Musculoskeletal · Orthopedic Trauma
The facts most likely to be tested
Anterior shoulder dislocation is the most common type and typically results from abduction and external rotation of the arm.
Patients with an anterior shoulder dislocation present with the arm held in slight abduction and external rotation with a squared-off shoulder deformity.
Axillary nerve injury is the most common associated complication, manifesting as sensory loss over the lateral deltoid and weakness in shoulder abduction.
Posterior shoulder dislocation is classically associated with seizures or high-voltage electrical injuries and presents with the arm held in adduction and internal rotation.
Hill-Sachs lesion is a posterolateral humeral head compression fracture caused by impact against the anterior glenoid rim during an anterior dislocation.
Bankart lesion is an avulsion fracture of the anterior-inferior glenoid labrum that occurs during an anterior shoulder dislocation.
Radiographic evaluation for suspected shoulder dislocation requires an axillary or scapular Y-view to confirm the direction of the humeral head displacement.
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A 28-year-old male presents to the emergency department after falling onto his outstretched hand while playing football. He is holding his right arm in slight abduction and external rotation, and physical examination reveals a squared-off shoulder contour. There is decreased sensation over the lateral deltoid muscle. A radiograph shows the humeral head displaced inferior and anterior to the glenoid fossa.
Which of the following nerves is most likely injured in this patient?
Axillary nerve
The patient's presentation of an anterior shoulder dislocation with lateral deltoid sensory loss is a classic board presentation of an axillary nerve injury, which is the most common nerve injury associated with this condition.
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Etiology / Epidemiology
Most common joint dislocation; anterior type accounts for >95% of cases.
Clinical Manifestations
Arm held in abduction and external rotation; squared-off shoulder deformity.
Diagnosis
X-ray (AP, scapular Y, axillary views) is the gold standard to confirm dislocation.
Treatment
Closed reduction is first-line; axillary nerve injury is the primary complication.
Prognosis
High recurrence rate in young patients; monitor for Bankart or Hill-Sachs lesions.
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Epidemiology & Etiology
Shoulder dislocations are most common in young males (sports/trauma) and elderly patients (falls). Anterior dislocations result from a blow to an abducted, externally rotated arm. Posterior dislocations are classically associated with seizures or electric shock.
Pertinent Anatomy
The glenohumeral joint is the most mobile joint in the body, relying on the labrum and rotator cuff for stability. The axillary nerve runs inferior to the glenohumeral joint, making it highly vulnerable during displacement.
Pathophysiology
Anterior dislocation occurs when the humeral head is forced anteriorly and inferiorly out of the glenoid fossa. Posterior dislocation involves forceful internal rotation and adduction. Chronic instability often results from structural damage to the glenoid labrum.
Clinical Manifestations
Patients present with severe pain and a squared-off shoulder appearance due to the loss of the normal deltoid contour. Anterior dislocations present with the arm in abduction and external rotation. Check axillary nerve sensation over the lateral deltoid before and after reduction to rule out nerve palsy.
Diagnosis
X-ray (AP, scapular Y, and axillary views) is the gold standard for diagnosis. The axillary view is essential to distinguish anterior from posterior displacement. If fracture is suspected, CT scan is the preferred imaging modality.
Treatment
Perform closed reduction (e.g., Stimson or Scapular manipulation) after adequate sedation. Do not attempt reduction without ruling out fracture via imaging. Post-reduction, the shoulder is immobilized in a sling; early physical therapy is indicated to prevent adhesive capsulitis.
Prognosis
Recurrence is common, especially in patients <20 years old. Bankart lesion (avulsion of the anterior-inferior labrum) and Hill-Sachs lesion (dent in the humeral head) are frequent complications requiring orthopedic follow-up.
Differential Diagnosis
Proximal humerus fracture: localized bony tenderness and crepitus
Rotator cuff tear: weakness in abduction/rotation without deformity
Acromioclavicular joint separation: step-off deformity at the AC joint
Posterior dislocation: arm held in adduction and internal rotation
Glenohumeral arthritis: chronic pain with limited range of motion