High-yield overview

Previous midline incision, may need extensile exposure (quad snip, VY turndown, tibial tubercle osteotomy) | advanced

Critical Danger Structures

Popliteal Artery

Location: 2cm posterior to tibial plateau, runs within popliteal fossa between medial and lateral heads of gastrocnemius

Protection: Mark maximum drill depth on all tibial instruments, use depth stops, avoid posterior cortex breach during tibial stem preparation and cement removal, maintain knee flexion during posterior work

Common Peroneal Nerve

Location: Crosses fibular neck 3-4cm below fibular head, wraps around lateral fibular neck, at risk with valgus correction and lateral retraction

Protection: Minimize lateral retraction, use bent retractors around fibular head, release lateral structures before valgus correction >10°, avoid lateral stem perforation

Extensor Mechanism

Location: Patellar tendon from patella to tibial tubercle, quadriceps tendon from VMO/VL/VI/RF to patella, at risk during exposure and closure

Protection: Never force patellar eversion - use extensile exposure if tight, careful TTO technique (5-7cm osteotomy, 1cm thick, hinge laterally), meticulous repair with non-absorbable suture

Medial Skin Blood Supply

Location: Medial genicular branches supply knee skin; multiple parallel incisions compromise lateral-to-medial flow

Protection: Use most LATERAL previous incision if multiple scars, avoid undermining flaps, full-thickness skin dissection, never create bridge between parallel scars less than 7cm apart

Posterior Tibial Cortex

Location: Posterior cortex only 2cm anterior to popliteal artery; at risk during tibial stem reaming, cement removal, and component extraction

Protection: Use fluoroscopy to confirm instrument position, hand ream initially, mark maximum depth on all instruments, avoid excessive posterior angulation of tibial stem

Mnemonic

AORI

Bone Loss Classification for Revision TKR

Mnemonic

CONSTRAINT

Implant Selection Ladder for Ligament Status

Anderson Orthopaedic Research Institute Classification

Purpose: Standardized assessment of bone loss to guide reconstruction strategy

Type 1 - Intact Metaphysis

Minor bone defects only, intact supportive metaphyseal bone
Reconstruction: Primary-style components with or without stems
Small defects: cement fill or morselized bone graft
Stems optional but often used for added stability

Type 2A - Unilateral Damage

One condyle (femur) or one plateau (tibia) involved
Metaphyseal bone damaged on ONE side only
Reconstruction: Unilateral augments (5-10mm metal blocks)
Short stems (100mm) mandatory for fixation bypass
Opposite side intact provides reference for sizing

Type 2B - Bilateral Damage

BOTH condyles or BOTH plateaus involved
Metaphyseal bone damaged bilaterally
Reconstruction: Large augments OR metaphyseal cones/sleeves
Longer stems (150mm) for better diaphyseal fixation
Cones provide osseointegration platform for biologic fixation

Type 3 - Deficient Metaphysis

Non-supportive metaphyseal bone, cannot support implant
Massive bone loss precludes standard reconstruction
Reconstruction Options:
- Structural allograft (distal femoral or tibial head)
- Tumor prosthesis (distal femoral replacement)
- Arthrodesis if salvage impossible
- Consider amputation if no viable reconstruction

Positioning and Preparation

Patient Position: Supine with thigh support/leg holder. Tourniquet available (may limit to 90 min or avoid). Prepare for extensive exposure.

Surgical Approach: Previous midline incision, may need extensile exposure (quad snip, VY turndown, tibial tubercle osteotomy)

Incision: Previous midline or most lateral scar, 15-20cm, extending proximal and distal

