SLAC/SNAC stage drives procedure choice — Stage II–III with a good capitate means 4-corner; Stage I–II with an intact capitate head means PRC; end-stage or failed partial means total wrist fusion
- SLAC = Scapholunate Advanced Collapse; SNAC = Scaphoid Nonunion Advanced Collapse — both progress Stage I then II then III from radial styloid to capitolunate
- 4-corner fusion (lunate, triquetrum, capitate, hamate, with scaphoid excision) preserves radiolunate motion of about 15–20° — it REQUIRES intact radiolunate cartilage
- PRC (excise scaphoid, lunate and triquetrum) is simpler with faster recovery — it REQUIRES intact capitate head articular cartilage
- Total wrist fusion: dorsal AO plate to the 3rd metacarpal; position 10–20° extension, neutral radial/ulnar deviation; the most reliable pain relief of the three
- “SLAC/SNAC Stage III (capitolunate arthritis): PRC is CONTRAINDICATED — the capitate head is arthritic, so use 4-corner or total fusion
- “Radiolunate joint preservation is the conceptual basis for 4-corner fusion — the examiner will ask why you preserve this joint
- “Non-union is the most common complication of 4-corner fusion (10–15%) — cancellous bone graft from the distal radius is mandatory
- “Total fusion in 10–20° extension and neutral radioulnar deviation replicates the functional hand position for grip and power
When & Why
The three wrist salvage procedures address different points on the spectrum of carpal degenerative arthritis. The choice is driven by the pattern of cartilage destruction (SLAC versus SNAC stage), the state of the capitate head and the radiolunate joint, patient age, occupation and functional demands. None of the three restores a normal wrist — they are pain-relieving salvage operations, and every patient must understand that pre-operatively.
- Total wrist arthrodesis
- Any stage; end-stage panarthritis; failed prior procedure
- 4-corner fusion
- Stage II–III with intact radiolunate cartilage
- Proximal row carpectomy
- Stage I–II with intact capitate head cartilage
- Total wrist arthrodesis
- None — complete fusion
- 4-corner fusion
- About 15–20° arc (radiolunate preserved)
- Proximal row carpectomy
- About 50% of normal (capitate in lunate fossa)
- Total wrist arthrodesis
- 70–80% of contralateral
- 4-corner fusion
- 60–70% of contralateral
- Proximal row carpectomy
- 60–70% of contralateral
- Total wrist arthrodesis
- Moderate — plate fixation
- 4-corner fusion
- High — precise carpal fusion
- Proximal row carpectomy
- Low — excision only, no fusion required
- Total wrist arthrodesis
- 3–4 months in cast
- 4-corner fusion
- 3–4 months in cast; union confirmation needed
- Proximal row carpectomy
- 6–8 weeks in cast; faster return to function
- Total wrist arthrodesis
- Less than 5% with a plate
- 4-corner fusion
- 10–15% (most common complication)
- Proximal row carpectomy
- Not applicable — no fusion required
- Total wrist arthrodesis
- Definitive — no escalation
- 4-corner fusion
- Convertible to total wrist fusion if needed
- Proximal row carpectomy
- Convertible to total wrist fusion if needed
- Total wrist arthrodesis
- No cartilage requirement
- 4-corner fusion
- Intact radiolunate cartilage (MANDATORY)
- Proximal row carpectomy
- Intact capitate head cartilage (MANDATORY)
- Total wrist arthrodesis
- Weiss et al. JBJS 1995 — reliable pain relief
- 4-corner fusion
- Tomaino 1994 PMID 7499166 — good outcomes at 3 years
- Proximal row carpectomy
- Wyrick 1995 PMID 7538834 — PRC vs 4-corner
The Operation
The goal is a dorsal exposure common to all three procedures, an assessment of the radiolunate and capitate head cartilage at arthrotomy that commits the patient to the correct procedure, and then a precise execution of PRC, 4-corner fusion or total wrist fusion. The dorsal exposure is laid out in full as the first steps below — it is the heart of the operation.
Operative sequence — shared dorsal exposure (all three procedures)
- Patient supine, arm on a hand table, upper-arm tourniquet to 250 mmHg.
- Exsanguinate with an Esmarch bandage or arm elevation.
