Perilunate Fracture Dislocations Workup
- Author: Peter M Murray, MD; Chief Editor: Harris Gellman, MD more...
Although perilunate dislocations are frequently missed, the diagnosis should be made on the initial injury plain films.[21, 22] 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.)
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. 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 instability 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 30-60°. The capitolunate angle is normally 0-15°. Disruption of these angles may imply scapholunate dissociation.[24, 25, 26]
The oblique radiograph is taken as a 45º off-plane PA radiograph.
Computed tomography/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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