Ulnocarpal Abutment | TFCC Degenerative Tears | Positive Ulnar Variance
Palmer Classification (Degenerative)
Critical Must-Knows
- Positive Ulnar Variance: Ulna over 2mm longer than radius = increased ulnocarpal loading
- TFCC Central Tear: Palmer 2C most common - degenerative perforation from chronic impaction
- Ulnar Shortening Osteotomy (USO): Gold standard - shortens ulna 2-4mm to unload ulnocarpal joint
- Wafer Procedure: Arthroscopic distal ulna resection - for positive variance less than 2-3mm
- Palmer 2E: End-stage with arthritis - requires salvage (Darrach, Sauvé-Kapandji, ulnar head replacement)
Clinical Pearls
- "Positive ulnar variance = ulna longer = increased ulnocarpal impaction
- "Each millimetre of positive variance markedly increases ulnocarpal load; shortening reverses this
- "Wafer only for variance under about 4mm with stable DRUJ - USO for greater variance
- "DRUJ stability must be preserved with any ulnar procedure
Critical Ulnar Impaction Exam Points
Ulnar Variance is Key
Positive ulnar variance is the fundamental pathology. Ulna over 2mm longer than radius increases ulnocarpal loading. Measure on PA wrist X-ray with forearm in neutral rotation, shoulder at 90 degrees abduction, elbow at 90 degrees flexion.
Palmer 2C Most Common
Degenerative TFCC tear from chronic impaction. Palmer 2C (TFCC perforation + chondromalacia) requires ulnar shortening. Do not confuse with Palmer 1B traumatic peripheral tears (which are repairable).
USO vs Wafer Decision
Ulnar shortening for variance over 2-3mm. Wafer procedure (arthroscopic distal ulna resection) only for mild positive variance under 2-3mm. USO is more powerful but requires 3-4 months healing.
Preserve DRUJ Stability
DRUJ must remain stable. Excessive ulnar shortening (over 4mm) or Darrach in young patient causes instability. Check DRUJ stability intraoperatively with forearm rotation.
Quick Decision Guide
| Palmer Stage | Variance | Treatment | Key Pearl |
|---|---|---|---|
| 2A-2B | Mild positive | Conservative 3-6 months, NSAIDs, splint | Many respond to activity modification |
| 2C | 2-3mm positive | USO or wafer procedure | Wafer faster recovery but less powerful |
| 2C-2D | Over 3mm positive | Ulnar shortening osteotomy | Gold standard, 85-90% success |
| 2E | Any variance + arthritis | Darrach, Sauvé-Kapandji, or ulnar head replacement | Salvage procedures for end-stage |
ABCDEPalmer Classification Class 2 (Degenerative)
| A | Attritional wear TFCC thinning, no perforation |
| B | B = Bone changes Lunate or ulnar head chondromalacia |
| C | Central perforation TFCC central tear + chondromalacia |
| D | D = Disrupted LT ligament 2C + lunotriquetral tear |
| E | End-stage arthritis Ulnocarpal arthrosis |
| A | Attritional wear TFCC thinning, no perforation | D | D = Disrupted LT ligament 2C + lunotriquetral tear |
| B | B = Bone changes Lunate or ulnar head chondromalacia | E | End-stage arthritis Ulnocarpal arthrosis |
| C | Central perforation TFCC central tear + chondromalacia |
Hook:ABCDE = alphabetical progression from early wear to end-stage arthritis in ulnar impaction!
PUDIClinical Features of Ulnar Impaction
| P | Pain (ulnar-sided) Dorsal ulnar wrist pain |
| U | Ulnar deviation worsens Pain with ulnar deviation and grip |
| D | DRUJ tenderness Tender over ulnocarpal joint |
| I | Impaction test positive Axial load + ulnar deviation reproduces pain |
| P | Pain (ulnar-sided) Dorsal ulnar wrist pain | D | DRUJ tenderness Tender over ulnocarpal joint |
| U | Ulnar deviation worsens Pain with ulnar deviation and grip | I | Impaction test positive Axial load + ulnar deviation reproduces pain |
Hook:PUDI = Pain with Ulnar Deviation and Impaction - the classic presentation!
