Isolated carpal dislocations

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Isolated dislocations of the carpal bones are relatively rare injuries. More often individual carpal bone dislocation is associated with a more global wrist dislocation pattern, such as progressive per-ilunate instability or the axial dislocations patterns. Because of their rarity, most of our information on isolated dislocations comes from a relatively small amount of case reports and technique papers. Although it is critically important to recognize the clinical and radiologic features of these injuries, definitive treatment recommendations have yet to be confirmed for many of these dislocations.

Lunate dislocation: palmar

The most common of the isolated carpal dislocations is the palmar lunate dislocation. As

Wrist Dislocation

Peri-trapezoid PerRrapezium Trans-trapezium

Peri-trapezium

Peri-trapezoid PerRrapezium Trans-trapezium

Peri-trapezium

Carpal Dislocations

Trans-hamate Peri-hamate Peri-hamate

Peri-pisiform peri-pisiform Trans-triquetrum

Fig. 14. Axial carpal dislocation classification. (Top) Axial-radial dislocations: the radial part of the carpus is dislocated and unstable. (Bottom) Axial-ulnar dislocation: the ulnar part of the carpus is dislocated and unstable. Combined dislocation: in which both types of dislocation coexist in the same wrist. Arrows indicate the direction of the bony displacement as is evident with the bone separated from the rest of the hand. (From Garcia-Elias M, Geissler WB. Carpal instability. In: Green DP, Hotchkiss RN, Pederson WC, et al, editors. Operative hand surgery. 5th edition. Philadelphia: Elsevier; 2005; with permission.)

Trans-hamate Peri-hamate Peri-hamate

Peri-pisiform peri-pisiform Trans-triquetrum

Fig. 14. Axial carpal dislocation classification. (Top) Axial-radial dislocations: the radial part of the carpus is dislocated and unstable. (Bottom) Axial-ulnar dislocation: the ulnar part of the carpus is dislocated and unstable. Combined dislocation: in which both types of dislocation coexist in the same wrist. Arrows indicate the direction of the bony displacement as is evident with the bone separated from the rest of the hand. (From Garcia-Elias M, Geissler WB. Carpal instability. In: Green DP, Hotchkiss RN, Pederson WC, et al, editors. Operative hand surgery. 5th edition. Philadelphia: Elsevier; 2005; with permission.)

previously discussed in the section on perilunate dislocations, this injury is not an isolated dislocation, but represents Stage IV of the progressive perilunate instability pattern. This injury is addressed as outlined in the section on perilunate dislocations.

Lunate dislocation: dorsal

Although the majority of lunate dislocations are palmar, a significant palmar flexion force to the carpus or significant blow to the dorsum of the hand can result in palmar displacement of the carpus in relation to the lunate. This mechanism can result in a palmar perilunate or dorsal lunate dislocation [27]. Isolated dorsal lunate dislocation is extremely rare injury, with only four cases reported in the literature [28]. Swelling, tenderness, and a palpable firm mass on the dorsum of the wrist are found on clinical examination.

Standard radiographs reveal an overlap of the carpal bones on the PA view and a volarly tilted, dorsally displaced lunate on the lateral. For the four cases reported, two were seen acutely and two were seen late. Attempts at closed reduction failed in both acute injuries, and open reduction and fixation was required, with pinning of the lunate, capitate, scaphoid, and triquetrum. The two patients who presented late were treated with a proximal row carpectomy. One of the late presenting patients also underwent extensor tendon repair, because of multiple tendon ruptures caused by attrition of the tendons from the pressure of a dorsally dislocated lunate [28].

Scaphoid dislocation

Scaphoid dislocation is a rare injury, but has occurred with enough frequency to warrant its own classification: Type I, isolated anterolateral dislocation of the proximal pole; and Type II, scaphoid dislocation associated with an axial derangement of the capitate-hamate joint. Type I injuries are believed to result from violent forced hyperpronation to the extended and ulnarly deviated wrist while grasping a fixed object [29]. This force first causes an SL disruption followed by displacement of the scaphoid around the RC ligament. Another possibility is a self-reduced palmar perilunate dislocation, with the scaphoid remaining unreduced because of soft tissue interposition. Type II injuries fall under the realm of axial-ulnar dislocations (Fig. 15).

On examination of the wrist, swelling and a palpable firm mass either palmar, radial, or rarely dorsal to the radius are noted. Standard wrist series may reveal: (1) anterior, radial, or dorsal dislocation of the scaphoid; (2) normal axial alignment of the lunate on the PA view, but likely dorsal tilt of the lunate on the lateral view; and (3) proximal radial migration of the capitate.

