SLAC Wrist

SLAC (scapholunate advanced collapse) wrist is a pattern of progressive degenerative arthritis that follows chronic scapholunate ligament injury. Watson and Ballet coined the term in 1984 to describe the predictable sequence of arthritic change, and it is the most common pattern of degenerative wrist arthritis.

Causes. Every route runs through an incompetent scapholunate (SL) ligament:

• Chronic SL ligament tear (the most common)
• Failed SL repair or reconstruction
• An unrecognised acute injury that progresses
• Idiopathic SL incompetence

Not every tear progresses. An untreated static SL dissociation is the classic route to a SLAC wrist over 5-15 years, but the progression is not universal for every SL tear. Where a low-grade tear was found incidentally at distal radius fixation and left alone, 13-to-15-year follow-up found no static dissociation and no SLAC, so grade and the presence of a fixed gap decide the risk. Once the arthritis is established it is progressive and irreversible.

SLAC and SNAC. Scaphoid nonunion advanced collapse produces an identical arthritis pattern from a different cause. The treatment principles are identical too, because the biomechanical problem (loss of the scaphoid's bridge function) and the arthritis pattern are the same.

The scaphoid as a bridge. The scaphoid is the mechanical link between the proximal and distal carpal rows, and losing that link (SL dissociation) leads to predictable carpal collapse and progressive arthritis. In the normal wrist it does four jobs:

• Span - it bridges the radiocarpal and midcarpal joints
• Load transmission - approximately 60% of the axial load passes from the distal row to the radius through the radioscaphoid articulation, and 40% through the radiolunate
• Motion coupling - it coordinates flexion-extension between the rows
• Stability - it prevents proximal migration of the capitate

Secondary restraints. The dorsal intercarpal and dorsal radiocarpal ligaments supplement the scapholunate interosseous ligament. Failure of these secondary restraints is what converts a partial scapholunate tear into static dissociation, which is why an acute isolated tear can look radiographically normal.

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When the ligament fails. The scaphoid and lunate lose their coupling and each goes its own way:

• Scaphoid - loses its connection to the lunate and flexes with the distal row, driven by the trapezium and trapezoid. It rotates into a vertical position (the cortical ring sign on the PA film), and its dorsal lip comes into abnormal contact with the radial styloid.
• Lunate - loses the scaphoid's restraint and extends under the influence of the triquetrum, the DISI pattern. It keeps a normal articulation with the radius because its spherical geometry is preserved.
• Capitate - loses distal support from the flexed scaphoid, migrates proximally into the widened SL gap and makes abnormal contact with the lunate, which degenerates the capitolunate joint progressively.

Why the radiolunate joint survives. This is the key anatomical concept of the topic. The lunate sits in a congruent fossa that is loaded axially, and it keeps its spherical articulation there: the radius of curvature is unchanged, the contact area normal and the pressure distribution even, so the lunate "fits" normally in the lunate fossa despite the arthritis around it. There are no abnormal shear forces, the loading vectors stay normal, intrinsic stability is preserved and cartilage nutrition is adequate, so nothing mechanical drives degeneration at this articulation.

Why that matters. A preserved radiolunate joint makes motion-preserving salvage possible in most patients (Stages I-III):

• Four-corner fusion relies on the intact radiolunate joint for its motion
• Proximal row carpectomy relies on the capitate articulating with an intact lunate fossa

The cascade begins. Scapholunate ligament rupture, from acute trauma or chronic attenuation, uncouples the scaphoid from the lunate and starts a carpal instability pattern. Over the following months to years the scaphoid flexes and the lunate extends as described above, and the SL gap widens progressively: over 3mm marks static instability.

Where the load goes. In SLAC the load concentrates abnormally at the styloscaphoid and scaphocapitate joints, while radiolunate loading is unchanged, which explains why that joint is preserved. Load concentrates on the radial styloid and radioscaphoid facet, which is where arthritis appears first.

Stage I, the radial styloid (years 1-5). Repetitive impingement at the styloscaphoid articulation concentrates force as abnormal point loading. Cartilage microtrauma and degradation begin, with synovitis and osteophyte formation ("beaking") at the styloid, and the pain localises to the radial side of the wrist.