WAFER-DSurgical Options for UIS
| W | Wafer procedure Arthroscopic distal ulna resection 2-3mm |
| A | Arthroscopic debridement TFCC debridement alone (Palmer 2A) |
| F | Formal ulnar shortening USO - osteotomy and plate fixation |
| E | End-stage options Darrach or Sauvé-Kapandji |
| R | Replacement Ulnar head arthroplasty |
| D | Distal ulna hemiresection Bowers procedure (rare) |
| W | Wafer procedure Arthroscopic distal ulna resection 2-3mm | F | Formal ulnar shortening USO - osteotomy and plate fixation | R | Replacement Ulnar head arthroplasty |
| A | Arthroscopic debridement TFCC debridement alone (Palmer 2A) | E | End-stage options Darrach or Sauvé-Kapandji | D | Distal ulna hemiresection Bowers procedure (rare) |
Hook:WAFER-D = the spectrum of surgical treatments from arthroscopic to salvage!
Overview and Epidemiology
Why UIS Matters
Ulnar impaction syndrome is a common cause of ulnar-sided wrist pain. Understanding the relationship between ulnar variance, TFCC degenerative tears, and treatment options is essential for hand surgery practice.
Ulnar Impaction Syndrome is a degenerative condition resulting from excessive load transmission between the distal ulna and ulnar carpus (lunate and triquetrum).
Demographics
- Age: 40-60 years (degenerative process)
- Gender: Equal distribution
- Occupation: Manual laborers, overhead workers
- Bilateral: Common (50% have bilateral variance)
Chronic overload leads to progressive degeneration.
Risk Factors
- Positive ulnar variance (constitutional or acquired)
- Radial shortening after distal radius fracture malunion
- Radial head excision (shifts load ulnarly)
- Essex-Lopresti injury (proximal radius migration)
- Repetitive pronation-supination activities
Any process increasing ulnar variance predisposes to UIS.
Pathophysiology and Biomechanics
Ulnocarpal Loading Mechanics
In a neutral wrist with neutral ulnar variance, approximately 60% of axial load transmits through the radius and 40% through the ulna (TFCC). With positive ulnar variance of 2.5mm, ulnocarpal load increases to over 60%. This excessive loading causes TFCC degeneration and chondromalacia.
Biomechanical Cascade:
- Positive ulnar variance (constitutional or acquired)
- Increased ulnocarpal loading (especially lunate-triquetrum)
- TFCC central wear and perforation (Palmer 2C)
- Lunate and ulnar head chondromalacia (Palmer 2B-2C)
- Lunotriquetral ligament tear (Palmer 2D)
- Ulnocarpal arthritis (Palmer 2E - end-stage)
Ulnar Variance Measurement:
- PA wrist X-ray
- Forearm neutral rotation (key - pronation increases variance)
- Shoulder abducted 90 degrees, elbow flexed 90 degrees
- Perpendicular line from ulnar articular surface to radial articular surface
- Positive variance: ulna extends distal to radius
- Negative variance: ulna proximal to radius
Why Positive Variance Matters
Every 1mm of positive ulnar variance increases ulnocarpal load. Studies show 2.5mm positive variance increases TFCC load by over 40%. This explains why shortening 2-4mm dramatically relieves symptoms.
Biomechanical correction is the goal of surgery.
Dynamic Variance
Forearm rotation affects variance. Pronation increases positive variance by 1-2mm. Supination decreases it. Always measure in neutral rotation for accuracy. Grip force also increases dynamic loading.
Symptoms worse with pronation and grip.
Classification Systems
Palmer Classification Class 2 (Degenerative TFCC Tears)
Degenerative tears from chronic ulnar impaction, distinct from Class 1 traumatic tears.
| Type | TFCC Status | Associated Pathology | Treatment |
|---|---|---|---|
| 2A | Attritional thinning | No perforation, minimal chondromalacia | Conservative, debridement |
| 2B | Thinning + chondromalacia | Lunate or ulnar head cartilage damage | USO or wafer |
| 2C | Central perforation | TFCC tear + chondromalacia | USO (gold standard) |
| 2D | 2C + LT tear | Lunotriquetral ligament disruption | USO + LT repair |
| 2E | 2D + arthritis | Ulnocarpal arthrosis | Darrach, SK, or replacement |
Palmer 2C is most common presentation requiring surgical intervention.
