A 26-year-old falls on an outstretched hand. Lateral wrist X-ray shows the capitate lying posterior to the lunate, and the lunate has a triangular appearance on the anteroposterior film. On the lateral view the lunate itself looks like a cup tipped forward with no bone sitting in it. Which structure is at greatest risk of acute compression, and what does the lateral sign represent?

• A Radial artery; perilunate dislocation stage II
• B Median nerve; lunate dislocation, the spilled teacup sign ✓
• C Ulnar nerve; scapholunate dissociation, the Terry Thomas sign
• D Anterior interosseous nerve; transscaphoid perilunate fracture-dislocation

Explanation

In stage IV of Mayfield's sequence the lunate dislocates out of the lunate fossa into the carpal tunnel. On the AP view it appears triangular (piece of pie), and on the lateral view it looks like a tipped cup with the capitate displaced behind it, the classic spilled teacup sign. The lunate compresses the median nerve within the carpal tunnel, so acute decompression is needed. The Terry Thomas sign describes scapholunate widening, a different injury.

Reference: Green's Operative Hand Surgery, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.