Stage II, the radioscaphoid fossa (years 5-10). Loss of the scaphoid's bridge function is now complete and the scaphoid no longer articulates congruently in its fossa. Contact pressure rises, the cartilage degenerates to bone on bone with subchondral sclerosis and cysts, and the capitate begins its proximal migration into the SL gap.

Stage III, the capitolunate joint (years 10-15). Proximal capitate migration exceeds 2-4mm, and the capitate head contacts the lunate abnormally. The normal capitolunate geometry is lost and its cartilage progressively destroyed, with severe carpal collapse that affects grip strength and motion. The radiolunate joint is still preserved, its spherical fit maintained.

Stage IV, pancarpal (rare, over 20 years). Only in very advanced, neglected cases does the arthritis finally reach the radiolunate articulation. The lunate loses its spherical geometry, the carpus collapses completely and no motion-preserving options remain.

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Why progression is inevitable. Once SLAC arthritis begins, progression is inexorable:

1. Irreversible cartilage loss - chondrocytes cannot regenerate
2. Perpetuating biomechanics - abnormal loading continues with every wrist motion
3. Loss of shock absorption - cartilage loss increases bone contact pressure
4. Inflammatory cascade - synovitis and cytokine release accelerate degeneration
5. Subchondral bone changes - sclerosis and cysts represent end-stage damage

Early intervention with SL ligament repair prevents SLAC. Once arthritis is established, salvage procedures are the only option.

The Watson classification (1984) is the gold standard staging system for SLAC wrist, based on the radiographic pattern of arthritis. The stage determines the surgical approach and the expected outcome.

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Who presents when. Stage II is the most common presentation (40-50% of patients) and Stage III the second most common (30-40%). Stage I may be managed non-operatively or with styloidectomy. Stage IV is exceedingly rare, under 5% of SLAC cases: most SLAC wrists never reach it.

Modified staging. Some authors subdivide the stages for more granular treatment decisions, to help decide between scaphoid excision alone, four-corner fusion and PRC. Substaging is controversial, and most surgeons use the standard four-stage Watson system.

• Stage IIA - radioscaphoid arthritis without capitate migration
• Stage IIB - radioscaphoid arthritis with early capitate migration (less than 2mm)
• Stage IIIA - capitolunate arthritis, capitate migrated 2-4mm
• Stage IIIB - advanced capitolunate arthritis, capitate migrated over 4mm

History. Dorsal wrist pain, activity-related, with weakness (grip reduced 30-60%) and progressive loss of motion, worsening gradually over years. There may be a wrist sprain years before, but often there is no clear inciting event and the onset is insidious. Manual labour is a common occupation.

Examination. Look for a dorsal prominence and swelling, tenderness over the dorsal wrist and pain with axial loading. Flexion-extension is reduced by 30-60%, and grip on examination is 40-60% of normal. These are late-stage findings, not those of early SL dissociation.

Special tests. The Watson scaphoid shift test is usually negative in a SLAC wrist, because the deformity is chronic and fixed; it may be positive in earlier SL dissociation before arthritis, and should be compared with the other side. The scaphoid compression test applies an axial load along the thumb metacarpal: pain at the radioscaphoid joint is positive and suggests Stage II arthritis.

Symptoms by stage. Pain, stiffness and weakness track the Watson stage:

Differential diagnosis. Chronic radial or dorsal wrist pain has several mimics, and imaging differentiates them. Midcarpal instability and extensor tenosynovitis also belong on the list.

Plain radiographs first. PA, lateral and scaphoid views. The PA shows the SL gap, scaphoid rotation (the cortical ring sign), joint space narrowing and sclerosis; the lateral shows the SL and capitolunate angles and proximal capitate migration. Measurements quantify the carpal malalignment, confirm the diagnosis and track progression:

An SL angle over 70 degrees is the dorsal intercalated segment instability (DISI) pattern, the hallmark of chronic SL incompetence.

Gilula's arcs. Trace them on every wrist film. A step or break in any arc indicates carpal malalignment before arthritis is visible.

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Stress views. Scapholunate widening is dynamic, and a neutral PA film alone will miss it. The clenched-fist PA loads the capitate between scaphoid and lunate, so the SL gap widens with axial loading, and it is the single most useful provocative projection. Compare with the contralateral wrist, since a gap above 3mm is significant only relative to the other side.