Classification guides treatment algorithm based on pathology stage.
Clinical Assessment
History
- Pain: Dorsal-ulnar wrist pain
- Worse with: Ulnar deviation, grip, pronation
- Better with: Rest, avoiding provocative activities
- Clicking: Occasional with forearm rotation
- Weakness: Grip strength reduced
- Occupation: Manual work, repetitive pronation
Insidious onset over months to years is typical.
Examination
- Inspection: Minimal swelling usually
- Palpation: Tender over ulnocarpal joint (just distal to ulnar styloid)
- ROM: Normal or slightly reduced
- Provocative tests: Ulnar impaction test, TFCC load test
- Strength: Grip weakness (pain-limited)
- DRUJ: Assess stability (piano key sign)
Ulnar-sided tenderness is hallmark finding.
Provocative Tests
| Test | Technique | Positive Finding | Sensitivity |
|---|---|---|---|
| Ulnar impaction test | Axial load + ulnar deviation + pronation | Reproduces ulnar pain | 70-80% |
| TFCC load test | Forearm pronation-supination with ulnar deviation | Pain over TFCC | 60-70% |
| Press test | Push up from chair using hands | Ulnar-sided pain | 50-60% |
Differential Diagnosis of Ulnar-Sided Wrist Pain
Distinguishing UIS from Mimics
| Condition | Key feature | Variance | Discriminator |
|---|---|---|---|
| Ulnar impaction syndrome | Load-related dorsal-ulnar pain, worse pronation/grip | Positive (over 2mm) | Lunate/ulnar-head sclerosis and cysts; central (2C) TFCC tear |
| TFCC peripheral (Palmer 1B) tear | Trauma history, DRUJ instability | Often neutral/negative | Foveal tenderness, positive fovea sign, repairable peripheral tear |
| Lunotriquetral ligament tear | Ulnar pain, painful clunk | Variable | Positive ballottement/shear test, LT widening |
| ECU tendinopathy/subluxation | Pain along ECU groove | Normal | Snapping with supination, tenderness over tendon not joint |
| Pisotriquetral arthritis | Volar-ulnar pain | Normal | Tender pisiform, pain on pisiform grind |
| DRUJ arthritis | Pain on forearm rotation | Any | Positive piano-key, joint-space loss on radiograph |
Differential Diagnosis Pearl
The decisive discriminator for UIS is positive ulnar variance plus subchondral sclerosis/cysts in the lunate and ulnar head. A traumatic peripheral (1B) tear with DRUJ instability is repaired and is NOT treated by shortening alone — confirm variance and TFCC tear pattern before committing to USO.
Investigations
Investigation Protocol
PA and lateral wrist X-rays. Measure ulnar variance on PA view (neutral rotation critical). Look for: lunate or ulnar head sclerosis, cystic changes, ulnocarpal joint narrowing. Clenched-fist view may increase variance and demonstrate pathology.
T1, T2, and proton density sequences. Detects TFCC central tear, lunate chondromalacia, bone marrow edema, LT ligament status. MR arthrogram increases sensitivity for TFCC tears but usually not necessary.
Diagnostic and therapeutic gold standard. Directly visualizes TFCC tear, chondromalacia extent, and allows treatment (debridement, wafer). Radiocarpal and midcarpal portals assess all pathology.
