Perilunate Dislocation
- Carpal dislocations described by extent of
ligamentous injury (Mayfield)
- Stage I
- Isolated rotatory subluxation of scaphoid
- Mechanism: acute dorsiflexion of wrist
- May be associated with rheumatoid arthritis
- Characterized by increased distance between
scaphoid and lunate > than 2 mm (Terry Thomas sign)
- Scaphoid ring sign – ring-shaped shadow of
cortex of distal pole of scaphoid seen on end
- Associated more than 50% of the time with
distal radial fractures
- Stage II
- Dislocation or subluxation of capitate
- Stage III
- Perilunate dislocation
- Triquetrial and
scaphoid malrotation
- Result of a fall on an outstretched,
hyperextended hand
- Relatively rare
- Occurs when the lunate maintains normal
position with respect to the distal radius while all other carpal
bones are dislocated posteriorly
- Very commonly associated with a scaphoid waist
fracture
- Sometimes ulnar styloid as well
- Lunate appears triangular in shape on frontal
view
- Lunate rotates forward slightly on lateral
view
- In lateral view, all other carpal bones are
dislocated posterior with respect to lunate
Perilunate dislocation - Lunate maintains normal
position
while all other carpal bones dislocate posterior to it
- Stage IV
- Lunate Dislocation
- Most severe of carpal instabilities
- Most commonly associated with a trans-scaphoid
fracture
- Involves all the intercarpal joints and
disruption of most of the major carpal ligaments
- Produces volar dislocation and forward rotation
of lunate
- Concave distal surface of lunate comes to face
anteriorly
- Capitate drops into space vacated by lunate
- Capitate and all other carpal bones lie
posterior to lunate on lateral radiograph
- Triangular appearance of lunate on frontal
projection
Lunate dislocation - volar displacement and forward
rotation of lunate
on lateral view
with triangular shape of lunate on frontal view
Harris and Harris
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