Dorsal Dislocation of the Trapezoid with Metacarpal Instability: A Boxing Injury

Abstract

Background  The second and third metacarpals are firmly attached, immobile structures which for the stable pillar of the hand. The trapezoid has been described as the keystone of the wrist, allowing a wide range of functional motion as well as inherent anatomic and biomechanical stability to the carpus.

Case Description  We describe a novel boxing injury with a 180-degree in situ dislocation of the right trapezoid with concomitant second and third carpometacarpal (CMC) joint dislocations. Open anatomic reduction of the trapezoid was obtained, and subsequent percutaneous pinning of the metacarpals allowed for a full functional recovery and return to sports at 6 months.

Literature Review  Combined trapezoid and CMC dislocations are extremely rare and have only been previously described in high-energy mechanism injuries, involving a direct dorsal force such as from the steering wheel in a motor vehicle collision. There are no previous reports of this injury occurring in the setting of direct axial load along the metacarpals in a clenched fist such as in a punch or fighting injury.

Clinical Relevance  The rare nature of this combined injury, its novel mechanism, and the difficulty in interpreting acute injury and postreduction radiographs require that the treating physician have a high degree of clinical suspicion for associated injuries when CMC dislocations are identified. Treatment strategies incorporating intraoperative fluoroscopy, open anatomic reduction of the trapezoid under direct visualization along with closed reduction, and pinning of the metacarpals reestablish carpal stability and provide excellent long-term results.

Dislocations of the carpometacarpal (CMC) joints are rare, accounting for less than 1% of hand injuries. ¹ When these dislocations occur, the fourth and fifth metacarpals are most frequently involved since the ulnar side forms the mobile border of the hand. ² In contrast, the second and third metacarpals are rigidly fixed, forming the stable pillar of hand.

The presence of CMC dislocation with concomitant subluxation or dislocation of the carpal bones is uncommon and suggests a higher energy mechanism of injury. ^{2 3 4} The exact mechanism by which these combined injuries occur is not fully elucidated. A few case reports have suggested that a direct dorsally applied force is responsible, as these injuries have been noted in the setting of wheel grip during motor vehicle collisions. ³

Here, we describe a case of combined second to third CMC joint dislocation and trapezoid dislocation due to a different mechanism, boxing injury. There was suspicion of a trapezoid dislocation at the time of initial reduction in the emergency department (ED). However, only at the time of surgical intervention was the trapezoid dislocation confirmed. As such, we recommend that suspicion for carpal injury remain high as these can easily be missed on routine radiographs. While computed tomography (CT) of the wrist can be helpful, we believe that a high degree of suspicion, open reduction, and intraoperative fluoroscopy are often sufficient in assessing carpal congruity and stability. Additionally, we suggest an alternative mechanism by which combined dislocation of the CMC joints and trapezoid may occur, as these injuries in boxers have not been previously described.

Case Report

A 30-year-old healthy male professional boxer presented with right wrist pain and deformity following a boxing match. On examination, he had swelling and obvious deformity dorsally over the base of the second and third metacarpals which were found to be grossly unstable. Finger flexion and extension was full and the patient was neurovascularly intact. Radiographs demonstrated dorsal dislocation of the second and third metacarpals ( Fig. 1 ). No additional injuries were initially appreciated. The patient's right hand was reduced and splinted in a position of stability. Repeat radiographs confirmed CMC joint congruity; however, a void was noted with widening and irregularity of the scaphotrapeziotrapezoidal joint ( Fig. 2 ). The patient was indicated for operative repair and fixation of his injuries. Intraoperative fluoroscopy was used to confirm the trapezoid was dislocated dorsally. A dorsal approach was used, and the trapezoid was observed to be rotated 180-degree dorsally and caudally, lying on underlying capsule and not articulating with any structures ( Fig. 3 ). Interposed torn structures, including the dorsal capsule, dorsal capitate–trapezoid ligament, and dorsal trapezoid–radial thirdmetacarpal base ligament, initially blocked reduction. With manipulation, the trapezoid reduced to its anatomic location under direct visualization. This reduction was held in place, and the torn ligamentous structures were primarily repaired. The second and third metacarpals were then reduced and pinned anatomically ( Fig. 4 ). The patient was allowed early finger range of motion (ROM). The Kirshner wires were removed at 6 weeks, and the patient had full return of wrist strength by 3 months with radiographic sclerosis of the trapezoid noted ( Fig. 5 ). He began training and returned to competitive boxing at 6 months.

