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Volar Intercalated Segment Instability (VISI)

- See: Carpal Instability

- Discussion:
    - by definition, consists of volar flexion of the lunate relative to the longitudinal axis of the radius and capitate, when the wrist rests in a neutral position;
    - lunate will tend to flex when there is loss of ulnar support from the triquetrum;
    - may result from disruption of radial carpal ligaments on ulnar side of wrist & is characterized by scapholunate angle < 30 deg;
    - volar flexion instability pattern is usually associated w/ triquetrolunate dissociation or triquetral-hamate instability;
    - the dorsal-radial-triquetral and triquetro-scaphoid ligaments have an increase space (increased "V") between them;
          - see: ligaments of the wrist

- Static VISI:
    - when lunate slips into a statically fixed position > 15 deg of flexion;
    - early treatment: closed reduction and casting (w/ or w/o K wires);

- Dynamic VISI:
    - normal wrist may assume a VISI pattern when relaxed, however, this is not considered abnormal unless it is symptomatic;
    - etiology may be a laxity in the volar capitotriquetral ligament;
    - these patients may note pain on volar stress testing;
    - radiographs may show a widening between the capitate and the triquetrum, when wrist is placed in radial deviation;
    - treatment: capitolunate fusion;

- Radiographs: lateral view of wrist

- Management:
    - space of Poirier is reenforced and is closed, which closes down the space between the triquetro-hamate and triquetro-capitate ligaments

Volar intercalated segment instability secondary to medial carpal ligamental laxity.

Traumatic instability of the wrist. Diagnosis, classification, and pathomechanics.

Intercarpal arthrodesis for static and dynamic volar intercalated segment instability.

Kinematics of the ulnar carpus related to the volar intercalated segment instability pattern.

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