Wrist Trauma • Xray
This patient fell off his bicycle, landing on his hyperextended ulnar-deviated wrist. There is anterior dislocation of the lunate, and the lunate is rotated 270 degrees such that the concavity of the lunate is directed dorsally rather than distally. The lunate is also displaced inferiorly, resulting in a fracture of the anterior articular surface of the distal radius with a small fracture fragment noted anteriorly.
The lunate is the most frequently dislocated carpal bone. The most common type of dislocation is volar, rotated 90 degrees. In this case the lunate has flipped over and rotated an additional 180 degrees, for a total rotation of 270 degrees. This is a rare form of lunate dislocation, comprising less than 5% of cases. Dislocation of 270 dgrees should be treated as a surgical emergency due to the risk of acute carpal tunnel syndrome, which manifests as decreased sensation in the median nerve distribution and excruciating pain. Operative stabilization is required to maintain the reduction.
The above is the most common type of lunate dislocation with the lunate volar, rotated 90 degrees. The distal radius is abnormally articulating with the capitate, rather than the lunate.(Image courtesy James Heilman, MD via Wikicommons: https://commons.wikimedia.org/wiki/File:LunatedislocationL.jpg
(This post was originally published on The Global Radiology CME Blog http://www.globalradcme.com/#!global-radiology-cme-blog/czj6 )