Exclude infection, grade the bone loss (AORI), reconstruct with stems, augments and cones, and match constraint to ligament integrity. The exposure protects the extensor mechanism.
- Infection exclusion is MANDATORY before any revision. ESR and CRP, then knee aspiration for cell count (greater than 3000 WBC or greater than 80 percent PMN suggests infection) and culture held 14 days. Alpha-defensin if equivocal. Occult infection requires conversion to two-stage.
- AORI classification guides reconstruction, graded separately for femur and tibia: Type 1 intact metaphysis, Type 2A damaged metaphysis with intact rim, Type 2B damaged metaphysis with deficient rim (needs augments and stems), Type 3 severe deficiency (needs cones or allografts).
- Constraint follows ligament integrity: PS if MCL and LCL intact with opening less than 5mm, CCK if attenuated with 5 to 15mm opening (MOST COMMON in revision), rotating hinge if incompetence greater than 15mm or global instability.
- Stems are recommended for all significant revisions (AORI 2B or 3, or deficient anterior femoral cortex). Press-fit, largest diameter that fits without hoop stress, length bypassing defects by a minimum of 2 cortical diameters (100 to 150mm femur, 75 to 125mm tibia).
- Use the previous incision, preferentially the most lateral scar to preserve the medial blood supply. If you cannot evert the patella safely, plan an extensile exposure (quadriceps snip, V-Y quadricepsplasty, or tibial tubercle osteotomy) rather than forcing it.
When & Why
Indications. Revise a painful primary total knee arthroplasty when loosening is demonstrated objectively and infection has been excluded. Absolute indications: - Aseptic tibial loosening — progressive weight-bearing pain, radiolucent lines greater than 2mm (complete or progressive), subsidence on serial films, or progressive varus/valgus tilting of the platform.
- Aseptic femoral loosening — progressive pain with radiolucent lines at the bone-cement interface (complete lines in all zones are most concerning), component migration, rotation change, or condylar lift-off.
- Polyethylene wear with extensive osteolysis — large osteolytic lesions (tibial metaphysis or femoral condyles), impending periprosthetic fracture, or mechanical symptoms from loose bodies.
- Component malposition from the index surgery — severe malalignment (varus greater than 5 degrees, valgus greater than 10 degrees) driving accelerated wear and secondary loosening, or flexion instability from femoral malrotation. Relative indications include instability with component loosening (giving way, recurrent effusions, secondary bone loss) and progressive pain with objective radiographic loosening even without gross instability. Pain alone is subjective — it must be paired with radiographic progression to justify revision. Assess the whole knee before committing. Document the timeline (pain beginning years after the index procedure favours aseptic loosening), the pain character (mechanical versus inflammatory), range of motion (stiffness complicates exposure), stability, extensor mechanism integrity, neurovascular status, and skin quality with all previous incisions. Serial radiographs (AP, lateral, skyline) compared to previous films are mandatory — progressive change is far more concerning than a static finding. Look for complete radiolucent lines, component subsidence (joint line to tibial tubercle distance on serial films), and scalloped osteolysis that may need CT to size, especially posterior tibial defects. Infection exclusion — non-negotiable. Occult infection is found in roughly 10 to 15 percent of presumed aseptic cases, and revising an infected knee as a single stage fails. Work through it systematically:
- Features
- Late loosening, normal ESR/CRP, dry aspiration
- Workup and plan
- Proceed with single-stage but ALWAYS take intraoperative frozen sections (5 to 6 samples)
- Features
- Early loosening (less than 5 years), mildly raised markers, equivocal aspiration
- Workup and plan
- Repeat aspiration off antibiotics for 2 weeks, alpha-defensin, consider labelled WBC scan, frozen sections with conversion to two-stage if positive
- Features
- Raised ESR and CRP, positive aspiration, clinical signs
- Workup and plan
- Two-stage revision — do NOT proceed single-stage: remove components, debride, antibiotic spacer, 6 weeks IV antibiotics, normalise markers, then reimplant
Serology and aspiration thresholds. CRP greater than 10 mg/L or ESR greater than 30 mm/hr are concerning but non-specific (chronic loosening can raise them), and normal levels do NOT exclude infection. Aspiration (sterile technique) is the critical test: greater than 3000 WBC or greater than 80 percent PMN highly suggests infection; send Gram stain (low sensitivity) and culture aerobic/anaerobic/fungal held a minimum of 14 days. If equivocal, add alpha-defensin (high specificity), synovial CRP greater than 10 mg/L, or next-generation sequencing for culture-negative suspicion.
