REVISION TOTAL KNEE ARTHROPLASTY
AORI Classification | Constraint Selection | Bone Loss Management | Outcomes
AORI BONE DEFECT CLASSIFICATION
Critical Must-Knows
- Aseptic loosening is the most common indication for revision TKA (50% of cases)
- AORI classification guides bone loss management: Type 1 (intact), Type 2 (damaged), Type 3 (deficient)
- Constraint progression: PS to CCK to hinged based on bone loss and soft tissue competence
- Infection must be ruled out in ALL cases before revision - aspirate, inflammatory markers, culture
- Two-stage revision is gold standard for chronic PJI with antibiotic spacer interval
Examiner's Pearls
- "AORI Type 3 requires structural support (metaphyseal sleeve, cone, or bulk allograft)
- "Constrained condylar knee (CCK) for MCL/LCL insufficiency but intact bone stock
- "Rotating hinge for massive bone loss or global instability
- "Modular stems for stability and load sharing, cemented distally in diaphysis
Clinical Imaging
Imaging Gallery
Critical Revision TKA Exam Points
AORI Classification Drives Treatment
Type 1 = Intact metaphysis (standard components). Type 2A/B = Damaged (augments, cement). Type 3 = Deficient (structural graft/sleeve/cone). Know which reconstruction for which defect.
Rule Out Infection FIRST
Aspirate ALL knees before revision. ESR, CRP, synovial WBC and differential. Alpha-defensin if clinical suspicion. Never proceed without excluding PJI.
Constraint Selection Algorithm
PS to CCK to hinged based on:
- Bone loss (AORI grade)
- Collateral ligament integrity
- Flexion-extension gap balance
- Extensor mechanism function
Two-Stage for Infection
Stage 1: Debridement, explant, antibiotic spacer. 6-8 weeks IV antibiotics then 2-week holiday. Stage 2: Aspirate negative, then reimplant. 90% infection control rate.
Quick Decision Guide - Revision TKA Approach
| Indication | AORI Grade | Constraint Level | Key Technique |
|---|---|---|---|
| Aseptic loosening, minimal bone loss | Type 1 (intact) | PS or CCK | Standard components, cement fixation |
| Instability, moderate bone loss | Type 2A/B (damaged) | CCK with augments | Metal augments or cement-fill, stems for stability |
| Massive bone loss, global instability | Type 3 (deficient) | Rotating hinge | Metaphyseal sleeve/cone, long cemented stems |
| Chronic PJI confirmed | Variable (assess at stage 2) | CCK or hinge | Two-stage with spacer, 6-8 weeks antibiotics |
FAIL-TIndications for Revision TKA
Memory Hook:The knee has FAILED T(otally) - these are the five main reasons for revision TKA!
I-D-D-DAORI Bone Defect Classification
Memory Hook:I'm D-D-D (I'm devastated) - the progressive severity of bone loss in revision TKA!
CLAMPConstraint Selection Principles
Memory Hook:CLAMP down on instability - use increasing constraint as needed to stabilize the revision knee!
SPACETwo-Stage Revision Protocol
Memory Hook:Create SPACE for the knee to heal - the two-stage revision protocol for chronic PJI!
Overview and Epidemiology
Why Revision TKA Matters
With over 100,000 primary TKAs performed annually in Australia, the burden of revision surgery is substantial. Revision TKA is technically demanding, associated with higher complication rates (20-30% vs 5-10% for primary), longer operative times, and inferior functional outcomes. Understanding indications, bone loss classification (AORI), and constraint selection is critical for Orthopaedic exam success and clinical practice.
Demographics
- Age: Mean 65-70 years at revision (younger than primary)
- Gender: F greater than M (2:1) - same as primary TKA
- Time to revision: Mean 7-10 years post-primary
- Re-revision risk: 15-20% within 5 years
Burden and Outcomes
- Complication rate: 20-30% (vs 5-10% primary)
- Operative time: 2-3 hours (vs 1-1.5 hours primary)
- Functional scores: 70-80% of primary TKA outcomes
- Survivorship: 85-90% at 10 years (vs 95% primary)
Anatomy and Biomechanics
Knee Anatomy Relevant to Revision TKA
Understanding knee anatomy is critical for revision TKA. The metaphysis (wide flared bone at joint) provides primary component support but is often compromised in revision. The diaphysis (narrow shaft) is where stems gain fixation. The MCL and LCL (collateral ligaments) provide varus-valgus stability - their integrity determines constraint needs. The popliteal artery runs posteriorly and is at risk during exposure in revision cases.
