The hand is frequently injured. Carpometacarpal (CMC) dislocations are an uncommon injury, composing less than 1% of all hand and wrist injuries.1,2 The mechanism usually occurs during hyperextension from high-velocity blunt trauma, mainly punching or falling.2 The most commonly involved joints are the fourth and fifth CMC joints. Most injuries are dorsal dislocations, with volar dislocations being less common. These dislocations are usually seen in adults.
Missed diagnosis of a CMC dislocation can result in chronic pain and decreased function of the affected hand. Up to 87% of patients with CMC injuries will return to full daily activities with negligible pain if they receive appropriate management.3 The method of optimal treatment is still being debated. CMC dislocations are intrinsically unstable and usually require a Hand Surgeon evaluation for surgical fixation with percutaneous pinning, plates, or screw placement after closed or open reduction. There have been rare cases of closed reduction with conservative immobilization for CMC dislocations without associated fracture.4-8
ANATOMY AND PATHOPHYSIOLOGY
There are numerous bones in the hand and wrist (Figure 105-1). The CMC joints of the hand are gliding-type joints (i.e., arthrodial diarthrosis). The bases of the metacarpals articulate with the distal row of the carpal bones and with each other using an interlocking mechanism (Figure 105-1). Stability at the CMC joints is provided by four ligaments (i.e., the dorsal and palmer metacarpal ligaments and the dorsal and palmar interosseous ligaments). Intermetacarpal ligaments, wrist extensor ligaments, and wrist flexor ligaments that insert at the bases of the second, third, and fifth metacarpals further reinforce and stabilize the joints.9 Strong anterior joint capsules often result in dorsal dislocations. The thumb and fifth finger have a wide range of motion. The CMC joints of the ring and little finger are relatively more mobile than the rest of the CMC joints. This makes them more susceptible to dislocation injury. The ulnar nerve passes adjacent to the hook of the hamate and just volar to the fifth CMC joint. Dislocation of the fourth or fifth CMC joint can cause traumatic nerve injury. Monitoring for a compartment syndrome (Chapter 93) is essential as there are 10 separate osteofascial compartments in the hand. These compartments are accessible for surgical release (Chapter 94).
The hand and wrist bones. (Used with permission from Hand Specialists of TX.)
CMC dislocations are rare.1,2 The thumb CMC joint is rarely dislocated. It usually results from an axial load with flexion of the thumb metacarpal resulting in a dorsal dislocation. A dislocation commonly occurs in association with a fracture. Closed reduction is usually unstable and requires operative stabilization. CMC dislocation of fingers 2 through 5 is also uncommon. It usually affects the fifth CMC ...