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Except for the thumb, fractures and dislocations of the carpometacarpal (CMC) joints are a relatively uncommon pattern of injury, and are usually due to high energy trauma. These injuries account for less than 1% of injuries affecting the hand.1,2 These injuries are often missed initially even by orthopedic surgeon, because of the diffuse hand swelling obscuring deformity and misinterpretation of subtle radiographic features as normal.3 Hence, diagnosis requires a high index of suspicion and good-quality radiographs.
A 24-year-old, right hand dominant male patient had sustained injury to his right hand in a road traffic accident 10 days back. Initially he had a painful swelling of hand and a palmer wound which was managed in casualty with irrigation, antibiotics and primary suturing. Radiographs were taken initially which had been interpreted as normal without any major fracture. The individual presented at the tertiary care center with persistent pain and swelling over the dorsum of the hand. The palmer wound had healed (Fig. 1).
On reviewing the initial radiographs on posteroanterior (PA) view there was superimposition of fourth and fifth metacarpal bases with the hamate with widened space between the third and fourth metacarpal. The Gilula arcs were maintained (Fig. 2). There was a doubtful fracture of the base of fourth metacarpal. Even the second and third CMC joints showed overlapping and loss of parallelism. The lateral view of the hand was suggestive of some injury to the CMC joints, however this initial lateral view was of poor quality and interpretation was difficult. CT scan with reconstruction demonstrated dorsal dislocation of fourth and fifth metacarpals, with subluxation of third CMC joint and no major fractures. The hamate articular surface was empty (Fig. 3). A diagnosis of open dorsal dislocation of fourth and fifth CMC joint was made.
Initial two attempts of closed reduction were not successful and the patient was planned for open reduction. The fourth and fifth CMC joints were exposed using a dorsal skin incision. The hamate was found lying volarly and capsule was interposed and preventing reduction. There were no fractures found. The reduction was achieved by applying longitudinal traction and gently levering the fourth metacarpal base over the hamate. The subluxation of the third CMC joint reduced following reduction of fourth CMC joint. The fourth and fifth CMC joint reduction was not stable there was a tendency of the metacarpals to subluxate dorsally. The reduction was therefore stabilized using K wires.
Post-operative radiographs showed satisfactory reduction and restoration of parallelism of CMC joints (Fig. 4). A splint was used to immobilize the CMC joints; MCP and IP joints movements were started immediately.
Pure dislocations of the CMC joints are very unusual injuries. Generally, these dislocations are fracture dislocations due to avulsion of the ligaments. Most of the literature available is case reports and small series of fracture dislocations. Open dislocation of the CMC joint is even rarer injury. In 2001, Prokuski et al,4 published a retrospective review of 12 cases of patients with dorsal dislocations and fracture-dislocations of the second, third, fourth, and fifth CMC joints treated with open reduction and internal fixation. This was the first report of an open CMC dorsal dislocation which was present in one of these cases.
Dislocations of the CMC joints can be easily missed because of the diffuse swelling which may mask the deformity and due to subtle radiological findings. In 1983, Fisher et al5 analyzed radiological findings in these injuries. On the PA radiograph, the CMC joints can be evaluated according to the principles of parallelism, symmetry and overlapping structures developed by Gilula.6 A PA radiograph of a normal hand should show a clear joint space between the bases of the metacarpals and the carpus, with parallel joint surfaces. Drawing lines through the distal cortical surfaces of the trapezoid, capitate, hamate and the bases of the second to fifth metacarpals, there should be two parallel zigzag lines approximating the letter M (so-called ‘parallel M lines’). The key radiographic diagnosis lies in the subtle loss of joint space and the loss of the parallel articular surfaces of the CMC joints, which are seen on the PA views. The true lateral radiograph is very important and must be taken to demonstrate the dorsally dislocated metacarpals and for any associated fractures. In doubt, and if a CMC dislocation is suspected, a CT scan can be used. In the present case the Gilula arcs of the wrist were maintained and there was subtle overlap seen in the PA view. Lateral view was not of a good quality and hence the diagnosis must have been missed initially. If proper lateral view would have been taken the dorsally dislocated fourth and fifth CMC joints could have been easily appreciated.
A dislocated CMC joint can lead to chronic pain and reduced grip strength. Therefore, reduction is necessary to achieve proper function of the hand. Most authors advocate reduction with operative stabilization to prevent secondary dislocation.7–9 In 2011, Storken et al10 reported four cases of acute fourth and fifth CMC dislocations treated conservatively by closed reduction and splinting. However frequent radiographs are needed to rule out secondary redislocation if managed nonoperatively.
In the present case the injury was 10 days old and the initial attempts of closed reduction were unsuccessful. There was interposition of dorsal capsular tissue preventing the reduction. Even following open reduction the fourth and fifth CMC was unstable with a tendency to subluxate dorsally. Surgical fixation of reduction was hence warranted.
The present case report is an example to the fact that the carpometacarpal injuries present with clinical signs and radiographic features which can be easily overlooked during initial assessment. Identification of these injuries requires proper assessment of PA and lateral radiographs with careful looking for subtle features of dislocations. Operative stabilization is frequently needed as these injuries have a tendency to be unstable.
The author has none to declare.