Metaphysis vs Diaphysis
- Metaphysis: Wide flared bone at joint - primary component support
- Compromised in revision: Bone loss (AORI classification) affects this region
- Diaphysis: Narrow shaft below metaphysis - stem fixation site
- Cemented stems: 14-16cm fixation length in diaphysis for stability
Collateral Ligaments
- MCL (medial collateral): Prevents valgus instability
- LCL (lateral collateral): Prevents varus instability
- Integrity assessment: Intraoperative stress testing determines constraint
- CCK vs hinge: One collateral deficient = CCK, both = hinge
Popliteal Artery at Risk
The popliteal artery runs posterior to the knee joint, approximately 1cm from the posterior capsule. In revision TKA:
- Posterior capsule is attenuated from prior surgery, wear, loosening
- Anatomical planes are lost - difficult to identify neurovascular structures
- Posterior releases for stiff knees bring instruments close to artery
Protection strategies: Stay subperiosteal, use retractors carefully, avoid blind posterior releases, gentle tissue handling.
Indications for Revision TKA
| Indication | Frequency | Key Features | Treatment Approach |
|---|---|---|---|
| Aseptic loosening | 50% | Radiolucent lines over 2mm, progressive, painful | Revise components, address bone loss, stems |
| Instability | 20% | MCL/LCL insufficiency, flexion-extension gap imbalance | Increase constraint (CCK or hinge), soft tissue reconstruction |
| Infection (PJI) | 15% | Chronic pain, effusion, elevated inflammatory markers | Two-stage revision with antibiotic spacer |
| Polyethylene wear/osteolysis | 10% | Focal osteolysis, thin poly, no gross loosening | Poly exchange, curettage and grafting of lesions |
| Stiffness/arthrofibrosis | 3-5% | Less than 90° flexion, failed manipulation | Open arthrolysis, poly exchange, consider hinge |
Rule Out Infection in ALL Cases
Every revision knee must have infection excluded before proceeding with aseptic revision. Perform:
- Serum: ESR, CRP
- Synovial fluid: WBC (greater than 3000 cells/µL), PMN% (greater than 80%), culture
- Alpha-defensin or synovial CRP if high suspicion
- Consider aspiration biopsy if imaging shows loosening
Proceeding with aseptic revision in the setting of occult infection results in failure in over 90% of cases.
Classification Systems
Why AORI Matters
The Anderson Orthopaedic Research Institute (AORI) classification is the gold standard for assessing bone loss in revision TKA. It guides selection of augments, stems, and structural grafts. Type 1 defects can be managed with standard components, Type 2 requires augmentation, and Type 3 demands structural support (metaphyseal sleeve, cone, or bulk allograft).
AORI Classification - Femoral Bone Loss
| Type | Description | Bone Loss | Treatment |
|---|---|---|---|
| Type 1 | Intact metaphyseal bone with cancellous defects only | Minimal - contained defects | Standard components, cement fill or morcellized graft |
| Type 2A | Damaged metaphysis - one femoral condyle | Moderate - unilateral condylar loss | Metal augments (blocks), cement, or autograft |
| Type 2B | Damaged metaphysis - both femoral condyles | Moderate - bilateral condylar loss | Bilateral metal augments or step-cut sleeves |
| Type 3 | Deficient metaphysis - major loss affecting stability | Severe - threatens component stability | Metaphyseal sleeve, cone, or structural allograft |
Femoral bone loss is common at the posterior condyles due to posterior capsular release and wear patterns.
Clinical Assessment
Constraint Ladder Concept
Constraint selection follows a ladder approach: start with the least constraint possible (PS if feasible), escalate to CCK if one collateral ligament is deficient or moderate bone loss exists, and use rotating hinge only for massive bone loss (AORI Type 3) or global instability. Over-constraining increases interface stress and loosening risk; under-constraining risks instability.