Operative Technique

Step 1: Preoperative Planning & Infection Workup

Preoperative Planning & Infection Workup: MANDATORY INFECTION WORKUP using the 2018 ICM/Musculoskeletal Infection Society evidence-based criteria. Serum markers: ESR >30 mm/hr (1 point) and CRP >10 mg/L i.e. >1 mg/dL (2 points); D-dimer >860 ng/mL (2 points) is the newer serum marker. Joint aspiration with cell count (synovial WCC >3000 cells/μL = 3 points), differential (PMN >80% = 2 points), leukocyte esterase (++ = 3 points), synovial alpha-defensin (positive = 3 points) and synovial CRP (>6.9 mg/L = 1 point); send fluid for culture and hold 14 days for low-grade organisms (Cutibacterium acnes, coagulase-negative staphylococci). Aggregate preoperative score greater than or equal to 6 = infected; 2-5 is inconclusive and needs intraoperative findings (frozen section, purulence, single positive culture). If infected: 2-STAGE REVISION protocol. IMPLANT IDENTIFICATION: review previous operative notes, query the relevant national joint registry, analyse X-ray features (cruciate-retaining vs PS vs CCK), contact manufacturer for explant tools. CT SCAN with metal artifact reduction for bone loss assessment (AORI classification). TEMPLATE: measure bone defects, plan for AORI reconstruction (augments, cones/sleeves, stems 100-150mm to engage 4-6cm of diaphysis), determine constraint level needed based on ligament status, plan for backup implants.

Clinical Pearl

Technical Tip: EXAM KEY: 'Before ANY revision TKR, must RULE OUT INFECTION. This is MANDATORY. Using the 2018 ICM/MSIS scoring: ESR >30 mm/hr, CRP >10 mg/L (>1 mg/dL), or aspiration synovial WCC >3000 (PMN >80%, positive alpha-defensin or leukocyte esterase ++) suggests infection requiring 2-stage revision. Cannot proceed to 1-stage revision with an unresolved positive infection workup - reinfection rates are unacceptably high. Identify implant brand - need correct extraction equipment or risk massive bone destruction. I template comprehensively: AORI bone loss classification, stem lengths (typically 100-150mm for 4-6cm diaphyseal fixation), augment sizes, constraint level. Must have backup implants available - bone loss often worse than expected on X-ray.'

Dangers at this step

Missing occult infection = disaster (proceeding with aseptic-style revision over an unrecognised infection leads to high reinfection and persistent infection rates, risk of further revision and rarely limb loss)
Wrong extraction equipment = extensive bone destruction trying to remove components
Inadequate implant inventory = aborted procedure or suboptimal reconstruction
Underestimating bone loss on plain X-rays (CT more accurate)

Step 2: Positioning & Tourniquet Strategy

Positioning & Tourniquet Strategy: Position supine with leg holder or thigh post allowing knee flexion >120°. TOURNIQUET DECISION: Many revision surgeons AVOID tourniquet or limit to 90 minutes. Rationale: (1) Better cement penetration into sclerotic bone when bleeding (cement fills vascular channels), (2) Allows monitoring of vascular status, (3) Avoids tourniquet-related complications in prolonged case. If using tourniquet: set to 100mmHg above systolic, exsanguinate with elevation (not Esmarch if PVD suspected). Prepare ENTIRE leg circumferentially sterile - may need longer stems, may need to extend proximally if bone loss worse than expected. Cell saver available for blood conservation. Antibiotics within 60 minutes (cefazolin 2g or vancomycin 15mg/kg if MRSA risk or PCN allergy).

Clinical Pearl

Technical Tip: EXAM KEY: 'Supine with leg holder allowing >120° flexion for tibial exposure. Many surgeons AVOID tourniquet in revision - rationale is better cement interdigitation in bleeding sclerotic bone vs bloodless field. If using tourniquet, limit to 90 minutes to reduce compartment syndrome risk in prolonged case. I prepare full leg circumferentially sterile - may need longer stems if metaphyseal bone loss worse than templated, and access to entire leg allows stem passage. Cell saver reduces transfusion needs in these higher blood loss cases.'

Dangers at this step

Prolonged tourniquet time (>120 min) = compartment syndrome risk increases significantly
Not preparing full leg = unable to extend stem if needed (aborted case)
PVD with tourniquet = ischemic complications
No cell saver = higher transfusion rates (revision TKR loses more blood than primary)

Step 3: Incision Planning & Skin Entry

Incision Planning & Skin Entry: INCISION SELECTION CRITICAL: If multiple previous incisions, use MOST LATERAL incision (preserves medial blood supply to skin). If scars <7cm apart, use most lateral. If scars >7cm apart, use closest to midline. Excise previous scar en bloc with full-thickness elliptical incision. Midline incision preferred if no previous scar. Skin length 15-20cm (longer than primary). Full-thickness flaps to avoid undermining. Raise medial and lateral flaps carefully off deep fascia. Assess flap vascularity - white, non-bleeding edges suggest vascular compromise. Medial parapatellar arthrotomy standard (8-10cm proximal to patella superior pole, curving medially around patella, extending to tibial tubercle). Extend arthrotomy PROXIMALLY into quadriceps tendon to facilitate exposure. Release adhesions between quad tendon and femur. Attempt patellar eversion gently - DON'T FORCE.

