Barton's Fracture- Lunate Dislocation

Carpal Instabilities

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   Perilunate Dislocation   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

 

Lunate and 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
  • 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