A carpometacarpal joint connect a finger to the hand.
The usual carpometacarpal dislocation involves the small finger CMC joint. Although a well molded cast can be effective, the treatment usually requires "pinning" of the dislocated joint for approximately 4 weeks.
Dislocations of the other carpometacarpal joints are less common, but the treatment principle is the same: each joint has to be reduced and held in place - with as many pins as needed.
The injury described below was from an industrial accident.
Here's a PA view. Notice that:
The trapezoid is easier to see in this oblique view: it is dislocated from the rest of the carpus.
A 3D reconstruction view is not particularly helpful.
One way to think of this injury is as the hand equivalent of a Lisfranc injury of the foot.
The injury was approached through a large dorsal midline incision. A large amount of hematoma was removed, and then reduction was performed starting from the ulnar side and proceeding towards the thumb. Stabilization was performed with percutaneous pins. Here it is:
Patient was kept in a splint with pins for 2 weeks. Physical therapy was started at 2 weeks in order to prevent stiffness. Patient followed up weekly to check and care for the percutaneous pins, and to make sure physical therapy progressed correctly. Pins were removed at 4 weeks.
The patient eventually made a full recovery and was able to resume work at the same job. Here are the final xrays several months later: