SLAC & SNAC Wrist

SLAC Wrist

Stages:

• Stage 1: Radial styloid - scaphoid OA
• Stage 2: Whole Scaphoid fossa OA
• Stage 3: Mid carpal OA (Lunocapitate & Scaphocapitate OA)
  • Capitate drives into scapholunate interval
• Stage 4: Pan Carpal Arthritis

SNAC Wrist

• Same stages except Stage 4 is not usually part of it
• Key Difference:
  • In SNAC, proximal scaphoid pole remains attached to lunate by SL ligament
  • This spares the area from OA
  • In SLAC, SL ligament incompetence allows OA to develop between scaphoid and lunate
  • Capitate drives into this area

Common Features in Both

• Dissociative carpal instability (proximal row)
• DISI (Dorsal Intercalated Segment Instability) caused by:
  • Bony uncoupling in SNAC (flexed at fracture)
  • Soft tissue disruption in SLAC (whole scaphoid flexed)
• SL Angle >60° (normal is 40-60°)
• Lunate fossa of radius only affected in most severe cases
  • Usually spared but more likely affected in SLAC
  • Due to capitate driving into the gap, displacing lunate ulnarly

Aetiology

SNAC

• Traumatic non-union +/- AVN

SLAC

• Usually SL ligament trauma
• May be caused by pseudogout (pyrophosphate deposition disease)
  • Often bilateral if pseudogout
• No evidence that SL repair prevents SLAC
• Even without SLAC, SL rupture may cause persistent pain

Management

Non-Surgical Management

• No long-term studies on non-operative treatment
• Natural history not fully understood
• Splinting, activity modification, and analgesia may suffice for some

Surgical Treatment

Goals:

• Relieve pain
• Maintain motion (in early stages)
• Restore function

Broad Surgical Options:

1. Wrist denervation
2. Radial Styloidectomy (+/- distal scaphoid excision in SNAC)
3. Limited Lunocapitate fusion (+/- excision of triquetrum)
4. 4-corner fusion (+ excision of un-united proximal scaphoid)
5. Proximal Row Carpectomy (PRC)
6. Total Wrist Fusion

Surgical Procedures

Wrist Denervation

• AIN & PIN denervation to eliminate articular branches
• Unpredictable results
• No change to long-term mechanics
• Safe option as it does not burn surgical bridges

Radial Styloidectomy +/- Distal Scaphoid Excision (SNAC)

• Useful in early stages (esp. Stage 1)
• SNAC: Un-united distal pole excised to reduce pain
• Problem: Pain may continue, and collapse may progress
• May be a good temporizing measure

Isolated Lunocapitate Fusion

• Scaphoid & triquetrum excision may improve union rates
• Increases Radiolunate contact pressure
• Outcomes equivalent to 4CF

4-Corner Fusion (4CF)

• Lunate, capitate, triquetrum, and hamate fusion
• +/- Scaphoid excision
• Fixation: K-wires or plates

Problems with 4CF

• Non-union risk
• Broken metalware
• Tendon irritation
• Continued pain & restricted motion

Key Surgical Tips for 4CF Success

• Use bone graft (from distal radius)
• If using spider plate, use 2 screws per bone
• Avoid burrs/power instruments
• Lunate position at fusion does not affect motion

Proximal Row Carpectomy (PRC)

• Contraindicated if proximal capitate pole is severely arthritic
  • Will cause continued pain
• Advantages:
  • No metalware
  • No need for fusion
  • Faster rehab
• Disadvantages:
  • Slightly diminished grip strength

Choosing Between 4CF and PRC

• 4CF preferred in younger, high-demand patients
• PRC better for older or lower-demand patients
• Surgeon preference plays a large role as both have good reported outcomes

Total Wrist Fusion

• Most predictable results
• Treatment of choice for Stage 4 disease (or Stage 3 if preferred)
• Disadvantages:
  • Stiff wrist
  • Hardware complications
  • Non-union (especially of 3rd CMCJ)

Treatment Algorithm

Stage 1

• Neurectomy
• Radial styloidectomy

Stage 2

• Lunocapitate fusion + scaphoid excision
• PRC
• 4-corner fusion + scaphoid excision

Stage 3

• 4-corner fusion + scaphoid excision

Stage 4

• Total wrist fusion

Summary

• No clear evidence on natural history of SLAC/SNAC symptoms
• Treatment is focused on symptom relief
• Goal is to preserve motion if possible