Lunate Dislocation
Also Perilunate Dislocation

• General Considerations
  
  
• Mechanism of injury is usually fall onto an outstretched hand with wrist in ulnar deviation and dorsiflexion
• Wrist dislocations are uncommon but lunate is the most common bone in the wrist to dislocate
• Most severe of carpal instabilities
• Involves all the intercarpal joints and disruption of most of  the major carpal ligaments
• Capitate and all other carpal bones will lie posterior to lunate on lateral radiograph
  
  
• Clinical Findings
  
  
• Wrist pain, tenderness and swelling
  
  
• Imaging findings
  
  
• Normal anatomy
• Normally, the lunate has a quadrilateral appearance on a true frontal view
  of the wrist
• The lunate sits at the distal end of the radius with its convex surface apposed to the radius
• The capitate normally rests within the concave surface of the lunate (the lunate cup), especially well seen on the lateral view
• The lunate cup “points” towards the fingertips
• Dislocation
• Triangular appearance of lunate on frontal projection
• Not always reliable because of differences in projection
• Produces volar (anterior) dislocation and forward rotation of lunate
• Concave distal surface of lunate comes to face anteriorly
• The lunate cup “points” towards the palm
• Capitate may drop into the space vacated by lunate
  
  
• Complications
  
  
• Vascular complications may occur but are uncommon unless there is an associated fracture present, especially of the distal radius
• Soft tissue complications may include disruption of carpal ligaments which can lead to long-term carpal instability
• Many develop chronic wrist pain

Perilunate dislocation

• Triquetral 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 trans-scaphoid waist fracture
• Sometimes ulnar styloid as well
• Lunate appears triangular in shape on frontal view
• Lunate rotates forward slightly on lateral view
• On lateral view, all other carpal bones are dislocated posterior with
  respect to lunate