Dorsal intercalated segment instability

Case contributed by Assoc Prof Frank Gaillard

The lunate is dorsally tilted with an increased capitolunate angle (normal <30o) suggesting dorsal intercalated segment instability (DISI). 

Case Discussion

Beware of calling dorsal intercalated segment instability (DISI) on MRI alone as relationships vary with wrist position, and standard measurements are based on lateral wrist radiographs. 

The thick dorsal portion of the scapholunate ligament is the primary structure balancing the forces across the scapholuate joint, preventing posterior rotary tilt of the lunate. If a DISI pattern exists, this structure is most likely not intact. In contrast, the thick volar lunotriquetral ligament resists volar rotary turn of the lunate, which if ruptured would increase the capitolunate angle in the reverse direction as is seen here (i.e. VISI). 

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Case information

rID: 7244
Published: 22nd Sep 2009
Last edited: 16th Oct 2019
Inclusion in quiz mode: Included