A 24-year-old man is brought to the emergency department after falling directly onto his outstretched arm while snowboarding. He reports intense pain and an inability to move his right shoulder. On physical examination, the right arm is held in slight abduction and external rotation. The normal rounded contour of the deltoid is lost, appearing squared off, and there is a palpable fullness inferior to the coracoid process. The patient is unable to touch his left shoulder with his right hand. Neurovascular examination reveals decreased sensation over the lateral aspect of the right shoulder, but distal pulses are intact.
Which of the following is the most likely complication associated with the injury in this patient?
The correct answer is:
A) Axillary nerve injury
This patient presents with a classic anterior shoulder dislocation, which accounts for over 95% of all shoulder dislocations. The clinical findings of an abducted, externally rotated arm and the squared-off appearance of the shoulder shoulder, due to the humeral head no longer being in the glenoid fossa, are diagnostic. The axillary nerve is the most commonly injured nerve in anterior dislocations because it winds closely around the surgical neck of the humerus. Injury to this nerve results in weakened shoulder abduction (deltoid) and decreased sensation over the the lateral deltoid.
Answer choice B: Brachial artery rupture, is incorrect. While vascular injuries can occur with shoulder trauma, they are much more commonly associated with displaced supracondylar humerus fractures or high-energy axillary trauma rather than standard anterior dislocations.
Answer choice C: Hill-Sachs lesion, is incorrect. Although a Hill-Sachs lesion (a compression fracture of the posterolateral humeral head) is a common consequence of an anterior dislocation, the decreased sensation over the lateral shoulder is suggests an axillary nerve injury.
Answer choice D: Long thoracic nerve palsy, is incorrect. Injury to the long thoracic nerve causes winging of the scapula and is typically caused by repetitive trauma or surgery in the axillary region, not by a glenohumeral dislocation.
Answer choice E: Rotator cuff tear, is incorrect. While rotator cuff tears are frequent complications of shoulder dislocations in elderly patients, the decreased sensation in the lateral shoulder and the age of this patient are more consistent with an axillary nerve injury.
Key Learning Point
Anterior shoulder dislocation typically presents with the arm in abduction and external rotation with a loss of the normal deltoid contour. The most common nerve injury associated with this displacement is the axillary nerve, which should be assessed by testing sensation over the lateral shoulder and checking deltoid contraction.
