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
• 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

Diagnosis

• Perilunate Dislocation
  • Lateral view
    • Capitate displaced dorsal to lunate
    • Lunate retains its normal contact w/ radius
  • PA view
    • Capitolunate joint space is obliterated as the bones overlap one another
• Lunate Dislocation
  • PA view
    • Lunate has triangular shape ("piece-of-pie sign")
  • Lateral view
    • Lunate is pushed off the radius into the palm ("spilled teacup" sign)

Differential Diagnosis

Carpal Dislocations

• Lunotriquetral ligament instability
• Scapholunate dissociation
• Perilunate and lunate dislocations

Carpal fractures

thumb|AP view

• Scaphoid fracture
• Lunate fracture
• Triquetrum fracture
• Pisiform fracture
• Trapezium fracture
• Trapezoid fracture
• Capitate fracture
• Hamate fracture

Treatment

1. Both dislocations require emergent ortho consultation (very difficult to reduce)
2. Closed reduction and long-arm splint

Images

• Perilunate Dislocation

• Lunate Dislocation

Source

• Emergency Orthopedics, The Extremeties
• Radiopaedia.org
• Tintinalli