- A longitudinal dorsal incision centred over the radiocarpal joint.
- Open the extensor retinaculum in the interval between the 3rd (EPL) and 4th (EDC) extensor compartments.
- Identify and protect the dorsal sensory branches of the radial nerve in the subcutaneous tissue — they are superficial and dorsoradial and are the structure most often injured.
- The PIN lies on the floor of the 4th compartment. Identify it and, for a total wrist fusion, resect it deliberately — PIN denervation is a valid adjunct for pain relief.
- Elevate the dorsal wrist capsule as a capsular flap based on the radius, for later repair.
- Inspect the radiolunate joint and the capitate head directly.
- If the capitate head cartilage is damaged, abandon PRC. If the radiolunate cartilage is damaged, abandon 4-corner and convert to total wrist fusion. This intra-operative finding overrides the pre-operative imaging.
- With the cartilage assessed, proceed to Procedure A (PRC), Procedure B (4-corner) or Procedure C (total wrist fusion) below.
Procedure A — Proximal Row Carpectomy (the simplest — no fusion) Prerequisite: macroscopically normal capitate head cartilage confirmed at Step 6. If damaged, abandon PRC. 1. Excise the scaphoid first — release all ligamentous attachments (radioscaphocapitate, scapholunate, scaphocapitate). Fragment with a rongeur and osteotome and remove piecemeal to protect surrounding structures; confirm complete removal with fluoroscopy.
- Excise the lunate — release the radiocarpal ligaments from the distal pole and protect the radiolunate facet articular surface. Remove en bloc or piecemeal.
- Excise the triquetrum — release the lunotriquetral and triquetrohamate ligaments. The pisotriquetral joint does not need to be disrupted.
- Seat the capitate head into the lunate fossa; confirm articular congruence with fluoroscopy. No fixation is required; if the capitate is unstable, a temporary K-wire for 6 weeks can be used.
- Repair the dorsal wrist capsule with absorbable sutures, repair the extensor retinaculum, close the skin, and apply a short-arm thumb spica cast for 6 weeks. ### Procedure B — 4-Corner Arthrodesis (scaphoid excision plus lunotriquetrocapitate–hamate fusion) Prerequisite: normal radiolunate articular cartilage confirmed at Step 6. If damaged, convert to total wrist fusion. 1. Excise the scaphoid as described above; confirm complete removal fluoroscopically — retained scaphoid fragments will impede the fusion.
- Denude articular cartilage from all four fusion surfaces: lunate (distal), triquetrum (distal), capitate (proximal) and hamate (proximal-medial), down to bleeding subchondral bone.
- Apply bone graft (cancellous from distal radius via Lister's tubercle resection, or iliac crest) into all fusion intervals.
- Reduce carpal alignment — lunate in neutral flexion (avoid DISI); reduce the capitate onto the radius–lunate axis under fluoroscopy.
- Fixation — a circular plate (Spider plate) with headless compression screws is the current gold standard, placed centrally spanning all four bones. Alternatives are staples (Acutrak) or K-wires (less stable, higher non-union).
- Confirm fusion position and hardware placement with intra-operative fluoroscopy; apply a cast for 8–12 weeks until CT confirms union. ### Procedure C — Total Wrist Arthrodesis (complete radiocarpal and midcarpal fusion) 1. Expose the dorsal wrist widely; identify all extensor compartments and retract or protect all extensor tendons. Resect Lister's tubercle — it provides cancellous graft material AND creates a flatter plate-bed.
- Strip articular cartilage from the distal radius (radiocarpal articular surface), the proximal carpal row (scaphoid, lunate, triquetrum — all proximal surfaces) and the midcarpal joint surfaces as needed.
- Position the wrist at 10–20° extension and neutral radial/ulnar deviation; check the position clinically and with fluoroscopy before applying the plate.
- Apply the AO wrist fusion plate — a pre-contoured plate with 10° of built-in extension — along the dorsal surface from the distal radius to the 3rd metacarpal shaft (the middle-finger ray is co-linear with the radius). Insert screws: 2–3 cortical screws in the distal radius, 2 screws across the carpus, and 2 cortical screws in the 3rd metacarpal shaft.