When to ask for them. Stress views are useful when static films are normal but clinical suspicion is high, and less helpful in established SLAC, where the deformity is already static. A complete instability series is PA and lateral for static alignment, ulnar deviation to extend the scaphoid, and clenched fist to provoke the gap; order all four when the history suggests instability and the neutral films look normal.

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MRI is optional, to exclude other pathology: Kienböck disease, TFCC tears and occult fractures. It also assesses cartilage status, and it is less critical when plain films are diagnostic of SLAC.

The stage decides. Stage I is treated with radial styloidectomy or denervation, Stages II-III with motion-preserving salvage (four-corner fusion or proximal row carpectomy), and Stage IV with total wrist fusion. Most patients present at Stage II-III.

Algorithm

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ConservativeStage I TreatmentStage II-III SalvageStage IV Treatment

Who. Patients who refuse surgery or whose medical comorbidities prohibit it, the low-demand sedentary patient, and Stage I with minimal symptoms.

Activity modification. Avoid provocative activities, reduce heavy manual work, arrange an ergonomic assessment and modify the job where possible. Success depends heavily on occupation and compliance: a manual worker often cannot comply, which is itself part of the surgical decision.

Wrist orthoses. For symptom flares, a short opponens-style splint worn during aggravating activity, with night use for pain. It rests an arthritic joint; it does not alter the natural history.

Drugs and injection. NSAIDs, topical agents such as diclofenac gel, and paracetamol. Corticosteroid injection gives temporary relief only and has no disease-modifying effect.

What conservative care can do. The three can be used alone or together; they manage symptoms, and none of them touches the disease. The reason is mechanical and irreversible: once the scapholunate ligament has failed, the scaphoid flexes and the capitolunate joint takes load it was never designed for, so cartilage is being worn away by an altered contact pattern that no splint or tablet can correct.

Palliation buys time. Conservative treatment suits the low-demand or elderly patient and anyone not yet ready for surgery, while surgery is the definitive option for most. Say this explicitly when consenting, so the patient understands they are choosing when to operate rather than whether to.

Total/Partial Wrist Denervation — Keep the Motion, Just Lose the Pain

Wrist denervation is more than a Stage I adjunct: it can be offered as a stand-alone procedure at any stage for the patient who wants to keep wrist motion and avoid bony surgery. It works by dividing the articular sensory branches to the wrist — principally the terminal posterior interosseous nerve (PIN) and anterior interosseous nerve (AIN) branches (a limited PIN/AIN neurectomy), with more extensive options dividing additional dorsal and volar sensory branches (the total, Wilhelm-type denervation). Crucially it relieves pain without altering the arthritis, the carpal alignment or the range of motion — nothing is fused or excised, so it burns no bridges to a later four-corner fusion, PRC or total wrist fusion. A diagnostic local-anaesthetic block of the PIN/AIN (temporary pain relief) helps predict who will respond. The trade-offs are that it does not halt disease progression and a proportion lose benefit over time, but for a high-demand worker who needs motion, or as a lower-morbidity option in the elderly or unfit, it is a legitimate motion-preserving choice. The exam point: denervation treats the pain, not the joint.

Indications. Stage I SLAC with radial-sided pain after failed conservative management.

The options. There are three surgical options:

1. Radial styloidectomy alone - excising the styloid tip removes the impingement point and preserves all motion, with pain relief in 60-70%. It does not address the underlying instability.
2. Styloidectomy with wrist denervation - adding denervation of the PIN, AIN and dorsal sensory branches improves pain relief to 75-80%, and the combined procedure is increasingly favoured.
3. Scaphoid excision with four-corner fusion or PRC - consider it in a young, high-demand patient: more definitive treatment, accepting motion loss for durability.

Technique. Through a dorsal approach between the third and fourth extensor compartments, expose the radial styloid and excise its tip with an osteotome or rongeur. Remove 4-6mm (avoiding DRUJ instability) and smooth the edges with a burr.

Outcomes. Pain relief is 60-80% depending on the adjuncts, motion is preserved and return to work takes 8-12 weeks. Styloidectomy is palliative: it buys time but does not prevent progression, which is inevitable to Stage II-III over years.

The goal at Stages II-III is pain relief while preserving motion, and there are two main options.

