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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
        • Exceedingly rare
    • 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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