- Pack cancellous bone graft from Lister's tubercle into the radiocarpal and midcarpal fusion spaces.
- Confirm plate position, screw placement and fusion position with fluoroscopy in two planes; repair the extensor retinaculum and skin; apply a long-arm thumb spica cast for 4 weeks, then a short-arm cast until fusion is confirmed (usually 10–12 weeks total).
Total wrist fusion fuses the radiocarpal and midcarpal joints but NOT the distal radioulnar joint. Post-fusion, forearm rotation (pronation and supination) depends entirely on a functional DRUJ. Assess the DRUJ pre-operatively with fluoroscopy and examination — if DRUJ arthritis is present, a concurrent or staged Sauvé-Kapandji or Darrach procedure is required. Failure to assess the DRUJ is the most common planning error in total wrist fusion.
The dorsal sensory branches of the radial nerve are superficial in the subcutaneous tissue and are the most often injured structure — identify and protect them in every case. The PIN on the floor of the 4th compartment may be deliberately resected for denervation in a total fusion. All six extensor compartments must be identified and retracted; the EPL is particularly at risk from a prominent dorsal plate.
The AO wrist fusion plate runs from the distal radius across the carpus to the 3rd metacarpal because the middle-finger ray is co-linear with the radius — a straight line of fixation. The 10–20° of extension (the plate has 10° built in) replicates the position of function for power grip: the wrist naturally extends during grip to maximise the mechanical advantage of the digital flexors. Fusion in flexion severely compromises grip strength.
Always confirm the capitate head cartilage before PRC and the radiolunate cartilage before 4-corner fusion — directly, at arthrotomy, not on imaging alone. If the finding contradicts the pre-operative imaging, convert to total wrist fusion. Have the total fusion discussed and consented pre-operatively as the backup plan.
Aftercare & Complications
Rehabilitation | Procedure | Immobilisation | Motion | Strengthening and return | |-----------|----------------|--------|--------------------------| | PRC | Short-arm thumb spica cast for 6 weeks | Wrist ROM from 6 weeks | Strengthening from 3 months; full activity at 3–4 months | | 4-corner fusion | Short-arm cast for 8–12 weeks until CT confirms union | ROM only when union confirmed | Full activity at 4–6 months if union achieved | | Total wrist fusion | Long-arm cast 4 weeks, then short-arm cast 6–8 weeks (10–12 weeks total) | No wrist ROM (fused); finger and shoulder ROM from day 1 | Light activity at 3 months; heavy manual work at 4–6 months once fusion is solid | For 4-corner fusion, follow up with CT at 8–12 weeks — do not remove the cast on X-ray alone, which has insufficient sensitivity for carpal union. After total wrist fusion there is no wrist motion to regain, so finger, elbow and shoulder range of motion begins on day 1. Expected outcomes
- Total wrist fusion
- About 6/10
- 4-corner fusion
- About 5.5/10
- PRC
- About 5/10
- Total wrist fusion
- 85–95%
- 4-corner fusion
- 75–85%
- PRC
- 75–85%
- Total wrist fusion
- None (fused)
- 4-corner fusion
- 15–20° arc
- PRC
- 50–60% of normal
- Total wrist fusion
- 70–80% of contralateral (strongest)
- 4-corner fusion
- 60–70% of contralateral
- PRC
- 60–70% of contralateral
- Total wrist fusion
- Not applicable
- 4-corner fusion
- 10–15%
- PRC
- 10–20%
- Total wrist fusion
- Excellent
- 4-corner fusion
- Good
- PRC
- Progressive degeneration
Complications
- Total wrist fusion
- Less than 5% with a plate
- 4-corner fusion
- 10–15% (most common) — at capitate-hamate or LT interface
- PRC
- Not applicable — no fusion
- Total wrist fusion
- Dorsal plate palpable — removal in 15–20%
- 4-corner fusion
- Circular plate may be prominent — removal in 10%
- PRC
- Minimal — no metalwork unless a temporary K-wire
- Total wrist fusion
- EPL most at risk — plate may contact tendon
- 4-corner fusion
- Spider plate central — less tendon contact
- PRC
- Rare — no metalwork
- Total wrist fusion
- 5–10% — pseudarthrosis or DRUJ pathology
- 4-corner fusion
- 10–15% — investigate non-union with CT
- PRC
- 10–20% — capitate remodels but may be painful initially
- Total wrist fusion
- Dorsal sensory radial nerve branches
- 4-corner fusion
- Dorsal sensory radial nerve — same risk
- PRC
- Dorsal sensory radial nerve — same risk
- Total wrist fusion
- Intentional — complete fusion
- 4-corner fusion
- Expected — 15–20° arc preserved
- PRC
- Progressive loss over time — capitate-radius remodelling
- Total wrist fusion
- None — definitive
- 4-corner fusion
- 10–15% to total wrist fusion
- PRC
- 10–20% long-term to total wrist fusion
Managing 4-corner non-union. Non-union is the most important complication to know. Diagnosis is persistent pain at 3–6 months confirmed by CT scan (not X-ray alone — CT is required to assess cortical bridging). Management is repeat bone grafting with rigid fixation (revision to a circular plate if not already used); a failed 4-corner non-union is converted to total wrist fusion. Inform the patient pre-operatively that the non-union risk is 10–15% and conversion may be needed.
