Lunate Dislocation (Perilunate dissociation) - Hand

Summary
- Lunate/perilunate dislocations are high energy injuries to the wrist associated with neurological injury and poor functional outcomes.
- Diagnosis requires careful evaluation of plain radiographs.
- Treatment requires urgent closed versus open reduction and stabilization.

Epidemiology
- Incidence
  - rare
    
    < 1 per 100,000 injuries annually
  - commonly missed (~25%) on initial presentation

Etiology
- Mechanism of injury
  - 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
- 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

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
  - treatment
    
    observation (benign and self-limiting)