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Difficulty: MediumOrthopedic Surgery

A 34-year-old man is brought to the emergency department for severe right shoulder pain. Thirty minutes ago, he experienced a witnessed generalized tonic-clonic seizure that lasted 2 minutes. On physical examination, the right arm is held firmly in adduction and internal rotation. The patient actively resists any attempt at passive external rotation due to severe pain. The radial pulse is 2+ and sensation is intact to light touch over the deltoid and distal fingers. An initial anteroposterior (AP) radiograph of the right shoulder reveals a symmetric, rounded appearance of the humeral head with no obvious fracture lines. Which of the following is the most appropriate next step in the management of this patient?

  1. Obtain an axillary or scapular Y-view radiograph of the right shoulderAnswer
  2. B
    Perform an immediate closed reduction using procedural sedation
  3. C
    Provide a supportive sling and arrange for outpatient follow-up
  4. D
    Obtain a non-contrast computed tomography scan of the right shoulder
  5. E
    Administer prophylactic intravenous antibiotics and prepare for surgical exploration

Answer

Obtain an axillary or scapular Y-view radiograph of the right shoulder
The correct next step is to obtain an axillary or scapular Y-view radiograph. This patient's clinical presentation—arm locked in internal rotation and adduction following a seizure—is highly characteristic of a posterior shoulder dislocation. The intense muscle contractions during a generalized seizure cause the strong internal rotators (latissimus dorsi, pectoralis major, subscapularis) to overpower the external rotators (infraspinatus, teres minor). Posterior dislocations are frequently missed on standard anteroposterior (AP) radiographs because the humeral head rotates internally, masking the typical overlap seen in anterior dislocations and creating a symmetric, rounded appearance known as the 'lightbulb sign'. Therefore, a dedicated orthogonal view (such as an axillary or scapular Y-view) is strictly required to verify the posterior displacement and identify any associated defects (e.g., reverse Hill-Sachs lesion) prior to attempting closed reduction.

Step-by-Step Solution

1
Analyze the mechanism of injury and physical exam findings.
The patient had a seizure, followed by the arm being locked in adduction and internal rotation with severe pain on external rotation.
Violent muscle contractions during a seizure or electrocution overpower external rotators, classically causing a posterior shoulder dislocation.
2
Evaluate the initial imaging provided.
The AP radiograph shows a symmetric, rounded humeral head (the 'lightbulb sign') and no obvious fracture.
Posterior dislocations are notorious for looking deceptively normal on standard AP views because the humeral head rotates internally, causing the articular surface to face posteriorly and appear symmetric on a 2D anterior-to-posterior plane.
3
Determine the necessary diagnostic intervention to confirm the suspected diagnosis.
An orthogonal plain radiographic view (axillary or scapular Y-view) must be obtained.
An orthogonal view will definitively show the humeral head displaced posteriorly relative to the glenoid fossa and help rule out associated fractures (such as a reverse Hill-Sachs lesion) before any reduction is attempted.

Key Concept

Posterior Shoulder Dislocation Diagnosis
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Topics

Orthopedic Surgery

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