Viva & Exam Focus
SLACSLAC — staging scapholunate advanced collapse
Hook:SLAC staging is identical in pattern to SNAC — both spare the radiolunate joint until Stage III — this is the key fact that enables partial salvage procedures (4-corner, PRC) in Stage I–II disease
FUSIONFUSION — total wrist arthrodesis critical steps
Hook:FUSION walks you through every critical intra-operative decision for total wrist arthrodesis — Fixation plate, Ulnar assessment, Strip cartilage, Insert graft, Orientation 10–20°, Nerve protection
Stage I is the radial styloid to scaphoid articulation only; Stage II is the entire scaphoid fossa of the radius; Stage III involves the capitolunate joint (pantrapezial in SLAC). The stage determines which cartilage is preserved and which procedure is appropriate. The examiner will ask you to stage the wrist from the radiograph before choosing surgery.
The radiolunate articulation is spared in both SLAC and SNAC because the lunate does not articulate with the damaged scaphoid fossa. 4-corner fusion relies on this preserved joint for the residual 15–20° of wrist motion. Always confirm radiolunate cartilage is normal on pre-operative imaging AND at arthrotomy before committing to 4-corner over total fusion.
PRC creates a new articulation between the capitate head and the lunate fossa of the radius. If the capitate head cartilage is damaged (Stage III SLAC, avascular necrosis, rheumatoid disease), PRC produces a painful arthritic joint. Always assess the capitate head on MRI pre-operatively and directly at arthrotomy before performing PRC.
Total wrist arthrodesis must be positioned at 10–20° extension and neutral to slight radial deviation — the position of function for grip. Fusion in flexion severely compromises grip strength and hand function. The AO wrist fusion plate has 10° of built-in extension to guide correct positioning.
The AO wrist fusion plate runs dorsally from the radius across the carpus into the 3rd metacarpal (middle-finger ray), which is co-linear with the radius. Screws go into the radius (2–3), across the carpus (2) and into the 3rd metacarpal shaft (2). Correct plate positioning prevents hardware prominence and malunion.
Non-union occurs in 10–15% of 4-corner fusions, most often at the capitate-hamate or lunotriquetral interfaces. Prevention needs meticulous cartilage removal to bleeding subchondral bone, cancellous bone graft (from distal radius or iliac crest) and rigid internal fixation (a circular plate with headless compression screws is gold standard). Persistent pain at 6 months warrants a CT scan.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A 48-year-old manual worker has a 3-year history of progressive right wrist pain. X-rays show arthritis across the entire scaphoid fossa of the radius. The capitolunate joint appears preserved on plain X-ray but you are unsure. MRI shows cartilage loss across the radioscaphoid joint, intact radiolunate cartilage, and intact capitate head cartilage — SLAC wrist Stage II. Walk me through your choice of procedure and surgical planning.”
“You are planning a total wrist arthrodesis for a 55-year-old with end-stage SLAC Stage III wrist. What position will you fuse the wrist in, and why? How is the plate positioned?”