Fig. 1.

Radiographs demonstrated dorsal dislocation of the second and third metacarpals.

Fig. 2.

A void with widening and irregularity of the scaphotrapeziotrapezoidal joint.

Fig. 3.

Trapezoid observed to be rotated 180-degree dorsally and caudally, lying on underlying capsule and not articulating with any structures.

Fig. 4.

The second and third metacarpals were reduced and pinned anatomically.

Fig. 5.

The patient had full return of wrist strength by 3 months with radiographic sclerosis of the trapezoid.

Discussion

Due to the stability of the second and third metacarpals and trapezoid, combined dislocations of these osseous structures have rarely been reported. A review of the published English literature produced only three similar cases. ^{5 6} Dunkerton and Singer reported an injury in a soccer player after a fall onto a flexed hand with resultant divergent dorsal dislocation of the second metacarpal and volar dislocation of the trapezoid. ⁶ Keith and Wollstein described two cases in which dorsal dislocation of the trapezoid and multiple metacarpals occurred due to wheel grip during a motor vehicle collision, and termed this as the steering wheel injury. ³

The proposed mechanism of injury of combined dorsal dislocation of the metacarpals and trapezoid by Keith and Wollstein in their study is a dorsally directed force acting directly on the CMC joint and trapezoid as in crush or steering wheel injuries. ³ The present case provides evidence for an alternative mechanism which has been suggested previously but never described clinically. ^{5 6 7} In the present case, injury occurred as a result of a proximally directed axial force applied to the distal second and third metacarpal heads, with a closed fist and the wrist in neutral, or slight flexion as seen in a boxer's punch. The proximal aspect of the metacarpals was likely then forcibly impacted into the trapezoid levering it dorsally, imparting a rotational force, and ultimately causing dislocation of the trapezoid and complete disruption of the CMC joints. The energy required to produce this injury is significant, and this case provides further insight into the magnitude of forces applied across a boxers' hand and wrist.

Knowledge of trapezoid anatomy provides a basis to understand how dislocation occurs dorsally. The trapezoid is a wedge-shaped bone with a dorsal surface roughly double the size of the volar surface. With the wrist in slight flexion, the scaphoid which normally buttresses the trapezoid in place, rotates slightly, exposing the dorsal surface of the trapezoid. Additionally, the dorsal ligamentous attachments are weaker than the palmar ligaments, and as a result, the trapezoid can become unstable if forcibly levered dorsally. ^{4 7}

Dislocations of the trapezoid are often missed on initial presentation and these injuries have proven difficult to diagnose. Wright and Umaar ⁸ describe “the missing carpal sign” as evidence of dorsal trapezoid dislocation, but this can be particularly challenging to evaluate in the setting of concomitant metacarpal dislocations. In their review, Koenig and West ⁹ found that a third of all trapezoid dislocations in the literature are missed on initial presentation. Broadbent et al ² describe a case of trapezoid dislocation identified only on postoperative CT scan following fixation of CMC joints that required a return to the operating room for reduction. Our case provides an additional example in which this injury was difficult to fully assess on initial injury films. While advanced imaging would certainly aid in making this diagnosis, we believe that fluoroscopic evaluation at the time of surgical intervention is sufficient to evaluate for carpal malalignment. In the present case, fluoroscopic imaging confirmed a dorsal position of the trapezoid, and aided in the decision to use an open approach to achieve an anatomic reduction.

Regarding operative management, dislocation of the trapezoid typically requires open reduction, as the dorsal ligamentous and capsular structures can become interposed and can block attempts at closed reduction as observed in the present case. ³ In our case, the trapezoid had rotated 180 degrees in the sagittal plane and 180 degrees in the coronal plane, making a closed reduction impossible. The metacarpal dislocations can be reduced in a closed fashion and held in place with Kirschner wires. This requires a stable carpus to build on, thus we recommend fixation of the trapezoid prior to metacarpal fixation. Outcomes for these injuries in the literature are excellent, with full ROM and nearly full grip strength at short-term follow-up in prior studies. ^{2 4 5} In the current case, our patient was a high-level athlete who was able to return to his sport at 6 months postoperatively. The radiographic evidence of trapezoid sclerosis may herald the future development of avascular necrosis and collapse. We counselled the patient regarding this risk, but to date, he has remained asymptomatic and continues to box at a high level.