Carpometacarpal dislocation of the thumb associated with fracture of the trapezium
© The Author(s) 2014
Received: 3 July 2013
Accepted: 2 March 2014
Published: 27 March 2014
Carpometacarpal dislocation (CMC) of the thumb associated with fracture of trapezium is an extremely rare injury, with only 12 cases that sustained similar injuries reported in the literature. In this article, another patient with this rare injury was reported, and all previously published cases were extensively reviewed. The presented case and all previously published cases had a longitudinally oriented trapezium fracture, which is naturally unstable and almost always associated with dislocation of the CMC joint. In contrast to previous descriptions, we believe that CMC joint dislocation and trapezium fracture are not two distinct pathologies that occur simultaneously by chance but share cause and consequence.
Previously published cases in the English literature of carpometacarpal (CMC) dislocation of the thumb associated with trapezium fracture
Mechanism of injury
Trapezium fracture classification
Tolat and Jones 
Fall onto an outstretched hand (skateboard)
Closed reduction splinting 6 weeks
Excellent without instability, full ROM
Mody and Dias 
Open reduction and K-wire fixation; ligament reconstruction
Kukreti and Harrington 
Sport injury (rugby tackling)
Closed reduction and K-wire fixation
Slight pain, minimal loss of CMC flexion of CMC
Garavaglia et al. 
Fall while holding the handle of a bucket
Open reduction and screw fixation
Garneti and Tuson 
Sport injury (rugby tackling)
Open reduction and internal fixation with a minifragment 2.7-mm lag compression screw
Sport injury (rugby)
Open reduction and internal fixation with a single 2.7-mm lag screw
Afshar and Mirzatoloei 
Closed reduction and K-wire fixation
No pain and instability, full ROM
Parker et al. 
Fall onto an outstretched hand (rollerblade)
Closed reduction, spanning external fixation
Morizaki and Miura 
Fall onto flexed thumb
Open reduction and internal fixation using suture anchor and K-wire fixation
Chamseddine et al. 
Open reduction and K-wire fixation
Ramoutar et al. 
Fall onto an outstretched hand (football)
Closed reduction and K-wire fixation
Mumtaz and Drabu 
Direct trauma due to hammer hit (open injury)
Irrigation, debridement, and K-wire fixation
Gross impairment in opposition and abduction
Closed reduction and splinting for 6 weeks
Although the thumb CMC joint has wide ROM, which goes from extension through abduction to flexion, it is a highly stable joint. Integrity between mobility and stability is essential for performing an effective key pinch and grasp . Thumb CMC joint stability is provided by several structures, including the joint capsule, dorsal and volar ligaments, tendons transpassing the joint, and the saddle-shaped trapeziometacarpal (TMP) joint configuration [3, 4]. Four main ligamentous structures are accepted to be the primary source of static stability: anterior oblique ligament (AOL), intermetacarpal ligament, radial collateral ligament (RCL), and palmar oblique ligament . Several biomechanical and cadaver studies investigating the contribution of these ligaments to thumb stability and preventing dorsoradial dislocation of the TMP joint showed that RCL is the primary restraint against dorsal dislocation [1–4].
Two different mechanism of injury have been proposed for CMC dislocation and associated fractures of the trapezium [1, 2, 16]. According to the first mechanism of injury, CMC dislocation of the thumb occurs from axial loading on a flexed thumb metacarpal, which drives the metacarpal base dorsally over the trapezium and ruptures the RCL. TCL rupture results in dorsal dislocation, which may be a pure dislocation without any accompanying fracture . In pure CMC dislocations, the AOL is also torn or stripped subperiosteally. During this injury, if AOL avulses a piece of bone fragment from the base of the first metacarpal, Bennett’s fracture–dislocation occurs . In some instances, a vertical split fracture of the trapezium may occur, with the pullout effect of the intact RCL and axial loading of the metacarpal base on the trapezium. In the second proposed mechanism of injury, a commissural shearing produced by the impact of an object against the first web space causes CMC joint dislocation. This type of injury may happen with a fall while grasping an object, or if the individual is thrown forward while holding the handlebar of a motorcycle. Varying impact angles result pure CMC dislocation, Bennett’s fracture–dislocation, or a trapezium fracture. If the vector of the force passes toward the trapezium, a trapezium fracture will occur . Our patient was involved in a motorcycle accident and was thus more likely to be injured by commissural shearing forces produced by one of the handlebars during the collision. Other than these mechanisms of injuries, direct trauma (hit by a heavy hammer), fall onto an outstretched hand, and sporting injuries, have been reported in published cases [7–10].
