Perilunate and lunate dislocations

Background
  • Occur via high-energy FOOSH injury (fall from height, MVC)
    • Perilunate Dislocation = Lunate stays in place, capitate is displaced
    • Lunate Dislocation = Capitate stays in place, lunate is displaced
  • Commonly missed (~25%) on initial presentation
  • Must rule-out median nerve injury
  • Must rule out carpal bone fractures

Clinical Features
  • Perilunate dislocation: dorsal swelling with palpable mass
  • Lunate dislocation: volar swelling with palpable mass

Evaluation
Perilunate Dislocation
Lunate Dislocation
Mayfield ClassificationLevel of carpal instability
Stage I: scapholunate dissociationDisruption of scapholunate ligament with +Terry Thomas sign; exacerbated in clenched fist view
Stage II: perilunate dislocation+Disruption of capitolunate joint; high association with scaphoid fractures
Stage III: midcarpal dislocation+Disruption of triquetrolunate joint; neither capitate or lunate is aligned with distal radius
Stage IV: lunate dislocation+Disruption of radiolunate joint

Perilunate Dislocation
  • Lateral view
    • Capitate displaced dorsal to lunate
    • Lunate retains its normal contact with radius
  • PA view
    • Capitolunate joint space is obliterated as the bones overlap one another

Lunate Dislocation
  • Lateral view
    • Lunate is pushed off the radius into the palm ("spilled teacup" sign)
  • PA view
    • Lunate has triangular shape ("piece-of-pie sign")

Differential Diagnosis

Carpal Dislocations

Carpal fractures
AP view

Management
  • Closed reduction and long-arm splint
    • Requires emergent ortho consultation (very difficult to reduce with high incidence of median nerve compression), and usually emergent operative management

See Also

References
    • Emergency Orthopedics, The Extremeties
    • Radiopaedia.org
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