This is an image provided by one of our UC Davis resident physicians:
Great example of a lunate dislocation!
The key portion of the film above is the half-moon shaped bone (Lunate) which is dislocated in the palmar direction and has a “spilled teacup” appearance (it is rotated from its normal position with the concave portion of the bone facing the distal fingers).
The AP view on this patient is also interesting. It shows a “Piece of pie” sign, also frequently found with lunate dislocation. This is an abnormal triangular hyperdensity seen in the lunate on the AP projection (can also be seen in perilunate dislocation).
The distinguishing feature of this radiograph to differentiate between perilunate and lunate dislocation is the alignment on the lateral projection. The capitate and distal radius are still aligned, the lunate is dislocated. In a perilunate dislocation the lunate will not have a “spilled teacup” rotation and the capitate will be dorsally displaced off the alignment of the distal radius. An example of a perilunate dislocation:
Tip: on lateral wrist xrays, always draw a line through the distal radius, lunate, and capitate. It should look like an apple sitting in a teacup on a saucer.
Author: Russell Jones, M.D.
Image Contributor: Dane Stevenson, M.D.
Another eponym fracture, courtesy of John Neuffer, MD at WVU. Dr. Neuffer saw a patient with a fall on an outstretched hand (FOOSH) and this was the result:
This is an example of a Colles Fracture. Colles fracture is a distal radius fracture with dorsal displacement of the distal fracture fragment and wrist. FOOSH is a popular mechanism of this injury as well as any other mechanism that causes an axial load on the distal wrist with extension of the hand.
There are two other interesting parts of this image: 1. There is an ulnar styloid fracture 2. The pisiform is dislocated.
Ulnar styloid fractures are very common with FOOSH mechanism and in conjunction with distal radius fractures. Common xray findings with a Colles fracture include (1):
- Transverse radius fracture
- Dorsal displacement and angulation
- Radial angulation of the wrist
- Location 1 inch proximal to the radiocarpal joint
- Radial shortening
- Ulnar styloid fracture
- Salter-Harris fractures in children
Pisiform dislocation is rare. On the lateral view above you can see the pisiform is displaced off the triquetral bone (its only articulation).
This is what it should look like:
(Above is a link to Wikipedia. James Heilman, MD has a post about the pisiform with a great lateral radiograph demonstrating a normal positioned pisiform. Go check it out!)
Author: Russell Jones, MD
Image Contributor: John Neuffer, MD
Thanks to Dr. Neuffer at WVU for the image as well as pointing out a good EM blog for me to follow: EMchatter.com. Keep up the good work and send me more good images!
1. Broder JS. ”Imaging the Extremities.” In: Broder JS. Diagnostic Imaging for the Emergency Physician. Elsevier Saunders, 2011.