Updated: Oct 3, 2020
A 30 year old male presented to ED following a fall from his bicycle with left- sided shoulder pain. He landed forwards directly into the shoulder and maintains the arm adducted and has restricted movement. This is his x-ray
What is the diagnosis?
On the frontal x-ray the shoulder is internally rotated and on the lateral view the humeral head does appear posteriorly dislocated compared to the glenoid. This, with the associated clinical findings, is suspicious for posterior shoulder dislocation.
See here for another case from Radiopaedia archives
Tell me about posterior shoulder dislocation
This case highlights the use and outcome of ultrasound guided intra-articular posterior shoulder injection for the treatment of pain associated with shoulder dislocations and their subsequent reduction in the Emergency Department.
The glenohumeral joint is inherently unstable. It is the most commonly dislocated joint and usually it dislocates anteriorly. Posterior dislocations is less frequent (2-4%) and commonly missed.
Usually they are associated with high energy traumatic events, epileptic seizures and electrocutions often more prevalent in males.
In a traumatic setting, it is cause mostly due to the fall onto an outstretched and internally rotated arm.
Clinically a patient with posterior shoulder dislocation presents with the arm in adducted and internally rotated with resistance to external rotation
'Lightbulb' sign in AP
Empty glenoid sign: widening between anterior glenoid and articular surface of head of humerus
Lightbulb sign - notice the lightbulb shape on this shoulder x-ray
Point of care ultrasound findings
Ultrasound can be very useful for diagnosing shoulder dislocation and to facilitate intra-articular joint injection of local anaesthetic agent A recent paper published this year in Annals of emergency medicine compared x-ray to ultrasound findings in ED patients with anterior shoulder dislocation found that POCUS had high sensitivity (100%) and specificity (100%) to diagnose dislocations in ED and also allows to visualise fractures with good sensitivity (92%). With the caveat that most patients had anterior dislocations, so diagnosis could have been made by clinical examination alone by the physicians, and the scans were performed by ultrasound fellows with experience in POCUS, this study shows that bedside ultrasound can be an useful adjunct to the clinical exam and x-rays when the diagnosis is uncertain.
1: Lidocaine 1% or 2%
2: Syringe 10ml
3: 21 G needle (Green needle) or needle from nerve block pack
4: Dressing pack
5: Chlorhexidine or Iodine solution
6: Ultrasound machine with curvilinear probe
7: A steady hand!
These supplies are in our nerve block trolley
Position the curvilinear probe posterior to the shoulder facing forward with the marker towards the patient's humeral head
Find scapula and the head of humerus. These two should be aligned if the joint is enlocated
In a posterior shoulder dislocation the head of humerus is moved towards the probe so superiorly on the screen
Can use to facilitate intra-articular injection by allowing to localize the joint space and visualizing the needle tip injecting in the glenohumeral joint
Non-dislocated shoulder - notice how the glenoid labrum is at the same level as the head of the humerus
Posterior shoulder dislocation - notice how the humeral head is closer to the probe face than the glenoid labrum
Shoulder injection - see hyperechoic needle in top right corner. Dark material is the injectate
Adequate sedation is often vital to reduce muscle tension and facilitate reduction
Reduce the shoulder applying inferior and posterior traction to humerus and have an assistant applying direct pressure to the posterior head of the humerus foward
Always obtain post reduction x-rays to ensure satisfactory reduction and looking for fractures
Back to the case:
The patient was diagnosed with a traumatic posterior shoulder dislocation. We injected using ultrasound guided intra-articular bupivacaine and he had a fentanyl and had a successfully reduction
Here’s the post reduction x-ray: notice how normal anatomy has been restored
Take home points:
Consider using US for diagnosis of anterior or posterior shoulder dislocation, especially when:
the diagnosis in uncertain
during procedural sedation to ensure satisfactory reduction if not clinically obvious
to administer early intra-articular anaesthetic for analgesia
Post written by Anirudh Iyengar , Claudio Dalla Vecchia
peer review Cian McDermott