Clinical Pearl

Technical Tip: EXAM KEY: 'Incision choice is critical in revision TKR. Multiple parallel scars <7cm apart increase necrosis risk - use most lateral incision to preserve medial blood supply. I excise previous scar, create full-thickness flaps without undermining. Standard medial parapatellar arthrotomy extended PROXIMALLY into quadriceps. Release all adhesions but don't force patellar eversion - if stuck despite adhesiolysis, need extensile exposure. Forced eversion = patellar tendon avulsion disaster.'

Dangers at this step

Wrong incision choice (parallel scar <7cm) = skin necrosis requiring flap coverage
Thin flaps with undermining = marginal blood supply, necrosis
Forced patellar eversion = patellar tendon avulsion (catastrophic complication requiring allograft reconstruction)
Inadequate proximal quadriceps release = cannot expose femur, need extensile approach

Step 4: Extensile Exposure Selection

Extensile Exposure Selection: THREE MAIN EXTENSILE TECHNIQUES if standard approach inadequate: (1) QUAD SNIP (Insall): 45° oblique incision into vastus lateralis, 3-4cm proximal to superior arthrotomy edge. Simple, effective, heals reliably, no special postop protocol. Most common. (2) VY TURNDOWN (Coonse-Adams): Split quadriceps tendon in midline proximally 5-8cm, turn down as VY flap. More exposure than quad snip but compromises extensor mechanism - quad weakness common, repair complex. Reserved for very difficult cases. (3) TIBIAL TUBERCLE OSTEOTOMY (TTO): 5-7cm osteotomy of tibial tubercle, 1cm thick, hinged laterally on periosteum and patellar tendon. GOLD STANDARD for difficult revisions - excellent exposure, preserves extensor mechanism, heals reliably. Fixation with 2-3 bicortical screws (4.5mm) and cerclage wire. Postop: NWB or TTWB 6 weeks, no active SLR 6 weeks.

Clinical Pearl

Technical Tip: EXAM KEY: 'Extensile exposure often needed in revision. Three options: QUAD SNIP most common - 45° into vastus lateralis, 3-4cm proximal to arthrotomy, heals without special protocol. VY TURNDOWN gives most exposure but weakens quad - reserve for very stuck knees. TIBIAL TUBERCLE OSTEOTOMY is my preferred approach for difficult revisions - gold standard because it provides excellent exposure while preserving extensor mechanism and heals reliably. TTO technique: 5-7cm long, 1cm thick, hinged laterally, fixed with 2-3 screws plus wire. Postop NWB 6 weeks, no active SLR 6 weeks, union 8-12 weeks.'

Dangers at this step

Quad snip too distal = extends into arthrotomy (ineffective)
Quad snip too far lateral = into vastus lateralis muscle belly (bleeding)
VY turndown = significant quad weakness (10-20% extensor lag common)
TTO fracture during osteotomy = complex fixation problem
TTO non-union postop (2-5%) = persistent pain, extensor lag
TTO displacement with early weight-bearing or active extension

Step 5: Component & Polyethylene Removal

Component & Polyethylene Removal: SYSTEMATIC APPROACH: (1) Remove polyethylene INSERT first (easiest with knee flexed, gives access to interfaces). (2) Break cement-bone interface circumferentially: thin flexible osteotomes (3-5mm), Gigli saw posteriorly if accessible. Work methodically around entire component - femoral condyles, posterior condyles, tibial base. (3) FEMORAL COMPONENT removal: universal femoral extractor or brand-specific slap hammer system. Apply to anterior flange, impact carefully. If well-fixed, may need multiple osteotomes simultaneously. (4) TIBIAL COMPONENT removal: universal tibial extractor. Beware posterior cortex perforation. (5) CEMENT REMOVAL: ALL cement must be removed for stem fixation - ultrasonic cement removal (vibrates cement-bone interface), high-speed burr with careful technique, thin straight osteotomes in canals. Curettes for small fragments. May need canal reaming to achieve clean diaphyseal bone for stem. Preserve bone - accept some cement if removal risks significant fracture. Inspect for membrane (indicates loosening).

