The axillary nerve (C5–C6, posterior cord of the brachial plexus) is the most common peripheral nerve injury affecting the shoulder, most often resulting from anterior glenohumeral dislocation, proximal humerus fracture, or direct blunt trauma to the deltoid. [1-2] It is vulnerable as it courses around the surgical neck of the humerus and through the quadrilateral space. [3-4]
1. History
- Mechanism of injury: shoulder dislocation (most common), proximal humerus fracture, direct blow to the deltoid, contact sports tackle, crutch use, or prior shoulder surgery [1][3]
- Onset and timing: acute post-traumatic vs. insidious (quadrilateral space syndrome, brachial neuritis) [2]
- Symptom characterization: weakness of shoulder abduction and external rotation, numbness/paresthesia over the lateral deltoid ("regimental badge" area) [3]
- Difficulty with overhead activities, inability to raise the arm above 90° [3]
- Ask about repetitive overhead use, prior dislocations, recent surgery, or injections [1][4]
- Important negatives: neck pain, radicular symptoms, hand weakness (to distinguish from cervical radiculopathy or brachial plexopathy) [3]
2. Alarm Features
- Complete deltoid paralysis with dense sensory loss — suggests axonotmesis or neurotmesis requiring urgent electrodiagnostic evaluation [2][5]
- Rapidly progressive weakness or involvement of multiple nerve distributions — consider brachial plexus injury or vascular compromise [6]
- Associated vascular injury (diminished pulses, expanding hematoma) after shoulder dislocation — surgical emergency [7]
- Penetrating trauma to the shoulder — high suspicion for nerve transection [2]
- No clinical or electrophysiologic recovery by 3–4 months — warrants surgical exploration [2][8]
3. Medications
- Acute pain management: NSAIDs, acetaminophen; short-course opioids if severe post-traumatic pain
- Neuropathic pain: gabapentin or pregabalin if persistent burning/paresthesia develops
- Corticosteroids: may be considered in brachial neuritis (Parsonage-Turner syndrome) as an underlying etiology, though evidence is limited [9]
- Avoid: repeated corticosteroid injections near the quadrilateral space without clear indication
- No specific medications accelerate nerve regeneration; management is primarily rehabilitative and surgical
4. Diet
- No specific dietary triggers or restrictions
- Adequate protein intake supports nerve healing and muscle recovery
- Vitamin B12 and folate sufficiency should be ensured, particularly in patients with neuropathy risk factors
5. Review of Systems
- Neurologic: numbness/tingling in other upper extremity distributions (C5–T1), neck pain, bilateral symptoms (suggests cervical pathology or systemic neuropathy)
- Musculoskeletal: shoulder instability, prior dislocations, rotator cuff symptoms, scapular winging
- Vascular: coolness, color changes, or swelling of the arm (vascular injury)
- Constitutional: fevers, weight loss, night sweats (if considering neoplastic plexopathy)
- Rheumatologic: joint hypermobility, connective tissue disease
6. Collateral History and Family History
- Witnesses to the mechanism of injury (e.g., direction of fall, position of arm during dislocation)
- Prior episodes of shoulder dislocation or subluxation
- Family history of hereditary neuropathy with liability to pressure palsies (HNPP) — increases susceptibility to nerve injury
- Occupational and sport history (contact sports, overhead athletes, military) [8]
7. Risk Factors
- Anterior shoulder dislocation — nerve injury incidence ranges from 5% to as high as 65% depending on detection method; axillary nerve is the most commonly affected [7][10]
- Proximal humerus fracture (especially surgical neck) [1]
- Contact sports (football, rugby, wrestling, hockey) [8]
- Older age (≥60 years) — higher risk of nerve injury with dislocation and poorer recovery [6-7]
- Prolonged duration of dislocation before reduction — associated with persistent motor weakness [11]
- Iatrogenic: shoulder arthroplasty, open/arthroscopic shoulder surgery, particularly procedures involving the inferior capsule [1][12]
- Crutch use with axillary pressure [3]
- Quadrilateral space syndrome: compression by fibrous bands, hypertrophied muscles, or vascular anomalies [1][4]
8. Differential Diagnosis
- Rotator cuff tear — weakness in abduction/external rotation but preserved sensation; very commonly coexists with axillary nerve injury after dislocation [7]
- C5–C6 cervical radiculopathy — neck pain, dermatomal sensory loss, biceps/brachioradialis reflex changes; broader distribution than isolated axillary nerve
