SLAC WRIST - SCAPHOLUNATE ADVANCED COLLAPSE
Progressive Arthritis from SL Dissociation | Watson Classification | Radiolunate Preserved
WATSON CLASSIFICATION
Critical Must-Knows
- Most common degenerative wrist arthritis - from chronic SL ligament incompetence
- Radiolunate joint preserved until very late (Stage IV rare) - allows motion-preserving salvage
- Identical pattern to SNAC wrist - only etiology differs (SL dissociation vs scaphoid nonunion)
- Watson classification guides treatment: Stages II-III are most common presentation
- Four-corner fusion vs PRC both preserve approximately 50% motion with comparable outcomes
- DISI pattern - dorsal intercalated segment instability from scaphoid flexion and lunate extension
Examiner's Pearls
- "SLAC = SNAC in pattern, different in cause
- "Radiolunate preserved = motion-preserving salvage possible
- "4CC fuses capitate-lunate-hamate-triquetrum after scaphoid excision
- "PRC removes scaphoid-lunate-triquetrum, capitate articulates with radius
Clinical Imaging
Imaging Gallery
Critical SLAC Wrist Exam Points
Most Common Pattern
SLAC is the most common pattern of degenerative wrist arthritis. Results from chronic scapholunate ligament incompetence leading to progressive carpal malalignment and cartilage degeneration. Understand the natural history and predictable progression.
Radiolunate Preserved
Radiolunate joint preserved until very late Stage IV. This is the key anatomic feature allowing motion-preserving salvage procedures. Lunate maintains congruent articulation with radius despite surrounding arthritis.
Stage Determines Treatment
Watson staging guides treatment algorithm. Stage I: styloidectomy/denervation. Stage II-III: motion-preserving salvage (4CC or PRC). Stage IV: total wrist fusion. Most patients present at Stage II-III.
4CC vs PRC Decision
Both preserve approximately 50% motion. 4-corner fusion maintains carpal height, better grip strength. PRC is simpler surgery, faster rehab, requires intact capitate cartilage. No definitive superiority - surgeon and patient factors guide choice.
RSCPSLAC Stage Progression (Watson Classification)
Memory Hook:RSCP: Radial Styloid, Scaphoid fossa, CapitoLunate, Pancarpal - the predictable march of SLAC arthritis!
SPHERICALWhy Radiolunate Joint is Preserved
Memory Hook:SPHERICAL lunate: The radiolunate joint stays intact because the lunate remains SPHERICAL and congruent!
PRESERVESalvage Options - 4CC vs PRC Decision
Memory Hook:PRESERVE motion: Both procedures PRESERVE approximately 50% of wrist motion - choose based on cartilage status!
Overview and Definition
Why SLAC Wrist Matters
SLAC wrist is the most common pattern of degenerative wrist arthritis, making it essential knowledge for hand surgery examinations and clinical practice. Understanding the predictable progression, staging, and treatment algorithm is critical.
SLAC (Scapholunate Advanced Collapse) wrist is a pattern of progressive degenerative arthritis following chronic scapholunate ligament injury. The term was coined by Watson and Ballet in 1984 to describe the predictable sequence of arthritic changes.
Key Concepts
Etiology
- Chronic SL ligament tear (most common)
- Failed SL repair or reconstruction
- Unrecognized acute injury progressing
- Idiopathic SL incompetence
Untreated SL dissociation inevitably leads to SLAC wrist over 5-15 years.
Natural History
- Stage I: Radial styloid arthritis (years)
- Stage II: Radioscaphoid fossa (5-10 years)
- Stage III: Capitolunate joint (10-15 years)
- Stage IV: Pancarpal (very rare, over 20 years)
Progressive and irreversible once established.
SLAC vs SNAC Wrist
Identical arthritis pattern, different etiology:
| Feature | SLAC Wrist | SNAC Wrist |
|---|---|---|
| Etiology | Scapholunate ligament tear | Scaphoid nonunion |
| Arthritis pattern | Radial styloid → scaphoid fossa → capitolunate | Identical progression |
| Radiolunate preservation | Yes (until Stage IV) | Yes (until Stage IV) |
| Treatment | Same staging and surgical options | Same staging and surgical options |
| Prevalence | More common | Less common |
The treatment principles are identical because the biomechanical problem (loss of scaphoid bridge function) and arthritis pattern are the same.
Anatomy
Scaphoid Bridge Function
The scaphoid normally serves as a critical mechanical link between the proximal and distal carpal rows. Loss of this function (SL dissociation) leads to predictable carpal collapse and progressive arthritis.