Posterior-Stabilized (PS) Revision
Indications:
- AORI Type 1 bone loss
- Intact MCL and LCL
- Balanced flexion-extension gaps
- Simple aseptic loosening or poly wear
Requirements:
- Adequate metaphyseal bone stock
- Competent collateral ligaments (MCL and LCL)
- No significant instability
- Good extensor mechanism
Advantages
- Lowest constraint = least interface stress
- Better ROM preservation
- Lower revision rate compared to hinged
- Familiar implant for surgeons
Disadvantages
- Requires good bone stock and ligaments
- Not suitable for moderate-severe bone loss
- Risk of instability if mis-selected
- May need stems for fixation
PS revision is rarely used in practice - most revisions require at least CCK constraint.
Investigations
Preoperative Workup
History: Onset of symptoms, pain character, mechanical symptoms (locking, catching), prior infections, previous surgeries. Examination: ROM, stability (varus-valgus, AP drawer), extensor lag, wound integrity, neurovascular status.
Serum: ESR, CRP (elevated suggests infection) Aspiration: Synovial WBC, PMN%, culture (aerobic, anaerobic, fungal) Alpha-defensin or synovial CRP if high clinical suspicion Aspiration biopsy: If imaging shows loosening
AP and lateral radiographs: Component position, alignment, radiolucent lines, osteolysis Long-leg alignment films: Assess mechanical axis CT scan: If severe bone loss suspected - quantify defects, plan reconstruction Nuclear medicine: If infection suspected but aspiration negative (Tc-99m, Indium-111 WBC)
AORI classification: Estimate bone loss from imaging Constraint level: Based on bone loss and ligament integrity Augments and stems: Plan for Type 2/3 defects Implant availability: Ensure CCK, hinge, sleeves, cones available
Management Algorithm
Systematic Approach to Revision TKA
Revision TKA requires a systematic algorithm: (1) Rule out infection first (aspirate, ESR/CRP), (2) Assess bone loss (AORI classification from imaging and intraoperative findings), (3) Evaluate soft tissues (collateral ligament integrity, extensor mechanism), (4) Select constraint (PS to CCK to hinge based on bone loss and instability), (5) Plan reconstruction (augments for Type 2, sleeves/cones for Type 3, stems for stability). This stepwise approach ensures appropriate implant selection and technique.
Algorithm for Aseptic Loosening (50% of Revisions)
Management Steps
Radiographs: Radiolucent lines greater than 2mm, progressive, component subsidence. Rule out infection: Aspirate (WBC, PMN%, culture), ESR/CRP normal or mildly elevated. CT scan: If severe bone loss suspected - quantify AORI grade preoperatively.
AORI classification: Type 1 (intact), Type 2A/B (damaged), Type 3 (deficient). Constraint needs: Assess collateral ligament integrity from examination and prior radiographs. Implant availability: Ensure CCK, augments, stems, sleeves/cones available.
Remove loose components and cement - assess final bone loss intraoperatively. Type 1: Standard components, cement fill, short stems (50-75mm). Type 2: Metal augments, modular stems (75-100mm), CCK constraint. Type 3: Metaphyseal sleeve/cone, long cemented stems (100-150mm), hinge constraint.
Weight-bearing: WBAT for most cases (protected if TTO performed). ROM: Start immediately, goal 0-110° by 6 weeks. Surveillance: Annual radiographs and clinical exam for loosening.
Key Decision Point
The critical decision is constraint selection: PS if bone loss minimal and ligaments intact (rare in revision), CCK if Type 2 bone loss or one collateral deficient (most common), hinge if Type 3 bone loss or both collaterals deficient. Over-constraining increases loosening risk; under-constraining causes instability.
Surgical Technique
Pre-operative Planning
Consent Points
- Infection: 4-8% (higher than primary)
- Aseptic loosening: 5-10% at 10 years
- Periprosthetic fracture: 3-5% (higher with stems)
- Stiffness: 10-15% (less than 90° flexion)
- Neurovascular injury: Less than 1% (popliteal artery at risk)
- Re-revision: 15-20% at 5 years
- DVT/PE: Standard prophylaxis required
Equipment Checklist
- Revision implant system: CCK and hinge options
- Augments: Metal blocks (5mm, 10mm, 15mm)
- Stems: Modular, various lengths (50-150mm)
- Metaphyseal sleeves/cones: For Type 3 defects
- Extraction tools: Component removal set, cement removal
- C-arm: Essential for alignment and stem placement
- Pulse lavage: High-volume irrigation
Surgical Approach and Exposure
Exposure Steps
Use prior incision if feasible - most lateral if multiple scars. Extend proximally and distally as needed for exposure (often 20-25cm). Skin flaps: Medial and lateral, full-thickness to preserve blood supply.
