Wrist Arthritis: SLAC & SNAC Wrist
Understanding the most common patterns of wrist arthritis. Complete guide to staging, treatment options, and surgical outcomes.
Understanding SLAC & SNAC Wrist
SLAC Wrist (Scapholunate Advanced Collapse): The most common pattern of degenerative arthritis in the wrist. It results from injury to the scapholunate ligament, which connects the scaphoid and lunate bones. When this ligament tears, the scaphoid rotates and the wrist mechanics change, leading to progressive arthritis.
SNAC Wrist (Scaphoid Nonunion Advanced Collapse): A similar pattern of arthritis that develops after an untreated or poorly healed scaphoid fracture. The nonunion causes the same abnormal wrist mechanics as a scapholunate ligament tear, resulting in the same progression of arthritis.
Both conditions spare the radiolunate joint until very late stages, which is why motion-preserving surgeries are possible even with significant arthritis.
Watson Classification (SLAC/SNAC Stages)
Radial Styloid
Arthritis between scaphoid and radial styloid only. Rest of wrist spared.
Radioscaphoid
Entire radioscaphoid joint involved. Radiolunate joint still preserved.
Capitolunate
Radioscaphoid AND midcarpal (capitolunate) arthritis. Radiolunate still spared.
Pancarpal
Involvement of radiolunate joint. Diffuse wrist arthritis.
Key Point: The radiolunate joint is typically spared until very late disease. This is why motion-preserving surgeries (four-corner fusion, proximal row carpectomy) work well - they preserve or utilize this healthy joint surface.
Signs & Symptoms
• Pain: Dorsal wrist pain, often radial-sided initially, becomes diffuse
• Activity-related pain: Worse with gripping, lifting, pushing
• Stiffness: Progressive loss of wrist motion
• Weakness: Reduced grip strength due to pain
• Swelling: Dorsal wrist swelling
• Crepitus: Grinding sensation with wrist movement
History: Patients may recall a remote wrist injury (scapholunate tear or scaphoid fracture) that was never treated, or they may have no memory of injury. SLAC/SNAC often develops silently over years before becoming symptomatic.
Diagnosis
Clinical Examination:
- Tenderness over dorsal wrist
- Reduced range of motion (especially extension)
- Watson scaphoid shift test (positive in SLAC with SL instability)
- Crepitus with motion
- Grip strength testing
X-rays: PA, lateral, and scaphoid views. Look for:
- Scapholunate gap widening ("Terry Thomas sign") in SLAC
- Scaphoid nonunion in SNAC
- DISI (Dorsal Intercalated Segment Instability) - lunate tilted dorsally
- Joint space narrowing at specific locations based on stage
- Osteophytes and sclerosis
CT Scan: Helpful for surgical planning, assessing articular surfaces, and identifying the stage of disease.
Treatment Options
May provide temporary relief, especially in early disease:
- Activity modification: Avoid aggravating activities
- Splinting: Wrist splint for support during activities
- NSAIDs: For pain and inflammation
- Corticosteroid injections: Temporary relief, may be repeated
Note: SLAC/SNAC is progressive - conservative treatment delays but does not prevent eventual surgery in most symptomatic patients.
Stage I - Radial Styloidectomy
Removal of radial styloid to eliminate impingement. Preserves full motion. Limited role - only for isolated styloid arthritis.
Stage II/III - Scaphoid Excision + Four-Corner Fusion
Gold standard. Scaphoid removed. Lunate, triquetrum, capitate, hamate fused together. Motion through radiolunate joint. Preserves ~50% wrist motion. Excellent pain relief.
Stage II/III - Proximal Row Carpectomy (Alternative)
Scaphoid, lunate, triquetrum removed. Head of capitate articulates with lunate facet of radius. No fusion required. Preserves similar motion to four-corner fusion. No risk of nonunion.
Stage IV - Total Wrist Fusion (Arthrodesis)
Fusion of entire wrist. Eliminates all motion but provides excellent pain relief and strong grip. Reserved for pancarpal arthritis or failed previous surgery.
Total Wrist Arthroplasty (Selected Cases)
Wrist joint replacement. Preserves motion. Reserved for low-demand patients. Limited long-term data. Risk of loosening/failure.
Recovery Timeline
Evidence & References
- • Watson HK, Ballet FL. The SLAC wrist: scapholunate advanced collapse pattern of degenerative arthritis. J Hand Surg Am. 1984
- • Vance MC, et al. Scapholunate advanced collapse: a systematic review. J Hand Surg Am. 2021
- • Mulford JS, et al. Proximal row carpectomy vs four corner fusion for scapholunate advanced collapse wrists: a systematic review. J Hand Surg Eur. 2009
- • Weiss AP, et al. Four-corner arthrodesis. J Am Acad Orthop Surg. 2001
Last Updated: January 2025 | Content reviewed by Dr. Deepthi Nandan Reddy, FRCS (Ortho)
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Dr. Deepthi Nandan Reddy
Senior Consultant Orthopaedic & Upper-Limb Surgeon | Apollo Hospitals
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