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Dorsal Intercalated Segment Instability: (DISI)

- See:
- Carpal Instability
- Kinematics of the Wrist

- Discussion:
- lunate will tend to flex w/ loss of ulnar ligamentous support from the triquetrum;
- lunate extends when there is loss of radial ligamentous stability;
- DISI may arise as a result of:
- scaphoid frx;
- scapho-lunate dissociation;
- perilunate dislocation (esp trans-scaphoid perilunate dislocation);
- end result may be SLAC wrist;

- Radiographic Analysis:
- on lateral x-rays, when lunate slips into statically dorsiflexed position > 10 deg, condition is defned as DISI;
- similarly, when lunate lies palmar to capitate but faces dorsally, collapse pattern is also consistent w/ dorsiflexion instability;
- DISI deformity is also present when the scapholunate angle is greater than 70 deg;
- when diagnosising this condition, be sure that the lateral radiograph was taken w/ proper technique and that the wrist is not dorsiflexed