- Brachial neuritis (Parsonage-Turner syndrome) — acute severe shoulder pain followed by weakness; may involve axillary nerve among others; often atraumatic [2][9]
- Brachial plexopathy (upper trunk) — broader motor/sensory deficits involving supraspinatus, infraspinatus, biceps in addition to deltoid [6]
- Quadrilateral space syndrome — insidious onset, posterior shoulder pain with overhead activity, compression neuropathy of axillary nerve [1][4]
- Suprascapular neuropathy — weakness of external rotation and abduction but different sensory pattern
- Adhesive capsulitis — restricted passive and active ROM without neurologic deficits
9. Past Medical History
- Prior shoulder dislocations or instability
- Previous shoulder surgery (arthroplasty, Bankart repair, rotator cuff repair) [12]
- History of proximal humerus fractures
- Diabetes mellitus or other systemic neuropathy risk factors
- Connective tissue disorders (Ehlers-Danlos, Marfan) predisposing to recurrent dislocation
- Prior brachial neuritis episodes
10. Physical Exam
- Inspection: deltoid atrophy (flattening of the lateral shoulder contour) — may take weeks to become apparent; compare bilaterally [5][8]
- Motor testing:
- Shoulder abduction (deltoid — all three heads): weakness or inability to abduct against gravity
- Shoulder external rotation (teres minor): weakness
- Abduction in internal rotation test: most sensitive clinical test — ask patient to abduct the shoulder in internal rotation; inability to do so or a lag compared to the contralateral side indicates deltoid palsy (100% sensitivity in one validation study) [13]
- Swallowtail test / deltoid extension lag test: ask patient to extend the shoulder posteriorly; lag indicates posterior deltoid weakness (identified injury in 10/14 patients) [13]
- Sensory testing: decreased pinprick/light touch over the lateral deltoid ("regimental badge" area) [3][5]
- Reflexes: biceps and brachioradialis reflexes should be intact (helps distinguish from C5–C6 radiculopathy)
- Shoulder ROM: assess passive ROM to rule out mechanical block or adhesive capsulitis
- Cervical spine exam: rule out radiculopathy
- Vascular exam: distal pulses, capillary refill (especially post-dislocation)
11. Lab Studies
- Routine labs are generally not indicated for isolated traumatic axillary nerve injury
- If brachial neuritis is suspected: consider ESR, CRP, CBC
- If systemic neuropathy is a concern: HbA1c, B12, TSH, serum protein electrophoresis
- If vasculitis or autoimmune etiology suspected: ANA, ANCA, complement levels
12. Imaging
- Shoulder X-ray (AP and axillary lateral): first-line to evaluate for fracture, dislocation, or bony abnormality [3]
- MRI of the shoulder: identifies denervation edema in the deltoid and teres minor (increased T2 signal), rotator cuff tears, and nerve signal abnormalities; nerve changes within the quadrilateral space correlate with poorer recovery [14]
- MR neurography: gold standard for visualizing the axillary nerve directly; can identify hourglass constrictions, nerve discontinuity, and perineural edema [9][14]
- Ultrasound: can assess nerve caliber and identify entrapment sites; useful as a point-of-care tool [3]
- Imaging should be performed immediately if severe weakness or multiple nerve involvement is present; otherwise can be initiated after 6–8 weeks of conservative treatment [3]
13. Special Tests
- EMG/Nerve Conduction Studies (NCS): the confirmatory diagnostic standard [2][8]
- Baseline EMG/NCS should be obtained within 4 weeks of injury, with follow-up at 12 weeks [2]
- EMG findings: fibrillation potentials and positive sharp waves in deltoid and teres minor indicate denervation (appear ~3 weeks post-injury) [5][15]
- NCS: reduced compound muscle action potential (CMAP) amplitude from Erb's point stimulation; >40% CMAP asymmetry between sides has 95% sensitivity and 97% specificity for axillary nerve lesion [16]
- Both NCS and EMG should be ordered simultaneously [3]
- Abduction in internal rotation test: clinical exam maneuver with highest sensitivity for axillary nerve palsy [13]
- Scratch collapse test: positive at the level of nerve compression [4]
The following figure illustrates the temporal evolution of electrodiagnostic findings after nerve injury, demonstrating why EMG should be delayed at least 3–4 weeks post-injury for accurate assessment:
14. ECG
- Not routinely indicated for isolated axillary nerve injury
- Consider ECG if procedural sedation is planned for shoulder reduction or if the patient is elderly with cardiac comorbidities
15. Assessment