Key Radiographic Findings:
- Positive ulnar variance (over 2mm)
- Lunate sclerosis (increased density on PA view)
- Ulnar head cysts (subchondral cystic changes)
- Ulnocarpal joint narrowing (end-stage Palmer 2E)
MRI Findings:
- TFCC central perforation (high signal on T2)
- Lunate bone marrow edema (low T1, high T2 signal)
- Chondromalacia (cartilage thinning or defects)
- LT ligament tear (discontinuity or high signal)
Management Algorithm
Conservative Management
Indications: Palmer 2A, mild symptoms, patient prefers non-operative trial
Conservative Treatment Steps
Avoid provocative activities. Reduce repetitive pronation, grip, and ulnar deviation. Ergonomic workplace modifications. Trial 3-6 months.
Forearm-based splint. Immobilize wrist in neutral position. Wear during activities and at night. May decrease symptoms 30-50%.
NSAIDs for inflammation. Corticosteroid injection into ulnocarpal joint may provide temporary relief (weeks to months). Limited injections (maximum 2-3).
Outcomes: 30-40% improve with conservative management. Palmer 2C and beyond usually require surgery.
Conservative treatment is reasonable initial approach for early disease.
Surgical Technique
Ulnar Shortening Osteotomy - Step by Step
Operative Steps
Supine, arm table, tourniquet. Direct lateral or dorsal approach to mid-distal ulna. 8-10cm incision. Identify and protect dorsal sensory branch of ulnar nerve.
Elevate ECU and FCU from ulna. Subperiosteal dissection. Expose 6-8cm of ulnar shaft. Protect interosseous membrane.
Mark osteotomy site (mid-diaphyseal or metaphyseal). Measure and mark bone to remove (2-4mm based on pre-op plan). Transverse or oblique osteotomy with saw. Remove segment. Compress osteotomy.
Apply 6-8 hole compression plate. 3-4 screws each side of osteotomy. Ensure rigid fixation with interfragmentary compression. Locking or non-locking plate acceptable.
Release tourniquet. Check DRUJ stability with forearm rotation. Should be smooth and stable. Close in layers, splint in neutral.
Technical Pearls:
- Pre-op planning: measure exact variance and plan amount
- Mark bone segment before cutting to ensure accuracy
- Maximum compression at osteotomy site (decreases nonunion)
- Low-profile plate to minimize prominence
- Check DRUJ - if unstable, shortening is excessive
Pitfalls:
- Inadequate shortening - fails to relieve symptoms
- Excessive shortening (over 4mm) - DRUJ instability
- Nerve injury - protect dorsal sensory branch
- Nonunion - ensure compression and rigid fixation
USO requires meticulous technique for optimal results.
Complications
Complications by Treatment
| Treatment | Early Complications | Late Complications | Management |
|---|---|---|---|
| USO | Infection, nerve injury (dorsal sensory) | Nonunion (5-10%), hardware prominence | ORIF with bone graft, hardware removal |
| Wafer | Portal site infection, synovitis | Recurrent impaction (if inadequate resection) | Revision to USO |
| Darrach | Hematoma, nerve injury | DRUJ instability, convergence, ulnar stump pain | Revision to SK or ulnar head replacement |
Common Complications
Hardware irritation after USO (most common):
- The dominant complication in pooled series; plate removal needed in roughly 1 in 8 cases
- Prevention: low-profile or buried implants
- Manage with plate removal once union is confirmed and remodelled
Nonunion after USO (uncommon, about 3-6%):
- Risk factors: smoking, diabetes, inadequate fixation
- Management: ORIF with bone graft, compression plating
- Prevention: rigid fixation, interfragmentary compression, smoking cessation
DRUJ Instability:
- Caused by excessive ulnar shortening (over 4mm)
- Worse in supination (dorsal subluxation)
- Management: splinting if mild; SK procedure if severe
Persistent Pain after USO:
- Hardware prominence (most common) - remove plate after union
- Inadequate shortening - consider revision
- Unrecognized pathology (LT tear, arthritis) - MRI, arthroscopy
Postoperative Care
Postoperative Protocol
Sugar-tong splint or cast. Protect osteotomy. Finger and shoulder ROM. No forearm rotation. Wound check 10-14 days.
Transition to removable splint. Begin gentle wrist ROM at week 3-4. No strengthening. X-ray at 6 weeks to assess union.
Progressive strengthening if union progressing. Therapy for ROM and grip. Full activities by 3-4 months if healed.