Clinical Pearl

Technical Tip: EXAM KEY: 'I remove polyethylene first - gives access. Break cement-bone interface methodically with thin flexible osteotomes and Gigli saw posteriorly. Specialized extraction instruments ESSENTIAL for each brand - universal extractors available but brand-specific better. Key principle: PRESERVE BONE - accept some cement residue if removal risks fracture, but ALL canal cement must be removed for stem fixation. Ultrasonic cement removal extremely useful - vibrates interface without osteotome trauma. Complete cement removal from medullary canals critical - residual cement prevents stem seating and fixation. May need sequential reaming to clear canals.'

Dangers at this step

Fracture during extraction (femoral condyle, tibial plateau, femoral shaft) - requires immediate fixation and changes implant plan
Aggressive bone loss from osteotomes - increases AORI grade, worsens prognosis
Retained cement in canal = inadequate stem fixation = early loosening
Popliteal artery injury from posterior tibial cortex breach during cement removal or reaming (catastrophic)
Anterior cortex perforation of femur during canal preparation
Not having extraction equipment = prolonged surgery time, excessive bone loss

Step 6: Bone Loss Assessment - AORI Classification

Bone Loss Assessment - AORI Classification: ASSESS WITH TRIAL COMPONENTS IN SITU: AORI (Anderson Orthopaedic Research Institute) CLASSIFICATION guides reconstruction: TYPE 1 (intact metaphyseal bone, minor defects) - primary components with or without stems, minimal augmentation, cement/bone graft for small defects. TYPE 2A (damaged metaphyseal bone, ONE condyle/plateau involved) - small/medium augments (5-10mm), short stems (100mm), unilateral reconstruction. TYPE 2B (damaged metaphyseal bone, BOTH condyles/plateaus involved) - large augments (>10mm), metaphyseal cones or sleeves, longer stems (150mm), bilateral reconstruction. TYPE 3 (deficient metaphysis, non-supportive bone) - massive structural allograft (femoral or tibial head), metaphyseal sleeves with stems, tumor prosthesis (distal femoral replacement or hinged knee with long stems), or consider arthrodesis. Assess BOTH femoral and tibial bone loss separately. Contained vs uncontained defects. Confirm with trial spacers.

Clinical Pearl

Technical Tip: EXAM KEY: 'AORI classification is the standard: Type 1 = intact metaphysis (primary components work, stems optional). Type 2 = damaged metaphysis - A is one side, B is both sides - requires augments, cones/sleeves, and stems mandatory. Type 3 = deficient unsupportive metaphysis - needs structural allograft, tumor prosthesis, or consider arthrodesis if salvage. I assess bone loss WITH TRIAL COMPONENTS IN PLACE - this shows what will support implants. Classify femur and tibia separately. Type 1: augments <5mm, stems optional. Type 2A/2B: augments 5-15mm or cones/sleeves, stems 100-150mm mandatory. Type 3: consider salvage options, prognosis poor. Know that bone loss often worse than X-ray suggests - CT better for assessment.'

Dangers at this step

Underestimating bone loss = inadequate implant choice = early failure
Not having appropriate implants available (augments, cones, long stems) = aborted case or suboptimal reconstruction
Type 3 bone loss without salvage options = may require arthrodesis or amputation
Contained vs uncontained distinction important - uncontained requires different reconstruction (cones vs augments)

Step 7: Soft Tissue & Ligament Assessment

Soft Tissue & Ligament Assessment: LIGAMENT-BASED CONSTRAINT DECISION: Insert trial spacer block (8-10mm). Assess MCL and LCL integrity in extension and throughout flexion arc. GRADING: Grade 0 (intact, <5mm opening to varus/valgus stress) = both collaterals functional, PS possible. Grade 1 (5-10mm opening, firm endpoint) = MCL attenuated, CCK recommended. Grade 2 (>10mm opening, no endpoint) = MCL deficient, CCK minimum, consider rotating hinge. Grade 3 (both collaterals deficient) = rotating hinge mandatory. Test in extension, 30° flexion, 90° flexion. PCL rarely relevant in revision (usually sacrificed in primary PS knee or incompetent). EXTENSOR MECHANISM: assess patellar bone stock (may be severely deficient from multiple previous resurfacings), quadriceps and patellar tendon quality (chronic tear?), tracking (lateral subluxation suggests VMO deficiency). May need lateral release. Severely deficient patella = consider patellar resection (patellectomy) vs no resurfacing vs augments.