Proceeding to a single-stage revision with occult infection leads to persistent infection, treatment failure, and worse outcomes than a properly planned two-stage exchange. Even with a negative preoperative workup, ALWAYS take 5 to 6 interface samples for frozen section intraoperatively — greater than 5 PMN per high-power field indicates infection and should trigger conversion to two-stage.
Preoperative planning. Obtain the previous operative notes — manufacturer, component sizes, constraint level (CR/PS/CCK/hinge), fixation method, and any augments or stems. Contact the index hospital for implant records if needed. Ensure the full revision system is available (multiple sizes, femoral and tibial stems in a range of diameters and lengths, wedge/block/step augments, metaphyseal cones, PS/CCK/hinged options, bone graft) and have the company representative present. Template the expected AORI grade for femur and tibia separately (components often downsize 1 to 2 sizes from primary due to bone loss), plan stems to bypass defects by 2 cortical diameters, and plan the constraint from the history of instability. Patient optimisation and consent. Medical clearance for a long case with potential blood loss. Optimise comorbidities — diabetes (HbA1c less than 8 percent), nutrition (albumin greater than 3.5 g/dL), smoking cessation at least 6 weeks preoperatively. Blood management: type and screen, consider cell saver and a tranexamic acid protocol (1g IV preoperative, 1g intraoperative, optional 1g intra-articular at closure). Consent specifically for realistic outcomes — lower ROM than primary (0 to 110 degrees is excellent in revision), 6 to 12 month recovery, higher complication rates (infection 3 to 5 percent, re-revision about 5 percent at 5 years) — and for extensile exposure with non-weight-bearing if a tibial tubercle osteotomy is used, stems and augments, possible hinged prosthesis, bone grafting, possible two-stage if unexpected infection, transfusion, neurovascular injury, and periprosthetic fracture. Setup. Supine with the operative leg free to flex 120 degrees and extend fully (foot of table dropped, or a leg holder at hip level), a well-padded lateral thigh post for valgus stress, and a bump under the ipsilateral hip for 15 to 20 degrees of external rotation. Proximal thigh tourniquet — consider not inflating, or releasing early, if the case will exceed 2 hours, because cement interdigitation does not depend on exsanguination and prolonged inflation raises complications; if used, exsanguinate by elevation only (no Esmarch, to avoid dislodging thrombus from previous surgery). Drape the leg circumferentially including the foot, and have fluoroscopy and cell saver available.
The Operation
The goal: revise the loose components while protecting the extensor mechanism and the popliteal neurovascular bundle, remove all cement and membrane, reconstruct the bone loss with stems, augments or cones, match the constraint to the ligament quality, and cement a stable, well-aligned construct. The exposure — getting in safely without avulsing the patellar tendon — is the make-or-break part of the case and is laid out in full as the first steps below.
Structures at risk. Revision skin and the extensor mechanism are at far higher risk than in a primary. The neurovascular bundle behind the tibia is the constant danger during posterior tibial work.
10 to 15mm posterior to the posterior tibial cortex. At increased risk in revision from scar, retraction difficulty and bone loss exposing the vessels (injury 0.1 to 0.2 percent versus 0.05 percent primary). ALWAYS use broad posterior Hohmann retractors during tibial component removal and posterior cement extraction, work anterior-to-posterior, and consider releasing the tourniquet before posterior dissection in a prolonged case.
Winds around the fibular neck 2 to 3cm distal to the fibular head. Increased risk in revision (2 to 3 percent versus 0.5 to 1 percent primary) from scar tethering, valgus correction, lateral releases and prolonged retraction. Minimise lateral dissection, retract gently, limit tourniquet time (release at 2 hours), and correct valgus gradually.
Medial and lateral geniculate arteries form a peri-patellar anastomosis. A previous medial arthrotomy already compromises the medial supply; a lateral release worsens perfusion and risks patellar necrosis or fracture. Use the most lateral previous incision, optimise femoral rotation instead of releasing laterally, and if a lateral release is unavoidable limit it to the distal third with meticulous haemostasis.