Soft dressing, removable splint. Finger ROM immediately. Begin wrist ROM at 1-2 weeks. Much faster than USO.
Progressive strengthening. Return to normal activities by 6-8 weeks. No hardware to heal.
Return to Work:
- Desk work: 2-3 weeks (wafer), 4-6 weeks (USO)
- Light manual: 6-8 weeks (wafer), 10-12 weeks (USO)
- Heavy labor: 12 weeks (wafer), 16 weeks (USO)
Outcomes and Prognosis
Outcomes by Treatment
| Treatment | Pain Relief | Function Preservation | Durability |
|---|---|---|---|
| Conservative | 30-40% improvement | Maintained | Temporary, often progresses |
| USO | 85-90% good-excellent | Grip 85-90% normal | Durable 10+ years |
| Wafer | 70-80% good | Grip 80-85% normal | Good 5-7 years |
| Darrach | 80-90% pain relief | Instability issues | Variable |
Prognostic Factors:
| Factor | Better Outcome | Worse Outcome |
|---|---|---|
| Palmer stage | 2B-2C | 2E (arthritis) |
| Variance amount | 2-4mm (correctable) | Over 6mm |
| Age | Under 60 | Over 65 |
| Compliance | Good therapy adherence | Non-compliant |
Long-term Natural History (Untreated):
- Progression from Palmer 2A to 2E over 5-15 years
- Most symptomatic patients eventually require surgery
- Conservative management temporizing only
Controversies and Areas of Uncertainty
Wafer vs USO threshold
The variance cut-off for choosing arthroscopic wafer over USO is not firmly evidence-based. Feldon's original description contraindicates wafer above 4mm positive variance, but trials and meta-analysis pooling subtle-variance patients (under 4mm) show equivalent patient-rated outcomes — with the wafer offering faster recovery and fewer complications. Most surgeons reserve wafer for stable-DRUJ, low-variance disease.
Osteotomy configuration
Transverse, oblique and step-cut osteotomies are all used. Oblique/step-cut increase the union surface and allow interfragmentary compression, but high-quality comparative data are limited. The dominant complication is implant irritation requiring removal, not nonunion, which has reframed the debate toward low-profile fixation.
Does shortening help an unstable DRUJ?
Shortening re-tensions the TFCC and can stabilise the DRUJ — but cadaveric data show this only works if the radioulnar ligament remains attached to the fovea. A complete foveal avulsion is not corrected by shortening and requires separate foveal repair.
Salvage choice in Palmer 2E
For end-stage ulnocarpal/DRUJ arthritis there is no consensus winner. Darrach is simple but risks instability and stump convergence; Sauvé-Kapandji preserves an ulnar buttress; ulnar head arthroplasty preserves stability and rotation but has cost and long-term wear uncertainty. Selection is driven by age, demand and resources rather than robust comparative trials.
