Findings: Image #1 demonstrates dorsal dislocation of the capitate in relationship to the lunate and distal radius. The lunate is tilted volarly, but maintains its articulation with the distal radius.

Image # 2 demonstrates a fracture through the radial styloid. In addition, there is overlapping of the proximal and distal rows of the carpus.

Diagnosis: Dorsal trans-radial styloid perilunate dislocation.

Discussion: Perilunate and lunate dislocations are most often the result of a fall or the outstretched hand with subsequent dorsiflexion. The proximal row of carpal bones are held tightly in position by a group of ligaments between the radius and carpus. Therefore, perilunate dislocations are more common than lunate dislocations. Perilunate dislocations are characterized by dorsal (usually) displacement of the capitate which comes to rest on the posterior aspect of the lunate causing the lunate to tilt volarly. The lunate maintains articulation with the distal radius. With lunate dislocations, the capitate maintains its normal alignment with the distal radius while the lunate is dislocated volarly. The vast majority of perilunate dislocations are dorsal and approximately 75% are accompanied by a fracture. The most common associated fracture is through the scaphoid waist, but perilunate dislocation is also associated with radial styloid, capitate, and ulnar styloid. The PA film will demonstrate the proximal and distal rows of the carpus to be overlapped giving the "crowded carpal" appearance. The lateral film is diagnostic, demonstrating the dorsal displacement of the capitate while the lunate maintains its normal alignment with the radius.

Reference:
1. Rogers LF. Radiology of Skeletal Trauma. Churchill-Livingstone, London; 1992:911-921.

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