Dorsal intercalated segment instability (DISI) is a form of carpal instability featuring dorsal tilt of the lunate. It occurs mainly after the disruption of the scapholunate ligament and is more often encountered than volar intercalated segment instability (VISI).
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
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
CT
On sagittal CT, the same findings as on lateral radiographs are seen.
MRI
On sagittal MRI 9, the same findings as on plain radiograph are seen. However, bone contusion, scaphoid osteonecrosis, and scapholunate ligament injury are evaluated with more precision.