Axillary nerve injury is the most common peripheral nerve injury of the shoulder, arising from the nerve's anatomic vulnerability as it traverses the quadrilateral space and wraps around the surgical neck of the humerus. [1-2] The injury spectrum ranges from neurapraxia (mild, transient conduction block with full recovery expected) to neurotmesis (complete nerve disruption requiring surgical repair). [3] The vast majority of patients recover with nonoperative treatment. [2] Key prognostic factors include injury severity (Seddon/Sunderland grade), patient age, time to surgical intervention, and BMI. [17]
Severity stratification:
- Mild (neurapraxia): transient weakness, preserved sensation, expected full recovery in weeks to months
- Moderate (axonotmesis): denervation on EMG, recovery over months via axonal regeneration (~1 mm/day)
- Severe (neurotmesis/rupture): dense fibrillation potentials, no voluntary motor unit activation on EMG, requires surgical reconstruction [2][5]
16. Treatment Plan
Acute Phase (0–4 weeks)
- Rest and immobilization of the shoulder; treat associated injuries (fracture fixation, dislocation reduction) [1][8]
- Shoulder dislocations with motor deficits should be reduced expediently — prolonged dislocation is associated with persistent weakness [11]
- Analgesics: NSAIDs, acetaminophen; neuropathic pain agents if needed
- Baseline EMG/NCS within 4 weeks [2]
Rehabilitation Phase (4 weeks onward)
- Passive and active-assisted ROM to prevent shoulder contracture — loss of mobility may permanently affect functional outcome even if nerve recovers [8]
- Progressive strengthening of rotator cuff, deltoid, and periscapular musculature as reinnervation occurs [1][8]
- Serial clinical and electrodiagnostic monitoring at ~12 weeks [2]
Surgical Intervention (if no recovery by 3–6 months)
- Surgical exploration is indicated if no clinical or electrophysiologic improvement by 3–4 months [2][8]
- Best outcomes when surgery is performed within 3–6 months of injury [2][17]
- Surgical options:
- Neurolysis: for nerve-in-continuity lesions
- Nerve grafting (e.g., sural nerve graft): for nerve gaps; MRC grade 4.3 average in one series [18]
- Nerve transfer (triceps motor branch to axillary nerve): increasingly used; 87.6% of isolated axillary nerve injury patients achieved MRC ≥3; all patients regained ≥90° abduction in another series [19-20]
- Neurotization: various donor nerves available; triceps branch (80% success), subscapular nerve (79%), and fascicle transfer from ulnar/median nerve (74%) had the highest success rates in a large series of 206 patients [21]
- Factors affecting surgical outcome: delay from injury to surgery (most important), patient age, and BMI [17]
17. Disposition
- Discharge criteria (ED): isolated axillary nerve injury after successful dislocation reduction with stable neurovascular exam, adequate pain control, and reliable follow-up arranged
- Admission criteria: associated vascular injury, irreducible dislocation, polytrauma, or fracture-dislocation requiring operative fixation
- Observation: consider for elderly patients with complex injury patterns or multiple nerve involvement
- Specialist consultation triggers:
- Orthopedics/hand surgery: all suspected axillary nerve injuries for longitudinal follow-up
- Peripheral nerve surgeon: if no recovery by 3–4 months, or if mechanism suggests nerve rupture (high-energy trauma, penetrating injury) [2][8]
- PM&R/electrodiagnostics: for EMG/NCS at 4 weeks and 12 weeks [2]
18. Follow Up / Return Precautions
- Follow-up timing: clinical reassessment at 2–4 weeks; EMG/NCS at 4 weeks (baseline) and 12 weeks (follow-up); ongoing monitoring every 4–6 weeks thereafter [2]
- Return precautions — seek immediate reassessment for:
- Worsening weakness or new neurologic deficits
- Increasing pain, swelling, or vascular compromise
- No improvement in strength by 3 months
- Expected recovery: most neurapraxic injuries recover within weeks to 3 months; axonotmetic injuries may take 6–12 months with axonal regeneration at ~1 mm/day [2]
- Return to sport/activity: permitted when full active ROM is achieved and shoulder strength is documented as good to excellent by manual muscle testing or isometric testing [8]
- Patient counseling: emphasize adherence to rehabilitation, importance of preventing shoulder contracture, and the time-sensitive nature of surgical referral if recovery stalls [1][8]
References
1. Axillary Nerve Injury. — Perlmutter GS. Clinical Orthopaedics and Related Research. 1999.
2. Axillary Nerve Injury: Diagnosis and Treatment. — Steinmann SP, Moran EA. The Journal of the American Academy of Orthopaedic Surgeons. 2001.