Medial parapatellar arthrotomy (standard approach). Extend proximally into vastus medialis obliquus if tight. Release adhesions carefully - dense scar tissue common.
Attempt gentle eversion - do NOT force if tight. If unable to evert: Consider quadriceps snip (45° oblique extension of VMO) or tibial tubercle osteotomy (TTO). TTO indications: Severe stiffness, patella baja, need for extensile exposure.
Release scar tissue from suprapatellar pouch, medial and lateral gutters. Protect popliteal artery - posterior capsule may be attenuated. Assess collateral ligaments - note MCL/LCL integrity for constraint decision.
Popliteal Artery at Risk
The popliteal artery is at greater risk in revision TKA due to:
- Posterior capsule thinning from wear and loosening
- Loss of anatomical planes from prior surgery
- Need for posterior releases in stiff knees
Protection strategies: Stay subperiosteal, use retractors carefully, avoid blind releases posteriorly.
Stems are Not Optional in Most Revisions
Modular stems provide rotational stability and load sharing, protecting the metaphyseal bone-implant interface. Use stems in:
- AORI Type 2: 75-100mm press-fit metaphysis, cemented diaphysis
- AORI Type 3: 100-150mm fully cemented diaphysis (14-16cm fixation length)
- Rotating hinge: Mandatory - long cemented stems always
Stems reduce stress at bone-component interface and improve survivorship.
Two-Stage Revision for Periprosthetic Joint Infection
Gold Standard for Chronic PJI
Two-stage revision is the gold standard for chronic periprosthetic joint infection (PJI) in the knee, with infection control rates of 85-90%. Stage 1 involves component removal, debridement, and antibiotic spacer placement. After 6-8 weeks of IV antibiotics and a 2-week antibiotic holiday, Stage 2 reimplantation proceeds if infection markers have normalized and aspiration is negative.
Two-Stage Protocol
Remove all components: Femur, tibia, polyethylene, cement. Aggressive debridement: Synovectomy, remove all infected tissue, necrotic bone. Send cultures: Multiple samples (5-6) from different areas - aerobic, anaerobic, fungal. Antibiotic spacer: Static (block) or articulating (prefabricated or hand-made with mold). Antibiotics in cement: Vancomycin and tobramycin or gentamicin (organism-directed if known).
Organism-specific therapy: Based on intraoperative cultures (ID consult). Typical duration: 6 weeks IV antibiotics. Monitor: ESR, CRP weekly - should trend downward. Mobilization: Weight-bearing as tolerated with spacer in situ (articulating spacers allow ROM).
Stop all antibiotics for 2 weeks before reimplantation. Allows clearance of antibiotics from system for accurate aspiration. Repeat inflammatory markers: ESR, CRP should be normalizing (may not be fully normal).
Aspirate knee joint (through spacer) for culture and cell count. Criteria for reimplantation:
- Synovial WBC less than 3000 cells/µL
- PMN% less than 80%
- Negative culture (or low virulence organism with biofilm coverage)
- ESR and CRP trending down (not necessarily normal)
Remove spacer: Similar to primary revision technique. Debride again: Remove spacer cement, reassess bone loss (final AORI grading). Implant revision components: CCK or hinge based on bone loss and instability. Augments and stems: As needed for AORI Type 2/3 defects. Antibiotic-loaded cement: Consider organism-directed antibiotics in cement (controversial). Postoperative antibiotics: 6 weeks oral antibiotics (organism-directed, ID consult).
