Box 67.1 Viegas’ classification of carpal instability

I. Ulnar-sided perilunate instability

A. Stage I: Partial to complete lunotriquetral tear (no VISI)

B. Stage II: Complete tear of lunotriquetral ligaments, interosseous and volar (dynamic VISI)

C. Stage III: As in Stage II plus disruption of the dorsal radiotriquetral ligament (static VISI)

II. Radial-sided perilunate instability

A. Stage I: Partial to complete scapholunate tear (no DISI)

B. Stage II: Complete scapholunate interosseous ligament tear plus tear of attenuation of the volar ligaments (dynamic DISI)

C. Stage III: Complete disruption of the ligaments of Stage II plus dorsal radiotriquetral ligament disruption (static DISI)

D. Stage IV: Complete disruption of all ligaments noted in Stage III (static DISI)

III. Dissociative
Ligament lesion that is usually between the bones of the proximal carpal row but occasionally between the bones of the distal carpal row, the metacarpals, or even the radius and ulna