Dorsal intercalated segment instability

Dorsal intercalated segment instability (DISI) is a deformity of the wrist where the lunate bone angulates to the dorsal side of the hand.^[2][3]

The SL angle is an indicator of dorsal intercalated segment instability deformity (DISI). The SL angle goes between:^[1]
- A line through the long axis of the scaphoid bone.
- A line perpendicular to the distal articular surface of the lunate bone.
It should normally be 30°-60°.^[1]

Causes

The main cause of DISI is^[4] wrist trauma, with or without a fracture:

• Scaphoid fracture: bony DISI
• Distal radius fracture: compensatory DISI
• Malunion of radius fracture: adaptive DISI
• Scapholunate ligament instability: ligamentous DISI