injuries poisoning
Shoulder Dislocations
Posterior Shoulder Dislocations
Occasionally, dislocations are posterior—a commonly missed injury (see table Examination for Some Commonly Missed Fractures ). It is classically caused by seizures, electric shock, or electroconvulsive therapy done without muscle relaxants. Suspect a posterior shoulder dislocation if patients have shoulder pain, keep their arm adducted, and cannot externally rotate their arm and x-rays show no obvious abnormality. Deformity may not be obvious. The arm is held adducted and internally rotated. Typically, when the elbow is flexed, passive external rotation is impossible. If such rotation is impossible, an anteroposterior (AP) shoulder x-ray should be taken. If it shows no obvious fracture or dislocation, posterior shoulder dislocation should be considered. A clue to the diagnosis on the AP view is the light bulb or ice cream cone sign; the humeral head is internally rotated, and the tuberosities do not project laterally, making the humeral head appear circular. Bony injuries occur in about 65% of posterior dislocations ( Reference ). The axillary view or trans-scapular Y view is diagnostic. A posterior dislocation cannot be excluded without a Y view. In the left image (anteroposterior view), the humeral head is internally rotated, resulting in the light bulb or ice cream cone sign (projections of the greater and lesser humeral tuberosities are not seen), which suggests a posterior dislocation. In the right image (Y view), the humeral head is posterior to the glenoid fossa, which demonstrates a posterior dislocation. Image courtesy of Danielle Campagne, MD. In the Y view, lines drawn through the acromion (blue arrow), coracoid (black arrow), and scapular body (red arrow) intersect at the center of the glenoid fossa. In this x-ray, the humeral head is outside of and posterior to the glenoid fossa, indicating a posterior dislocation. Image courtesy of Danielle Campagne, MD. Reduction is often possible using longitudinal traction (as with the Traction-countertraction technique for reducing anterior shoulder dislocations ). (See also 1.Rouleau DM, Hebert-Davies J: Incidence of associated injury in posterior shoulder dislocation: systematic review of the literature.J Orthop Trauma26(4):246-51, 2012. doi: 10.1097/BOT.0b013e3182243909 