A 30-year-old male presents with right shoulder pain after a motorcycle accident. You obtain shoulder x-rays and see the following images (Image 1: AP, scapular Y, and axillary views of the right shoulder. Author’s own images). What is the most likely diagnosis, typical mechanism of injury, expected physical exam findings, appropriate imaging modalities, and management plan?
- Pearl:Posterior dislocations are rare and account for less than 4% of all shoulder dislocations [1-6]. The diagnosis is missed on the initial evaluation in more than 50% of cases, and may not be recognized for weeks or even months [2, 5, 6]. This delay in diagnosis increases the risk of complications including articular cartilage injury, avascular necrosis, arthropathy, and functional impairment [2, 5, 6].
- Pearl: Clinical evaluation is limited in the postictal period as the patient often cannot localize their complaints and the physical examination is unreliable [6].
- Pearl: You cannot always rely on a physical exam to distinguish between anterior and posterior shoulder dislocations.
A single AP film may appear normal in a posterior dislocation [2, 5, 6]. Subtle findings on the AP film include lightbulb sign (shape of the humeral head caused by internal rotation), lack of normal overlap between the glenoid and humeral head, and trough sign: an impaction fracture of the humeral head illustrated in Figure 2 [4-6]. Thus, it is essential to obtain additional views, such as an axillary, scapular Y, or Velpeau view [1-6].
Bedside ultrasound may also be used to quickly confirm the diagnosis (Figure 3).
Figure 2: Left: Note that the head of the humerus appears to be shaped like a lightbulb due to persistent internal rotation, there is an impaction fracture of the anteromedial humeral head (red line), and that the articular surface of the glenoid and the humeral head are not parallel (blue lines). Right: Compare this to the post-reduction AP radiograph with improved alignment. Author’s own image, illustrations by Dr Tabitha Ford.
Figure 3: Ultrasound image demonstrating the humeral head dislocated posteriorly relative to the glenoid. The dotted lines represent the normal position of the humeral head. Author’s own images with illustrations by Dr Victor Huang.
- Reduction should be performed under adequate analgesia/sedation.
- Ultrasound-guided joint injection
- Interscalene block
- Intravenous pain medication
- Procedural sedation if necessary [2, 4, 5, 7]. Procedural sedation should be used for reduction [2,4,5,7].
- Reduction technique: Traction-countertraction should be applied on the adducted and internally rotated arm, and posterior-to-anterior pressure should be applied on the humeral head. You may also create leverage by applying lateral pressure to the medial aspect of the proximal humerus to dislodge an impacted humeral head [4-7].
- After reduction:
- Perform repeat neurovascular examination and imaging.
- Immobilize the shoulder in a sling or shoulder immobilizer in 10-20 degrees of external rotation with the elbow at the side and slight abduction [4-6].
Figure 4: Post-reduction images that demonstrate the reduction of the glenohumeral joint and impaction fracture of the humeral head. Author’s own images.
Indications for surgical intervention include irreducible dislocations, “locked” posterior dislocations, certain associated fractures, and articular defects greater than 25% [1,3,5].
References and Resources:
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- Guehring M, Lambert S, Stoeckle U, Ziegler P. Posterior Shoulder Dislocation with Associated Reverse Hill-Sachs Lesion: Treatment Options and Functional Outcome After a 5-year Follow-up. BMC Musculoskeletal Disorders. 2017;18(442):1-7. PMID: 29132328
- Jacobs RC, Meredyth NA, Michelson JD. Posterior Shoulder Dislocations. BMJ. 2015;350(h75):31-32. PMID: 25630372
- Rezazadeh S, Vosoughi AR. Closed Reduction of Bilateral Posterior Shoulder Dislocation with Medium Impression Defect of the Humeral Head: A Case Report and Review of Its Treatment. Case Reports in Medicine. 2011;124581:1-4. PMID: 22162694
- Curtis RJ. Glenohumeral Instabilities. DeLee & Drez’s Orthopaedic Sports Medicine: Principles and Practice. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2009: 932-946.
- Daya MR, Bengtzen RR. Shoulder. Rosen’s Emergency Medicine Concepts and Clinical Practice. 8th ed. Philadelphia, PA: Elsevier Saunders; 2014: 618-642.
- Horn AE, Ufberg JW. Management of Common Dislocations. Roberts & Hedges’ Clinical Procedures in Emergency Medicine. 6th ed. Philadelphia, PA: Elsevier Saunders; 2014: 954-998.
- Reichman EF. Shoulder Joint Dislocation Reduction. Emergency Medicine Procedures. 2nd ed. New York, NY: McGraw Hill; 2013: 531-549.
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