At high risk from scar, stiffness and bone-ingrowth. Forcing patellar eversion can avulse the patellar tendon — catastrophic and very hard to reconstruct. A tibial tubercle osteotomy gives excellent exposure while protecting the mechanism, and should be chosen electively whenever eversion is difficult.
Operative sequence
- Supine, leg free to flex 120 degrees, lateral thigh post at hip level, bump under the ipsilateral hip for 15 to 20 degrees external rotation.
- Identify the previous incision and mark the most lateral scar (preserves the medial skin blood supply); plan a 15 to 20cm incision with room to extend 5 to 7cm above the patella and 3 to 5cm below the tubercle.
- Tourniquet on the proximal thigh — inflate selectively, or release early, if the case will exceed 2 hours.
- Use the previous incision, preferentially the most lateral scar. Excise a previously adherent or necrotic scar completely.
- Sharp dissection through subcutaneous tissue to capsule — scar is often densely adherent. Create full-thickness flaps of a minimum of 5mm.
- Revision skin is at much higher risk (wound complications 5 to 10 percent versus 2 to 5 percent primary): preserve all tissue possible and avoid tension.
- Identify the previous arthrotomy (usually medial parapatellar). Carefully develop the plane between scar tissue and the underlying implant with sharp scalpel dissection to avoid tearing the extensor mechanism.
- Release scar from the medial and lateral gutters, the suprapatellar pouch, and both femoral condyles systematically.
- Assess the ability to evert the patella. If it is difficult, STOP and do not force it — plan an extensile exposure (Step 4).
If the patella will not evert safely, or components are well-fixed and bone-ingrown, choose one of three extensile techniques: - Quadriceps snip (moderate stiffness) — a lateral extension of the proximal arthrotomy at 45 degrees from the supralateral patella, extending 4 to 5cm into vastus lateralis. Simple and effective; repair with interrupted figure-of-8 sutures at closure. Risk: propagation into vastus lateralis.
- V-Y quadricepsplasty (severe stiffness) — a full-thickness V-shaped incision in the quadriceps tendon extended 6 to 8cm proximally, advanced distally and closed as a Y. Maximal exposure; technically demanding with a risk of quadriceps weakness and extension lag.
- Tibial tubercle osteotomy (preferred for bone-ingrowth or severe stiffness) — mark a 5 to 6cm long, 1cm wide osteotomy starting 5cm distal to the joint line, create the lateral and distal cuts with thin osteotomes leaving a medial soft-tissue hinge, and reflect the tubercle with the intact patellar tendon proximally. Excellent exposure that protects the extensor mechanism. At closure fix with two 4.5mm cortical screws (18mm bicortical, perpendicular to the osteotomy with slight compression), or cables in osteoporotic bone; non-weight-bearing 6 weeks. Complications: fracture extension and non-union each about 5 percent.
Patellar tendon avulsion or mid-substance rupture in revision is catastrophic and very difficult to reconstruct. If eversion is difficult, convert to an extensile exposure — a tibial tubercle osteotomy for bone-ingrowth or severe stiffness — before applying traction to an attenuated mechanism.
- Remove the polyethylene liner first (it may be locked, or loose from wear) using an extractor or osteotome.
- Test femoral and tibial fixation with gentle pressure and an osteotome; loose components in aseptic loosening often elevate more easily than well-fixed cementless ones.
- Femur: insert thin flexible osteotomes at the bone-cement interface starting anteriorly and work circumferentially (medial, lateral, distal, posterior), then use a component-specific extraction device or slap hammer. Avoid aggressive levering that fractures condyles.
- Tibia (usually harder, larger interface): work peripherally 360 degrees with osteotomes, then posteriorly VERY carefully under broad retractors protecting the popliteal bundle; use the extraction device rather than levering.
- Patella: if loose, extract with thin osteotomes at the cement-bone interface; if well-fixed and tracking well, consider retaining it to preserve bone stock.
- Take 5 to 6 interface samples for frozen section — greater than 5 PMN per high-power field means infection and mandates conversion to two-stage.
- Remove ALL cement and the interface membrane completely — the membrane drives osteolysis and prevents bone healing. Use thin osteotomes, curettes, a high-speed burr (with cooling irrigation to avoid thermal necrosis) and an ultrasonic cement-removal system, working systematically around femur and tibia while preserving bone.
- Curette sclerotic bone to punctate bleeding; copious pulsatile lavage (6 to 9L).
