Shoulder Dislocation and Axillary Nerve Injury: The Key Facts

The axillary nerve arises from the posterior cord of the brachial plexus, mainly from the C5 and C6 nerve roots (occasionally with a contribution from C4). It passes through the quadrilateral space at the back of the upper arm and divides into an anterior and a posterior branch. The anterior branch runs around the posterolateral (surgical) neck of the humerus and supplies the anterior and middle parts of the deltoid. The posterior branch divides into a motor branch and a sensory branch: the motor branch supplies the teres minor and the posterior deltoid, and the sensory branch becomes the upper lateral cutaneous nerve of the arm, providing sensation over the lateral shoulder.

Common causes of axillary neuropathy include shoulder dislocation, humeral neck fracture, and direct blunt trauma. This injury can lead to weakness of shoulder abduction and external rotation and can affect sensation over the lateral upper arm.

The unhappy triad of the shoulder includes shoulder dislocation leading to a rotator cuff tear and axillary nerve injury, occurring in 9–18% of anterior shoulder dislocations; after the age of 40, the risk of the unhappy triad following anterior shoulder dislocation increases.

Epidemiology

• Axillary neuropathy is relatively rare and has been reported to account for less than 1% of all peripheral nerve injuries.
• After anterior shoulder dislocation, the incidence of axillary nerve injury is around 5–45%.
• Male to female ratio is 3:1.
• This injury is more common in contact sports (such as rugby and wrestling) and in athletes who frequently perform shoulder abduction and external rotation (such as volleyball and baseball players).

Risk Factors

• Anterior shoulder dislocation, especially recurrent dislocation.
• Humeral neck fracture, especially proximal humeral fracture.
• Iatrogenic injury after shoulder surgery, particularly shoulder instability surgery and rotator cuff repair.
• Skiing and soccer are the sports most often associated with axillary nerve injury.
• Direct blunt trauma to the anterolateral deltoid, common in contact sports such as skiing, hockey, soccer, and rugby.
• Participation in sports requiring repetitive overhead movement, such as volleyball, tennis, and baseball, which may cause chronic compression of the axillary nerve.

Pathophysiology

• Common causes of axillary nerve injury include traction injury, for example when the shoulder is forcibly pulled away from the chest wall during anterior shoulder dislocation, stretching or compressing the nerve.
• Blunt trauma or a direct blow can cause nerve compression or injury.
• Quadrilateral space syndrome is usually caused by fibrous bands or hypertrophied muscle compressing the axillary nerve, and can also result from space-occupying lesions such as tumors, aneurysms, or cysts causing nerve compression.
• The axillary nerve can be injured during shoulder surgery, particularly during shoulder arthroscopy or rotator cuff repair.

History

• The clinical presentation of axillary nerve dysfunction is variable and easily overlooked, because the dislocation or fracture may mask the symptoms; in some cases this persists for 2–4 weeks after the injury.
• Patients often report shoulder weakness, especially with abduction and external rotation, due to impaired function of the deltoid and teres minor.
• Sensation over the upper lateral arm may be reduced or lost.
• Patients with an accompanying dislocation or fracture often have a history of severe shoulder pain, after which the weakness and sensory loss may be discovered.
• A non-traumatic history may suggest a chronic compression lesion, such as quadrilateral space syndrome.

Physical Examination

• On examination, common findings include reduced strength and atrophy of the deltoid and teres minor, which are responsible for shoulder abduction and external rotation.
• Examine the active and passive range of motion for shoulder abduction and external rotation, and assess deltoid function.
• Test for reduced sensation over the lateral upper arm, which is characteristic of axillary neuropathy.
• Quadrilateral space syndrome may be accompanied by tenderness over the posterior shoulder space or diffuse shoulder pain; symptoms usually appear when the arm is in an overhead position, particularly during the late cocking or early acceleration phase of throwing.
• Cervical spine pathology should be ruled out, using the Spurling test to check for cervical radiculopathy.

Differential Diagnosis

• Cervical radiculopathy, particularly involving the C5 and C6 nerve roots.
• Brachial plexus injury, particularly stinger syndrome.
• Rotator cuff tendinopathy or other soft-tissue injury of the shoulder.
• Quadrilateral space syndrome.
• Parsonage-Turner syndrome (acute brachial plexus neuropathy).

Diagnostic Tools

• Initial evaluation should include shoulder and cervical spine X-rays to rule out fracture, dislocation, and cervical spine pathology.
• MRI is the most commonly used imaging tool for assessing shoulder tissue and nerve compression, such as fibrous tissue or cysts around the nerve.
• Electromyography (EMG) and nerve conduction velocity (NCV) testing help confirm the extent and location of nerve injury, and should be performed 3 to 4 weeks after the injury to establish a baseline of nerve function.
• If there is no clinical improvement after 3 months, EMG and NCV should be repeated.

