A 22 year old male patient comes into the emergency department after reportedly “falling” on his fist.
On examination, he has pain and swelling to the dorsum of his hand. An x-ray is ordered looking for a “boxer’s fracture” and the results are shown below.
What’s the diagnosis? What’s the treatment?
Scroll down for the answer.
Diagnosis: Carpometacarpal Dislocation
Notice how on the PA view, the 4th and 5th metacarpals don’t line up with the carpal bones as well as the 2nd and 3rd metacarpals (arrow)? Easy to miss.
The dislocations are more apparent on the lateral films (dotted arrow) which is why it is important to look at all views of the x-rays that are obtained.
This is an uncommon injury that most often occurs in the dominant hand of young males and is often misdiagnosed. A metacarpal dislocation usually occurs from punching objects with a flexed wrist, falls, or direct trauma (such as from handlebars hitting palm of hand).
Fourth and fifth metacarpals are most commonly dislocated due to comparatively looser ligamentous attachments of those bones to the hamate.
If significant pain persists despite a normal appearing x-ray and a fracture or dislocation is expected, consider obtaining a CT scan or MRI.
Reduction of a carpometecarpal dislocation is relatively simple, and involves traction on the involved fingers using one hand along with longitudinal and volar pressure on the dislocated bones with the thumb of the other hand. The bones usually pop into place fairly easily.
After reduction, place in hand in a volar splint.
One article recommends Kirschner wire fixation for 4-6 weeks, while another article recommends closed reduction in stable injuries less than 10 days (see references below)
Failure to stabilize these injuries can lead to loss of grip strength and to decreased range of motion at the involved metacarpophalyngeal joints – both of which reduce hand function.
Additional articles on Carpometacarpal/Metacarpal Dislocations:
Carpometacarpal joint dislocation
Carpometacarpal Dislocation – An Easily Missed Diagnosis