PERILUNATE INJURIES

Question 1

Role of lunate in the carpus

Answer 1

• Is the keystone of the carpus

- Acts as the intercalated segment = link between distal radius-ulna and distal carpal row

Question 2

Space of Poirier

Answer 2

• Is a weak area in the floor of the carpal tunnel
• At the volar aspect of capitolunate articulation where capsule is not reinforced by ligaments
• Lies between to V-shaped convergence of ligaments

Question 3

Types of perilunate injuries

Answer 3

Lesser arc (purely ligamentous) vs. greater arc (associated fractures)
Perilunate dislocations = 4 main types
- Perilunate dislocation
- Trans-scaphoid perilunate fracture-dislocation
- Trans-radial styloid
- Trans-scaphoid trans-capitate
Lunate dislocations

Question 4

Classification of perilunate injuries

Answer 4

Mayfield classification = radiographic classification with 4 stages indicating progressive instability of lunate within carpus

1. Stage I = SL dissociation
2. Stage II = capitolunate disruption (through space of Poirier)
3. Stage III = LT disruption
   - and disruption of dorsal radiocarpal ligament
   - results in dorsal dislocation of carpus
4. Stage IV = volar dislocation of lunate into carpal tunnel
   - lunate rotates around intact volar radiolunate ligaments

Question 5

Gilula’s arcs

Answer 5

• 3 parallel arcs on a PA wrist xray
  Break in Gilula’s arcs seen with:
  1. Carpal fractures
  2. Carpal instability

Question 6

4 key radiographic features of perilunate injury on PA view

Answer 6

1. Terry Thomas sign = increased SL interval > 3mm
2. Cortical/ signet ring sign = scaphoid flexion
3. Break in Gilula’s arcs = overlap of capitate and lunate
4. Piece of pie sign (triangular/ wedge shaped lunate) = lunate flexion

Question 7

4 key radiographic features of perilunate injury on lateral view

Answer 7

1. Loss of collinearity between DR, lunate and capitate
2. Dorsal dislocation of carpus
3. Volar dislocation of lunate
4. Spilled tea cup sign = lunate flexion

Question 8

4 main indications for emergent CR of perilunate dislocations

Answer 8

1. Pain relief
2. To decrease risk of median nerve injury
3. To decrease risk of chondral injury
4. To preserve blood supply to lunate

Question 9

CR maneuver for perilunate dislocations

Answer 9

Chinese finger trap suspensory traction (10lb for 10min)
Thumb to stabilise lunate
Wrist extension while maintaining traction
Wrist flexion to reduce capitate onto lunate
Post-reduction xray
Immobilise in thumb spica
Plan for definitive surgery in 5-7 days once soft-tissues settled

Question 10

Combined volar and dorsal approach for perilunate injuries:
Advantages
Disadvantages

Answer 10

1. Advantages
   Volar approach allows
   - carpal tunnel decompression = CTS in 20% patients
   - reduction of lunate
   - repair of volar capsule (space of Poirier)
   Dorsal approach allows
   - exposure of proximal carpal row and midcarpal joint for ligament repair/ reconstruction
2. Disadvantages = combined approach results in
   - more swelling = higher risk of wound problems
   - more devascularisation of carpus
   - weakness and loss of grip strength

Question 11

Prognosis following perilunate injuries

Answer 11

Nonoperative management has universally poor outcomes = recurrent dislocation due to carpal instability
All perilunate injuries have guarded prognosis
Most patient will have
- stiffness
- weakness and decreased grip strength
- early radiographic arthritis
Consider change in occupation

Question 12

2 main surgical options with delayed diagnosis of perilunate injuries

Answer 12

20% of perilunate injuries are initially missed

1. PRC
2. Wrist arthrodesis

Question 13

2 main complications associated with perilunate injuries

Answer 13

1. Carpal instability

2. Carpal arthritis