Clinical Pearl

Technical Tip: EXAM KEY: 'Constraint decision based on LIGAMENT STATUS with spacer trial in situ. Both collaterals intact (<5mm varus-valgus laxity): PS implant possible but most use CCK for revision given bone loss. MCL attenuated or deficient (5-10mm opening): CCK mandatory - provides varus-valgus constraint. Both collaterals gone (>10mm or no endpoint): rotating hinge. PCL status rarely matters in revision. Key principle: don't UNDER-constrain (leads to instability) but also don't OVER-constrain (increases stress on bone-implant interface, accelerates loosening). CCK allows ±8° varus-valgus but preserves some rotation (5-6°). Hinge fully constrains coronal and sagittal plane (allows axial rotation only). Extensor mechanism: assess patella bone stock - may be paper-thin from multiple resurfacings. Options: resurface if >10mm bone, augment if 5-10mm, leave unresurfaced if <5mm (patelloplasty), or patellectomy if severe arthritis.'

Dangers at this step

Under-constraining (PS with MCL deficiency) = instability, dislocation, reoperation
Over-constraining (hinge with intact collaterals) = accelerated loosening from increased constraint forces
Poor extensor mechanism assessment = patellar fracture, tendon rupture, maltracking postop
Inadequate lateral release with tight lateral structures = patellar maltracking, anterior knee pain
Patella too thin for resurfacing (<10mm) = fracture risk

Step 8: Femoral Reconstruction

Femoral Reconstruction: DEFECT RECONSTRUCTION LADDER: Small defects (<5mm) = cement or morselized bone graft. Medium defects (5-10mm) = AUGMENTS (modular metal blocks, cemented separately or built-in to component) - posterior, distal, or posterior-oblique. Large defects (>10mm metaphyseal, uncontained) = METAPHYSEAL CONES or SLEEVES (porous metal cones press-fit into metaphysis, provide stable platform, osseointegrate over time). Sleeve vs cone: sleeve cylindrical and extends into diaphysis, cone conical and seats in metaphysis. SIZE FEMORAL COMPONENT after defect reconstruction: choose size matching intact bone (not deficient condyle). AP and ML sizing. ROTATION critical: 3° external to transepicondylar axis, or parallel to posterior condyles of non-deficient side, or perpendicular to Whiteside's line. FEMORAL STEM: press-fit (preferred if canal adequate) aiming for at least 4-6cm of scratch-fit diaphyseal engagement (typically 100-150mm stems), or cemented if poor bone quality or wide/sclerotic canal. Stems should bypass metaphyseal defects - goal is diaphyseal fixation. Offset stems available for bowed femurs or canals with deformity. Modular vs fixed stem.

Clinical Pearl

Technical Tip: EXAM KEY: 'Femoral reconstruction follows defect ladder: <5mm use cement, 5-10mm use augments, >10mm use cones or sleeves. Augments are modular metal blocks - cemented separately or built into component. Cones and sleeves for large uncontained metaphyseal defects - press-fit porous metal that osseointegrates, very successful. Size component to INTACT bone not deficient condyle. Rotation absolutely critical in revision - use multiple references (transepicondylar axis +3° ER, posterior condyles if one intact, Whiteside's line). FEMORAL STEM philosophy: must achieve at least 4-6cm of diaphyseal engagement (typically 100-150mm stems) bypassing metaphyseal defects. Press-fit stems preferred - rely on diaphyseal canal fill. Cemented stems if poor bone quality or cannot achieve press-fit. Modular systems allow intraop adjustment of offset and version. Offset stems essential for bowed femurs or post-fracture deformity.'

Dangers at this step

Augment not adequately supported by host bone = fracture or subsidence
Stem too short (less than 4cm diaphyseal engagement) = relies on failed metaphyseal bone, early loosening
Malrotation = patellar maltracking (internal rotation), pain, instability, accelerated wear
Femoral fracture during stem preparation (especially with previous deformity)
Cone/sleeve not adequately seated or press-fit = subsidence, failure to osseointegrate
Varus or valgus stem alignment = eccentric loading, loosening

