Anterior Shoulder Dislocation

Risk factors

• Young age at first dislocation (recurrence risk)
• Contact and overhead sports (football, rugby, wrestling, swimming, volleyball, throwing)
• Generalized ligamentous laxity (Ehlers-Danlos, Marfan)
• Prior dislocation, Bankart lesion, glenoid bone loss
• Seizure disorder (although seizures more commonly cause posterior dislocations)

Pathophysiology

Forceful abduction, external rotation, and extension levers the humeral head out of the glenoid anteriorly. The anteroinferior labrum-capsule complex avulses from the glenoid (Bankart lesion), and the posterolateral humeral head impacts the anterior glenoid rim, producing a compression fracture (Hill-Sachs lesion). The axillary nerve is at risk as it wraps the surgical neck of the humerus.

Clinical presentation

Differential diagnosis

• Posterior shoulder dislocation — Often missed; arm held in internal rotation and adduction; mechanism includes seizure, electrocution, direct anterior blow; 'lightbulb' sign on AP radiograph
• Inferior dislocation (luxatio erecta) — Rare; arm locked overhead in abduction; high rate of neurovascular injury
• Proximal humerus fracture — Older osteoporotic patient; ecchymosis; deformity but no empty glenoid sign
• AC joint separation — Step-off at AC joint, tender over AC; shoulder contour different
• Rotator cuff tear — Often coexists in older patients; weakness on resisted testing after reduction

Diagnostic workup

Diagnostic algorithm

flowchart TD
  A[Shoulder injury<br/>squared-off contour] --> B[Neurovascular exam<br/>axillary nerve]
  B --> C[Pre-reduction X-ray<br/>AP, scap-Y, axillary]
  C --> D{Anterior<br/>dislocation?}
  D -->|Yes| E[Procedural sedation<br/>or intra-articular lidocaine]
  D -->|Posterior or fracture| F[Orthopedic consult]
  E --> G[Reduction technique<br/>scapular manipulation, FARES, etc.]
  G --> H[Post-reduction X-ray<br/>+ repeat NV exam]
  H --> I[Sling 1-3 weeks<br/>+ PT referral]
  I --> J{Young athlete or<br/>recurrent dislocation?}
  J -->|Yes| K[Consider surgical<br/>stabilization]
  J -->|No| L[Conservative<br/>rehabilitation]

Complications

• Recurrent dislocation (70-90% in patients <20)
• Axillary nerve injury (most common; usually neurapraxia that resolves; check sensation over lateral deltoid and deltoid strength)
• Rotator cuff tear (older patients)
• Bankart lesion, Hill-Sachs lesion, glenoid bone loss
• Adhesive capsulitis from prolonged immobilization (especially in older patients)
• Vascular injury (rare; axillary artery)
• Avascular necrosis (after associated fracture)

PANCE pearls

• Always image BEFORE reduction in any first-time or atypical-mechanism dislocation — proximal humerus fractures can be displaced by reduction attempts.
• Axillary view (or modified Velpeau) is essential to differentiate anterior from posterior dislocation.
• Always document axillary nerve function before and after reduction — sensation over the lateral deltoid.
• Young first-time dislocators benefit from early surgical stabilization given high recurrence risk.
• Older patients with shoulder dislocation often have an associated rotator cuff tear — examine and image after reduction.

References

• AAOS 2023 — AAOS Clinical Practice Guideline on Glenohumeral Joint Instability (2023)
• ACEP 2017 — Clinical Policy: Procedural Sedation in the Emergency Department (Godwin et al., Ann Emerg Med 2014/2017 update)