Dorsal intercalated segment instability (DISI) is a form of instability involving the wrist. It occurs mainly after the disruption of the scapholunate ligament and is more often encountered than volar intercalated segment instability (VISI).
- radial or dorsal wrist pain, maximal on radial deviation and wrist extension
- weakness and/or instability
- clicking wrist
- positive Watson test: during ulnar to radial deviation, pressure applied to the volar aspect of the scaphoid elicits an audible and/or palpable clunk (due to dorsal subluxation of the scaphoid with respect to the radius)
- wrist trauma, with or without a fracture
- scapholunate ligament dissociation: ligamentous DISI
Fixed DISI deformity only occurs after combined injury of scapholunate ligament and other stabilizers of the scaphoid, namely radioscaphocapitate and scaphocapitate ligaments.
On an AP view, the normal trapezoidal configuration of the scaphoid may be lost and it may appear triangular.
On the lateral radiograph with the wrist in a neutral position, DISI typically demonstrates dorsal tilt of the lunate with both of the following present:
- scapholunate angle >60º: a sign of scapholunate ligament dissociation
- capitolunate angle >30º: the capitate is displaced posteriorly compared to the distal radius
On sagittal CT, the same findings as on plain radiograph are seen.
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