Four-corner fusion (4CC). Excise the entire scaphoid, denude the cartilage between capitate, lunate, hamate and triquetrum, and fuse those four bones, preserving the radiolunate articulation. It maintains carpal height, gives better grip strength, addresses midcarpal instability and allows a secondary PRC if it fails. The price is a more complex operation, a nonunion risk because it depends on union across the fusion mass, longer immobilisation, and plate irritation that may require removal.

Proximal row carpectomy (PRC). Excise the entire proximal row (scaphoid, lunate and triquetrum) so that the capitate articulates directly with the lunate fossa of the radius. No fixation or fusion is required: a simple, reliable procedure with a shorter operative time, faster rehabilitation, no nonunion risk and no implant-related complications. It requires intact cartilage on the capitate head and in the lunate fossa, which is essential; it loses carpal height, gives a slightly weaker grip than 4CC and cannot be converted to 4CC if it fails.

Motion preserved

4-Corner Fusion

50% (30-40 degrees F/E)

Proximal Row Carpectomy

50% (30-40 degrees F/E)

Grip strength

4-Corner Fusion

70-80% of normal

Proximal Row Carpectomy

60-75% of normal

Pain relief

4-Corner Fusion

75-85% good to excellent

Proximal Row Carpectomy

75-85% good to excellent

Nonunion risk

4-Corner Fusion

5-10%

Proximal Row Carpectomy

0% (no fusion)

Carpal height

4-Corner Fusion

Maintained

Proximal Row Carpectomy

Reduced 10-15mm

Surgery time

4-Corner Fusion

90-120 min

Proximal Row Carpectomy

45-60 min

Immobilisation and rehabilitation

4-Corner Fusion

Cast 8-12 weeks

Proximal Row Carpectomy

Splint 2 weeks; rehabilitation 4-6 weeks

Requirement

4-Corner Fusion

None specific

Proximal Row Carpectomy

Intact capitate cartilage

Feature	4-Corner Fusion	Proximal Row Carpectomy
Motion preserved	50% (30-40 degrees F/E)	50% (30-40 degrees F/E)
Grip strength	70-80% of normal	60-75% of normal
Pain relief	75-85% good to excellent	75-85% good to excellent
Nonunion risk	5-10%	0% (no fusion)
Carpal height	Maintained	Reduced 10-15mm
Surgery time	90-120 min	45-60 min
Immobilisation and rehabilitation	Cast 8-12 weeks	Splint 2 weeks; rehabilitation 4-6 weeks
Requirement	None specific	Intact capitate cartilage

Reading the comparative evidence. Multiple studies show equivalent outcomes at 5-10 years, and neither procedure has definitive superiority: surgeon and patient factors guide the choice, with capitate cartilage status deciding whether PRC is possible. Meta-analyses have shown no significant difference in pain relief or motion, a slight grip strength advantage for 4CC (10-15%), faster recovery and a lower complication rate with PRC (no nonunion), and equivalent long-term function. The largest of them, the 2024 meta-analysis of 3,174 wrists in the Evidence Base, differs on two points: PRC gave significantly greater extension and ulnar deviation, and grip strength did not differ significantly.

Algorithm

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Beyond Four-Corner Fusion — Limited Fusion Variants

The classic salvage fusion is the four-corner fusion (capitate-lunate-hamate-triquetrum after scaphoid excision), but several limited (fewer-bone) fusion variants target its two main problems — nonunion and dorsal hardware. Two-corner (capitolunate) fusion unites only the capitate to the lunate after excising the scaphoid (and often the triquetrum), giving fewer surfaces to fuse and allowing fixation with two headless compression screws so a dorsal plate is avoided; excising the triquetrum at the same time off-loads the ulnar carpus and reduces ulnocarpal impaction. Three-corner fusion (capitate-lunate-triquetrum, leaving out the hamate) is a further variant aimed at lowering nonunion while maintaining carpal height. All share the same prerequisite as four-corner fusion — a preserved radiolunate joint and intact lunate fossa — and the same goal of a pain-free wrist that keeps roughly half of its flexion-extension arc. The exam point: four-corner fusion is the prototype, but two- and three-corner variants exist specifically to cut the nonunion and hardware-irritation rates.

Indications. Pancarpal arthritis with radiolunate involvement, which is rare in SLAC.