- Now grade the bone loss with the AORI classification, femur and tibia separately (see Background and Evidence): Type 1 intact metaphysis, 2A damaged metaphysis with intact rim, 2B damaged metaphysis with deficient rim, 3 severe deficiency.
- Distal femoral cut perpendicular to the mechanical axis (5 to 7 degrees valgus), resecting the minimum to a stable bleeding surface (typically 2 to 4mm more than primary to clear sclerotic bone).
- Augment posterior condylar asymmetry with wedge augments (5, 10, 15mm) building up the deficient side (usually medial in valgus loosening, lateral in varus); use step or block augments for distal defects.
- Size the component (often downsize 1 to 2 sizes from primary) and set rotation from three references — transepicondylar axis (gold standard), Whiteside's line, and posterior condyles plus 3 degrees external rotation (least reliable with asymmetric bone loss).
- Ream the canal sequentially and add a press-fit stem (100 to 150mm) bypassing defects by 2 cortical diameters. Using augments without a stem overloads the augment-bone interface and fails early.
- Proximal tibial cut perpendicular to the mechanical axis with 3 to 5 degrees posterior slope (less than primary — CCK and hinged implants do not rely on slope for rollback), resecting the minimum to a stable surface. Avoid joint-line elevation greater than 8mm.
- Wedge augments (5 to 20mm) for peripheral defects (medial in varus loosening); block or step augments for larger segmental defects.
- Metaphyseal cones (porous tantalum or trabecular titanium, 25 to 45mm diameter) for Type 2B or 3 defects — press-fit into the metaphysis with excellent ingrowth and durable fixation (around 96 percent survivorship at 10 years with aseptic loosening as endpoint).
- Size the baseplate for maximum coverage without overhang (often smaller than primary), ream the canal (offset reamer if the canal is not centred under the cut), and add a press-fit stem (75 to 125mm) bypassing the defect by 2 cortical diameters.
- With the components out and cement debrided, stress-test the collaterals: MCL (most critical) with valgus stress at 0 and 90 degrees, LCL with varus stress. The PCL is usually absent or incompetent in loosening and is not a factor.
- Choose the least constraint that gives a stable knee: PS if MCL and LCL are intact with opening less than 5mm (uncommon in revision); CCK (varus-valgus constrained) if attenuated with 5 to 15mm opening, or a flexion-extension gap imbalance under 10mm not correctable with bone resection — the MOST COMMON choice in revision, giving 2 to 4 degrees more constraint than PS through a taller post and deeper cam; rotating hinge for incompetence greater than 15mm, global instability, massive bone loss, or failed CCK.
- Reassess after component removal — loosening attenuates ligaments even when the knee felt stable preoperatively.
- Trial the femoral component with augments and stem, the tibial component with augments and stem, and a polyethylene (start 10 to 12mm, thicker than primary).
- Assess extension and flexion gaps with spacers — they should be equal height for a CCK design.
- Balance with AUGMENTS and component sizing more than soft-tissue releases (the ligaments are already attenuated; further release risks forcing a higher constraint level). Extension tight: resect more bone (if the joint line allows) or downsize augments. Extension loose: larger augments or thicker poly. Flexion tight: downsize the femoral component or reduce posterior augments. Flexion loose: upsize the femur, increase posterior augments, or thicker poly. Asymmetric gaps: build up the deficient side with a wedge augment.
- Alignment rod from hip to ankle through the knee centre — neutral mechanical axis within 3 degrees.
- Stability — varus/valgus stress at 0 and 90 degrees; a CCK should open less than 3mm. Greater than 10mm opening, consider a hinge.
- Range of motion — target a minimum of 0 to 90 degrees; 0 degrees extension is critical. Accept lower goals than primary (0 to 110 degrees is very good); do not overstuff chasing 120 degrees.
- Patellar tracking through the range; check femoral rotation and patellofemoral overstuffing.
- Joint line — inferior pole of the patella to the tibial cut should be about 10mm (8 to 12mm acceptable); elevation greater than 8mm is concerning.
- No posterior impingement in deep flexion; stems and augments stable with no rocking. Revise anything doubtful before cementing.
- Remove trials. Pulsatile lavage 6 to 9L, dry meticulously, pack with dilute adrenaline-soaked sponges for haemostasis. Use multiple cement batches (typically 3 to 4 for a revision with stems).