Normal Carpal Kinematics
Scaphoid role in wrist mechanics:
- Span function: Bridges radiocarpal and midcarpal joints
- Load transmission: Transmits approximately 60% of axial load from distal row to radius
- Motion coupling: Coordinates flexion-extension between rows
- Stability: Prevents proximal migration of capitate
Consequences of SL Ligament Incompetence
When the scapholunate ligament fails:
Scaphoid Behavior:
- Loses connection to lunate
- Flexes with distal carpal row (driven by trapezium-trapezoid)
- Rotates into vertical position ("cortical ring sign" on PA X-ray)
- Creates abnormal contact with radial styloid (dorsal lip impingement)
Lunate Behavior:
- Loses scaphoid restraint
- Extends under influence of triquetrum (DISI pattern)
- Maintains normal articulation with radius (spherical geometry preserved)
- Scapholunate angle increases beyond 70 degrees
Capitate Behavior:
- Loses distal support from flexed scaphoid
- Migrates proximally into widened SL gap
- Creates abnormal contact with lunate
- Progressive capitolunate degeneration
The SLAC Progression Cascade
Biomechanical Cascade Leading to SLAC
Flexed scaphoid impinges on radial styloid. Abnormal point loading on dorsal lip of scaphoid against styloid tip. Osteophyte formation ("beaking"). Relatively early stage, may take several years.
Loss of congruent articulation. Scaphoid no longer sits properly in scaphoid fossa of radius. Increased contact pressure. Cartilage degeneration begins. Most common presentation.
Proximal capitate migration. Capitate moves into widened SL gap. Loss of normal capitolunate relationship. Incongruent articulation causes degeneration. Advanced stage but radiolunate still preserved.
Finally involves radiolunate. Only in very advanced, long-standing cases. Loss of spherical lunate-radius articulation. End-stage disease. No motion-preserving options remain.
Why Radiolunate Joint is Preserved
This is the key anatomic concept that allows motion-preserving salvage:
Geometric Factors
- Spherical articulation maintained
- Congruent radius of curvature unchanged
- Normal contact area preserved
- Even pressure distribution continues
The lunate "fits" normally in lunate fossa despite surrounding arthritis.
Biomechanical Factors
- No abnormal shear forces across joint
- Normal loading vectors maintained
- Intrinsic stability preserved
- Cartilage nutrition adequate
No mechanical factors driving degeneration at this articulation.
Clinical significance: Preserved radiolunate joint allows:
- Four-corner fusion (relies on intact radiolunate for motion)
- Proximal row carpectomy (capitate articulates with intact lunate fossa)
- Motion-preserving salvage in most patients (Stages I-III)
Pathophysiology
Mechanism of Progressive Arthritis
The progression from SL ligament tear to advanced arthritis follows a predictable biomechanical cascade:
Initial Injury:
- Scapholunate ligament rupture (acute trauma or chronic attenuation)
- Loss of scaphoid-lunate coupling
- Onset of carpal instability pattern
Early Changes (Months to Years):
- Scaphoid assumes flexed position (driven by distal row)
- Lunate extends under triquetrum influence (DISI pattern)
- SL gap widens progressively (over 3mm = static instability)
- Dorsal scaphoid lip impinges on radial styloid
Stage I Progression (Years 1-5):
- Repetitive impingement at styloscaphoid articulation
- Abnormal point loading concentrates force
- Cartilage microtrauma and degradation begins
- Synovitis and osteophyte formation at styloid
- Pain localizes to radial aspect of wrist
Stage II Progression (Years 5-10):
- Loss of scaphoid bridge function complete
- Scaphoid no longer articulates congruently in fossa
- Increased contact pressure at radioscaphoid joint
- Cartilage degeneration progresses to bone-on-bone
- Subchondral sclerosis and cyst formation
- Capitate begins proximal migration into SL gap
Stage III Progression (Years 10-15):
- Proximal capitate migration exceeds 2-4mm
- Capitate head contacts lunate abnormally
- Loss of normal capitolunate articulation geometry
- Progressive capitolunate cartilage destruction
- Severe carpal collapse (carpal height ratio under 0.48)
- Radiolunate joint still preserved (spherical fit maintained)
Stage IV Progression (Rare, over 20 years):
- Only in very advanced, neglected cases
- Finally involves radiolunate articulation
- Loss of lunate spherical geometry
- Complete carpal collapse and pancarpal arthritis
- No motion-preserving options remain
Biomechanical Factors Driving Progression
Load Distribution Changes
Normal: 60% load through radioscaphoid, 40% through radiolunate articulation.
