Scaphoid Nonunion Advanced Collapse (SNAC)

Epidemiology:

• Scaphoid fractures are the most common carpal fracture, occurring predominantly in young adult males
• Up to a third of confirmed scaphoid fractures are radiographically occult on initial films (Burns/Duckworth, Edinburgh prospective series, PMID 23960052)
• Nonunion develops in roughly 5-10% of scaphoid fractures overall; proximal pole and displaced fractures carry the highest risk
• Mack 1984 (PMID 6707028) showed that few displaced or unstable nonunions remain free of arthritis beyond 10 years (the classic "untreated nonunion becomes arthritic" teaching)
• Male predominance, peak incidence in the second-to-fourth decades

Risk Factors for Scaphoid Nonunion:

• Proximal pole fracture location
• Delayed presentation (greater than 4 weeks)
• Displacement greater than 1mm
• Vertical oblique fracture pattern
• Smoking
• Non-compliance with immobilization

Risk Factors for SNAC Progression:

• Established nonunion with instability
• Heavy manual labor
• Recurrent trauma
• Delay in nonunion treatment

Scaphoid Blood Supply and Nonunion: The scaphoid has a retrograde blood supply entering through the dorsal ridge. Fractures of the proximal pole or waist disrupt blood flow to the proximal fragment, leading to:

• Avascular necrosis of proximal pole
• Delayed or nonunion
• Progressive collapse if untreated

Natural History of Scaphoid Nonunion: Mack 1984 (PMID 6707028) established that, without treatment, displaced and unstable scaphoid nonunions progress through a time-dependent, predictable sequence (scaphoid-confined change at a mean of ~8 years, radioscaphoid arthritis at ~17 years, generalised wrist arthritis at ~32 years):

1. DISI develops - Lunate tilts dorsally without scaphoid tether
2. Abnormal loading - Scaphoid fragments malrotate, causing point loading
3. Radial styloid arthritis - First site of cartilage wear
4. Radioscaphoid arthritis - Progressive involvement of scaphoid fossa
5. Capitolunate arthritis - Final stage with midcarpal involvement

Why is the Radiolunate Joint Spared? The radiolunate articulation has:

• Spherical, congruent articulation
• Minimal shear forces during wrist motion
• Protected from abnormal point loading
• Preserved even in advanced SNAC/SLAC

This sparing is the KEY to understanding why motion-preserving surgery works.

History:

• Remote wrist injury - Often forgotten fall onto outstretched hand
• Gradual wrist pain - Progressive over months to years
• Radial-sided wrist pain - Worse with gripping, twisting
• Weakness - Reduced grip strength
• Clicking or clunking - Mechanical symptoms with motion
• Stiffness - Loss of wrist flexion and extension

Physical Examination:

Red Flags:

• Acute injury with deformity - acute fracture-dislocation
• Rapid onset in young patient - consider infection, tumour
• Night pain, constitutional symptoms - systemic cause

Differential Diagnosis of Chronic Radial-Sided Wrist Pain:

Plain Radiographs:

Key Radiographic Measurements:

Proximal Row Carpectomy Complications:

SE4CF Complications:

Proximal Row Carpectomy (PRC) Protocol:

SE4CF Postoperative Protocol:

Key Postoperative Considerations:

• PRC: Earlier motion than SE4CF (no fusion to protect)
• SE4CF: Strict immobilization until fusion - smoking cessation critical
• Both procedures: Hand therapy for ROM and strength
• Pain management: Multimodal analgesia, minimize opioids
• DVT prophylaxis: Mechanical; chemical if high risk

Comparative Outcomes - PRC vs SE4CF:

Long-term Considerations:

• Both PRC and SE4CF show progressive radiographic changes over time
• Clinical outcomes remain stable despite radiographic deterioration
• Conversion to total wrist fusion remains salvage option if needed
• Younger patients may require revision surgery in their lifetime

Global epidemiology (PMID-backed):

• Scaphoid fractures are the commonest carpal fracture, predominating in young adult males, and are a leading cause of wrist disability when missed.
• Up to one-third of confirmed scaphoid fractures are radiographically occult on initial presentation, driving wide international variation in imaging pathways (Burns/Duckworth, Edinburgh, PMID 23960052).
• The natural history of untreated displaced/unstable nonunion to SNAC is the most consistently reproduced finding across decades (Mack 1984, PMID 6707028).

Guidance and society positions (no single global guideline mandates one salvage procedure):

Registry and high-level evidence:

• There is no dedicated SNAC arthroplasty registry; salvage of SNAC predates and largely avoids prosthetic replacement, so national joint registries (AOANJRR/NJR) capture little SNAC-specific data.
• The best comparative evidence remains systematic review level (Mulford 2009, PMID 19369301): PRC and SE4CF give similar pain relief and satisfaction, with PRC offering slightly more motion but higher subsequent radiographic arthritis.

Practice variation:

• PRC is often preferred in lower-demand and older patients (simpler, no fusion to heal); SE4CF is favoured when the capitate head is damaged (Stage III) or in younger/higher-demand wrists.
• Fixation for SE4CF varies internationally between K-wires, headless compression screws and circular plates; reported nonunion and hardware-complication rates depend heavily on technique (Vance 2005, PMID 16344166; Merrell 2008, PMID 18590844).

Australian context: Scaphoid nonunion is common in young males from sport, motor-vehicle and workplace trauma, frequently presenting late. Australian hand units offer both PRC and SE4CF guided by surgeon preference and patient factors; total wrist fusion is reserved for salvage. Workers compensation cases require careful documentation of functional outcomes for return-to-work planning.