“A patient had a 4-corner fusion 9 months ago and returns with persistent wrist pain rated 7/10. The X-ray looks inconclusive. How do you investigate and manage?”
SLAC and SNAC staging
- Stage I: radial styloid tip to distal scaphoid (or scaphoid fragment in SNAC) only
- Stage II: entire scaphoid fossa of the radius (radioscaphoid arthritis) — the radiolunate joint is PRESERVED
- Stage III: capitolunate joint involved — PRC is contraindicated
- The radiolunate joint is SPARED in all stages of both SLAC and SNAC until late disease
- A DISI deformity (dorsal intercalated segment instability) accompanies SLAC — the lunate is dorsiflexed
Procedure-selection algorithm
- Stage I–II with intact capitate head: PRC (simpler, faster) OR 4-corner fusion
- Stage II–III with intact radiolunate: 4-corner fusion (preserves a 15–20° arc of motion)
- Stage III (capitolunate arthritis): 4-corner fusion or total wrist fusion (NOT PRC)
- End-stage panarthritis or a failed partial procedure: total wrist fusion only
- ALWAYS confirm articular cartilage at arthrotomy before committing — have a backup plan
4-corner fusion — critical points
- Fuse: lunate plus triquetrum plus capitate plus hamate. Excise: the scaphoid.
- The radiolunate joint must be intact — this is the motion-preserving basis of the operation
- A circular plate (Spider plate) plus headless compression screws is the current gold standard
- Bone graft is mandatory (from distal radius Lister's tubercle resection or iliac crest)
- Non-union 10–15% — the most common complication — diagnose with CT, not X-ray
- Final motion: a 15–20° arc from the radiolunate joint. Grip: 60–70% of contralateral.
PRC — critical points
- Excise all three proximal-row bones: scaphoid, lunate and triquetrum
- The capitate head articulates with the lunate fossa of the radius (a new pseudarthrosis)
- The capitate head cartilage must be intact — if damaged, PRC is contraindicated
- Technical simplicity: no fusion, no bone graft, no union to wait for
- Cast for 6 weeks — faster return to function than 4-corner
- Progressive long-term degeneration — conversion to total fusion is needed in 10–20%
Total wrist fusion — critical points
- Position: 10–20° extension plus neutral radial/ulnar deviation — the power-grip position
- AO wrist fusion plate: dorsal surface, radius then carpus then 3rd metacarpal (co-linear with radius)
- Screws: 2–3 in the radius, 2 in the carpus, 2 in the 3rd metacarpal shaft
- Resect Lister's tubercle: a flat plate bed plus cancellous graft material
- The DRUJ is NOT fused — assess pre-operatively; if arthritic, add a Sauvé-Kapandji or Darrach
- PIN resection on the floor of the 4th compartment — a denervation adjunct for pain relief
- Non-union less than 5% with a plate. Grip: 70–80% of contralateral (the strongest of the three).
Complications to know
- 4-corner non-union (10–15%): diagnose with CT, treat with revision graft plus rigid fixation or convert to total fusion
- Extensor tendon irritation: a prominent dorsal plate — the EPL is at risk — hardware removal in 15–20%
- Persistent pain after total fusion: check the DRUJ (not fused), PIN neuritis, hardware issues
- Dorsal sensory radial nerve: at risk in all three dorsal approaches — identify and protect
- DRUJ arthritis post-fusion: failure to assess the DRUJ pre-operatively is the most common planning error
Key evidence
- Watson 1980 (PMID 7364756): SLAC classification and the 4-corner fusion concept — a landmark paper
- Tomaino 1994 (PMID 7499166): 4-corner fusion outcomes — good pain relief, 50% motion at 3 years
- Wyrick 1995 (PMID 7538834): PRC versus 4-corner for SLAC Stage II — comparable outcomes
- Weiss 1995 (PMID 7545122): total wrist fusion — 95% patient satisfaction with plate fixation
- Imbriglia 1990 (PMID 2324448): PRC long-term — durable results at a mean 7-year follow-up
Background & Evidence
Carpal kinematics and the basis of SLAC/SNAC. The wrist moves through a coupled kinematic mechanism in which the scaphoid bridges the proximal and distal carpal rows: with wrist flexion the scaphoid flexes, and with extension it extends. Loss of this coupling — from scapholunate ligament disruption (SLAC) or a scaphoid waist nonunion (SNAC) — creates a rotary subluxation of the scaphoid, the basis of both deformities. In both patterns the radiolunate (radiocarpal) joint is spared, because the uncontrolled lunate assumes a dorsiflexed (DISI) posture and articulates with a normal part of the radius. This preservation of the radiolunate joint is the anatomical basis for 4-corner fusion and PRC.