Total wrist fusion is the gold standard for Stage IV. The radius is fused through the entire carpus to the third metacarpal with a dorsal precontoured plate, in 10-15 degrees of extension and neutral deviation. It eliminates wrist motion entirely but keeps forearm pronation-supination, and pain relief is reliable (85-95%).

What fusion leaves. Grip strength is 70-80% of normal and function for activities of daily living is surprisingly good. Nonunion occurs in 5-10%.

Total wrist arthroplasty (TWA) is an emerging option for low-demand patients. Modern implants show improved outcomes and preserve 30-40 degrees of motion, but TWA requires intact bone stock and stable soft tissues, has a higher complication rate than fusion, and can be revised to a fusion if it fails.

Selecting for arthroplasty. The selection criteria are low-demand bilateral wrist arthritis, rheumatoid arthritis, age over 60 years and realistic expectations. The contraindications are high-demand manual labour, young age (under 50), poor bone quality and previous wrist infection.

Set-up. Both salvage operations are done supine with the arm on a hand table, a tourniquet high on the arm and the forearm pronated.

The dorsal approach. A longitudinal dorsal incision of 8-10cm over Lister's tubercle. Elevate the extensor retinaculum as a radially based flap, enter the wrist between the third and fourth compartments and protect the PIN branches. PRC uses the same approach.

A modified approach. Mark a gently curved incision, raise flaps above the retinaculum, then open the third compartment and step-cut the retinaculum for later closure. Preserving the dorsal capsular ligaments during the capsulotomy protects what stability remains.

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4CC TechniquePRC Technique

Scaphoid excision. Open the dorsal capsule through a longitudinal T-shaped incision, then:

1. Expose and excise the entire scaphoid piecemeal, using rongeurs to remove all fragments
2. Protect the radial artery volarly
3. Inspect the radioscaphoid joint to confirm the stage

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Preparing the fusion. Denude the cartilage from the proximal capitate, distal lunate, proximal hamate and distal triquetrum with a curette, rongeur or burr, down to bleeding subchondral bone. Shape the surfaces for good apposition and pack autograft from the excised scaphoid into the interfaces.

Fixation. A dorsal circular (spider) plate is the most common choice, being low profile and rigid with fewer screws; individual screws or headless compression screws are the alternative.

Reduce before fixing. Correct the lunate out of DISI and into neutral before fixation, because fusing the lunate in extension leaves the capitate impinging on the dorsal radius and limits the extension arc permanently. A joystick wire in the lunate must enter the lunate body and stop short of its concave midcarpal articular surface, or it damages the very cartilage a salvage depends on.

Applying the plate. In order:

1. Reduce the carpal alignment (20-30 degrees flexion)
2. Stabilise temporarily with K-wires
3. Apply the dorsal circular plate
4. Verify the screw trajectories under fluoroscopy
5. Insert the screws (typically 4-6 in total)
6. Confirm there is no radiocarpal or CMC joint penetration

Closure. Repair the dorsal capsule, close the retinaculum over the plate and close the skin. Four-corner fusion is technically demanding but provides reliable outcomes.

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Removing the scaphoid. Incise the dorsal capsule, expose the scaphoid and detach the radial collateral ligament from the styloid. Excise the scaphoid piecemeal with rongeurs, protecting the radial artery.

Removing the lunate and triquetrum. Expose the centrally placed lunate, detach the SL and LT ligament remnants and remove it carefully, preserving the volar radiolunotriquetral ligament if possible. Then expose the triquetrum ulnarly, detach its ulnar attachments and excise it, preserving the TFCC and ulnocarpal ligaments.

The critical step: the cartilage. Inspect the capitate head cartilage and the lunate fossa of the radius directly. If either has severe degeneration (Grade IV), abort the PRC and convert to 4CC.

Finishing. Irrigate thoroughly, confirm a smooth capitate-radius articulation and test motion, which should achieve 40-50 degrees. No fixation is required; repair the capsule and close in layers. PRC is simpler and faster than 4CC, with comparable outcomes.

Complication rates are acceptable for both procedures when properly indicated. Early complications are those in the first 6 weeks; late complications come after.