SLAC: Abnormal concentration at styloscaphoid and scaphocapitate joints. Radiolunate loading unchanged - explains preservation.
Carpal Height Loss
Mechanism: Proximal capitate migration as scaphoid bridge collapses.
Consequence: Carpal height ratio decreases from 0.54 to under 0.45 in Stage III. Affects grip strength and motion.
Why Progression is Inevitable
Once SLAC arthritis begins, progression is inexorable because:
- Irreversible cartilage loss - chondrocytes cannot regenerate
- Perpetuating biomechanics - abnormal loading continues with every wrist motion
- Loss of shock absorption - cartilage loss increases bone contact pressure
- Inflammatory cascade - synovitis and cytokine release accelerate degeneration
- Subchondral bone changes - sclerosis and cysts represent end-stage damage
Clinical implication: Early intervention (SL ligament repair) prevents SLAC. Once arthritis established, salvage procedures are only option.
Classification Systems
Watson Classification (1984)
The gold standard staging system for SLAC wrist, based on radiographic arthritis pattern.
| Stage | Arthritis Location | Radiographic Findings | Clinical Presentation |
|---|---|---|---|
| I | Radial styloid only | Narrowing/sclerosis at styloid tip; scaphoid flexed | Radial-sided pain, worse with radial deviation |
| II | Radioscaphoid fossa | Sclerosis of scaphoid fossa; preserved capitolunate | Diffuse dorsal pain, reduced motion 20-30% |
| III | Capitolunate added | Proximal capitate migration; sclerosis CL joint | Severe pain, reduced motion over 50%, weak grip |
| IV | Pancarpal (radiolunate) | Sclerosis/narrowing radiolunate joint | End-stage; rare (under 5% of SLAC cases) |
Key points:
- Stage II is the most common presentation (40-50% of patients)
- Stage III is second most common (30-40%)
- Stage I may be managed non-operatively or with styloidectomy
- Stage IV is exceedingly rare - most SLAC never reaches this stage
Staging determines surgical approach and expected outcomes.
Clinical Assessment
History
- Pain: Dorsal wrist pain, activity-related
- Weakness: Grip strength reduced 30-60%
- Stiffness: Progressive loss of ROM
- Remote injury: History of wrist sprain years prior
- Occupation: Manual labor common
- Progression: Gradual worsening over years
Often no clear inciting event - insidious onset.
Examination
- Inspection: Dorsal prominence, swelling
- Palpation: Tender over dorsal wrist
- ROM: Flexion-extension reduced 30-60%
- Strength: Grip weakness 40-60% of normal
- Watson test: Usually negative (chronic, fixed)
- Provocative: Pain with axial loading
Late-stage findings, not early SL dissociation.
Clinical Findings by Stage
Symptom Progression with Watson Stage
| Stage | Pain Pattern | Motion Loss | Grip Strength | Dominant Complaint |
|---|---|---|---|---|
| I | Radial-sided, activity-related | Minimal (under 20%) | Near normal | Radial styloid pain with radial deviation |
| II | Dorsal wrist, constant | Moderate (20-40%) | Reduced 30-40% | Stiffness and weakness |
| III | Severe, diffuse | Severe (over 50%) | Reduced over 50% | Pain and severe functional limitation |
Differential Diagnosis
Consider other causes of chronic wrist pain: Kienböck disease (lunate AVN), DRUJ arthritis, ulnocarpal impaction, midcarpal instability, occult scaphoid fracture/nonunion (SNAC), extensor tenosynovitis. Imaging differentiates.
Special Tests
Watson scaphoid shift test:
- Usually negative in SLAC wrist (chronic, fixed deformity)
- May be positive in earlier SL dissociation before arthritis
- Compare to contralateral side
Scaphoid compression test:
- Axial load along thumb metacarpal
- Positive = pain at radioscaphoid joint
- Suggests Stage II arthritis
Investigations
Imaging Protocol for SLAC Wrist
PA, lateral, scaphoid views. PA shows: SL gap widening (over 3mm), scaphoid rotation ("cortical ring sign"), joint space narrowing, sclerosis. Lateral shows: SL angle over 70 degrees (DISI), capitolunate angle over 15 degrees, proximal capitate migration.
May reveal dynamic instability. SL gap widens with axial loading. Useful if static films normal but clinical suspicion high. Less helpful in established SLAC (already static deformity).
