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Lunate Dislocation (Perilunate dissociation)

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Topic updated on 02/19/13 5:39pm
Introduction
  • High energy injury with poor functional outcomes
  • Commonly missed (~25%) on initial presentation
  • Categories
    • perilunate dislocation 
      • lunate stays in position while carpus dislocates
      • 4 types
        • transcaphoid-perilunate
        • perilunate
        • transradial-styloid
        • transscaphoid-trans-capitate-perilunar
    • lunate dislocation   
      • lunate forced volar or dorsal while carpus remains aligned
  • Mechanism
    • traumatic, high energy
    • occurs when wrist extended and ulnarly deviated, leading to intercarpal supination
  • Pathoanatomy
    • sequence of events 
      • scapholunate ligament disrupted -->
      • disruption of capitolunate articulation --> 
      • disruption of lunotriquetral articulation --> 
      • failure of dorsal radiocarpal ligament --> 
      • lunate rotates and dislocates, usually into carpal tunnel
    • dislocation can course through
      • bone (greater arc)
      • ligaments (lesser arc)
      • combination of both bone and ligaments
Classification
  • Mayfield classification
    • Stage I: scapholunate dissociation
    • Stage II: + lunocapitate disruption
    • Stage III:+ lunotriquetral disruption
    • Stage IV: lunate dislocation
      • lunate dislocated from lunate fossa (usually volar)
      • associated with median nerve compression
Presentation
  • Symptoms
    • acute wrist swelling and pain
    • median nerve symptoms may occur in ~25% of patients
Imaging
  • Radiographs
    • required views
      • PA/lateral wrist radiographs
    • findings
      • AP 
        • break in Gilula's arc
        • lunate and capitate overlap
        • lunate appears triangular "piece-of-pie sign"
      • lateral
        • loss of colinearity of radius, lunate, and capitate
        • SL angle >70 degrees
  • MRI
    • usually not required for diagnosis
Treatment
  • Nonoperative
    • closed reduction and casting
      • indications
        • no indications
      • outcomes
        • universally poor functional outcomes with non-operative management
        • recurrent dislocation is common
  • Operative
    • emergent closed reduction/splinting followed by open reduction, ligament repair, fixation, possible carpal tunnel release
      • indications
        • All acute injuries <8 weeks old
      • outcomes
        • emergent closed reduction leads to 
          • decreased risk of median nerve damage
          • decreased risk of cartilage damage
        • return to full function unlikely
        • decreased grip strength and stiffness are common
    • proximal row carpectomy
      • indications
        • chronic injury  (defined as >8 weeks after initial injury)
        • not uncommon, as initial diagnosis frequently missed
    • total wrist arthrodesis
      • indications
        • useful for chronic injuries with degenerative changes
Techniques
  • Closed Reduction 
    • technique
      • finger traps, elbow at 90 degrees of flexion
      • hand 5-10 lbs traction for 15 minutes
      • dorsal dislocations are reduced through wrist extension, traction, and flexion of wrist
      • apply sugar tong splint
      • follow with surgery
  • Open reduction, ligament repair and fixation +/- carpal tunnel release
    • approach (controversial)
      • dorsal approach
        • longitudinal incision centered at Lister's tubercle
        • excellent exposure of proximal carpal row and midcarpal joints
        • does not allow for carpal tunnel release
      • volar approach
        • extended carpal tunnel incision just proximal to volar wrist crease
      • combined dorsal/volar
        • pros
          • added exposure
          • easier reduction
          • access to distal scaphoid fractures
          • ability to repair volar ligaments
          • carpal tunnel decompression
        • cons
          • some believe volar ligament repair not necessary
          • increased swelling
          • potential carpal devascularization
          • difficulty regaining digital flexion and grip
    • technique
      • fix associated fractures
      • repair scapholunate ligament
        • Suture anchor fixation
      • protect scapholunate ligament repair
        • Controversy of k-wire versus intraosseous cerclage wiring
      • repair of lunotriquetral interosseous ligament
        • Decision to repair based on surgeon preference as no studies have shown improved results
    • post-op
      • short arm thumb spica splint converted to short arm cast at first post-op visit
      • duration of casting varies, but at least 6 weeks
  • Proximal row carpectomy
    • technique
      • perform via dorsal and volar incisions if median nerve compression is present
      • volar approach allows median nerve decompression with excision of lunate
      • dorsal approach facilitates excision of the scaphoid and triquetrum

 

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Qbank (2 Questions)

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(OBQ09.227) A 35-year-old professional football player complains of severe wrist pain after making a tackle. He reports paresthesias in his thumb and index finger. AP and lateral radiographs of the wrist are shown in figures A and B respectively. What is the most appropriate next step in management? Topic Review Topic
FIGURES: A   B        

1. short arm thumb spica cast
2. long arm thumb spica cast
3. urgent closed reduction and splinting
4. MR arthrogram of the wrist to assess ligamentous injuries
5. bone scan to assess vascularity

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