- Sequence: stems first (hand-pressurise cement into both canals and insert while still doughy), then augments (thin cement layer pressurised to bone), then the tibial component (proper rotation to the tubercle and second ray, stem fully seated), then the femoral component while the tibia cures (rotation to the transepicondylar axis).
- Remove ALL excess cement meticulously — especially at the stem tips (a stress riser), augment edges, and posteriorly. Cure time is 12 to 15 minutes (longer than primary, larger cement mass). Protect surfaces with a trial poly during cure.
- After cure, remove the trial poly, irrigate (3 to 6L), and insert the final polyethylene — thicker than primary, typically 12 to 15mm minimum for stability. Confirm the locking mechanism engages with a definitive click and verify it by attempting removal.
- Final check: ROM 0 to 90 degrees minimum without impingement, stable to stress at 0 and 90 degrees, central patellar tracking, neutral alignment, balanced gaps. Document every detail — component sizes, stem lengths, augment sizes and positions — for the next revision surgeon.
- Take intraoperative AP and lateral radiographs if fluoroscopy is available to confirm position, alignment, stem seating, no fracture, and an adequate cement mantle while still in theatre.
- If a tibial tubercle osteotomy was used: reduce the tubercle anatomically and fix with two 4.5mm cortical screws (18mm bicortical, perpendicular, slight compression) or cables in osteoporotic bone; verify stability.
- Quadriceps snip: repair with interrupted figure-of-8 sutures. V-Y turndown: advance and close in Y (may lengthen slightly).
- Release the tourniquet and achieve meticulous haemostasis (revision bleeds more than primary); consider tranexamic acid 1 to 3g intra-articular and a closed suction drain (remove at 24 to 48 hours, or under 30mL per 8 hours).
- Close the capsule in interrupted figure-of-8 fashion — critical for the extensor mechanism — then deep fascia, subcuticular skin or staples, and a compression dressing.
For severe stiffness or well-fixed bone-ingrowth components, a tibial tubercle osteotomy gives excellent exposure while PROTECTING the extensor mechanism. Mark a 5 to 6cm osteotomy starting 5cm distal to the joint line with a medial soft-tissue hinge, reflect the tubercle with the intact patellar tendon, and at closure fix with two 4.5mm cortical screws 18mm bicortical with 6 weeks non-weight-bearing. It carries about a 5 percent fracture-extension and 5 percent non-union rate — but it guards against patellar tendon avulsion, which is catastrophic and very difficult to reconstruct.
Any augment or cone must be protected by a stem that bypasses the defect by a minimum of 2 cortical diameters. Stems share load, offload the compromised interface, improve rotational stability, and reduce stress on the augments — without them the construct subsides and fails early.
Aftercare & Complications
Rehabilitation | Phase | Timing | Weight-bearing and immobilisation | Therapy focus | |-------|--------|-----------------------------------|---------------| | 1 | Day 0 to 2 weeks | If TTO: non-weight-bearing (toe-touch) 6 weeks with a walker. If no TTO: weight-bearing as tolerated with a walker | DVT prophylaxis 6 weeks; ankle pumps, quadriceps sets, active ROM; CPM may help | | 2 | 2 to 6 weeks | Wound check, remove sutures or staples; continue non-weight-bearing if TTO | ROM targeting 0 to 90 degrees; monitor wound (higher risk 5 to 10 percent) | | 3 | 6 weeks | Radiographs — alignment, component position, no subsidence or radiolucent lines, TTO bridging callus. If TTO healed, advance to weight-bearing as tolerated; otherwise wean walker to cane | Progressive ROM, quadriceps strengthening, proprioception | | 4 | 3 to 12 months | Night splint only if needed; low-impact activities (walking, swimming, cycling, golf) if ROM and strength adequate | ROM goals 0 to 90 degrees minimum, 0 to 110 degrees very good; avoid high-impact (running, jumping, pivoting) | Recovery is longer than a primary — maximal improvement takes 6 to 12 months (versus 3 to 6 months). Follow-up is more intensive: 2 weeks (wound), 6 weeks, 3 months, 6 months, 1 year, then annually for life with annual radiographs monitoring for progressive radiolucent lines greater than 2mm, subsidence, migration, osteolysis and stem fracture. Counsel the patient preoperatively that ROM expectations are lower than primary and the re-revision rate is about 5 percent at 5 years (versus about 1 percent primary). Complications — all more frequent than after a primary.
