Radiography
Although perilunate dislocations are frequently missed, the diagnosis should be made on the initial injury plain films. [28, 29] One cause of a missed diagnosis is inadequate posteroanterior (PA) and lateral radiographs. Other causes include radiographs obscured by splints and unfamiliarity with the anatomy of the carpus. When trauma to the carpus is suspected, it is incumbent upon the examining physician to obtain acute plain radiographs that are devoid of splint materials and dressings.
Standard PA, lateral, and oblique radiographs centered over the carpus should be obtained in all patients with significant wrist injury.
The PA radiograph is obtained with the patient seated, the shoulder abducted 90º, and the hand placed palm-down on the radiographic cassette. This positioning of the shoulder places the forearm in neutral rotation. In the acute setting, a PA distraction view of the carpus can be very helpful for better defining the injury anatomy. For example, small fractures or dislocations of the carpal bones may be better depicted by using the distraction PA radiograph. (See the images below.)
Posteroanterior plain radiograph of dorsal perilunate dislocation. Note reduction of radiolunate articulation.
Posteroanterior radiograph demonstrating transradial styloid dorsal perilunate dislocation.
A series of lines, described by Gilula, can be traced along the proximal edges of the scaphoid, lunate, and triquetrum, as well as along the proximal poles of the capitate and hamate. [30] The lines should be smooth and uninterrupted. The reference lines can be a quick screen for perilunate dislocation or perilunate fracture dislocation.
The lateral radiograph also is obtained with the patient seated. The shoulder is adducted with the hand and wrist at the side, enabling the ulnar border of the hand to be placed on the cassette. Care should be taken to avoid excessive ulnar deviation of the wrist, because this will give the false impression that the lunate is in the extended position. With the lunate in the extended position, the diagnosis of dorsal intercalated segment instability (DISI) could be made incorrectly.
A correct lateral radiograph of the wrist should have superimposition of the lunate, proximal scaphoid pole, and triquetrum. The radial styloid should appear centered within the metaphysis of the radius, and the metacarpal shafts should all line up. (See the image below.)
The lateral radiograph should be observed carefully for the wide carpus sign, in which the capitate is overriding the dorsal aspect of the lunate in the dorsal perilunate dislocation. In the volar lunate dislocation, the lunate is clearly volar to the radius. Although much less common, the perilunate dislocation may occur volar and the lunate dislocation dorsal.
In addition, the lateral scapholunate angle and the capitolunate angle on the lateral radiograph should be evaluated. The lateral scapholunate angle is formed by the intersection of the longitudinal axes of the lunate and the scaphoid. Normally, this angle is 30-60º. The capitolunate angle is normally 0-15º. Disruption of these angles may imply scapholunate dissociation. [31, 32, 33]
The oblique radiograph is taken as a 45º off-plane PA radiograph.
CT and Plain Tomography
In most situations, neither computed tomography (CT) nor plain tomography is needed to diagnose perilunate dislocations or perilunate fracture dislocations. However, these studies can be helpful for better defining greater-arc fractures, such as scaphoid fractures, capitate fractures, radial styloid fractures, and triquetral fractures.
In most situations, 1-mm CT scan cuts in the sagittal and coronal plane of the capitate are helpful. If a fracture of the scaphoid is suspected, it is more appropriate to obtain the 1-mm cuts in the plane of the scaphoid.
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Posteroanterior plain radiograph of dorsal perilunate dislocation. Note reduction of radiolunate articulation.
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Posteroanterior radiograph demonstrating transradial styloid dorsal perilunate dislocation.
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Lateral wrist radiograph demonstrating dorsal perilunate dislocation.
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Postoperative posteroanterior radiograph after open reduction and percutaneous pinning of dorsal perilunate dislocation. Note that suture anchors have been placed in scaphoid to directly repair scapholunate interosseous ligament. Suture anchors have also been used in distal radius to perform capsulodesis using dorsal intercarpal ligament.
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Capsulotomy approach to scapholunate interosseous interval, with preservation of dorsal intercarpal and dorsal radiocarpal ligaments. Image adapted from The Wrist: Diagnosis and Operative Treatment (Mosby, 1998).
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Reflected dorsal wrist capsulotomy preserving dorsal intercarpal and dorsal radiocarpal ligaments. Image adapted from The Wrist: Diagnosis and Operative Treatment (Mosby, 1998).
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Dorsal approach to wrist demonstrating disruption of scapholunate interosseous ligament.
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Volar wrist approach for repair of transverse capsular rupture (injury typically seen in perilunate dislocations).
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Drawing demonstrating 3 regions of scapholunate interosseous ligament: (A) dorsal portion, which is strongest and most important to repair; (B) central portion, which is often found to have atraumatic, asymptomatic, and biomechanically insignificant perforations; and (C) volar portion.
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Drawing showing reduction of scapholunate interval with Kirschner wire (K-wire) joysticks. Drill holes are made with straight needles for subsequent passage of suture. This scapholunate repair technique was originally described by Taleisnik.
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Drawing showing repair of the scapholunate interosseous ligament using drill holes and suture passed with straight needles, as described by Taleisnik. Image adapted from The Wrist: Diagnosis and Operative Treatment (Mosby, 1998).
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Drawing demonstrating suture anchor placement for repair of scapholunate interosseous ligament. Image adapted from The Wrist: Diagnosis and Operative Treatment (Mosby, 1998).
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Drawing showing final repair of scapholunate interosseous ligament using drill holes, as described by Taleisnik. Image adapted from The Wrist: Diagnosis and Operative Treatment (Mosby, 1998).
