The shoulder has the most range of motion of any joint in the body because the glenoid (shoulder joint) is very shallow. Unfortunately, this also means that the shoulder is the most frequently dislocated joint!
How does a shoulder dislocation happen?
Most shoulder dislocations are anterior, meaning that the humeral head pops out of the glenoid socket and rests in front of it. The most common way to dislocate a shoulder is falling on an outstretched arm.
For patients with multiple recurrent dislocations, even a minor pull can cause a dislocation. For example, rolling over in bed or reaching for a car seat belt may result in a dislocation! The younger the patient the more likely that a recurrence will happen.
The most important thing to realize is that the shoulder’s natural tendency will be to go back into the socket. Muscle spasms, swelling, and sometimes trapped soft tissue will prevent it from going back in. For this reason, you want to reduce the shoulder as soon as possible to stop the patient from favoring their shoulder and decrease the patient’s anxiety and guarding as soon as possible.
What are the types of anterior shoulder dislocations?
There are four types of anterior dislocations:
- Subcoracoid dislocation (75% of anterior shoulder dislocations)
- Subglenoid dislocation
- Subclavicular dislocation (less than 1% of anterior shoulder dislocations)
- Intrathoracic dislocation (less than 1% of anterior shoulder dislocations)
How to diagnose a shoulder dislocation
Physical signs of an anterior shoulder dislocation
Usually, a dislocated shoulder is obvious! There are seven signs to look for when diagnosing a shoulder dislocation:
- Patient is leaning towards the injured side.
- Patient is holding the arm away from the body.
- The arm is slightly externally rotated.
- There is a loss of the rounded shape of the normal shoulder (more obvious in thin patients).
- The acromion is prominent.
- There is a fullness under the collarbone (humeral head prominent).
- Patient cannot touch opposite shoulder with their injured arm.
Physical tests for an anterior shoulder dislocation
For your physical exam, it is very important to document each physical test:
- Distal pulse on injured arm—rule out axillary artery injury. This is rare and usually happens in the elderly.
- Light touch sensation over deltoid muscle—rule out axillary nerve injury. In anterior shoulder dislocations, it is common for the axillary nerve to be injured.
- Ulnar, median, and radial nerve exam—rule out brachial plexus injury.
- Anterior-posterior (AP) x-ray or scapular Y view—confirm dislocation.
- Pre-reduction fractures—15% of the time, there may be an associated fracture of the proximal humerus, humeral head, or glenoid fossa that should be documented.
Documenting the exam before the reduction also proves that you didn’t cause injury with your reduction. And if there is a nerve injury, you’ll have to be especially gentle. Don’t hesitate to send your patient to the operating room.
Great job! Now you know the basics for how to diagnose an anterior shoulder dislocation.
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