Posterior shoulder dislocation

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Anatomy - Posterior Shoulder Dislocation

An understanding of the anatomy of the shoulder in dislocation is essential when attempting reduction. The position of the glenoid rim of the scapula in relation to the humeral head is the key to a successful reduction, unintentional movement of one of these components during a manoeuvre will often determine success or failure. The humeral head needs to move anteriorly, medially and superiorly in order to return to the glenoid fossa.

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Clinical Presentation

A good clinical examination before attempted reduction. In a posterior dislocation there may be little or no obvious acromial step and the humeral head may be hard to palpate. The patient is usually holding the humerus in adduction and internal rotation, and will not be able to externally rotate the humerus without discomfort. 

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Other injuries

Proximal humeral fractures include anatomical neck and lesser tuberosity of the humerus.

Reverse Hill-Sachs lesion seen here (left) on an Xray from a patient who had sustained a posterior dislocation following a seizure. Also called a McLaughlin lesion, this is an impact fracture of the postero-medial humeral head.

Reverse Bankart's lesion - this is a detachment of the postero-inferior labrum. You may see a bony fragment avulsed on Xray, but an MRI will pick up this lesion best.

Glenohumeral ligament avulsion which may contribute to future instability.

POLPSA (posterior labrocapsular periosteal sleeve avulsion) lesion can occur with a posterior dislocation - damage to the periosteum of the scapula and posterior glenoid labrum. Again, best seen on MRI.

Imaging

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AP and lateral views

The humeral head sits posterior to the glenoid rim, twisting slightly into internal rotation with a resultant “lightbulb” sign seen on X-Ray in the AP view. A “reverse Hills-Sachs”/McLaughlin lesion may also be seen, this is an impact fracture of the anteromedial humeral head. The posterior dislocation can be missed on X-ray, so think about it if you have a patient reluctant to externally rotate their humerus, especially if confused or post-ictal. CT scan if X-Ray unclear or if you can’t get a decent axial view.

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Normal view in internal rotation

Taking just an AP X-ray can mean missing a posterior dislocation in up to 50% of cases. The normal 

Technique

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Theory

This technique is something of a ‘reverse Kocher’s’ and uses a combination of:

- Humeral head optimization with adduction to reduce wedging behind rim

- Voluntary retraction of scapula, reducing the fixed obstruction of the lateral aspect of the glenoid rim to the returning humeral head

- Tightening/shortening of the capsule using internal rotation and elevation of the humerus which then lifts the head up onto the rim, apposing the articular surface of the humeral head to the rim.

- Finally external rotation of the humerus which release the tension of the capsule and allows the head to slide into place 

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Step-by-step

Firmly and gently hold upper arm (above elbow) and forearm

Place into further adduction and internal rotation 

Lift elbow to level of shoulder

Externally rotate

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How-to video

Click here for a step-by-step explanation of the technique (thanks to Dr Matthew Kilmurray).

Posterior dislocation video