Posterior Shoulder Dislocation

Dr Terry Hammond

MBBS FRACS Orth

 

Case:

A 46-year-old lady presents with a painful shoulder following a fall. She was seen at a small regional hospital and the only x-ray obtained was an AP, which the medical officer thought was normal.

 

She re-presented at two weeks with ongoing pain and restricted movement in her shoulder. Examination findings confirmed a significant lack of external rotation to 5° on the affected side compared with 60° on the unaffected side. A new set of x-rays including a lateral view was obtained, these are seen below.

 

Left hand x-ray: AP view showing the humeral head rotated and overlapping the glenoid. However, it is very easy to misinterpret this as showing a normal shoulder.

 

Central x-ray: This x-ray shows the lateral view of the shoulder.

 

Right-hand x-ray: Same lateral x-ray as the central image. I have outlined the humeral head with a black circle and the glenoid with a red circle. You can see a posterior dislocation of the humeral head. Again it is a subtle finding and easily missed!!

 

A posterior shoulder dislocation was diagnosed. The shoulder was reduced and the patient was treated with 6 weeks of external rotation splintage. Luckily enough a good result was achieved.

 

This case illustrates how easy it is to miss a posterior shoulder dislocation. It is therefore very important to examine all patients who have had a fall even if x-rays appear normal. This is especially important in older patients who may not complain of a great deal of pain - especially if they have dementia. A history of ongoing pain and particularly a lack of external rotation should alert you to the possibility of a posterior dislocation. Lateral and axillary x-rays are vital and need to be reviewed very carefully. If there is any question a CT scan should be ordered. Treatment is usually non-operative and may involve use of external rotation splintage. Careful monitoring must be performed during the recovery period to ensure no further dislocation occurs. A referral to an orthopaedic surgeon is usually required.