Anterior Shoulder Dislocation

Why Axillary nerve injury at the neck is correct

• An abducted, externally rotated arm with an anteriorly palpable humeral head indicates anterior glenohumeral dislocation.
• The axillary nerve wraps the surgical neck of the humerus and is the nerve most commonly injured in this dislocation.
• Look for numbness over the lateral deltoid (regimental badge area) and weak shoulder abduction.

Why the others are wrong

• Radial nerve palsy with wrist drop — The radial nerve is injured with mid-shaft humeral fractures, not anterior shoulder dislocation (right-bone-wrong-injury).
• Suprascapular nerve entrapment injury — Entrapment at the suprascapular notch weakens supraspinatus and infraspinatus (spinoglenoid notch entrapment weakens infraspinatus alone), typically from overuse or a ganglion cyst, not acute dislocation (proximity decoy).
• Long thoracic nerve palsy with winging — Long thoracic injury causes scapular winging from serratus anterior weakness and is unrelated to glenohumeral dislocation (anatomic mismatch).
• Upper trunk brachial plexus stretch injury — a football collision can stretch the C5-C6 upper trunk (a burner or stinger), which also weakens shoulder abduction, but that traction injury occurs when the head and shoulder are forced apart, whereas an anteriorly dislocated humeral head stretches the axillary nerve around the surgical neck (overlapping-deficit trap).

Why Axillary view radiograph is correct

• The axillary view is part of the standard pre-reduction trauma shoulder series and is essential to confirm the direction of dislocation.
• It is the single most reliable plain film for distinguishing an anterior from a posterior dislocation, because the AP view alone can be ambiguous and posterior dislocations are notoriously missed on AP imaging.
• It also helps detect associated bony injury (Hill-Sachs, Bankart, greater tuberosity) before any reduction attempt.

Why the others are wrong

• MRI of the shoulder joint is appropriate after reduction in a young first-time dislocator to assess the labrum, capsule, and rotator cuff, but it is not the immediate next step before reduction and does not change acute management.
• CT scan of the shoulder is reserved for quantifying glenoid bone loss in recurrent instability or complex fractures, not for first-line confirmation of an acute dislocation.
• Ultrasound of the shoulder can identify a rotator cuff tear (more relevant in older patients) but does not establish dislocation direction or screen for fracture before reduction.
• Stryker notch view radiograph — it is a dedicated plain film for detecting a Hill-Sachs lesion, but it requires placing the hand on top of the head, a position this patient cannot assume while he splints the painful dislocated arm against his body, and it does not establish the direction of dislocation; it belongs to the post-reduction or recurrent-instability workup.

Per standard ED orthopedic practice, a complete pre-reduction radiographic series (true AP, scapular Y, and axillary views) should be obtained, with the axillary view being critical to differentiate anterior from posterior dislocation and to identify fractures that could be displaced by reduction.