For surgical planning. Defines extent of arthritis (staging). Assesses capitate cartilage (critical for PRC decision). Evaluates scaphoid position and proximal pole viability. Essential before salvage surgery.
To exclude other pathology. Rules out Kienböck disease, TFCC tears, occult fractures. Assesses cartilage status. Less critical if plain films diagnostic for SLAC.
Imaging Gallery
Radiographic Staging
Stage I: Radial Styloid Arthritis
- Narrowing between scaphoid and radial styloid
- Osteophyte formation at styloid tip ("beaking")
- Scaphoid flexed (ring sign), lunate extended
- No sclerosis in scaphoid fossa of radius
- Capitolunate joint preserved
Stage II: Radioscaphoid Fossa Arthritis
- Joint space narrowing at radioscaphoid articulation
- Subchondral sclerosis in scaphoid fossa
- Proximal scaphoid pole may show cystic changes
- Capitolunate joint still preserved (key finding)
- Carpal height begins to decrease
Stage III: Capitolunate Arthritis
- Proximal migration of capitate into SL gap
- Joint space narrowing at capitolunate joint
- Sclerosis and cyst formation at CL articulation
- Severe carpal collapse (carpal height ratio under 0.48)
- Radiolunate joint STILL PRESERVED (critical)
Stage IV: Pancarpal Arthritis
- Radiolunate joint space narrowing
- Sclerosis at radiolunate articulation
- Complete carpal collapse
- Exceedingly rare (under 5% of SLAC cases)
CT Scan is Essential Before Salvage
Always obtain CT scan before four-corner fusion or PRC. Assesses: (1) capitate cartilage integrity (determines PRC feasibility), (2) exact arthritis extent (confirms staging), (3) bone quality for fusion, (4) scaphoid position for surgical planning.
Management Algorithm
Non-Operative Management
Indications:
- Patient refuses surgery
- Medical comorbidities prohibit surgery
- Low-demand, sedentary lifestyle
- Stage I with minimal symptoms
Conservative Treatment Options
Avoid provocative activities. Reduce heavy manual work. Ergonomic assessment. Job modification if possible. Success depends on patient compliance and occupation.
Wrist splint for symptom flares. Short opponens-style splint. Worn during activities. Nighttime use for pain relief. Does not alter natural history.
NSAIDs for pain control. Topical agents (diclofenac gel). Acetaminophen. Corticosteroid injections (temporary relief only). No disease-modifying effect.
Reality: Conservative treatment is palliative only in SLAC wrist. Arthritis is progressive and irreversible. Surgery is definitive treatment for most patients.
Conservative management is temporizing, not curative.
Surgical Technique Details
Four-Corner Fusion Technique
Patient Positioning:
- Supine, arm on hand table
- Tourniquet high on arm
- Forearm pronated
Approach:
- Longitudinal dorsal incision (8-10cm) over Lister tubercle
- Elevate extensor retinaculum as radially-based flap
- Enter wrist between 3rd and 4th compartments
- Protect PIN branches
Scaphoid Excision:
- Incise dorsal capsule in longitudinal T-shape
- Expose and excise entire scaphoid piecemeal
- Use rongeurs to remove all fragments
- Protect radial artery volarly
- Inspect radioscaphoid joint (confirm stage)
Fusion Site Preparation:
- Denude cartilage from:
- Proximal capitate
- Distal lunate
- Proximal hamate
- Distal triquetrum
- Use curette, rongeur, or burr
- Expose subchondral bone (bleeding surface)
- Shape surfaces for good apposition
- Pack autograft (excised scaphoid) into interfaces
Fixation:
- Dorsal circular plate (spider plate) most common
- Alternative: Individual screws or headless compression screws
- Plate advantages: Low profile, rigid fixation, fewer screws
Plate Application:
- Reduce carpal alignment (20-30 degrees flexion)
- Temporary K-wire stabilization
- Apply dorsal circular plate
- Verify screw trajectories under fluoroscopy
- Insert screws (typically 4-6 screws total)
- Confirm no radiocarpal or CMC joint penetration
Closure:
- Repair dorsal capsule
- Close retinaculum over plate
- Skin closure
Postoperative:
- Short-arm cast 8-12 weeks
- Radiographs at 6 weeks for fusion assessment
- Remove cast when fusion solid
- Therapy for ROM and strengthening
Four-corner fusion is technically demanding but provides reliable outcomes.
