It is 1 am. Your resident has just seen a 22 year old man with wrist injury sustained in a MVA and would like your opinion on the wrist x-ray. His plan is to reduce the fracture under sedation and place a below elbow POP slab. Here are the wrist x-rays; would you agree with his plan?

Left wrist AP view:

Left wrist lateral view:

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This is an interesting x-ray as there are two different injuries associated.

1. The Smith’s fracture is very obvious. There is a comminuted fracture of the distal radius with marked volar angulation of the distal fragment with an associated ulnar styloid fracture.

The fracture should be immobilised in an above elbow slab after reduction and not a below elbow slab that is done in a Colles fracture post reduction.

Smith’s fracture is usually unstable and hence requires operative intervention most of the time.

2. There is also evidence of stage I carpal ligamentous instability.

• Positive Terry Thomas sign – the distance between scaphoid and lunate is more than 2 mm (should be < 2mm normally).
• Positive signet ring sign – rotation of the distal pole of the scaphoid on its axis secondary to scapholunate dissociation causes end on view of the distal pole.
• DISI – Dorsal Intercalated Segmental Instability – lunate is angulated dorsally on the lateral view. Normal scapholunate angle is 30-60 degrees. In this case, it is approximately 80 degrees.

AP view:

Lateral view:

More info on DISI and how to measure the scapholunate angle etc can be found here: http://www.radiologyassistant.nl/en/p42a29ec06b9e8/wrist-carpal-instability.html

Thanks to Dr John Larkin (@jjlarkin78) for the images.

I wish you all a very Happy New Year on behalf of the Emergucate team!

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