Spacer Types in Two-Stage Revision
| Spacer Type | Advantages | Disadvantages | Use Case |
|---|---|---|---|
| Static block spacer | Simple, inexpensive, high antibiotic elution | No ROM, muscle atrophy, difficult Stage 2 | Severe bone loss, unable to achieve stability |
| Articulating spacer (prefab) | Maintains ROM, easier Stage 2, patient mobility | More expensive, lower antibiotic concentration | Moderate bone loss, able to achieve stability |
| Hand-made articulating spacer | Customizable, high antibiotic dose, maintains ROM | Technically demanding, spacer fracture risk | When prefab spacer unavailable or special sizing needed |
Complications
| Complication | Incidence | Risk Factors | Management |
|---|---|---|---|
| Aseptic loosening | 5-10% at 10 years | AORI Type 3, hinged implants, inadequate fixation | Re-revision with longer stems, structural grafts, increase constraint |
| Infection (PJI) | 4-8% | Diabetes, obesity, prior infection, prolonged surgery | Two-stage revision with spacer, 6-8 weeks antibiotics |
| Periprosthetic fracture | 3-5% | Osteoporosis, long stems, stress riser at stem tip | ORIF if stem stable, revision if stem loose, consider strut allografts |
| Instability | 5-10% | Under-constraining, flexion-extension gap imbalance, poly wear | Increase constraint (PS to CCK to hinge), thicker poly, revise components |
| Stiffness (less than 90° flexion) | 10-15% | Arthrofibrosis, oversized components, overstuffing joint | Manipulation under anesthesia (within 12 weeks), open arthrolysis, poly exchange |
| Extensor mechanism disruption | 2-5% | Multiple prior surgeries, TTO, patellar fracture | Primary repair if acute, allograft reconstruction if chronic, consider gastrocnemius flap |
| Neurovascular injury | Less than 1% | Popliteal artery injury during exposure, common peroneal nerve palsy | Vascular repair emergently if arterial, nerve exploration if palsy (often traction neurapraxia) |
Periprosthetic Fracture at Stem Tip
Periprosthetic fractures often occur at the stem tip - a stress riser in osteoporotic bone. Prevention strategies:
- Use cemented stems in osteoporotic bone (better load sharing)
- Bypass prior stress risers by 2 cortical diameters (extend stem past screw holes)
- Consider strut allografts prophylactically in very osteoporotic bone
- Weight-bearing precautions (TDWB) for 6-12 weeks if high risk
Management: ORIF if stem stable (plate and strut allograft), revision to longer stem if loose.
Postoperative Care and Rehabilitation
Standard Revision TKA Postoperative Protocol
Rehabilitation Timeline
DVT prophylaxis: Chemical (enoxaparin or rivaroxaban) and mechanical (SCDs). Pain control: Multimodal analgesia (acetaminophen, NSAIDs, opioids as needed). Mobilization: Out of bed to chair on Day 1, ambulate with walker Day 2. Weight-bearing: WBAT (weight-bearing as tolerated) for most revisions. ROM: CPM or bedside PT - goal 0-90° by discharge. Drain removal: 24-48 hours when output less than 30mL per 8 hours.
Weight-bearing: Progress to full weight-bearing with assistive device. ROM exercises: Active-assisted and passive, goal 0-110° by 6 weeks. Quadriceps strengthening: Straight leg raises, quad sets, terminal knee extension. Gait training: Progress from walker to cane to independent. Wound care: Staples removed at 2 weeks, monitor for infection. Radiographs: 6-week films to assess alignment, component position, no early loosening.
Discontinue assistive device when safe gait without limp. Resistance exercises: Progress resistance training for quads, hamstrings, hip abductors. Functional activities: Stairs, sit-to-stand, balance exercises. ROM maintenance: Continue ROM exercises, goal 0-120° flexion. Return to activities: Light ADLs, avoid high-impact (running, jumping).
Functional milestones: Independent ADLs, driving (8-12 weeks), return to work (12-16 weeks). Activity modification: Avoid high-impact sports - low-impact only (cycling, swimming, golf). Annual follow-up: Radiographs and clinical exam to monitor for loosening, wear, osteolysis. Expectations: 70-80% function of primary TKA, pain improvement in 80-85% of patients.
