Normal wrist alignment, dorsal and volar intercalated segmental instability (illustration)
Normal alignment
The scapholunate angle is the angle between the long axis of the scaphoid and the mid axis of the lunate on the sagittal imaging of the wrist. In a normal situation, it should be between 30 and 60°.
The capitolunate angle is the angle between the long axis of the capitate and the mid axis of the lunate on the sagittal imaging of the wrist. In a normal situation, it should be less than 30°
DISI vs VISI
Normal vs dorsal intercalated segment instability vs volar intercalated segmental instability
DISI vs VISI
Here is a dynamic sequence to get an idea of how the alignment changes between DISI and VISI
A scapholunate angle >60º (scapholunate ligament dissociation) and a capitolunate angle >30º (capitate displaced posteriorly) are indicative of dorsal intercalated segment instability.
A scapholunate angle of <30° and a capitolunate angle of >30° is indicative of volar intercalated segmental instability,
Case Discussion
The scapholunate angle is the angle between the long axis of the scaphoid and the mid axis of the lunate on the sagittal imaging of the wrist. In a normal situation, it should be between 30 and 60°.
The capitolunate angle is the angle between the long axis of the capitate and the mid axis of the lunate on the sagittal imaging of the wrist. In a normal situation, it should be less than 30°
Conditions such as dorsal intercalated segment instability and volar intercalated segmental instability will see increases and decreases in these angles as seen above.
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