (rather than a cut nerve) may recover on its own over months
- Surgery — where the nerve has been cut or doesn’t recover, early nerve repair or grafting gives the best result, so prompt recognition matters; a muscle-transfer operation (the Eden-Lange procedure) can restore function in longer-standing cases.
Because early repair leads to better outcomes, a spinal accessory nerve injury after neck surgery should be recognised and acted on promptly rather than left.
Frequently asked questions about a spinal accessory nerve palsy
What’s the most common cause of a spinal accessory nerve damage?
Surgery in the neck — particularly a lymph node biopsy or neck dissection — because the nerve runs superficially through the posterior triangle and is easily injured there. Blunt trauma and traction injuries (including in contact sport) are other causes. A shoulder droop and pain that develop after neck surgery are a classic presentation. Parsonage-Turner syndrome is another cause.
How can you tell it apart from a long thoracic nerve injury?
By the direction of the scapular winging. Spinal accessory (trapezius) injury causes lateral winging — the shoulder blade drifts outwards — while long thoracic (serratus anterior) injury causes medial winging — inwards. This distinction, confirmed with nerve conduction studies, identifies which nerve is affected.
Will a spinal accessory nerve palsy recover?
It can. A stretch or minor injury may take months to recover with physiotherapy. A nerve that has been cut usually needs surgical repair, and — importantly — early repair yields much better results than late repair. This is why the injury should be recognised and acted on promptly, especially after surgery.
Why does it cause so much shoulder pain?
Because the trapezius normally stabilises the shoulder blade. When it’s weak, the shoulder droops and other muscles work harder to compensate, leading to aching and strain. The pain is often the main complaint, more than the weakness or the winging, which many people don’t notice.
Final word from Sport Doctor London about a spinal accessory nerve injury
A spinal accessory nerve injury weakens the trapezius, causing a drooping shoulder, aching pain, and lateral winging of the shoulder blade. It’s most often a complication of neck surgery, but also follows trauma. The lateral pattern of winging, confirmed with nerve studies, distinguishes it from a long thoracic nerve injury. Treatment ranges from physiotherapy to early nerve repair — and because early repair is more effective, prompt recognition matters.
If you have shoulder droop, weakness, or pain after neck surgery or an injury, Dr Masci can assess you in London. Contact the team here or call +44 (0) 203 488 0350.
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