5th carpometacarpal joint dislocation
FOOSH from bike at 10kph. Now pain at 4th and 5th MC shaft.
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The fifth metacarpal base is anteriorly dislocated, no longer articulating with the hamate. The radio-carpal joint and carpal bones appear anatomically aligned. No acute fracture is seen.
An example of 5th carpometacarpal joint dislocation. This injury is often missed by the inexperienced reader which is why CMC joint alignment is an important check area when assessing hand and wrist radiographs.
The 5th CMC joint space should normally be seen on the AP projection as a thin space between the metacarpal base and the hamate, or sometimes there may be slight overlap of the bones. There should never be a large degree of bony overlap and certainly the metacarpal base should not be seen anywhere near the triquetral as in this case. On a normal lateral projection the metacarpal bases should largely overlap one another, without any one base significantly offset compared to the others.