Traumatic carpal instability.

In general, two patterns of traumatic carpal instability can be discerned: palmar flexion intercalated segmental instability (PISI deformity) and dorsiflexion intercalated segmental instability (DISI deformity). Two case reports are described, demonstrating both types and their treatment. PISI deformity, seen less frequently, may require Kirschner wiring as well as plaster immobilization. DISI deformity with malunion may require osteotomy. The underlying causes should be sought before treatment is initiated.