Outcomes and Prognosis
Outcomes by Implant Type
| Implant Type | Survivorship (10 yr) | Functional Outcome | Re-revision Risk |
|---|---|---|---|
| PS revision (AORI Type 1) | 90-95% | Good - similar to primary TKA | 5-8% |
| CCK (AORI Type 2) | 85-90% | Fair - 70-80% of primary | 10-15% |
| Rotating hinge (AORI Type 3) | 80-85% | Fair to poor - 60-70% of primary | 15-20% |
| Two-stage (PJI) | 80-85% (infection control 85-90%) | Fair - 60-70% of primary | 20-25% |
Predictors of Poor Outcome
Factors associated with worse outcomes in revision TKA:
- AORI Type 3 bone loss (requires structural grafts - higher failure)
- Rotating hinge implant (higher loosening and infection rates)
- Multiple prior revisions (re-revision risk doubles with each revision)
- Chronic PJI (two-stage has lower function than aseptic revision)
- BMI over 35 (higher infection and complication rates)
- Extensor mechanism insufficiency (quadriceps dysfunction limits function)
Counseling patients realistically about expectations is critical - revision TKA does NOT achieve primary TKA outcomes.
Evidence Base and Key Trials
Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR)
- Revision TKA has 15-20% re-revision rate at 5 years vs 2-3% for primary TKA
- Aseptic loosening remains most common indication (50% of revisions)
- CCK implants have better survivorship than rotating hinge (88% vs 82% at 10 years)
- Two-stage revision for PJI has 85-90% infection control but 20-25% re-revision rate
- Metaphyseal sleeves and cones show excellent short-term results for Type 3 defects
Long-term Results of Rotating Hinge Implants for Revision TKA
- Systematic review: 15-year survivorship of rotating hinge 75-80%
- Aseptic loosening most common failure mode (10-15% at 10 years)
- Higher infection rate than CCK (8-10% vs 4-6%)
- Functional scores 60-70% of age-matched primary TKA controls
- Bushing wear and polyethylene damage seen in 15-20% long-term
Metaphyseal Sleeves vs Structural Allografts for Type 3 Defects
- Multicenter study: 250 revision TKAs with AORI Type 3 defects
- Metaphyseal sleeves: 92% survivorship at 5 years, 10% complication rate
- Structural allografts: 78% survivorship at 5 years, 25% complication rate (nonunion, resorption)
- Sleeves had faster rehabilitation and return to function
- Cost analysis favored sleeves despite higher implant cost (lower revision burden)
Two-Stage vs One-Stage Revision for Chronic PJI
- Meta-analysis: 15 studies, 1500 patients with chronic PJI
- Two-stage revision: 87% infection control vs 76% one-stage (p less than 0.01)
- Two-stage re-revision rate higher (22% vs 15%) but infection-related failures lower
- Functional outcomes similar between groups at 5 years
- Cost analysis favored two-stage due to lower infection recurrence
Constrained Condylar Knee (CCK) vs Rotating Hinge in Revision TKA
- Comparative cohort: 400 revision TKAs (200 CCK, 200 rotating hinge)
- CCK 10-year survivorship 88% vs hinge 82% (p equals 0.02)
- CCK had lower aseptic loosening (6% vs 12%) and infection (4% vs 9%)
- Functional scores slightly better with CCK (KSS 75 vs 68)
- Hinge group had more AORI Type 3 defects and global instability (selection bias)
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Painful Revision TKA Classification
"A 68-year-old woman presents with progressive medial knee pain 8 years after primary TKA. Examination shows stable knee with full extension and 110° flexion, no effusion. Radiographs demonstrate 2mm radiolucent lines under the medial tibial baseplate and small focal osteolysis. ESR 18, CRP 8. How would you assess and manage this patient?"
Scenario 2: Two-Stage Revision for PJI
"A 72-year-old diabetic man with prior TKA presents with chronic pain and recurrent effusions for 6 months. He has had two aspirations showing low-grade coagulase-negative staph. ESR 45, CRP 22. You have performed Stage 1 debridement and spacer placement. Walk me through your Stage 2 planning and technique."
Scenario 3: Massive Bone Loss (AORI Type 3)
"Intraoperatively during revision TKA, after component removal you find severe tibial bone loss - the entire medial and lateral plateaus are gone down to the metaphyseal-diaphyseal junction (AORI Type 3). How do you reconstruct this defect?"
MCQ Practice Points
AORI Classification Question
Q: A revision TKA patient has bone loss affecting both tibial plateaus but the metaphyseal rim is intact. What AORI grade is this and what reconstruction is appropriate? A: AORI Type 2B (damaged metaphysis, both condyles/plateaus involved). Appropriate reconstruction includes bilateral metal augments (5-15mm blocks) cemented to the host bone, with a modular tibial baseplate and press-fit stem (75-100mm length, cemented in diaphysis) for rotational stability and load sharing. Type 2B requires augmentation but does NOT need structural grafts (sleeves/cones).