Of the isolated cases reported, closed or open reduction and immobilization has been the mainstay of treatment, with most achieving good to excellent results [26,30]. Open reduction and ligament repair through a dorsal approach has more recently been advocated to facilitate and maintain anatomic reduction. In these instances, direct repair of the scapholunate interosseous ligament and scaphotrapezial ligament should be combined with K-wire fixation of the scaphotra-pezial and scapholunate joints for duration of 8

Scapholunate Ligament
Fig. 15. Anterolateral dislocation of the scaphoid, Type I. (From Garcia-Elias M, Geissler WB. Carpal instability. In: Green DP, Hotchkiss RN, Pederson WC, et al, editors. Operative hand surgery. 5th edition. Philadelphia: Elsevier; 2005; with permission.)

to 10 weeks in a thumb spica cast. This approach has also achieved good to excellent results.

Closed reduction technique

As for most dislocations, an attempt at reduction requires a sufficient amount of muscle relaxation. Ten pounds of traction is applied with finger traps to further fatigue the forearm musculature. The thumb of the dominant hand is placed over the volar aspect of the radius and moved distally until resting on the proximal pole of the scaphoid. The finger traps are then removed and traction is maintained by the opposite hand. A dorsally directed pressure is applied to the proximal pole of the scaphoid as the wrist is ulnarly deviated. With this maneuver a reduction of the scaphoid is usually achieved.

Triquetrum

Only a few reported cases of isolated trique-trum dislocation have been detailed in the literature. With so few cases, definitive conclusions about the mechanism of injury and treatment outcomes are not available. Direct force to the triquetrum or wrist extension and ulnar deviation have been the proposed mechanisms of injury in a few of the reported cases [31,32]. Both volar and dorsal displacements have been seen, with volar displacement being associated with transient median nerve compression. In almost all cases the diagnosis was delayed, despite a tender palpable mass over the dislocation. Treatment has included fragment excision, ORIF, and reduction without fixation, all with reasonably good results [33,34].

Trapezoid

A very rare carpal dislocation, with fewer than 20 isolated dislocations without fracture reported in the literature. Because the trapezoid is wedge-shaped, wider dorsally, the trapezoid is most often displaced dorsal to the carpus, and is most often accompanied by the second metacarpal. Volar dislocation has been reported, and is believed to be the result of a direct force on the bone withmidcarpal hyperextension. Closed reduction has been successfully accomplished with dorsal, but not volar, dislocations. Trapezoid excision has been associated with proximal migration of the second meta-carpal, and AVN has been reported with open reduction and fixation. Good outcomes were achieved despite these radiographic complications.

Trapezium

Most dislocations of the trapezium are associated with first metacarpal dislocations, and are more accurately described as peritrapezial axialradial dislocations [25]. True isolated dislocations of the trapezium are very rare, and are thought to be caused by a direct blow to the dorsolateral aspect of the wrist or a hyperextension-supination force to the wrist in radial deviation. In all instances the trapezium has displaced volarly and has been successfully treated with either open reduction or excision.

Hamate

Most reported cases of hamate dislocation are associated with fourth or fifth metacarpal displacement, and are appropriately classified as axial-ulnar dislocations [25]. True isolated hamate dislocations are very rare, with fewer than 20 cases in the literature [35]. Direct impact by a sharp tool penetrating the wrist and high energy traffic accidents have been the associated trauma. With both dorsal and volar dislocations reported, prompt treatment has achieved good results with both closed and open reduction with fixation, as well as fragment excision.

Pisiform dislocation

Isolated pisiform dislocation is an extremely rare injury, with only a handful of case reports in the literature [36]. The patient usually complains of ulnar palmar wrist pain with possible weakness of wrist flexion. A direct blow to the ulnar aspect of the hand or a strong traction on the flexor carpi ulnaris with the wrist in extension has been reported as possible mechanism of injury. Standard radiographs of PA, lateral, and 45° supinated views are usually clear in diagnosis. A carpal tunnel view is not required unless generalized pain and swelling raises suspicion of possible fracture of the hook of the hamate. Displacement of the pisiform has been reported distally, proximally, and ulnarly. With failure of both nonoperative and operative attempts at reduction, excision of the pisiform is recommended and is consistently the most successful treatment of pain [36].

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