Neck and shoulder injuries are common in sports, but not all pain and weakness are due to muscle or joint problems. One rare cause is spinal accessory nerve injury, which can result in shoulder dysfunction, weakness, and visible changes in shoulder posture. Awareness of accessory nerve damage is essential, as early recognition improves outcomes.

What Is the Spinal Accessory Nerve?

The spinal accessory nerve (cranial nerve XI) is responsible for controlling two critical muscles: the trapezius and the sternocleidomastoid. These muscles allow for shoulder elevation, head rotation, and stabilisation of the scapula during movement. When accessory nerve damage occurs, these muscles lose function, leading to weakness and altered mechanics of the neck and shoulder.

Nerve Injury can occur due to neck surgery, which damages the nerve as it passes through the posterior triangle of the neck. External pressure over the nerve in the posterior triangle, as from a blow with a hockey stick or a knot in a sling, can also damage the nerve. Finally, diseases affecting this nerve, such as brachial neuritis or syringomyelia, have also been reported. 

Symptoms of Spinal Accessory Nerve Injury

Athletes with spinal accessory nerve injury may report:

  • Shoulder pain, especially around the neck and upper back

  • Weakness in lifting the arm overhead or shrugging the shoulders

  • Difficulty with overhead sports such as swimming, volleyball, or tennis

  • Visible drooping of the shoulder on the affected side

  • Fatigue in the neck and shoulder muscles during activity

In chronic cases, some athletes also notice wasting of the trapezius muscle.

Clinical Presentation

On examination, features of accessory nerve damage include:

  • Weakness in shoulder shrugging against resistance

  • Drooping of the affected shoulder compared with the other side

  • Limited range of overhead movement due to poor shoulder blade control. Shoulder flexion is usually normal, but shoulder abduction is weak. The scapular flip sign is sometimes observed with resisted external rotation of the arm. The pull of the infraspinatus is unopposed by the trapezius muscle, causing the inner border of the scapula to flip off the thoracic wall. These findings should be differentiated from a winged shoulder blade that occurs with long thoracic nerve palsy. 

  • Wasting of the trapezius muscle in long-standing injuries

  • Head rotation weakness to the opposite side if the sternocleidomastoid is affected

These findings can mimic rotator cuff or cervical spine pathology, making clinical suspicion crucial. Other possible causes of these symptom constellations include quadrilateral space syndrome, suprascapular nerve palsy, long thoracic nerve damage and acute brachial neuritis. 

Investigations

Investigations help confirm the diagnosis and rule out other conditions:

  • Electromyography (EMG) and nerve conduction studies: confirm denervation of the trapezius and identify the site of spinal accessory nerve injury.

  • MRI of the neck and shoulder: useful for identifying structural causes such as trauma, surgery-related injury, or mass lesions. Other pathologies, such as those affecting the neck or shoulder joints, can also be diagnosed. 

  • Ultrasound: may help assess trapezius muscle atrophy and visualise the nerve pathway.

Treatment Options for Spinal Accessory Nerve Injury 

Management of accessory nerve damage depends on severity and cause.

  • Conservative treatment:

    • Rest and activity modification in the early stages

    • Physiotherapy to strengthen compensatory muscles (levator scapulae, rhomboids) and improve scapular mechanics. Studies suggest that range-of-motion exercise for the shoulder is essential to prevent adhesive capsulitis. 

    • Pain management with NSAIDs or neuropathic agents (such as Amitriptyline or Duloxetine) if required

  • Interventional treatments:

    • Ultrasound-guided nerve blocks may help with pain in selected cases

    • Electrical stimulation to support trapezius function during recovery

  • Surgery:

    • Nerve repair or grafting if the injury is identified early after trauma or surgery

    • Muscle transfer procedures, such as those involving the levator scapulae or rhomboids, are utilised in chronic cases to restore shoulder function.

Prognosis

The outlook after spinal accessory nerve injury varies. Some athletes recover function with physiotherapy, especially if the damage is mild or partial. Severe injuries, particularly following surgery or trauma, may require surgical repair to regain shoulder function. Early recognition and referral are key to preventing long-term disability.

Final Word from Sportdoctorlondon about Spinal Accessory Nerve Injury

Although rare, spinal accessory nerve injury is an essential cause of shoulder weakness and scapular dysfunction in athletes. Recognising the clinical signs—shoulder droop, trapezius wasting, and weakness with shrugging—can help distinguish it from more common shoulder problems. With timely diagnosis and treatment, ranging from physiotherapy to surgery, athletes with accessory nerve damage can achieve a meaningful recovery and return to their sport.

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