Initial Treatment

• Non-surgical treatment is often used first, with the main goals of avoiding further injury and promoting nerve recovery.
• Anti-inflammatory drugs (NSAIDs) can be used to relieve pain and inflammation and to reduce swelling caused by tissue compression.
• Electrical stimulation therapy may help prevent deltoid atrophy during nerve recovery.
• A nerve release with an ultrasound-guided injection at the site of compression or injury can be considered.
• Rehabilitation focuses on maintaining shoulder range of motion and strength, particularly restoring abduction and external rotation, strengthening shoulder abduction and external rotation, and stabilizing the shoulder joint to prevent muscle atrophy and joint stiffness.
• If the patient does not recover, surgical treatment should be considered.

Surgery

• If non-surgical treatment is ineffective or there is no recovery within 3 to 12 months, surgery should be considered.
• Surgical indications:
  • Suspected bone spur formation or compression within the quadrilateral space.
  • No observed recovery of the axillary nerve within 3 to 4 months of injury.
  • No evidence of EMG/NCV recovery within 3 to 6 months of injury.
• Neurolysis can be used to relieve nerve compression, particularly in quadrilateral space syndrome, where surgery may require excision of fibrous tissue or a space-occupying lesion.
• In cases of severe nerve injury, nerve suture or nerve graft surgery may be necessary.

Follow-up and Rehabilitation Training

• Follow-up every 4 to 8 weeks is recommended to monitor the recovery of strength and sensation.
• If no signs of recovery can be observed within 3 months, EMG and NCV testing should be repeated to assess the progress of nerve recovery.
• If progress is found to be slow, further treatment options such as surgery may need to be considered.

Postoperative Rehabilitation: Weeks 0–2

• Shoulder immobilization

  • Immobilize the shoulder in a sling (after reduction).
  • There is not yet enough evidence to support whether physical therapy should begin during or after the immobilization period.

• Isometric strengthening

  • Dose: 10 seconds × 6 repetitions × 2 days (limited to a pain-free range).

• Joint mobility

• Passive range of motion (PROM): flexion, extension, abduction, adduction, internal rotation.

• Active range of motion (AROM) (except external rotation): performed when pain is 3/10 or less, 10 repetitions × 2 days.

• Elbow: flexion, extension, pronation, supination.

• Wrist: flexion, extension, radial deviation, ulnar deviation.

• Hand: make a fist, release the fist.

Postoperative Rehabilitation: Weeks 2–4

• Joint mobility

  • PROM/AAROM: shoulder flexion, internal rotation, adduction (10 repetitions × 2 days).
  • Avoid end-range external rotation and abduction in the early treatment phase.

• Active range of motion (AROM)

  • Elbow: flexion, extension, pronation, supination (10 repetitions × 2 days).
  • Wrist: flexion, extension, radial deviation, ulnar deviation.
  • Hand: make a fist, release the fist.

• Pendulum exercises

  • 3 sets × 30 seconds (for the shoulder joint).

• Strengthening of target muscles

  • Postural and periscapular muscle strengthening and neuromuscular re-education
    • Deltoid: neuromuscular electrical stimulation to reduce atrophy.
    • Rhomboids (major/minor), serratus anterior, trapezius (upper/middle/lower).

• Precautions

  • Avoid shoulder abduction and flexion beyond 90 degrees, and external rotation beyond neutral (for the first 3 weeks).

• Special note for older patients

• The rate of recurrent shoulder dislocation is lower, but the rate of joint stiffness is higher.

• Progressive strengthening and proprioceptive training should be started earlier (younger patients usually begin at week 6).

Postoperative Rehabilitation: Weeks 4–6

• Discontinue the shoulder sling (D/C sling).

• Strengthening program

  • Light resistance exercises: target muscles include the deltoid, rotator cuff muscles, and postural muscles.

• Proprioceptive techniques

• PNF diagonal patterns.

• Closed-chain activities:

• Wall push-ups → table → floor.

• Weight shifts.

Postoperative Rehabilitation: Week 6 to Discharge

• Continued training

  • Range of motion, scapular and shoulder joint stability, strengthening exercises, proprioceptive training, and joint mobility.
  • While maintaining optimal conditions for tissue healing.

• Sport/work-specific activities

  • Progressively return to full participation based on the patient’s functional status.
  • General sporting activity is recommended to take about 12 weeks, and competitive sport about 16 weeks.

• Duration of conservative treatment

  • Physical therapy may continue for 3 to 6 months.
  • If there are no signs of improvement within 3 to 4 months, contact a physician.

• Precautions

• Increasing weight or resistance should be adjusted according to individual pain levels and the sense of joint stability.

Prognosis

• The prognosis depends on the severity of the nerve injury and the speed of nerve recovery.
• Most patients recover fully within 6 to 12 months, especially those whose injury was caused by shoulder dislocation or fracture.
• If surgery is delayed beyond 6 to 12 months, the prognosis may be worse, with reduced chances of long-term recovery.
• Studies have reported non-surgical success rates of around 85–100%, mainly for injuries caused by acute trauma; these figures reflect study populations and do not predict an individual patient’s outcome.

References

• June 2022. Journal of Orthopaedic Reports 1(1):100050
• https://www.physio-pedia.com/Axillary_Nerve_Injury
• https://thejns.org/focus/view/journals/neurosurg-focus/31/5/2011.8.focus11183.xml

Further reading

• Shoulder topic
• Sports injury overview
• PRP prolotherapy
• Rehabilitation exercise prescription
• Pain management