Diagnosing a shoulder dislocation
In this video, we'll review the mechanism behind a shoulder dislocation, the features that will help you to identify it during a physical exam, and how to use an x-ray to both confirm your diagnosis and document any pre-reduction fractures.
The shoulder has the widest range of motion of any joint in the body and, as a result, is the most frequently dislocated joint in the body. In this video, we'll review the mechanism behind a shoulder dislocation, the features that will help you to identify it during a physical exam, and how to use an x-ray to both confirm your diagnosis and document any pre-reduction fractures. Importantly, you'll learn how to handle an accompanying nerve injury and recognize the big red flag that signals you to call the orthopedic surgeon before attempting a reduction.
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Let's start by describing what a shoulder dislocation is. The shoulder has the most range of motion of any joint in the body because of the shallow nature of the glenoid fossa. The landmarks we need to review are the glenoid, or the shoulder socket, the humeral head, the coracoid process, and the acromion and the clavicle. That shallow glenoid fossa makes the shoulder the most frequently dislocated joint in the body.
Most shoulder dislocations are anterior, meaning the humeral head comes out of the glenoid socket and sits in front of it. Posterior joint dislocations are rare and make up less than 4% of shoulder dislocations. There are a couple of other types of dislocations that I've never seen in 20 years of emergency medicine.
So back to the more common anterior dislocation, how does this happen? Well, the classic mechanism is a fall causing a combination of both abduction and extension, as well as external rotation of the shoulder. Basically falling on an outstretched arm. The most important thing to realize is that the shoulder wants to go back into the glenoid fossa where it's happy.
But muscle spasm and later swelling, and sometimes trapped soft tissue keeps it from going back. So the trick is to reduce the shoulder as soon as possible and decrease the patient's anxiety and guarding as much as possible. In patients with multiple recurrent dislocations, the joint can be so loose that even a minor pull like a slight external rotation while rolling over in bed or reaching for a car seat belt can cause a dislocation.
The younger the patient, the more likely that a recurrence will happen. There are four subtypes of anterior dislocations. The most common is the subcoracoid dislocation, which accounts for 75% of anterior dislocations. The second most common is the subglenoid. The other two - subclavicular and intrathoracic, make up less than 1% of the other anterior shoulder dislocations.
So, how do we examine the shoulder dislocation? Well, it's usually obvious basically, it's the story and the way the patient is holding their arm. Usually the patient will be leaning forward toward the injured side and holding their arm abducted, meaning away from the body and slightly externally rotated.
If the patient is thin, you will see a loss of the rounded shape of the normal shoulder. the acromion is going to be prominent and you might even see some fullness under the collarbone. In a thin and non-muscular person, you can even put your finger in the empty glenoid fossa The patient will not want to externally rotate the shoulder because that really hurts.
So, if your patient can touch the opposite shoulder with their hand, it's really unlikely that the shoulder is out. For your physical exam, it's important to document that the pulses distally are intact. But honestly an axillary artery injury is very rare, and if it happens, it's usually happening in the elderly.
More importantly, you need to make sure that the axillary nerve is okay because that's the most common nerve that's going to be injured as a result of a dislocation. To test the nerve, lightly touch the deltoid muscle and see if the sensation is the same as the other side. It's good practice to also document the normal ulnar and medial and radial nerve exam to make sure that there's no brachial plexus injury.
If there is a nerve injury, you have to be especially gentle and have a low threshold for calling orthopedic surgery to take the patient to the operating room. Documenting the exam before the reduction also proves that you didn't cause any of the injuries with your attempted reduction. Unless this is a recurrent dislocation with a minor mechanism, you'll need to get an x-ray to both confirm your diagnosis and document any pre-reduction fractures.
About 15% of the time there may be an associated fracture. This is not going to be a subtle x-ray. The anterior posterior x-ray will be the best way to see if there's a dislocation or fracture. The scapular Y view, will show if the humeral head is in the glenoid fossa, in case the AP view is not obvious. Now that you know how to diagnose an anterior shoulder dislocation, let's talk about how to fix it.