Complications
Early Complications (Under 6 weeks)
Common to Both Procedures (4CC and PRC):
Wound Issues (2-5%)
- Delayed healing (thin dorsal skin)
- Superficial infection (redness, drainage)
- Deep infection (rare, under 1%)
- Wound dehiscence (tension on closure)
Prevention: Careful skin handling, prophylactic antibiotics, early suture removal.
Neurovascular Injury (Under 2%)
- Radial artery injury during scaphoid excision
- PIN neuritis from retraction
- Dorsal sensory branch injury
- Superficial radial nerve traction
Management: Recognize early, repair artery primarily, nerve injuries usually temporary.
Four-Corner Fusion Specific:
- Malreduction (5%): Improper carpal alignment before plating
- Screw malposition (3%): Penetration into radiocarpal or CMC joints
- Plate prominence (10%): Inadequate soft tissue coverage
PRC Specific:
- Excessive bleeding (2%): From exposed cancellous surfaces
- Capitate instability (rare): If volar ligaments disrupted
Late Complications (After 6 weeks)
Four-Corner Fusion:
-
Nonunion (5-10%)
- Most common late complication
- Risk factors: smoking, NSAIDs, diabetes, poor bone quality
- May be asymptomatic or painful
- Treatment: Revision fusion with bone graft and rigid fixation
-
Plate Irritation and Tendinopathy (10-15%)
- Dorsal plate prominence causes extensor tendon irritation
- Painful tenosynovitis over 4th compartment
- Usually manifests 6-18 months postop
- Treatment: Plate removal after fusion solid (12+ months)
-
Radiocarpal Arthritis (10-20% at 10 years)
- Progressive degeneration at radiolunate joint
- May be asymptomatic or cause recurrent pain
- More common in heavy manual laborers
- Treatment: Observation if tolerable; total wrist fusion if severe
Proximal Row Carpectomy:
-
Progressive Arthritis (10-20% at 10 years)
- Capitate-radius articulation degeneration
- Higher risk if pre-existing capitate damage
- Presents as recurrent pain, reduced ROM
- Treatment: Activity modification; convert to total wrist fusion if failed
-
Ulnar Impaction Syndrome (5-10%)
- Carpal height loss causes ulnocarpal abutment
- DRUJ symptoms, ulnar-sided wrist pain
- Treatment: Ulnar shortening osteotomy or TFCC debridement
-
Capitate Subluxation (Under 5%)
- Instability pattern from excessive ligament stripping
- Capitate migrates dorsally or volarly
- Treatment: Revision to four-corner fusion or total fusion
Functional Complications
Common to Both:
Functional Outcome Deficits
| Issue | Incidence | Impact | Management |
|---|---|---|---|
| Inadequate motion recovery | 20-30% | Under 30 degrees arc (goal 40-50) | Aggressive early physiotherapy |
| Weak grip strength | 30-40% | Under 60% of normal (goal 70-80%) | Strengthening program, occupational modifications |
| Persistent pain | 15-25% | Activity-limiting discomfort despite surgery | Wrist denervation, activity modification, revision surgery |
| CRPS | 3-5% | Disproportionate pain, swelling, stiffness | Early recognition, desensitization, sympathetic blocks |
Revision Surgery
Indications for Revision:
- Failed salvage procedure with persistent pain (most common)
- Nonunion of four-corner fusion
- Progressive arthritis after PRC
- Hardware irritation requiring removal
- Inadequate function or motion
Options:
- After failed 4CC: Revision fusion with bone graft; convert to PRC if radiolunate intact; total wrist fusion
- After failed PRC: Convert to total wrist fusion (cannot convert to 4CC)
- Nonunion 4CC: Revision with iliac crest graft and rigid fixation
Outcomes of Revision:
- Less predictable than primary surgery
- Total wrist fusion most reliable option
- Patient counseling critical for realistic expectations
Prevention Strategies
Preoperative:
- Smoking cessation 6 weeks before surgery
- Optimize comorbidities (diabetes control)
- CT scan to assess cartilage and plan procedure
- Patient selection (avoid salvage in end-stage arthritis)
Intraoperative:
- Meticulous soft tissue handling
- Fluoroscopic verification of hardware placement
