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?
Posterior shoulder (glenohumeral joint) dislocation with associated impaction fracture of the humeral head (Reverse Hill-Sachs lesion).
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].
The mechanism of injury is usually traumatic (67%) or due to convulsive seizures (31%) . Dislocation may occur from a direct force applied to the anterior shoulder, or after a fall on an outstretched hand with the shoulder flexed, adducted, and internally rotated [1, 2 ,4-6]. Seizures and electrical shock cause sudden contraction of the internal rotator muscles, which can result in unilateral and bilateral dislocations [1-6].
The shoulder will be held in adduction and internal rotation, with limited abduction and external rotation. There is a prominent coracoid process, loss of the anterior shoulder contour, and palpable humeral head posteriorly [1, 2, 4-6].
Pearl: Clinical evaluation is limited in the postictal period as the patient often cannot localize their complaints and the physical examination is unreliable .
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.
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].
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.
Nonoperative treatment is indicated for stable reduced dislocations with small articular defects of less than 25% [1,3]. This includes sling immobilization for 3 to 6 weeks, followed by a progressive rehabilitation program .
Indications for surgical intervention include irreducible dislocations, “locked” posterior dislocations, certain associated fractures, and articular defects greater than 25% [1,3,5].
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
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