Wound problems (2-5%, either operation). Delayed healing of the thin dorsal skin, superficial infection (redness, drainage), deep infection (rare, under 1%) and dehiscence from tension on closure. Prevent them with careful skin handling, prophylactic antibiotics and early suture removal.

Neurovascular injury (either operation). The radial artery can be injured during scaphoid excision (under 2%): repair it primarily if it is identified, and there are usually no long-term sequelae. PIN neuritis (5%) comes from retraction and traction on the dorsal sensory branch, and dorsal sensory branch injury and superficial radial nerve traction also occur; recognise them early. Nerve injuries are usually temporary, and PIN neuritis is treated with observation and NSAIDs.

Four-corner fusion, early. Three complications are specific to the fusion in the first weeks:

• Malreduction (5%) - improper carpal alignment before plating
• Screw penetration (5%) into the radiocarpal or CMC joints - intraoperative fluoroscopy prevents it; remove and redirect the screw
• Plate prominence (10%) - inadequate soft-tissue coverage

Four-corner fusion, late. Three late complications are specific to the fusion:

• Nonunion (5-10%) - the most common late complication and the principal failure of the operation. Risk factors are smoking, NSAIDs, diabetes, osteoporosis or poor bone quality, and infection. It may be asymptomatic or painful and is detected on sequential imaging rather than at a single visit; treat it with revision fusion, bone graft and rigid fixation.
• Plate irritation and tendinopathy (10-15%) - dorsal plate prominence irritates the extensor tendons, with painful tenosynovitis over the fourth compartment, usually manifesting 6-18 months postoperatively. After nonunion, dorsal plate impingement is the other recognised cause of persistent pain and loss of extension. Remove the plate after the fusion is solid (12+ months).
• Radiocarpal arthritis (10-20% at 10 years) - progressive degeneration at the radiolunate joint, more common in heavy manual labourers. It may be asymptomatic or cause recurrent pain; observe it if tolerable, total wrist fusion if severe.

Proximal row carpectomy. Five complications are specific to PRC:

• Excessive bleeding (2%, early) - from exposed cancellous surfaces
• Progressive capitate-radius arthritis (10-20% at 10 years) - more common with pre-existing capitate damage, presenting as recurrent pain and reduced motion. Activity modification; convert to total wrist fusion if that fails.
• Ulnar impaction syndrome (5-10%) - carpal height loss causes ulnocarpal abutment, ulnar-sided wrist pain and DRUJ symptoms. Ulnar shortening osteotomy or TFCC debridement.
• Capitate instability or subluxation (rare, under 5%) - usually from excessive soft-tissue and ligament stripping, the capitate migrating dorsally or volarly. Preserve the volar ligaments to prevent it; revise to total wrist fusion.
• Inadequate motion (10%) - less range than expected, often from prolonged immobilisation; an early motion protocol prevents it.

Either operation. Infection (under 2%), tendon adhesions (5-10%) and a need for revision surgery (5-10%). The functional shortfalls:

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Revision. The indications are a failed salvage with persistent pain (the most common), nonunion of a four-corner fusion, progressive arthritis after PRC, hardware irritation requiring removal, and inadequate function or motion.

• After a failed 4CC - revision fusion with bone graft, conversion to PRC if the radiolunate joint is intact, or total wrist fusion
• Nonunion of a 4CC - revision with iliac crest graft and rigid fixation
• After a failed PRC - total wrist fusion (it cannot be converted to 4CC)

Revision is less predictable than primary surgery, and total wrist fusion is the most reliable option; patient counselling is critical for realistic expectations.

Prevention. Before surgery, smoking cessation 6 weeks beforehand, optimised comorbidities (diabetes control), a CT to assess cartilage and plan the procedure, and patient selection (avoid salvage in end-stage arthritis). In theatre, meticulous soft-tissue handling, fluoroscopic verification of hardware placement, proper carpal alignment before fixation and preservation of the volar ligaments in PRC. Afterwards, an appropriate immobilisation duration, early protected motion when allowed, no NSAIDs until a four-corner fusion is solid, and aggressive hand therapy for motion recovery.

After four-corner fusion. A short-arm cast for 8-12 weeks, with radiographs at 6 weeks to assess fusion; remove the cast when the fusion is solid, then start therapy for motion and strengthening. Grip strengthening waits until the fusion is radiographically united, usually around three months.