- Recognition
- Early (under 3 months): persistent pain, wound drainage, fever, raised CRP/ESR. Late: progressive pain, effusion, positive aspiration (greater than 3000 WBC, greater than 80 percent PMN)
- Prevention
- Antibiotic prophylaxis with redosing every 2 to 4 hours, minimise operative time, meticulous haemostasis, layered closure, glycaemic control
- Management
- Early: debridement, poly exchange, retain components if well-fixed, 6 weeks IV antibiotics. Late or failed debridement: two-stage exchange
- Recognition
- Intraoperative: seen directly, sudden loss of stability. Postoperative: pain, cannot bear weight, deformity. Femoral supracondylar most common
- Prevention
- Careful extraction with thin flexible osteotomes, gentle cement removal, appropriate stem sizing without hoop stress, prophylactic cables if thin cortices
- Management
- Intraoperative: cables or ORIF, longer stems bypassing the fracture by 2 cortical diameters. Postoperative: ORIF if components stable, revise with long stems if loose
- Recognition
- Progressive weight-bearing pain, progressive radiolucent lines greater than 2mm, subsidence, migration
- Prevention
- Adequate stems bypassing defects, optimal cement technique, correct constraint, augments or cones for defects, avoid joint-line elevation
- Management
- Re-revision — usually higher constraint (CCK to hinge), larger defects needing cones or allograft, longer stems; each revision has a worse prognosis
- Recognition
- Giving way on stairs or turning, recurrent effusions, buckling. Varus/valgus laxity greater than 5mm with a CCK is concerning
- Prevention
- Accurate intraoperative stress testing, correct constraint, balanced gaps, proper femoral rotation, poly minimum 12 to 15mm, verify stability before cementing
- Management
- Mild (under 5mm): observe, strengthen, brace. Moderate: thicker poly if constraint adequate. Severe: revise to higher constraint (CCK to hinge), exclude infection
- Recognition
- Flexion under 90 degrees, pain at end range, firm end-point, reduced patellar mobility
- Prevention
- Early ROM from day 1, adequate analgesia, CPM in high-risk patients, avoid overstuffing, extensile exposure rather than forcing eversion
- Management
- Aggressive physiotherapy first. Manipulation under anaesthesia at 6 to 12 weeks if plateau under 90 degrees (higher fracture risk than primary). Arthroscopic or open debridement if MUA fails or heterotopic ossification present
- Recognition
- Extension lag, palpable tendon or quadriceps defect, patella alta or baja. Patellar tendon avulsion is catastrophic
- Prevention
- TTO for difficult exposures, gentle handling, avoid joint-line elevation over 8mm, layered capsular closure
- Management
- Acute patellar tendon rupture: primary repair if tissue adequate, else Achilles or mesh augmentation. Chronic: allograft reconstruction. Patella fracture: ORIF if displaced
- Recognition
- Superficial: erythema, drainage, separated edges. Deep: drainage over 7 days, exposed prosthesis, systemic signs. Necrosis: black eschar, non-bleeding edges
- Prevention
- Full-thickness flaps minimum 5mm, most lateral incision, excise necrotic scar, meticulous haemostasis, subcuticular closure, glucose under 180 mg/dL
- Management
- Superficial cellulitis: oral antibiotics. Dehiscence without exposed prosthesis: local care or delayed closure. Exposed prosthesis: urgent irrigation and debridement, flap cover (gastrocnemius most common)
Additional complications: - Neurovascular injury (0.2 to 0.5 percent): common peroneal nerve palsy (2 to 3 percent) — foot drop, AFO and observation. Popliteal artery injury (0.1 to 0.2 percent) — immediate vascular repair or bypass, high amputation risk if delayed. Popliteal vein injury (0.2 percent) — repair to prevent DVT and venous congestion.
- Venous thromboembolism (4 to 6 percent, higher than primary): longer surgery, more trauma. Extended prophylaxis a minimum of 6 weeks, early mobilisation, mechanical compression.
- Component malalignment or malposition (2 to 4 percent): stem perforation of the cortex, rotation error causing maltracking or instability, varus/valgus malalignment. May need early revision if severe.