3. Peripheral Nerve Entrapment and Injury in the Upper Extremity. — Silver S, Ledford CC, Vogel KJ, Arnold JJ. American Family Physician. 2021.
4. Upper Extremity Nerve Entrapments: The Axillary and Radial Nerves--Clinical Diagnosis and Surgical Treatment. — Hagert E, Hagert CG. Plastic and Reconstructive Surgery. 2014.
5. Posttraumatic Ruptured Axillary Mononeuropathy Without Shoulder Dislocation in an American Football Player: A Case Report and Review of the Literature. — Meiling JB, Bishop AT, Young NP. American Journal of Physical Medicine & Rehabilitation. 2023.
6. Brachial Plexus Injury After Shoulder Dislocation: A Literature Review. — Gutkowska O, Martynkiewicz J, Urban M, Gosk J. Neurosurgical Review. 2020.
7. Injuries Associated With Traumatic Anterior Glenohumeral Dislocations. — Robinson CM, Shur N, Sharpe T, Ray A, Murray IR. The Journal of Bone and Joint Surgery. American Volume. 2012.
8. Axillary Nerve Injuries in Contact Sports: Recommendations for Treatment and Rehabilitation. — Perlmutter GS, Apruzzese W. Sports Medicine. 1998.
9. Postprocedural Brachial Neuritis: Clinical, Electrodiagnostic, and Neuroimaging Features. — Ambati VS, Madugala N, Anderson N, et al. AJNR. American Journal of Neuroradiology. 2025.
10. Nerve Injuries After Glenohumeral Dislocation, a Systematic Review of Incidence and Risk Factors. — Lorente A, Mariscal G, Barrios C, Lorente R. Journal of Clinical Medicine. 2023.
11. Patterns of Nerve Injury and Recovery Rates of Infraclavicular Brachial Plexus Lesions Following Anterior Shoulder Dislocation. — Wu F, Dhir R, Ng CY. The Journal of Hand Surgery. 2022.
12. Prevention and Treatment of Nerve Injuries in Shoulder Arthroplasty. — Florczynski M, Paul R, Leroux T, Baltzer H. The Journal of Bone and Joint Surgery. American Volume. 2021.
13. Abduction in Internal Rotation: A Test for the Diagnosis of Axillary Nerve Palsy. — Bertelli JA, Ghizoni MF. The Journal of Hand Surgery. 2011.
14. Magnetic Resonance Imaging Features of Axillary Nerve Injuries Following Glenohumeral Dislocation: A Retrospective Observational Cohort Study. — Lui I, Naraghi A, Farag J, et al. Skeletal Radiology. 2025.
15. Assessment, management, and rehabilitation of traumatic peripheral nerve injuries for non‐surgeons. — Bateman EA, Pripotnev S, Larocerie-Salgado J, Ross DC, Miller TA. Muscle & Nerve. 2025.
16. Axillary Motor Nerve Conduction Study: Description of Technique and Provision of Normative Data. — Zis P, Hadjivassiliou M, Rao DG. Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology. 2018.
17. Factors Affecting Outcome of Triceps Motor Branch Transfer for Isolated Axillary Nerve Injury. — Lee JY, Kircher MF, Spinner RJ, Bishop AT, Shin AY. The Journal of Hand Surgery. 2012.
18. A Comparison of Outcomes of Triceps Motor Branch-to-Axillary Nerve Transfer or Sural Nerve Interpositional Grafting for Isolated Axillary Nerve Injury. — Baltzer HL, Kircher MF, Spinner RJ, Bishop AT, Shin AY. Plastic and Reconstructive Surgery. 2016.
19. Outcome Analysis of Medial Triceps Motor Nerve Transfer to Axillary Nerve in Isolated and Brachial Plexus-Associated Axillary Nerve Palsy. — Krauss EM, Noland SS, Hill EJR, et al. Plastic and Reconstructive Surgery. 2022.
20. Triceps Motor Branch Transfer for Isolated Axillary Nerve Injury: Outcomes in 9 Patients. — Yang X, Xu B, Tong JS, et al. Orthopaedics & Traumatology, Surgery & Research : OTSR. 2017.
21. Nerve Transfers for Axillary Nerve Repair in Brachial Plexus Injuries: Results From 206 Patients. — Haninec P, Hradecky J, Ouzky M, Samal F, Mencl L. Journal of Neurosurgery. Spine. 2025.