Evidence Base
- 31 wrists (29 patients) with idiopathic UIS treated by USO
- Mean ulnar variance reduced from +4.6mm to -0.7mm
- Modified Gartland-Werley score improved from 69.5 to 92.5; 29 of 31 good or excellent
- Dorsal DRUJ subluxation reduced and carpal cysts resolved after shortening
- 13 wafer resections in 12 patients; distal 2-4mm of ulnar head removed, styloid and ligaments preserved
- All good-to-excellent at minimum 1-year follow-up
- Explicitly contraindicated if positive ulnar variance exceeds 4mm
- Contraindicated with DRUJ instability or DRUJ degenerative arthritis
- 60 patients with idiopathic UIS randomised to arthroscopic wafer (AWP) or USO
- No significant difference in DASH, Modified Mayo Wrist Score, VAS, ROM or grip at 2 years
- All USO patients united by 12 weeks
- AWP had earlier return to work, fewer complications and fewer secondary procedures
- 42 patients aged 45+ with Palmer 2C/2D and under 4mm positive variance, stable DRUJ
- Equivalent clinical outcomes at 6, 12 and 24 months
- AWP superior at 3 months for grip, Mayo Wrist Score and DASH
- Complication rate 34.8% for USO (implant irritation, DRUJ arthritis, refracture) vs 10.5% for AWP
- 7 studies, 133 USO and 118 AWP patients pooled
- No difference in Mayo Wrist Score, DASH, VAS, revision rate or time to return to work
- Grip strength favoured AWP (SMD -0.73)
- Correction of positive variance favoured USO; overall evidence quality moderate
- Cadaveric study of DRUJ stiffness with progressive ulnar shortening
- 6mm shortening increased DRUJ stiffness 26-44% across rotation positions
- Stabilising effect depends on radioulnar ligament remaining attached to the fovea
- Complete foveal RUL avulsion abolishes the stabilising benefit of shortening
- 12 cohorts, 185 patients undergoing isolated USO
- Overall complication rate 33% (95% CI 16-51%)
- Implant irritation most common (22%); removal required in 13%
- Nonunion uncommon at 3%; buried/low-profile implants may reduce irritation
- Original classification dividing TFCC lesions into Class 1 (traumatic) and Class 2 (degenerative)
- Class 2 degenerative tears (2A-2E) reflect progressive ulnocarpal impaction
- 2C (central perforation + chondromalacia) is the common surgical lesion
- Framework still underpins treatment algorithms for ulnar-sided wrist pain
Exam Viva Scenarios
Use these scenarios to practise clinical reasoning and management decisions
Scenario 1: Classic UIS Presentation
"A 52-year-old carpenter presents with 12 months of ulnar-sided wrist pain, worse with gripping and pronation. X-rays show 3mm positive ulnar variance with mild lunate sclerosis. MRI shows Palmer 2C TFCC central tear and lunate chondromalacia. Conservative management with splint has failed over 3 months."
Scenario 2: Choosing Between USO and Wafer
"A 45-year-old woman has ulnar-sided wrist pain with 1.5mm positive ulnar variance. MRI shows Palmer 2B-2C tear. She is active and wants fastest return to work. What do you recommend?"
Scenario 3: Failed USO Management
"A patient returns 6 months after USO with persistent ulnar pain. X-rays show the osteotomy has healed, and variance is now neutral. What is your approach?"
MCQ Practice Points
Ulnar Variance Threshold
Q: What amount of positive ulnar variance typically causes ulnar impaction syndrome? A: Over 2mm positive ulnar variance significantly increases ulnocarpal loading and predisposes to UIS. Normal population: 60-70% neutral variance, 10-15% positive variance (usually under 2mm).
Palmer 2C Definition
Q: What defines Palmer 2C TFCC tear? A: Central TFCC perforation (degenerative tear) PLUS chondromalacia of lunate or ulnar head. Most common stage requiring surgical intervention.
USO vs Wafer Indication
Q: What is the variance threshold for choosing USO over wafer procedure? A: Over 2-3mm positive variance warrants USO. Wafer procedure can only address 2-3mm maximum shortening; greater variance requires formal ulnar shortening osteotomy.
USO Success Rate
Q: What is the success rate of ulnar shortening osteotomy for UIS? A: 85-90% good to excellent outcomes for pain relief and functional improvement in cohort series. The commonest complication is hardware irritation (plate removal in roughly 13%); nonunion is uncommon (about 3-6%).
Biomechanics of Load Reduction
Q: How does ulnar shortening decrease ulnocarpal loading? A: Positive ulnar variance shifts axial load onto the ulnocarpal joint and TFCC; each millimetre of positive variance increases ulnocarpal load substantially. Shortening to neutral (or slight negative) redistributes load back through the radius and re-tensions the TFCC, which can also improve DRUJ stability when the foveal attachment is intact.
Salvage for Palmer 2E
Q: What are salvage options for Palmer 2E (ulnocarpal arthritis)? A: Darrach procedure (distal ulna excision), Sauvé-Kapandji (DRUJ fusion with proximal pseudarthrosis), or ulnar head arthroplasty. Selection based on age and activity level.
