A 17-year-old boy presents to the emergency department complaining of severe left shoulder pain which began 1 hour ago. He was at his high school dodgeball game when he extended his arm out to reach for the ball. A member of the opposing team fell into him from the front, pushing against his abducted arm. The patient is unable to move his shoulder and holds it to his side. On physical examination, the area over the deltoid of his left arm appears flatter than that of his right arm. He holds his arm at a slightly abducted and externally rotated position. Radial pulses are normal and equal bilaterally.
Which of the following nerves is most likely to be injured in this type of dislocation?
A) Axillary nerve
Anterior dislocation of the shoulder is the most common (95%) of glenohumeral joint dislocations. The glenohumeral joint is most susceptible to dislocation when the humerus is in the abducted and externally rotated position. Extreme force may lead to anterior dislocation when in this position. Looking at the brachial plexus, the axillary nerve is most susceptible to injury from an anterior dislocation.
Injury to the median nerve would result in loss of sensation to the ventrolateral aspect of hand, loss of the ability to abduct and oppose the thumb ("ape hand" deformity), weakness in forearm pronation, and weakness in flexing the digits.
Musculocutaneous nerve injuries are rare, although they may be seen in severe trauma situations, such as a motor vehicle collision or severe crush injury to the arm.
The radial nerve can be damaged in humeral fractures at the mid-shaft. The patient would exhibit loss of sensation of the dorsal hand, posterior arm and forearm. In addition, these patients may lose the ability to extend the wrist and fingers.
Ulnar nerve injuries can be seen in trauma to the medial epicondyle. The patient may exhibit "claw hand" deformity and lose sensation of the medial aspect of the hand.
Key Learning Point
Forceful abduction and external rotation of the glenohumeral joint may lead to anterior shoulder dislocation, and the nerve that is most likely to be injured is the axillary nerve.
