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

Perilunate Dislocation

Lunate Dislocation

Mayfield Classification	Level of carpal instability
Stage I: scapholunate dissociation	Disruption 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

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

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

AP view

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

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