Viva & Exam Focus
I Can't Manage Severe DefectsAORI bone-defect classification
Hook:AORI is the Anderson Orthopaedic Research Institute knee classification (Engh and Ammeen) — do NOT confuse it with the Paprosky acetabular classification used at the hip. Grade femur and tibia separately. Type 2B and 3 require stems bypassing the defect by a minimum of 2 cortical diameters. Type 3 often needs metaphyseal cones — porous tantalum with durable long-term fixation (around 96 percent survivorship at 10 years with aseptic loosening as endpoint).
PSYCHConstraint selection
Hook:CCK is the MOST COMMON constraint in revision for aseptic loosening, because loosening attenuates the ligaments through abnormal kinematics. A CCK gives 2 to 4 degrees more varus-valgus constraint than PS through a taller post and deeper cam, with about 90 percent survivorship at 10 years when paired with proper stem fixation.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A 68-year-old presents with progressive pain 8 years after a primary TKA. Radiographs show complete radiolucent lines around the tibial component with 3mm subsidence on serial films. How do you exclude infection before proceeding with revision?”
“Explain the AORI classification for bone defects and how it guides your reconstruction strategy in revision TKA.”
“How do you determine the level of constraint needed in revision TKA? A patient has aseptic loosening with a moderate varus deformity — walk me through your constraint decision.”
Before the operation
- Exclude infection — ESR, CRP, aspiration (greater than 3000 WBC or greater than 80 percent PMN), alpha-defensin if equivocal, always intraoperative frozen sections (greater than 5 PMN per high-power field converts to two-stage)
- Obtain previous operative notes — manufacturer, sizes, constraint, fixation
- Template AORI grade for femur and tibia separately; plan stems, augments, cones, constraint
- Consent for extensile exposure, stems and augments, possible hinge, possible two-stage, transfusion, fracture
Exposure
- Previous incision, most lateral scar, full-thickness flasks minimum 5mm
- Do NOT force patellar eversion — choose extensile exposure
- Quadriceps snip (moderate), V-Y (severe), TTO preferred for bone-ingrowth or severe stiffness
- TTO: 5 to 6cm long, medial hinge, fix with 2 screws, non-weight-bearing 6 weeks
Component extraction and cement
- Polyethylene first, then femur, then tibia with posterior retractors protecting the popliteal bundle
- Thin flexible osteotomes at the bone-cement interface circumferentially; extraction device not aggressive levering
- Remove ALL cement and membrane completely; curette to punctate bleeding; lavage 6 to 9L
Reconstruction and constraint
- AORI: 1 cement, 2A cement and augments, 2B augments plus stems, 3 cones or allograft plus stems
- Stems bypass defects by a minimum of 2 cortical diameters (100 to 150mm femur, 75 to 125mm tibia)
- Constraint from ligaments: PS under 5mm, CCK 5 to 15mm (most common), hinge over 15mm or global instability
- Balance with augments and sizing more than soft-tissue releases
Danger zones
- Popliteal artery and vein 10 to 15mm behind the tibia — broad posterior retractors for all tibial work
- Common peroneal nerve at the fibular neck — minimal lateral dissection, release tourniquet at 2 hours
- Patellar blood supply — most lateral incision, avoid lateral release
- Extensor mechanism — TTO over forced eversion
Aftercare and prognosis
- DVT prophylaxis 6 weeks minimum; non-weight-bearing 6 weeks if TTO
- ROM goals lower than primary — 0 to 90 degrees minimum, 0 to 110 degrees very good
- Recovery 6 to 12 months; annual radiographs for life
- Higher complication rates — infection 3 to 5 percent, re-revision about 5 percent at 5 years
Background & Evidence
Why revision is harder than primary. Aseptic loosening is a leading aseptic cause of revision TKA (infection is the most common cause of failure overall). In a series of 349 revisions, overall 10-year survivorship was 90.6 percent. Every revision carries a worse prognosis than the one before — bone stock is poorer, ligaments are attenuated, and the constructs see higher forces — which is why durable fixation and realistic patient counselling matter so much. The AORI classification — grade femur and tibia separately. The Anderson Orthopaedic Research Institute system (Engh and Ammeen) is the standard framework for knee bone loss and is distinct from the Paprosky acetabular classification used at the hip. Reconstruction is selected on four variables: implant constraint, stem configuration, stem fixation (cement versus press-fit), and method of defect repair.
