Lunate (Perilunate) Dislocation

Question 1

How often are lunate dislocations missed initially?

Answer 1

25%

Question 2

How do lunate and perilunate dislocations differ?

Answer 2

Lunate: carpus stays intact while lunate is dislocated
Perilunate: carpus dislocates relative to aligned lunate

Question 3

What is the sequence of events of a lunate dislocation?

Answer 3

1) SL ligament disrupted
2) Capitolunate articulation disrupted
3) Lunotriquetral articulation disrupted
4) Failure of dorsal radiocarpal ligament
5) Lunate rotates and dislocates; usually into carpal tunnel

Question 4

How do lesser and greater arc injuries of perilunate dislocations differ?

Answer 4

Greater arc: involve radius, ulna, carpus fractures

Lesser arc: purely ligamentous (proximal row)

Question 5

What are radiographic signs of lunate/perilunate dislocation?

Answer 5

1) Lateral shows break in colinear relationship of radius, lunate, capitate
2) SL angle >70°
3) AP shows “piece of pie” sign
4) AP shows break in Gilula’s arc

Question 6

How are perilunate dislocations reduced?

Answer 6

Extend wrist, pull traction, then flex wrist