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Difficulty: HardOrthopedic Surgery

A 25-year-old man is brought to the emergency department after a skiing accident in which he fell directly onto his right shoulder. He complains of severe shoulder pain and an inability to move his arm. Vital signs are within normal limits. On physical examination, the right arm is held in slight abduction and external rotation. There is a prominent acromion and a loss of the normal rounded contour of the shoulder. He has decreased sensation to pinprick over the lateral aspect of the right shoulder. Radial and brachial pulses are 2+ and symmetric. Capillary refill is less than 2 seconds. Anteroposterior and axillary lateral radiographs of the right shoulder demonstrate an anterior, subcoracoid dislocation of the humeral head. The patient undergoes closed reduction in the emergency department using procedural sedation. Post-reduction radiographs confirm anatomic alignment of the glenohumeral joint. However, upon repeat physical examination, the patient is able to actively abduct the arm to 15 degrees, but is unable to actively abduct it any further. The decreased sensation over the lateral shoulder persists. Which of the following is the most appropriate next step in the management of this patient?

  1. Application of a shoulder sling and outpatient physical therapyAnswer
  2. B
    Immediate magnetic resonance imaging (MRI) of the right shoulder
  3. C
    Urgent surgical exploration and repair of the axillary nerve
  4. D
    Computed tomography (CT) angiography of the right upper extremity
  5. E
    Electromyography (EMG) and nerve conduction studies of the right arm

Answer

Application of a shoulder sling and outpatient physical therapy
The patient's ability to initiate abduction to 15 degrees confirms that the supraspinatus muscle is intact. However, his inability to abduct past 15 degrees isolates a functional deficit in the deltoid muscle. Combined with the sensory loss over the lateral shoulder (the 'regimental badge' area), this is the classic presentation of an axillary nerve injury. The axillary nerve is frequently stretched over the humeral head during an anterior shoulder dislocation. Because the vast majority of these injuries are neuropraxias that recover spontaneously within 6 to 12 weeks, the standard of care is conservative management. Applying a shoulder sling for comfort and initiating outpatient physical therapy maintains joint mobility while awaiting nerve recovery.

Step-by-Step Solution

1
Identify the primary injury from the initial presentation.
The mechanism, arm position, and loss of contour indicate an anterior shoulder dislocation, which is confirmed by the radiographs.
Establishing the primary trauma guides the assessment of specific associated complications.
2
Analyze the post-reduction physical examination findings.
The patient can initiate abduction (0-15 degrees) but cannot continue it, and has sensory loss over the lateral shoulder.
Identifying the specific muscle weakness isolates the affected anatomical structure.
3
Correlate the physical findings with functional anatomy.
The supraspinatus (suprascapular nerve) handles 0-15 degrees of abduction, while the deltoid (axillary nerve) handles 15-90 degrees. The sensory loss is in the regimental badge area.
This confirms an isolated axillary nerve injury, sparing the suprascapular nerve and rotator cuff.
4
Determine the standard of care for this specific complication.
Axillary nerve injuries from anterior dislocations are typically traction neuropraxias that resolve spontaneously over weeks to months.
Understanding the natural history prevents unnecessary invasive interventions or premature diagnostic testing.

Key Concept

Axillary nerve injury is a common complication of anterior shoulder dislocations, presenting with deltoid weakness (impaired abduction beyond 15 degrees) and lateral shoulder numbness; it is initially managed conservatively with a sling and physical therapy.

Alternative Method

When evaluating shoulder weakness after a dislocation, always separate the phases of abduction: 0-15 degrees tests the suprascapular nerve (supraspinatus), and 15-90 degrees tests the axillary nerve (deltoid).
Estimated Time:1m 30s
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Orthopedic Surgery

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