After proximal row carpectomy. A short-arm splint for 2 weeks, then suture removal and gentle motion, progressing to strengthening at 4-6 weeks and full activity at 3 months.

Outcomes over time. Beyond the pain, motion and grip figures in the Management comparison table:

Patient factors. Younger patients have better functional outcomes and manual labourers lower satisfaction. Realistic expectations correlate with satisfaction, and compliance with early motion is crucial for motion recovery.

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Global Epidemiology

SLAC is the single most common pattern of degenerative wrist arthritis worldwide. In Watson and Ballet's defining radiographic review of 4,000 wrists, the SLAC pattern accounted for 57% of all degenerative wrist arthritis (Watson & Ballet, J Hand Surg Am 1984; PMID 6725894), confirmed in Watson and Ryu's later series at 55%, with triscaphe arthritis 26% and combined disease 14% (PMID 3955970). Presentation is typically in the fifth to sixth decade, with a male predominance reflecting the manual-labour occupations (carpentry, construction, mining, agriculture) most affected by chronic scapholunate injury. The latency from the initiating scapholunate ligament injury to symptomatic arthritis is long (commonly 5-15 years), which has medicolegal relevance for occupational-injury causation in any jurisdiction.

Guidelines and Society Guidance (Side by Side)

There is no high-level dedicated society guideline for SLAC salvage; practice is guided by systematic reviews and surgeon consensus. The table summarises how the major bodies and the evidence base frame the key decisions.

Registry and Pooled Evidence

National joint registries (NJR, AOANJRR, AJRR) capture wrist arthroplasty but not the carpal salvage procedures (4CC, PRC, styloidectomy) that dominate SLAC management, so the evidence base is pooled cohort data rather than registry data:

• Largest pooled series (2024): 61 studies, 3,174 wrists - PRC associated with better motion and a lower conversion-to-fusion rate (5.2% vs 11%); grip equivalent; 4CF nonunion 8.9% (PMID 38416092).
• Systematic review (2015): 7 studies, 242 wrists - 4CC gave greater radial deviation and grip (74% vs 67%), PRC gave a wider flexion-extension arc and lower overall complication rate (14% vs 29%) (Saltzman et al., PMID 25294736).
• Long-term PRC cohort: 18% failure at minimum 10 years, concentrated entirely in patients aged 35 or younger (DiDonna et al., PMID 15523004).

Global Practice Variation

• Procedure preference: PRC predominates where simplicity, faster rehabilitation and implant-free salvage are prioritised; 4-corner fusion is favoured by surgeons prioritising carpal-height maintenance and in higher-demand patients, and is mandated when the capitate head cartilage is degenerate.
• Implant choice for 4CC: dorsal circular ("spider") plate versus headless compression screws versus K-wires varies by region and cost setting; circular-plate fixation carries a recognised dorsal-impingement/nonunion profile (Shindle et al.).
• Resource-limited settings: PRC and styloidectomy are attractive where implants, fluoroscopy or hand-therapy access are limited, as they need no internal fixation.
• Surgical-site antibiotic prophylaxis: a single preoperative dose of an intravenous first-generation cephalosporin (e.g. cefazolin) within 60 minutes of incision is the near-universal standard for clean hand surgery, with a glycopeptide alternative for beta-lactam allergy or MRSA risk.

Examination Relevance

SLAC wrist is high-yield across all major boards, particularly in:

• Hand/upper-limb viva (staging, treatment algorithm, surgical technique)
• Clinical stations (chronic wrist pain presentation)
• Radiology viva (DISI deformity, Terry Thomas sign, Watson staging)

Be ready to justify the biomechanical basis for radiolunate preservation and to argue the 4CC-versus-PRC decision from the contemporary evidence above.

1. Watson HK, Ballet FL. The SLAC wrist: scapholunate advanced collapse pattern of degenerative arthritis. J Hand Surg Am. 1984;9(3):358-365.

2. Watson HK, Ryu J. Evolution of arthritis of the wrist. Clin Orthop Relat Res. 1986;(202):57-67.

3. 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.

4. 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.

5. Krakauer JD, Bishop AT, Cooney WP. Surgical treatment of scapholunate advanced collapse. J Hand Surg Am. 1994;19(5):751-759.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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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