Dislocation of the Carpometacarpal Joints
By William J. Brady, MD
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The carpometacarpal (CMC) joints of the hand, excluding the thumb, are extremely stable joints with relatively limited motion. They have significant bony and ligamentous supports that fix them in position. As a result, isolated dislocations are uncommon. Dislocations usually are associated with significant trauma and most commonly are associated with fractures of the base of the metacarpal.1 Isolated dislocations do occur, however, and the fourth and fifth CMC joints are the most common sites because they have the greatest degree of motion and related laxity.2 Numerous attempts in the laboratory have failed to produce a precise reproducible mechanism for isolated dislocations to these joints. Usually, however, they result from extreme violence, such as motor vehicle accidents or direct blows from heavy falling objects. Alternatively, they occasionally are associated with direct blows with a closed fist against an immovable object (e.g, a brick wall). These dislocations are high-energy injuries and should alert the physician to search for other associated injuries to the hand and wrist. They commonly are associated with fractures of adjacent metacarpals.3
The gross deformity of the subluxed or dislocated joint often is obscured by the severe swelling present on the dorsum of the hand. An obvious step-off deformity may be observed and/or palpated at the level of the dislocation—i.e., note the proximal end of the metacarpal as it overrides the distal carpus. (See Figure 1.)
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The points of maximum tenderness will be over the metacarpal bases and any areas of corresponding fractures. There may be rotational deformity of the digits or shortening of the metacarpal with attempted fisting. In all of these injuries, a careful assessment should be made of the neurovascular status of the hand. In dislocations of the fifth CMC joint (the most common injury pattern), specific attention should be directed to the status of the deep branch of the ulnar nerve in that it lies immediately volar to the fifth CMC joint where it winds around the hook of the hamate. The median nerve also may be injured, particularly with dislocation patterns resulting from a direct blow to the hand. Vascular compromise, particularly in patients with injury to the third metacarpal, may involve the deep palmar arterial arch, which lies directly beneath the third CMC joint. Integrity of the wrist extensor tendons also must be assessed in these dislocation injuries in that disruption may occur. Additionally, those patients who have suffered a direct blow are at risk for compartment syndrome in the hand.4
The radiographic series to assess these injuries should include anteroposterior (AP), lateral, and oblique views of the wrist. The lateral radiograph often is diagnostic with obvious visualization of CMC joint dislocation. (See Figure 2.) The AP view may reveal an overlap of the carpal bones over the proximal metacarpals. (See Figure 3.)
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The oblique films, if needed, should be taken with the hand pronated and supinated, respectively, from the true lateral. The critical factor for the physician reviewing the films is to recognize the potential for this injury any time there is a displaced fracture of a metacarpal. The metacarpals are tethered tightly together and these injuries can be analogous to Galleazi and Monteggia fractures in the forearm. Any displaced metacarpal fracture should, therefore, elicit concern about injury to the adjacent CMC joints.
Acute treatment in the ED consists of ruling out compartment syndrome and attempting closed reduction. This usually can be done with longitudinal traction, most easily accomplished by hanging the patient in finger traps with 5-10 pounds of weight suspended from the arm. The hand then should be splinted and digital motion encouraged to prevent stiffness associated with swelling. The patient must be referred urgently for definitive care in that these injuries often will require percutaneous pinning or open reduction/internal fixation.
Dr. Brady, Associate Professor of Emergency Medicine and Internal Medicine, Residency Director and Vice Chair, Emergency Medicine, University of Virginia, Charlottesville, is on the Editorial Board of Emergency Medicine Alert.
References
1. Bergfield TG, et al. Fracture-dislocations of all five carpometacarpal joints: A case report. J Hand Surg 1985; 10:76-78.
2. Pack DB, et al. Isolated volar dislocation of the index carpometacarpal joint: A unique injury. Orthoped 1995; 18:389-390.
3. de Beer JD, et al. Multiple carpo-metacarpal dislocations. J Hand Surg 1989;14:105-108.
4. De Waard JW, et al. Carpometacarpal dislocation: Report of three cases. Neth J Surg 1990;42:20-23.
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