- Proper carpal alignment before fixation
- Preserve volar ligaments in PRC
Postoperative:
- Appropriate immobilization duration
- Early protected ROM when allowed
- Avoid NSAIDs until fusion solid (4CC)
- Aggressive hand therapy for motion recovery
Postoperative Care and Rehabilitation
Four-Corner Fusion Outcomes
Short-term (1-2 years):
- Pain relief: 75-85% good to excellent
- Motion: 50% of normal (30-40 degrees flexion-extension)
- Grip strength: 70-80% of normal
- Patient satisfaction: 75-85%
- Fusion rate: 90-95%
Long-term (5-10 years):
- Pain relief maintained in 70-80%
- Motion stable or slight decline
- Radiocarpal arthritis develops in 10-20%
- Revision rate: 5-10%
Proximal Row Carpectomy Outcomes
Short-term (1-2 years):
- Pain relief: 75-85% good to excellent
- Motion: 50% of normal (30-40 degrees flexion-extension)
- Grip strength: 60-75% of normal
- Patient satisfaction: 80-90%
- Return to work: 3-4 months
Long-term (5-10 years):
- Pain relief maintained in 65-75%
- Progressive capitate-radius arthritis in 10-20%
- Conversion to fusion: 5-10%
- Overall satisfaction remains good
Comparative Studies
Meta-analyses show:
- No significant difference in pain relief
- No significant difference in motion
- Slight grip strength advantage for 4CC (10-15%)
- Faster recovery with PRC
- Lower complication rate with PRC (no nonunion)
- Equivalent long-term function
Patient factors influencing outcomes:
- Age: Younger patients have better functional outcomes
- Occupation: Manual laborers have lower satisfaction
- Expectations: Realistic expectations correlate with satisfaction
- Compliance: Early ROM crucial for motion recovery
Evidence Base
Systematic Review: 4CC vs PRC for SLAC/SNAC Wrist
- No significant difference in pain relief between procedures
- Motion preserved equally (approximately 50% of normal)
- Grip strength slightly better with 4CC (10-15% advantage)
- Patient satisfaction equivalent at long-term follow-up
Long-term Follow-up: Four-Corner Fusion for SLAC
- Pain relief in 80% of patients at 5-year follow-up
- Motion averaged 40 degrees arc (flexion-extension)
- Grip strength 75% of contralateral side
- Nonunion rate 8% (all revised successfully)
- Radiocarpal arthritis developed in 15% (asymptomatic in most)
Long-term PRC Outcomes for SLAC Wrist
- Good to excellent results in 75% at 10+ years
- Motion averaged 50% of normal wrist
- Grip strength 70% of contralateral
- Progressive arthritis in 20% (mostly asymptomatic)
- Conversion to fusion in 8% for pain
Radial Styloidectomy for Stage I SLAC
- Pain relief in 65% of Stage I SLAC patients
- All patients eventually progressed to Stage II-III
- Mean time to progression 5-8 years
- Better outcomes in low-demand, older patients
- Addition of denervation improved pain relief to 75%
Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Stage II SLAC Decision-Making
"A 52-year-old male carpenter presents with 2 years of progressive left (dominant) wrist pain and weakness. He recalls a wrist sprain 8 years ago. Examination shows 40 degrees total flexion-extension arc, grip 30kg (right 55kg). Radiographs demonstrate scapholunate gap of 5mm, scapholunate angle 75 degrees, and sclerosis of the radioscaphoid fossa with preserved capitolunate joint. CT scan confirms Stage II SLAC with intact capitate cartilage. How would you manage this patient?"
Scenario 2: Four-Corner Fusion Technique
"You are performing a four-corner fusion for Stage III SLAC wrist. After scaphoid excision and fusion site preparation, you are ready for fixation. The examiner asks: Walk me through your technique for applying a dorsal circular plate. What are the key technical points?"
Scenario 3: SLAC vs SNAC - Examiner Grilling
"A 45-year-old female presents with chronic wrist pain. Radiographs show Stage II arthritis with radial styloid and radioscaphoid involvement. The examiner asks: How would you differentiate SLAC from SNAC wrist? Does it matter for treatment?"