- Bone condition
- Intact metaphyseal bone, minor defect
- Reconstruction
- Cement, with screws for fixation
- Bone condition
- Damaged metaphysis, intact peripheral cortical rim
- Reconstruction
- Cement, screws, small augments for contained defects
- Bone condition
- Damaged metaphysis, deficient peripheral rim
- Reconstruction
- Metal augments (wedge, block, step) plus stems for load sharing
- Bone condition
- Severe metaphyseal and epiphyseal deficiency
- Reconstruction
- Metaphyseal cones, structural allograft, custom components, possible hinge
The constraint ladder. Use the least constraint that achieves a stable knee — higher constraint transmits more stress to the bone-implant interface and demands more robust metaphyseal fixation.
- Indication
- MCL and LCL intact, opening less than 5mm, balanced gaps
- Notes
- Uncommon in revision for loosening
- Indication
- MCL or LCL attenuated, 5 to 15mm opening, or gap imbalance under 10mm
- Notes
- Most common in revision; 2 to 4 degrees more constraint than PS; about 90 percent survivorship at 10 years
- Indication
- Incompetence over 15mm, global instability, massive bone loss, failed CCK
- Notes
- Reserved for gross collateral disruption or extensor mechanism loss
Zonal fixation. Durable revision constructs aim for solid fixation in at least two of three zones — the epiphysis, the metaphysis, and the diaphysis (Morgan-Jones). Cemented or cementless diaphyseal-engaging stems share load and protect the compromised interface, which is the rationale for routinely pairing stems with augments and cones in AORI 2B and 3 defects.
References
Bone loss with revision total knee arthroplasty: defect classification and alternatives for reconstruction
- Defines the Anderson Orthopaedic Research Institute (AORI) classification for femoral and tibial bone defects, graded separately as Type 1, 2A, 2B and 3
- Reconstruction is selected on four variables: implant constraint, stem configuration, stem fixation (cement versus press-fit) and method of defect repair
- Principle of least constraint: use the lowest constraint that gives a stable knee to minimise stress at the compromised fixation interface
Classification and preoperative radiographic evaluation: knee
Midterm assessment of causes and results of revision total knee arthroplasty
The 2018 Definition of Periprosthetic Hip and Knee Infection: An Evidence-Based and Validated Criteria
- Multi-institutional study (684 PJI and 820 aseptic revisions) deriving a weighted scoring system, externally validated on 422 patients
- Major criteria (two positive cultures or a sinus tract) are diagnostic; weighted minor criteria include serum CRP, D-dimer, ESR, synovial WBC greater than 3000, alpha-defensin, leukocyte esterase and synovial CRP
- Reached 97.7 percent sensitivity versus 79.3 percent for the original MSIS definition, with 99.5 percent specificity
Zonal fixation in revision total knee arthroplasty
Tantalum Cones for Severe Bone Defects in Revision Knee Arthroplasty: A Minimum 10-Year Follow-Up
- 30 revision TKAs (42 cones: 25 tibial, 17 femoral) reconstructing AORI Type 2A, 2B and 3 defects, followed for a minimum of 10 years
- Minimum 10-year cone survivorship was 81 percent for any reason and 96 percent with aseptic loosening as the endpoint, with no radiographic loosening or migration on the most recent films
- Confirms metaphyseal fixation with porous tantalum cones is durable in massive bone loss from both aseptic loosening and second-stage reimplantation
The use of tantalum cones and diaphyseal-engaging stems in tibial component revision: a consecutive series
Ligament Balancing and Constraint in Revision Total Knee Arthroplasty
- Symmetrical gaps with intact collateral ligaments can be managed with cruciate-retaining, posterior-stabilised or ultracongruent inserts; collateral insufficiency mandates higher constraint
- Constrained condylar implants resist varus/valgus and rotational forces with a non-linked construct but transmit more stress to the implant-bone interface, requiring robust metaphyseal fixation
- Rotating-hinge constructs are reserved for gross collateral disruption, severe flexion-extension mismatch or extensor mechanism loss
Revision knee surgery: the practical approach
The role of stems and augments for bone loss in revision knee arthroplasty
- Reviews structural allograft, impaction grafting and prosthetic augments for revision bone defects; no comparative series proves superiority of any single technique
- Supplemental stem fixation should accompany any of these defect-management strategies to offload the compromised interface
- Cemented stem fixation gave a more reliable construct in severe bone deficiency, though cementless diaphyseal-engaging stems are now widely used in hybrid (zonal) fixation