Lunate Dislocation (Perilunate dissociation) - Hand

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
    - transcaphoid-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
  - leads 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
  - greater arc
    - ligamentous disruptions with associated fractures of the radius, ulnar, or carpal bones
  - lesser arc
    - purely ligamentous

Anatomy

Normal wrist anatomy
Osseous
- proximal row
  - scaphoid
  - lunate
  - triquetrum
  - pisiform
- distal row
  - trapezium
  - trapezoid
  - capitate
  - hamate
Ligaments
- interosseous ligaments
  - run between the carpal bones
    - scapholunate interosseous ligament
    - lunotriquetral interosseous ligament
  - major stabilizers of the proximal carpal row
- intrinsic ligaments
  - ligaments the both originate and insert among the carpal bones
    - dorsal intrinsic ligaments
    - volar intrinsic ligaments
- extrinsic ligaments
  - connect the forearm bones to the carpus
    - volar extrinsic carpal ligaments
    - dorsal extrinsic carpal ligaments

Classification

Mayfield Classification
Stage I	• scapholunate dissociation
Stage II	• + lunocapitate disruption
Stage III	• + lunotriquetral disruption, "perilunate"
Stage IV	• 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
  - most common in Mayfield stage IV where the lunate dislocates into the carpal tunnel

Imaging

Radiographs
- recommended views
  - PA
  - lateral
- findings
  - PA
    - break in Gilula's arc
    - lunate and capitate overlap
    - "piece-of-pie sign"
      - triangular appearance of lunate
      - due to palmar rotation from dorsal force of carpus
  - lateral
    - loss of colinearity of radius, lunate, and capitate
    - SL angle >70 degrees
    - spilled teacup sign
MRI
- usually not required for diagnosis

Treatment

Nonoperative
- closed reduction and casting
  - indications
    - no indications when used as definitive management
  - 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
    - 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

Complications

Transient ischemia of the lunate
- radiodense appearance of the lunate on radiograph reported in up to 12.5% of cases
- usually identified 1-4 months post-injury
- benign and self-limiting, treat with observation