- Radiographic features (SLAC and SNAC are identical in pattern)
- Arthritis at the radial styloid tip articulating with the distal scaphoid pole (or the distal scaphoid fragment in SNAC)
- Procedure implication
- Early — conservative care or radial styloidectomy
- Radiographic features (SLAC and SNAC are identical in pattern)
- Arthritis across the entire scaphoid fossa of the radius (radioscaphoid joint); the radiolunate joint is PRESERVED
- Procedure implication
- 4-corner fusion or PRC feasible — confirm cartilage
- Radiographic features (SLAC and SNAC are identical in pattern)
- Arthritis propagates to the capitolunate joint — the capitate migrates proximally into the gap
- Procedure implication
- PRC contraindicated — 4-corner or total wrist fusion
- Radiographic features (SLAC and SNAC are identical in pattern)
- Pantrapezial / pancarpal involvement (rare end stage)
- Procedure implication
- Total wrist fusion is the only option
Anatomy that drives the operations. The four bones fused in a 4-corner fusion are the lunate, triquetrum, capitate and hamate (after excision of the scaphoid); the lunate then articulates with the preserved radiolunate facet, giving the residual 15–20° arc. For PRC, the proximal row (scaphoid, lunate, triquetrum) is excised and the capitate head descends into the lunate fossa of the radius — a pseudarthrosis that is pain-free provided the capitate head cartilage is intact. The standard dorsal approach works the interval between the 3rd (EPL) and 4th (EDC) extensor compartments; the dorsal sensory branches of the radial nerve are superficial and at risk, and the PIN lies on the floor of the 4th compartment (often intentionally resected for denervation during total fusion). Global practice and evidence. In high-volume centres (UK NJR data, the AO Surgery Reference, and published BSSH guidelines), 4-corner fusion and PRC have equivalent intermediate-term outcomes for SLAC/SNAC Stage II disease with intact joint cartilage. Registry data from the Swedish Hand Surgery Registry and published European hand-surgery society guidelines note that surgeon preference and training remain significant factors in the choice between the two procedures. There is no randomised controlled trial comparing all three procedures directly; the highest-quality comparative evidence comes from retrospective cohort studies and meta-analyses (the Mulford 2009 systematic review and the DiDonna 2004 matched cohort).
- Finding
- The SLAC wrist pattern — classification and the 4-corner fusion concept
- PMID
- 7364756
- Finding
- 4-corner fusion — 3-year outcomes: good pain relief, 50% motion preserved
- PMID
- 7499166
- Finding
- PRC versus 4-corner — comparable outcomes for SLAC Stage II
- PMID
- 7538834
- Finding
- PRC — durable results at a mean 7-year follow-up
- PMID
- 2324448
- Finding
- Total wrist fusion — 95% patient satisfaction with reliable pain relief
- PMID
- 7545122
References
The SLAC wrist: scapholunate advanced collapse pattern of degenerative arthritis
The landmark paper defining the SLAC wrist classification and the 4-corner fusion concept — the basis for staging and procedure selection.
Long-term results following proximal row carpectomy and 4-corner fusion outcomes
3-year outcomes for 4-corner fusion demonstrating good pain relief and approximately 50% motion preservation.
Motion-preserving procedures in SLAC wrist: proximal row carpectomy versus four-corner arthrodesis
Comparative study of PRC versus 4-corner fusion for SLAC Stage II demonstrating comparable functional outcomes.
Proximal row carpectomy: clinical evaluation
Long-term outcomes of PRC at a mean 7-year follow-up demonstrating durable results in selected patients.
Upper extremity function after wrist arthrodesis
Total wrist arthrodesis outcomes — 95% patient satisfaction with reliable pain relief and plate fixation.