Carpometacarpal (CMC) joint dislocations are an uncommon dislocation of the hand.
There is a strong younger male predominance in the dominant hand.
The most common mechanisms of injury are punching followed by a fall.
The patient may present with ulnar deviation of the 5th digit if it is just the 5th CMC joint that is dislocated. They may present with a mass if the 3rd, 4th and 5th CMC joints are dislocated. Often the hand is so grossly swollen that these features may not be readily apparent.
Loss of the clear joint space and zigzag or M shape pattern between the carpals and metacarpals on the PA projection, although it may be normal, and the dislocation will only clearly be shown on oblique or lateral projections.
The following injuries should be actively searched for or raise the suspicion of in CMC joint dislocations:
- base of metacarpal fracture (common)
- hook of hamate fracture