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Intercalated Segment Instability

Normal Scapholunate angle = 47 degrees. Range = 30-60º. SL angle is created by the long axis of the scaphoid and a line perpendicular to the capitolunate joint.
VISI
  • Lunate tilted >15 degrees volarly
  • Scaphulunate angle <30

DISI

  • Lunate tilted >10 degrees in dorsal direction
  • Scapholunate angle >60°

 

*As seen on neutral lateral views
Distal Radius
Lunate
Scaphoid
Capitate
3rd metacarpal base

Radiographic Findings in Scapholunate Instability: P/A Wrist View
  1. “Cortical ring” sign(volar flexed scaphoid distal pole seen in cross section).
  2. Terry Thomas sign = enlarged scapholuante gap. Scapholunate gap of greater than 3 mm. Scapholunate gap >5mm confirms scapholunate interosseous ligament disruption.
  3. Scaphoid appears foreshortened.
  4. Distal Radius
  5. Lunate: should be quadrilateral in shape. May appear triangular with scapholunate instability.