Isolated nondisplaced trapezium fractures may be missed on direct radiographs due to overlapping adjacent bones, particularly on anteroposterior hand radiographs. In addition to meticulous physical examination and standard anteroposterior and oblique hand X-rays; a true anteroposterior view of the CMC joint of the thumb (Robert’s view) with full pronation of the thumb is an effective imaging technique by which to visualize these fractures. In case of suspicion, CT imaging can be utilized for further detailed demonstration . However, CMC dislocation associated with a trapezium fracture is usually evident, and there are only two cases which were initially missed the emergency department [11, 13]. Dorsoradial shift of the metacarpal, positive stress views and comparison with contralateral normal hand will be useful in confirming the subtle dislocations of the CMC joint. With an obvious dislocation of the thumb, attention must be paid for associated injuries including Bennett’s fracture-dislocation or trapezium fracture.
Several treatment methods are reported in the literature, ranging from closed reduction and cast immobilization to open reduction and ligamentous reconstruction, as summarized in Table 1. Usually, the dislocation can be reduced easily by thumb traction and abduction while gently pushing the metacarpal base medially [7, 13]. Nevertheless, the major factor affecting treatment outcome is reduction adequacy and maintenance. In this combination of injury, the RCL remains intact; therefore, if the joint is stable and reduction quality is good after closed manipulation, a thumb spica cast may be chosen . Thumb extension and slight pronation in the cast allows approximation of the stripped AOL and may enable ligamentous healing while contributing the joint stability . If conservative treatment is preferred, the patient should be checked for any radiological signs of reduction loss, particularly during the first 2 weeks after the injury. Serial radiographic follow-up is advocated to monitor the reduction quality achieved at initial reduction. Tolat et al. reported excellent outcome after conservative treatment in a skeletally immature patient (14 years old) . Although, our patient was an adult, conservative treatment yielded an excellent outcome. However, closed reduction and percutanous pin fixation seems to be a more appropriate treatment method, as it is both minimally invasive and safe against loss of reduction during follow-up. We believe that extensive surgery, such as ligamentous reconstruction using tendon grafts, is overtreatment, because trapezium union and AOL healing provide adequate joint stability [6, 17].
As the follow-up period for reported cases is short (mean 11.1 months, range 2–36 months), it is difficult to comment on long-term consequences and prognosis, particularly the development of posttraumatic osteoarthritis. Theoretically, inadequate TMP joint reduction or trapezium malunion that leads to incongruency of the articular surface leads to osteoarthritis and loss of thumb function in the long term . However, all reported cases expect one, a severe crush injury, resulted in good and excellent outcomes.
In conclusion thumb CMC dislocation associated with trapezium fracture is a rare injury, with few reported cases to date. Probable mechanism of injury is either axial loading on a flexed thumb or commissural shearing forces acting on the first web space. Radiographic evaluation of these patients should be done carefully to prevent missed diagnosis. Closed reduction and percutaneous K-wire fixation is sufficient to obtain a stable joint and promote proper ligamentous and bony healing. Although long-term follow-up is not available, prognosis is excellent in the short term.
Conflict of interest
The patient gave informed consent for publication of his medical records prior being included into this case study.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
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