Findings: The lunate is tilted in a volar direction and the capitate is tilted dorsally. This results in scaphoid flexion and gives a scaphoidlunate angle measurement of 21° which is normally 30° - 60°. No fractures are shown.

Diagnosis: Volar intercalated segmental instability (VISI).

Discussion: Stability of carpus and alignment of the carpal bones are maintained by the scaphoid, which acts as a strut between the proximal and distal carpal rows. This is maintained by the attachment of volar carpal and interosseous ligaments. A scaphoid fracture or ligamentous disruption may result in carpal instability and malalignment. The three most common causes of carpal instability are scapholunate dissociation (rotary subluxation), dorsal intercalated segmental instability (DISI), and volar intercalated segmental instability (VISI) with scapholunate dissociation being most common.

Volar instability occurs when the lunate tilts palmarword, and the capitate is tilted dorsally often resulting in flexion of the scaphoid. The combination results in a scaphoid lunate angle of <30 degrees. Carpal instability is associated with either a new or remote scaphoid fracture, perilunate dislocation or periligamentous injury. Lunate triquetral dislocations result in some degree of perilunar instability. The most severe involve the radiocarpal, radiotriquetral, and dorsal radiocarpal ligamentous injury with lunate dislocation.

Reference:
Resnick D. Bone and Joint Imaging, 2nd Edition. 1996.

Rogers L. Radiology of Skeletal Trauma, 2nd Edition, 1992.

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