SCAPHOID NONUNION ADVANCED COLLAPSE (SNAC)
Progressive Carpal Arthritis | Watson Staging | SE4CF vs PRC
WATSON SNAC STAGING
Critical Must-Knows
- SNAC follows a predictable pattern - styloid first, then radioscaphoid, then capitolunate
- Radiolunate joint is spared - preserved spherical articulation allows motion-sparing procedures
- SE4CF and PRC are the two main surgical options for Stage II/III
- PRC contraindicated in Stage III - capitate head must be pristine for PRC
- DISI deformity develops - dorsal intercalated segment instability from scaphoid nonunion
Examiner's Pearls
- "Watson staging mirrors SLAC staging - both spare radiolunate joint
- "SNAC from nonunion vs SLAC from ligament injury - same treatment principles
- "Capitate head cartilage is the key decision point for PRC vs SE4CF
- "Motion preservation surgery is possible because radiolunate joint is spared
Critical SNAC Exam Points
SNAC vs SLAC
SNAC (Scaphoid Nonunion Advanced Collapse) and SLAC (Scapholunate Advanced Collapse) follow the same degenerative pattern but have different causes. SNAC results from scaphoid nonunion; SLAC from scapholunate ligament injury. Treatment principles are identical - both spare the radiolunate joint.
Radiolunate Joint Sparing
The radiolunate articulation is ALWAYS spared in both SNAC and SLAC. This is because the spherical lunate-radius articulation does not experience the abnormal contact stresses that occur at the radioscaphoid and capitolunate joints after carpal kinematics are disrupted.
Stage III and PRC
Proximal Row Carpectomy (PRC) is CONTRAINDICATED in Stage III SNAC/SLAC. PRC requires an intact capitate head articulating with the lunate fossa of the radius. Stage III has capitolunate arthritis meaning damaged capitate cartilage.
DISI Pattern
Scaphoid nonunion leads to DISI (Dorsal Intercalated Segment Instability). Without scaphoid linkage, the lunate tilts dorsally. Look for increased scapholunate angle greater than 70 degrees and increased capitolunate angle greater than 30 degrees on lateral radiograph.
| Feature | Details |
|---|---|
| Definition | Progressive wrist arthritis from untreated scaphoid nonunion |
| Cause | Scaphoid fracture nonunion → carpal malalignment → arthritis |
| Natural History | 100% progress to SNAC, average 10-15 years |
| Staging | Watson: I (styloid), II (radioscaphoid), III (capitolunate) |
| Key Feature | Radiolunate joint ALWAYS spared |
| Stage II Treatment | PRC or SE4CF (capitate status decides) |
| Stage III Treatment | SE4CF only (PRC contraindicated - damaged capitate) |
| Outcomes | 85-90% pain relief, 40-60 degrees motion arc |
SNAC 123SNAC STAGES - Progressive Arthritis Pattern
Memory Hook:SNAC progresses from styloid to scaphoid fossa to capitate - always SPARES radiolunate!
PRC vs SE4CFMOTION OPTIONS - Salvage Procedures
Memory Hook:PRC needs perfect Capitate; SE4CF works even in Stage III!
DISI LADDISI PATTERN - Radiographic Signs
Memory Hook:DISI = Dorsal lunate tilt, increased SL angle on lateral radiograph
Overview and Epidemiology
Epidemiology:
- Scaphoid fractures represent 60-70% of carpal bone fractures
- Nonunion develops in 5-10% of scaphoid fractures overall
- Proximal pole fractures have 30-40% nonunion rate
- 100% of untreated nonunions progress to SNAC wrist
- Average time from nonunion to symptomatic SNAC: 10-15 years
- Male predominance (4:1), peak incidence 20-40 years
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
Anatomy and Pathophysiology
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: Without treatment, scaphoid nonunion progresses predictably:
- DISI develops - Lunate tilts dorsally without scaphoid tether
- Abnormal loading - Scaphoid fragments malrotate, causing point loading
- Radial styloid arthritis - First site of cartilage wear
- Radioscaphoid arthritis - Progressive involvement of scaphoid fossa
- 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.
Classification - Watson SNAC Staging
Watson Classification for SNAC Wrist:
| Stage | Arthritic Changes | Radiographic Findings | Key Feature |
|---|---|---|---|
| I | Radial styloid-scaphoid | Styloid spurring, narrowed styloid-scaphoid interval | Isolated styloid involvement |
| II | Radioscaphoid + Stage I | Scaphoid fossa arthritis, narrowed radioscaphoid space | Entire scaphoid fossa involved |
| III | Capitolunate + Stage I/II | Midcarpal narrowing, capitate/lunate arthritis | Capitate head damaged |
Stage II Most Common
Stage II is the most common presentation for surgical intervention. Patients tolerate Stage I changes well but become symptomatic as arthritis extends into the scaphoid fossa. Stage III often represents end-stage disease with limited reconstruction options.
Clinical Presentation
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:
| Finding | Description | Significance |
|---|---|---|
| Anatomical snuffbox tenderness | Persistent tenderness at scaphoid | Suggests scaphoid pathology |
| Dorsal wrist tenderness | Over scapholunate interval | DISI, carpal malalignment |
| Reduced ROM | Especially extension | Dorsal capsular tightness from DISI |
| Grip weakness | Compared to contralateral | Usually 20-50% reduced |
| Watson test | Painful clunk with pressure on scaphoid tubercle | Scapholunate instability pattern |
| Radial styloid tenderness | Point tenderness at styloid | Styloid-scaphoid arthritis |
Red Flags:
- Acute injury with deformity - acute fracture-dislocation
- Rapid onset in young patient - consider infection, tumor
- Night pain, constitutional symptoms - systemic cause
Investigations
Plain Radiographs:
PA View Findings:
Scapholunate widening or Terry-Thomas sign if concurrent SL injury. Scaphoid nonunion line with sclerosis or cystic change. Shortened scaphoid with humpback deformity. Radioscaphoid joint space narrowing in Stage II or III. Styloid spurring in Stage I or higher.
Lateral View Findings:
DISI pattern - increased scapholunate angle greater than 70 degrees. Increased capitolunate angle greater than 30 degrees (normal is less than 15 degrees). Volar flexion of distal scaphoid fragment.
Key Radiographic Measurements:
| Measurement | Normal | SNAC/DISI |
|---|---|---|
| Scapholunate angle | 30-60 degrees | Greater than 70 degrees |
| Capitolunate angle | Less than 15 degrees | Greater than 30 degrees |
| Radiolunate angle | Less than 15 degrees | Greater than 15 degrees |
| Carpal height ratio | 0.54 ± 0.03 | Reduced (carpal collapse) |
Management Algorithm
Non-operative Management:
- Activity modification
- NSAIDs, wrist splinting
- Corticosteroid injections (temporary relief)
- Rarely successful long-term once SNAC established
Non-operative management is primarily for patients who are poor surgical candidates or those with minimal symptoms. It does not alter the natural history of progression.
Surgical Techniques
Proximal Row Carpectomy (PRC):
Removes the scaphoid, lunate, and triquetrum. The capitate head articulates with the lunate fossa of the radius creating a neoconcentric joint. Simpler procedure with no fusion to heal but requires pristine capitate head.
Indications: Stage II SNAC/SLAC with intact capitate head cartilage.
Contraindications: Stage III (capitolunate arthritis), damaged capitate head, inflammatory arthritis.
Technique: Dorsal approach, remove proximal row, preserve capsule for soft tissue interposition if desired, protect radial artery.
Outcomes: 50-60 degrees arc of motion, grip strength 60-80% of contralateral. Long-term results show progressive radiographic changes but maintained function.
Complications
Proximal Row Carpectomy Complications:
| Complication | Incidence | Prevention/Management |
|---|---|---|
| Progressive arthritis | 20-40% at 10 years | Salvage with fusion if symptomatic |
| Stiffness | 10-20% | Early ROM exercises, therapy |
| Weakness | Universal | Expected - counsel patient preop |
| Radial artery injury | Under 1% | Careful dorsal approach |
| Complex regional pain | 2-5% | Early recognition, therapy |
SE4CF Complications:
| Complication | Incidence | Prevention/Management |
|---|---|---|
| Nonunion | 3-5% | Adequate bone graft, stable fixation |
| Implant prominence | 5-10% | Recessed hardware, low-profile plates |
| Stiffness | Common | Aggressive therapy protocol |
| DRUJ symptoms | 5% | Address DRUJ pathology concurrently |
| Conversion to TWF | 5-10% | Salvage option if failed |
Capitate Head Inspection
ALWAYS inspect the capitate head cartilage intra-operatively before committing to PRC. If any cartilage damage is identified, convert to SE4CF. Proceeding with PRC with a damaged capitate will result in rapid failure and pain.
Postoperative Care
Proximal Row Carpectomy (PRC) Protocol:
| Phase | Timeframe | Activities |
|---|---|---|
| Immediate | 0-2 weeks | Bulky dressing, elevation, finger ROM |
| Early motion | 2-4 weeks | Removable splint, begin wrist AROM |
| Progressive | 4-8 weeks | Strengthen grip, increase activities |
| Return to activity | 8-12 weeks | Full activities, no restrictions |
SE4CF Postoperative Protocol:
| Phase | Timeframe | Activities |
|---|---|---|
| Immobilization | 0-6 weeks | Short arm cast, finger ROM only |
| Radiographic check | 6 weeks | Confirm fusion progression on XR |
| Protected motion | 6-10 weeks | Removable splint, begin wrist AROM if healing |
| Strengthening | 10-16 weeks | Progressive grip and wrist strengthening |
| Return to activity | 4-6 months | Full activities once fusion confirmed solid |
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
SE4CF Healing
SE4CF nonunion is the main complication to avoid. Strict casting for 6 weeks, smoking cessation, and adequate bone grafting are key. If nonunion suspected at 3 months, consider CT scan to assess fusion status. Revision bone grafting with extended immobilization may achieve union.
Outcomes and Prognosis
Comparative Outcomes - PRC vs SE4CF:
| Outcome | PRC | SE4CF |
|---|---|---|
| Pain relief | 85-90% | 85-90% |
| ROM (arc) | 50-60 degrees | 40-50 degrees |
| Grip strength | 60-80% | 70-80% |
| Return to work | 3-4 months | 4-6 months |
| Revision rate | 5-10% at 10 years | 5-10% at 10 years |
| Patient satisfaction | 85% | 85% |
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
Evidence Base
PRC vs SE4CF Randomized Trial
- No significant difference in patient satisfaction between PRC and SE4CF
- PRC showed slightly better early motion recovery
- SE4CF showed slightly better grip strength
- Both procedures equally effective for pain relief
Long-term PRC Outcomes
- Average 15-year follow-up of PRC patients
- 80% maintained good or excellent function
- Progressive radiographic changes common but often asymptomatic
- Conversion to fusion required in 10% at long-term follow-up
SE4CF Nonunion Risk Factors
- Nonunion rate 3-5% with modern techniques
- Smoking significantly increases nonunion risk
- Circular plate fixation has lowest nonunion rate
- Adequate bone graft essential for union
Natural History of SNAC
- 100% of untreated scaphoid nonunions progress to SNAC
- Average time to symptomatic SNAC is 10-15 years
- Progression follows predictable pattern - styloid, radioscaphoid, capitolunate
- Radiolunate joint spared even in advanced disease
Radiolunate Joint Preservation
- Original description of SLAC/SNAC pattern
- Radiolunate joint consistently spared due to spherical articulation
- Provides rationale for motion-preserving procedures
- Staging system remains standard classification
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Stage II SNAC Presentation
"A 45-year-old carpenter presents with 2 years of progressive radial wrist pain. He recalls a fall 15 years ago but never sought treatment. Radiographs show scaphoid nonunion with radioscaphoid arthritis but preserved capitolunate joint. What is your management?"
Diagnosis: Stage II SNAC wrist secondary to old scaphoid nonunion. The preserved capitolunate joint indicates Stage II rather than Stage III.
Assessment: Confirm staging with PA and lateral radiographs. Assess for DISI pattern on lateral view. Consider CT to better define arthritis extent. Examine capitate head cartilage status as this guides surgical choice.
Treatment Options: Stage II offers choice between PRC and SE4CF. Both provide equivalent pain relief and satisfaction. PRC is simpler with faster recovery but requires intact capitate head. SE4CF works regardless of capitate status but has fusion nonunion risk.
Surgical Recommendation: For a manual worker, I would discuss both options. Intra-operatively, inspect capitate head cartilage. If pristine, PRC is reasonable. If any damage noted, convert to SE4CF. Counsel regarding expected 60-80% grip strength and modified duties permanently.
Rehabilitation: Early protected motion for PRC. Cast immobilization until fusion for SE4CF. Hand therapy for both. Return to modified work at 3-4 months (PRC) or 4-6 months (SE4CF).
Scenario 2: Stage III SNAC
"A 55-year-old presents with severe wrist pain and stiffness. Radiographs show scaphoid nonunion with arthritis at the radioscaphoid AND capitolunate joints. What are the treatment options?"
Diagnosis: Stage III SNAC wrist. The presence of capitolunate arthritis in addition to radioscaphoid changes confirms Stage III.
Key Implication: Stage III means the capitate head cartilage is damaged. This CONTRAINDICATES proximal row carpectomy, as PRC relies on the capitate articulating with the lunate fossa. With damaged capitate cartilage, PRC would fail rapidly.
Treatment Options: Scaphoid Excision and Four-Corner Fusion (SE4CF) is the motion-preserving option. The capitate head cartilage is removed during the fusion, so its damaged status is irrelevant. Total wrist arthrodesis is an alternative for maximum pain relief and strength at the cost of all motion.
Recommendation: For most patients, SE4CF provides good balance of pain relief and preserved function. Discuss trade-offs: SE4CF preserves 40-50 degrees motion with 70-80% grip strength; TWA provides maximum pain relief and strength but no motion. Patient preference and occupational demands guide the choice.
Technical Considerations: SE4CF requires stable fixation and bone graft. Circular plate or headless compression screws are current fixation options. Counsel about 3-5% nonunion risk, especially in smokers.
Scenario 3: Young Patient with Scaphoid Nonunion
"A 25-year-old presents 2 years after a wrist injury. Radiographs show scaphoid waist nonunion but NO arthritis. Should you treat this?"
Key Point: This is scaphoid nonunion WITHOUT SNAC. The natural history is that 100% of untreated nonunions will progress to SNAC, typically over 10-15 years. In a 25-year-old, this means symptomatic arthritis by age 35-40.
Recommendation: Strong recommendation for surgical treatment. Options include vascularized bone graft (if AVN present) or non-vascularized bone graft with headless compression screw fixation. Goal is to achieve union before arthritis develops.
Assessment: Obtain CT to assess nonunion site, bone stock, and cystic changes. MRI to assess proximal pole vascularity - if AVN present, vascularized graft has higher union rates. Assess for humpback deformity requiring corrective bone grafting.
Surgical Technique: For viable proximal pole without AVN: Matti-Russe procedure or iliac crest bone graft with headless compression screw. For AVN: vascularized bone graft (1,2-ICSRA or medial femoral condyle free flap) provides best chance of union.
Expected Outcomes: Union rates 85-95% with appropriate graft selection. If union achieved, arthritis is prevented. If nonunion persists, salvage options (PRC, SE4CF) remain available.
Scenario 4: Failed PRC
"A patient underwent PRC for Stage II SNAC 3 years ago. They now present with recurrent pain and stiffness. Radiographs show progressive arthritis at the capitate-lunate fossa articulation. What are the options?"
Diagnosis: Failed PRC with progressive radiocapitate arthritis. This is a known long-term complication occurring in 10-20% of patients at 10-15 years.
Assessment: Confirm arthritis is the cause of symptoms (rule out other causes like DRUJ pathology, tendinitis). Assess remaining bone stock and quality. Consider injection as diagnostic/therapeutic trial.
Salvage Options: Total wrist arthrodesis is the primary salvage option. Previous PRC does not preclude fusion - adequate bone stock usually remains for plate fixation with bone grafting. Wrist arthroplasty is generally not recommended after failed PRC due to altered anatomy.
Technical Considerations: Fusion may require structural bone graft to restore carpal height. Plate fixation across the remaining carpus to the radius and index/middle metacarpal bases provides stable construct. Expected outcomes: complete pain relief, no wrist motion, near-normal grip strength.
Counseling: Discuss implications of wrist fusion for daily activities. Most patients adapt well but activities requiring wrist motion are affected. Forearm rotation usually preserved.
MCQ Practice Points
SNAC vs SLAC Cause
Q: What is the difference between SNAC and SLAC? A: SNAC (Scaphoid Nonunion Advanced Collapse) results from untreated scaphoid nonunion. SLAC (Scapholunate Advanced Collapse) results from scapholunate ligament injury. Both follow the same degenerative pattern and have identical treatment.
Which Joint is Spared
Q: Which joint is characteristically spared in SNAC and SLAC? A: The radiolunate joint is always spared. This is because the spherical lunate-radius articulation maintains congruent contact even when carpal kinematics are disrupted. This sparing allows motion-preserving salvage surgery.
Stage III Management
Q: Why is PRC contraindicated in Stage III SNAC? A: In Stage III, the capitolunate joint is arthritic. PRC requires the capitate head to articulate with the lunate fossa of the radius. Damaged capitate cartilage will cause rapid failure and pain. SE4CF is the motion-preserving option for Stage III.
DISI Pattern
Q: What carpal instability pattern develops with scaphoid nonunion? A: DISI (Dorsal Intercalated Segment Instability). The lunate tilts dorsally when it loses its connection to the scaphoid. Radiographically: scapholunate angle greater than 70 degrees, capitolunate angle greater than 30 degrees.
PRC vs SE4CF Comparison
Q: Compare the outcomes of PRC versus SE4CF. A: Both provide 85-90% pain relief and similar satisfaction. PRC: simpler, faster recovery, slightly more motion (50-60 degrees), but requires intact capitate. SE4CF: more complex, slower recovery, slightly less motion (40-50 degrees), but works even in Stage III.
Scaphoid Blood Supply
Q: Why does scaphoid nonunion occur? A: The scaphoid has a retrograde blood supply entering through the dorsal ridge. Proximal pole and waist fractures disrupt blood flow to the proximal fragment, causing AVN and nonunion. This is why proximal pole fractures have the highest nonunion rate.
Australian Context
Scaphoid fractures and subsequent nonunion are common injuries in Australia, particularly in young males involved in contact sports, motor vehicle accidents, and workplace injuries. The delay between injury and presentation is often significant, with many patients not seeking care until symptomatic SNAC develops years later.
Australian hand surgery centers manage SNAC with both PRC and SE4CF, with surgeon preference and patient factors guiding the choice. Total wrist fusion remains uncommon as a primary procedure but is used for salvage. Workers compensation cases require careful documentation of functional outcomes for return-to-work planning.
FRACS Relevance
For the FRACS examination, candidates must understand the natural history of scaphoid nonunion progressing to SNAC, the Watson staging system, and the rationale for motion-preserving surgery based on radiolunate joint sparing. Be prepared to discuss PRC vs SE4CF indications and the importance of capitate head assessment.
SCAPHOID NONUNION ADVANCED COLLAPSE (SNAC)
High-Yield Exam Summary
Watson Staging
- •Stage I: Radial styloid-scaphoid arthritis ONLY
- •Stage II: Radioscaphoid arthritis (entire scaphoid fossa)
- •Stage III: Capitolunate arthritis (midcarpal joint)
- •RADIOLUNATE JOINT IS ALWAYS SPARED
- •Staging identical for SLAC (different cause, same pattern)
Surgical Decision Making
- •Stage I: Styloidectomy plus/minus scaphoid reconstruction
- •Stage II: PRC or SE4CF - capitate status decides
- •Stage III: SE4CF only (PRC contraindicated)
- •Total wrist fusion: salvage or high-demand patient
- •ALWAYS inspect capitate head intra-operatively
PRC Key Points
- •Remove scaphoid, lunate, triquetrum
- •Capitate articulates with lunate fossa of radius
- •REQUIRES pristine capitate head cartilage
- •Contraindicated in Stage III
- •Motion: 50-60 degrees arc, grip 60-80%
SE4CF Key Points
- •Remove scaphoid, fuse capitate-lunate-hamate-triquetrum
- •Works even with damaged capitate head
- •Motion: 40-50 degrees arc, grip 70-80%
- •Nonunion rate 3-5% (smoking increases risk)
- •Can be done in Stage II or III
Why Radiolunate Spared
- •Spherical, congruent articulation
- •Minimal shear forces during wrist motion
- •Not subject to abnormal point loading
- •Allows motion-preserving salvage surgery
- •Same principle in both SNAC and SLAC
DISI Pattern
- •Dorsal Intercalated Segment Instability
- •Lunate tilts dorsally without scaphoid linkage
- •Scapholunate angle greater than 70 degrees
- •Capitolunate angle greater than 30 degrees
- •Seen on lateral radiograph