Key Exam Takeaways
SLAC WRIST EXAM CHEAT SHEET
High-Yield Exam Summary
Definition and Etiology
- •SLAC = Scapholunate Advanced Collapse - most common degenerative wrist arthritis
- •Caused by chronic SL ligament incompetence (tear, failed repair, idiopathic)
- •Identical pattern to SNAC wrist (scaphoid nonunion) but different etiology
- •Progressive over 5-15 years: radial styloid → scaphoid fossa → capitolunate
- •Radiolunate joint preserved until very late (Stage IV rare, under 5%)
Watson Classification (Staging)
- •Stage I: Radial styloid arthritis only - styloidectomy or denervation
- •Stage II: Radioscaphoid fossa arthritis - most common presentation (40-50%)
- •Stage III: Capitolunate arthritis added - second most common (30-40%)
- •Stage IV: Pancarpal arthritis (radiolunate involved) - rare, under 5%
- •Staging determines treatment: I = palliative; II-III = salvage; IV = fusion
Pathophysiology
- •Loss of scaphoid bridge function - cannot coordinate proximal-distal rows
- •Scaphoid flexes with distal row, lunate extends (DISI pattern)
- •SL angle over 70 degrees on lateral X-ray = DISI malalignment
- •Abnormal contact: scaphoid dorsal lip impinges radial styloid (Stage I)
- •Proximal capitate migration into SL gap causes capitolunate arthritis (Stage III)
Clinical Presentation
- •Dorsal wrist pain, progressive over years, activity-related initially
- •Weakness: grip strength reduced 30-60% depending on stage
- •Stiffness: ROM reduced 30-60% (flexion-extension arc 40-80 degrees)
- •Watson test often negative (chronic, fixed deformity unlike acute SL tear)
- •Remote wrist injury history in 50%, but often no clear inciting event
Radiographic Findings
- •PA view: SL gap over 3mm (Terry Thomas sign), scaphoid ring sign (rotation)
- •Lateral: SL angle over 70 degrees (DISI), capitolunate angle over 15 degrees
- •Stage-specific arthritis: I = styloid; II = scaphoid fossa; III = capitolunate
- •CT scan essential before salvage: assess capitate cartilage (for PRC decision)
- •MRI to exclude other pathology: Kienböck, TFCC tear, occult fracture
Treatment Algorithm
- •Stage I: Radial styloidectomy (4-6mm) + wrist denervation = 70-80% relief
- •Stage II-III: Motion-preserving salvage - 4CC or PRC (both ~50% motion)
- •Four-corner fusion: Maintains height, better grip, but nonunion risk 5-10%
- •PRC: Simpler, faster recovery, requires intact capitate cartilage
- •Stage IV: Total wrist fusion (reliable) or arthroplasty (selected patients)
Surgical Technique Pearls
- •4CC: Excise scaphoid, fuse capitate-lunate-hamate-triquetrum with dorsal plate
- •PRC: Excise scaphoid-lunate-triquetrum, capitate articulates with radius
- •Critical: Assess capitate cartilage intraoperatively - if degenerated, abort PRC
- •4CC alignment: 20-30 degrees wrist flexion, verify screws under fluoroscopy
- •PRC: Preserve volar ligaments to prevent capitate subluxation instability
Outcomes and Complications
- •Both 4CC and PRC: 75-85% pain relief, 50% motion, 70-80% satisfaction
- •Grip strength: 4CC slightly better (70-80% vs 60-75% normal)
- •4CC complications: Nonunion 5-10%, plate irritation 10-15% (may need removal)
- •PRC complications: Progressive arthritis 10-20% at 10 years, ulnar impaction 5-10%
- •Conversion to total wrist fusion if salvage fails: 5-10% at long-term
High-Yield Exam Points
- •SLAC is MOST COMMON degenerative wrist arthritis pattern
- •Radiolunate preserved = allows motion-preserving salvage (key concept)
- •SLAC vs SNAC: Same pattern, different cause, same treatment
- •4CC vs PRC: No definitive superiority - equivalent outcomes in meta-analyses
- •Stage determines treatment: Do NOT offer styloidectomy for Stage II-III
Australian Context
Epidemiology and Presentation
SLAC wrist represents approximately 40-50% of advanced wrist arthritis cases presenting to Australian hand surgery units. Peak presentation age is 45-60 years with male predominance 2:1, reflecting higher rates of manual labor occupations in this demographic. Common affected occupations include carpenters, mechanics, electricians, mining and construction workers, and agricultural workers.
WorkCover claims are common for occupational wrist injuries that progress to SLAC wrist, particularly in patients with unrecognized or inadequately treated scapholunate ligament injuries. The long latency from initial injury to arthritis development (5-15 years) can complicate causation assessment for compensation purposes.
Management Considerations
Antibiotic Prophylaxis (eTG Guidelines): First-line prophylaxis for clean orthopaedic hand surgery is cefazolin 2g IV at induction (within 60 minutes of skin incision). Redosing is required if surgery exceeds 4 hours or blood loss over 1,500mL. For patients with penicillin allergy or MRSA risk factors, vancomycin 25-30mg/kg IV is the alternative. Single-dose prophylaxis is adequate for uncomplicated procedures.