Constraint Selection Question
Q: What is the key difference in indications between a CCK and a rotating hinge implant in revision TKA? A: CCK (constrained condylar knee) is indicated for AORI Type 1-2 bone loss with MCL or LCL insufficiency (one collateral deficient), or moderate flexion-extension gap imbalance (3-5mm). Rotating hinge is reserved for AORI Type 3 bone loss (deficient metaphysis), MCL and LCL insufficiency (global instability), or massive flexion-extension gap imbalance. CCK provides varus-valgus constraint through a taller post (5-10° laxity) but still relies on collaterals; hinge is a mechanical hinge allowing only flexion-extension (0° varus-valgus laxity).
Two-Stage Revision Question
Q: What are the criteria for proceeding to Stage 2 reimplantation after a two-stage revision for chronic PJI? A: Criteria include: (1) Completed 6-8 weeks IV antibiotics organism-specific, (2) 2-week antibiotic holiday to clear antibiotics from system, (3) Aspiration of knee joint showing synovial WBC less than 3000 cells/µL and PMN less than 80%, (4) Negative culture (or low-virulence organism with biofilm antibiotic coverage planned), (5) ESR and CRP trending downward (may not normalize completely, but should be improving). All criteria must be met before reimplantation - proceeding with persistent infection results in failure in over 90% of cases.
Stem Fixation Question
Q: What is the recommended stem fixation technique in revision TKA for AORI Type 3 defects? A: Long cemented stems (100-150mm length) with 14-16cm cemented fixation in the diaphysis. The stem provides load sharing and bypasses the deficient metaphysis (Type 3). Cementation technique: place cement restrictors, pressurize cement in the diaphyseal canal, insert stem and allow polymerization. Press-fit fixation in the metaphysis is inadequate for Type 3 defects - must have diaphyseal fixation. Stem length should bypass any stress risers (prior screw holes) by 2 cortical diameters to prevent periprosthetic fracture.
Metaphyseal Sleeve Question
Q: What are the advantages of metaphyseal sleeves over structural bulk allografts for AORI Type 3 defects? A: Metaphyseal sleeves have superior survivorship (92% at 5 years vs 78% for allografts), lower complication rates (10% vs 25%, particularly nonunion and resorption seen with allografts), biological fixation through osseointegration (porous-coated titanium), and faster rehabilitation (immediate press-fit stability vs waiting for graft incorporation). Allografts have risks of nonunion (10-15%), resorption over time, disease transmission (very low but non-zero), and technically demanding shaping/fixation. Sleeves are now first-line treatment for Type 3 defects.
Outcomes Question
Q: How do functional outcomes and survivorship of revision TKA compare to primary TKA? A: Revision TKA has inferior outcomes to primary TKA: (1) Functional scores 70-80% of primary TKA (worse with hinge or two-stage), (2) Survivorship 85-90% at 10 years vs 95% for primary TKA, (3) Re-revision rate 15-20% at 5 years vs 2-3% for primary, (4) Complication rate 20-30% vs 5-10% for primary. Patients must be counseled realistically - revision TKA does NOT restore primary TKA function and has higher risk of failure. Two-stage revisions for PJI have even worse outcomes (60-70% function, 80-85% survivorship).
