DISI
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).
Clinical presentation
- 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)
Pathology
Etiology
- wrist trauma, with or without a fracture
- scaphoid fracture: bony DISI
- distal radius fracture: compensatory DISI
- radius malunion: adaptive DISI
- scapholunate ligament dissociation: ligamentous DISI
Radiographic features
Fixed DISI deformity only occurs after combined injury of scapholunate ligament and other stabilizers of the scaphoid, namely radioscaphocapitate and scaphocapitate ligaments.
Plain radiograph
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
CT
On sagittal CT, the same findings as on plain radiograph are seen.
MRI
On sagittal MRI , the same findings as on plain radiograph are seen. However, bone contusion, scaphoid avascular necrosis and scapholunate ligament injury are evaluated with more precision.
See also
Siehe auch:
- PISI-Fehlstellung
- Scapholunäre Dissoziation
- scapholunärer Winkel
- Scaphoidfraktur
- perilunäre Instabilität
und weiter:
Assoziationen und Differentialdiagnosen zu DISI-Fehlstellung:
