Question

What is meant by perilunate dislocation?

• A. Lower radius, scaphoid, lunate and capitate all in same plane
• B. Lower radius, scaphoid and capitate in alignment, lunate alone out of plane
• C. Lower radius, scaphoid and lunate in alignment, capitate alone is out of plane
• D. Both lunate and capitate are out of plane

Hint:

Which single carpal bone keeps its grip on the radius while the rest dislocate?

Answer 1

The Correct Option is B

Step 1: Perilunate dislocation is a severe carpal injury caused by traumatic rupture of the radioscaphocapitate ligament, the scapholunate interosseous ligament and the lunotriquetral interosseous ligament. The lunate stays attached to the radius while the rest of the carpus dislocates around it.
Step 2: On the lateral radiograph there is loss of collinearity between the capitate, lunate and radius. Typically the capitate sits dorsal to the lunate yet remains aligned with the radius.
Step 3: So in a perilunate dislocation the lower radius, scaphoid and capitate keep their alignment while the lunate alone is displaced out of the line - this matches option b.
Step 4: Option c describes the reverse pattern (a lunate dislocation), option a describes a normal wrist, and option d is not the standard description. The key distinction is that in a perilunate dislocation it is the carpus that moves around a retained lunate.