Guidelines, Registries & Global Practice
Global epidemiology: Ulnar impaction syndrome is one of the commonest causes of chronic ulnar-sided wrist pain worldwide. Positive ulnar variance is present in roughly 10-15% of the general population, but only a subset becomes symptomatic. Manual workers (construction, agriculture, mining), gymnasts and athletes loading the wrist in pronation are over-represented. There is no dedicated international registry; high-quality evidence comes from cohort series and a small number of randomised trials and meta-analyses.
Guideline and society positions (side by side):
| Body / source | Position on UIS |
|---|---|
| AAOS (US) / ASSH | No disease-specific guideline; consensus favours staged care — conservative trial, then USO for significant variance, arthroscopic wafer for mild variance with stable DRUJ |
| BSSH / BOA (UK) | Emphasise MRI/arthroscopy confirmation and Palmer staging; USO regarded as the workhorse for positive-variance impaction |
| EFORT / European consensus | Recommend correcting variance to neutral or slight negative; preserve DRUJ stability and foveal TFCC attachment |
| AO Foundation | Provides technical standards for diaphyseal USO — rigid compression plating, oblique or step-cut osteotomy to reduce nonunion |
There is broad international agreement on the principle (unload the ulnocarpal joint by correcting positive variance) and the staged algorithm; the main variation is the threshold and enthusiasm for arthroscopic wafer versus formal USO.
Registry and outcome data: No arthroplasty-style registry tracks UIS. The best pooled evidence is the meta-analysis of USO versus arthroscopic wafer (no difference in patient-rated outcomes; grip favours wafer, variance correction favours USO) and a systematic review of isolated USO reporting a 33% overall complication rate dominated by implant irritation (removal in ~13%) with nonunion only ~3%.
High- vs limited-resource practice variation:
- Well-resourced settings: routine MRI and wrist arthroscopy; arthroscopic wafer and ulnar head arthroplasty available; low-profile/locking USO plates standard.
- Limited-resource settings: diagnosis is often clinical plus plain radiographs (ulnar variance, lunate sclerosis, cysts); USO with conventional compression plating remains the mainstay because it needs no arthroscopy tower; salvage defaults to Darrach or Sauvé-Kapandji rather than implant arthroplasty.
Consent and follow-up principles (globally applicable): Counsel for nonunion (uncommon but increased by smoking and diabetes), hardware prominence frequently requiring later removal, DRUJ stiffness, dorsal sensory ulnar nerve injury and a 3-4 month recovery. Document exact pre-operative variance and plan the precise amount of shortening; follow with serial radiographs to confirm union. Smoking cessation is the single most useful modifiable factor for bone healing.
ULNAR IMPACTION SYNDROME
Clinical summary
Key Pathophysiology
- •Positive ulnar variance = ulna longer than radius by over 2mm
- •Excessive ulnocarpal loading causes TFCC degeneration
- •Each 1mm positive variance increases TFCC load significantly
- •Biomechanical problem requiring mechanical solution
Palmer Classification (Class 2)
- •2A: TFCC wear, no perforation
- •2B: Wear + chondromalacia
- •2C: Central perforation + chondromalacia (most common surgical)
- •2D: 2C + LT tear
- •2E: 2D + ulnocarpal arthritis (end-stage)
Clinical Diagnosis
- •Ulnar-sided wrist pain, worse with pronation and grip
- •Ulnar impaction test: axial load + ulnar deviation reproduces pain
- •X-ray: measure ulnar variance (PA view, neutral rotation)
- •MRI: TFCC tear, chondromalacia, bone marrow edema
Treatment Algorithm
- •Conservative: activity modification, splint, injection (30-40% success)
- •Wafer: arthroscopic resection for variance under 2-3mm (70-80% success)
- •USO: gold standard for variance over 2-3mm (85-90% success)
- •Salvage: Darrach, SK, or ulnar head replacement for 2E
USO Technique
- •Shorten ulna 2-4mm to neutral or 1mm negative variance
- •Rigid plate fixation with compression (prevent nonunion)
- •Check DRUJ stability intraoperatively
- •Recovery 3-4 months, nonunion risk 5-10%