Surgical Access: SLAC salvage procedures (four-corner fusion, proximal row carpectomy, total wrist fusion) are covered by Medicare and private health insurance with appropriate documentation of failed conservative management and progressive functional limitation. Radial styloidectomy for Stage I disease is also covered.
Return to Work: Modified duties are typically possible at 8-12 weeks post-salvage surgery. Return to full unrestricted duties, particularly heavy manual work, requires 4-6 months. Permanent restrictions for repetitive heavy lifting over 20kg are common, necessitating occupational reassessment and potential retraining in manual workers.
Examination Relevance
SLAC wrist is a high-yield topic for FRACS Orthopaedic Surgery examination, particularly in:
- Hand surgery viva (staging, treatment algorithm, surgical technique)
- Clinical examination stations (chronic wrist pain presentation)
- Radiology viva (DISI deformity recognition, Watson staging)
Candidates should be prepared to discuss the biomechanical basis for radiolunate preservation, the decision-making process for four-corner fusion versus proximal row carpectomy, and the technical details of both salvage procedures.
References
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Watson HK, Ballet FL. The SLAC wrist: scapholunate advanced collapse pattern of degenerative arthritis. J Hand Surg Am. 1984;9(3):358-365.
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Watson HK, Ryu J. Evolution of arthritis of the wrist. Clin Orthop Relat Res. 1986;(202):57-67.
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Ashmead D 4th, Watson HK, Damon C, Herber S, Paly W. Scapholunate advanced collapse wrist salvage. J Hand Surg Am. 1994;19(5):741-750.
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Wyrick JD, Stern PJ, Kiefhaber TR. Motion-preserving procedures in the treatment of scapholunate advanced collapse wrist: proximal row carpectomy versus four-corner arthrodesis. J Hand Surg Am. 1995;20(6):965-970.
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Krakauer JD, Bishop AT, Cooney WP. Surgical treatment of scapholunate advanced collapse. J Hand Surg Am. 1994;19(5):751-759.
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DiDonna ML, Kiefhaber TR, Stern PJ. Proximal row carpectomy: study with a minimum of ten years of follow-up. J Bone Joint Surg Am. 2004;86(11):2359-2365.
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Dacho AK, Baumeister S, Germann G, Sauerbier M. Comparison of proximal row carpectomy and midcarpal arthrodesis for the treatment of scaphoid nonunion advanced collapse (SNAC-wrist) and scapholunate advanced collapse (SLAC-wrist) in stage II. J Plast Reconstr Aesthet Surg. 2008;61(10):1210-1218.
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Cohen MS, Kozin SH. Degenerative arthritis of the wrist: proximal row carpectomy versus scaphoid excision and four-corner arthrodesis. J Hand Surg Am. 2001;26(1):94-104.
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Vanhove W, De Vil J, Van Seymortier P, Boone B, Verdonk R. Proximal row carpectomy versus four-corner arthrodesis as a treatment for SLAC (scapholunate advanced collapse) wrist. J Hand Surg Eur Vol. 2008;33(2):118-125.
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Lumsden BC, Stone A, Engber WD. Treatment of advanced-stage Kienböck's disease with proximal row carpectomy: an average 15-year follow-up. J Hand Surg Am. 2003;28(3):422-430.
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Saltzman BM, Frank JM, Slikker W, Fernandez JJ, Cohen MS, Wysocki RW. Clinical outcomes of proximal row carpectomy versus four-corner arthrodesis for post-traumatic wrist arthropathy: a systematic review. J Hand Surg Eur Vol. 2015;40(5):450-457.
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Wall LB, Didonna ML, Kiefhaber TR, Stern PJ. Proximal row carpectomy: minimum 20-year follow-up. J Hand Surg Am. 2013;38(8):1498-1504.
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Chim H, Moran SL. Long-term outcomes of proximal row carpectomy: a systematic review of the literature. J Hand Surg Eur Vol. 2012;37(9):787-793.
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Mulford JS, Ceulemans LJ, Nam D, Axelrod TS. Proximal row carpectomy vs four corner fusion for scapholunate (SLAC) or scaphoid nonunion advanced collapse (SNAC) wrists: a systematic review of outcomes. J Hand Surg Eur Vol. 2009;34(2):256-263.
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Shindle MK, Burton KJ, Weiland AJ, Domb BG, Wolfe SW. Complications of circular plate fixation for four-corner arthrodesis. J Hand Surg Eur Vol. 2007;32(1):50-53.