Australian Context and Medicolegal Considerations
AOANJRR Data (2023)
- Revision burden: 15-20% re-revision rate at 5 years vs 2-3% for primary TKA
- Aseptic loosening: Remains most common indication (50% of all revisions)
- CCK vs hinge survivorship: 88% vs 82% at 10 years - CCK superior
- Two-stage for PJI: 85-90% infection control but higher re-revision rate
- Metaphyseal sleeves/cones: Excellent short-term results for Type 3 defects (5-year data emerging)
Australian Guidelines
- ACSQHC Surgical Site Infection Prevention: Strict antibiotic prophylaxis (cefazolin 2g within 60 min)
- DVT prophylaxis: Chemical and mechanical for all revision TKA (high-risk procedure)
- Antibiotic stewardship: Two-stage PJI antibiotics guided by ID consult and local resistance patterns
- PJI diagnosis: Australian consensus follows ICM 2018 criteria (synovial WBC/PMN, culture)
Medicolegal Considerations in Revision TKA
Key documentation and consent requirements:
-
Informed consent: Document discussion of:
- Infection risk 4-8% (higher than primary)
- Re-revision risk 15-20% at 5 years
- Functional outcomes 70-80% of primary TKA (not full restoration)
- Alternative options: Conservative management, arthrodesis (salvage), amputation (extreme)
-
PJI workup documentation:
- Every revision knee must have documented infection workup (ESR/CRP, aspiration)
- Proceeding with aseptic revision in setting of occult PJI is indefensible - leads to failure over 90%
-
Operative note details:
- AORI classification documented for both femur and tibia
- Constraint rationale (why PS vs CCK vs hinge based on bone loss and ligament integrity)
- Implant details: Stem lengths, augment sizes, sleeve/cone use if applicable
- Intraoperative complications: Fractures, ligament injuries, vascular injury
-
Postoperative counseling:
- Activity restrictions: No high-impact sports (running, jumping) - low-impact only
- Surveillance: Annual radiographs and clinical exam for loosening, wear, osteolysis
- Red flags: Increasing pain, instability, wound drainage (infection signs)
Common litigation issues: Failure to rule out infection before revision, under-constraining leading to instability, inadequate bone loss reconstruction causing early loosening, unrealistic outcome expectations not addressed preoperatively.
REVISION TOTAL KNEE ARTHROPLASTY
High-Yield Exam Summary
Key Indications
- •Aseptic loosening: 50% of revisions - radiolucent lines, subsidence, pain
- •Instability: 20% - MCL/LCL insufficiency, flexion-extension gap imbalance
- •Infection (PJI): 15% - two-stage revision gold standard (85-90% control)
- •Polyethylene wear/osteolysis: 10% - focal lysis, thin poly
- •Stiffness: 3-5% - less than 90° flexion, failed manipulation
AORI Bone Defect Classification
- •Type 1 (Intact): Metaphyseal bone intact - standard components, cement fill
- •Type 2A (Damaged one): One condyle/plateau - metal augment, cement, stem
- •Type 2B (Damaged both): Both condyles/plateaus - bilateral augments, stem
- •Type 3 (Deficient): Metaphysis deficient - sleeve/cone/allograft, long stem (14-16cm)
Constraint Selection Algorithm
- •PS: AORI Type 1, intact MCL and LCL, balanced gaps (rarely used in revision)
- •CCK: Type 2, MCL OR LCL deficient, 3-5mm gap imbalance (most common)
- •Rotating hinge: Type 3, MCL AND LCL deficient, massive bone loss, global instability
- •Increase constraint as bone loss worsens and soft tissue insufficiency increases
Surgical Technique Pearls
- •Rule out infection FIRST: ESR/CRP, aspirate (WBC, PMN%, culture) in ALL cases
- •Component removal: Peripheral osteotomes, circumferential disruption, preserve bone
- •Cement removal: Meticulous debridement - final AORI only visible after cement out
- •Stems: Modular, 75-100mm Type 2, 100-150mm Type 3, cemented in diaphysis (14-16cm)
- •Metaphyseal sleeves: Press-fit biological fixation for Type 3, 92% survivorship at 5 years
Two-Stage Revision Protocol
- •Stage 1: Debridement, explant, antibiotic spacer (vancomycin + tobramycin in cement)
- •6-8 weeks IV antibiotics organism-specific (ID consult), then 2-week holiday
- •Reimplantation criteria: WBC less than 3000, PMN less than 80%, negative culture, ESR/CRP trending down
- •Stage 2: Remove spacer, debride again, revise with CCK/hinge, augments/stems as needed
- •Infection control: 85-90%, but re-revision risk 20-25%, function 60-70% of primary
Complications and Outcomes
- •Aseptic loosening: 5-10% at 10 years (higher with hinge, Type 3 defects)
- •Infection: 4-8% (higher than primary 1-2%)
- •Periprosthetic fracture: 3-5% (stem tip stress riser, osteoporotic bone)
- •Survivorship: 85-90% at 10 years (vs 95% primary), re-revision 15-20% at 5 years
- •Function: 70-80% of primary TKA (worse with hinge or two-stage)