Step 9: Tibial Reconstruction

Tibial Reconstruction: Similar reconstruction ladder to femur: AUGMENTS for contained defects 5-10mm. METAPHYSEAL CONES for uncontained defects >10mm (highly porous tantalum or titanium cones placed into metaphyseal defect, press-fit, osseointegrate - provide stable platform for tibial component). Cones placed BEFORE tibial tray - tray then cemented onto cone. SLEEVES alternative - cylindrical porous metal extending from metaphysis into diaphysis. SIZE TIBIAL COMPONENT to maximize coverage of intact bone - underhang preferable to overhang (avoid vascular and ligamentous impingement). CHECK ROTATION: align tibial component with 2nd ray (medial 1/3 of tibial tubercle), match native rotation, ensure symmetric flexion/extension gaps. Tibial tubercle should be MIDLINE or slightly lateral (never medial). TIBIAL STEM: 100-150mm length (longer than femoral stem), cemented or press-fit. CRITICAL: POSTERIOR CORTEX AWARENESS - popliteal artery 2cm from posterior cortex. Mark drill depth, use depth stop, careful reaming. Stems must engage diaphysis in at least one plane (press-fit) or can be fully cemented. Offset stems if needed for deformity.

Clinical Pearl

Technical Tip: EXAM KEY: 'Tibial reconstruction mirrors femur: augments 5-10mm, cones >10mm for metaphyseal defects. Metaphyseal cones are game-changer in revision - tantalum or titanium porous metal cones press-fit into defect, osseointegrate, provide stable biologic platform. Place cone first, then cement tibial component onto cone. Very successful technique for Type 2B/3. Size tibial tray to maximize coverage - slight underhang OK (better than overhang). ROTATION critical - align with 2nd ray, tubercle midline or slightly lateral, match native rotation. Malrotation causes pain and patellar maltracking. TIBIAL STEM must engage diaphysis 4-6cm. Critical danger: POSTERIOR CORTEX perforation during stem prep. Popliteal artery only 2cm from posterior cortex - perforation = catastrophic vascular injury. I always mark maximum drill depth and use depth stop. Press-fit stem needs good canal fit. Cemented stem if poor bone or press-fit inadequate.'

Dangers at this step

POSTERIOR CORTEX PERFORATION = popliteal artery injury 2cm away (catastrophic, may require amputation)
Malrotation = patellar maltracking, pain, instability, accelerated poly wear
Cone not seated properly = subsidence, failure, pain
Stem perforation lateral = peroneal nerve injury (foot drop)
Stem too short = relies on damaged metaphysis, early subsidence
Tibial tray overhang = soft tissue impingement, pain, neurovascular compression
Undercorrection of tibial slope = instability or hyperextension; overcorrection = flexion loss

Step 10: Trialing, Gap Balancing & Alignment

Trialing, Gap Balancing & Alignment: Insert trial components with appropriate augments, cones/sleeves, and stems. ASSESS ALIGNMENT: mechanical axis should pass through center of knee (55% through lateral compartment). Varus/valgus <3° acceptable. Check with trial components and assess under image intensifier if available. ASSESS STABILITY: Extension gap and flexion gap testing. In revision often have asymmetric gaps due to bone loss - may need to accept slight imbalance to preserve bone stock. Insert trial poly of appropriate thickness - aim for 10-12mm but stability more important than thickness. Test medial/lateral laxity (varus/valgus stress). Test anteroposterior stability (drawer test). CCK should be stable throughout arc with mild varus-valgus laxity preserved. PATELLAR TRACKING: assess with trial components through full ROM. No-thumb test (patella centers without manual pressure). Patella should track centrally without subluxation. May need lateral release if tight (pie-crust technique or formal Z-lengthening). CHECK ROM: aim for 0-110° (0-120° better). Assess extension fully (no flexion contracture). Assess for midflexion instability (loose in midflexion, tight in extension/flexion = indicates incorrect gap balancing).

Clinical Pearl

Technical Tip: EXAM KEY: 'Revision gap balancing much more challenging than primary due to asymmetric bone loss. May need to accept slight imbalance rather than over-resect and worsen bone stock. CCK provides inherent stability compensating for imperfect soft tissue balance - this is advantage over PS. I assess alignment - mechanical axis through knee center. Check stability throughout arc with trial poly: varus-valgus laxity (should have mild laxity in CCK, none in hinge), AP stability (drawer test). Patellar tracking critical - no-thumb test, should center without subluxation. Lateral release if needed. ROM goals: 0-110° minimum, 0-120° preferred. Flexion contracture unacceptable - may need posterior capsule release or downsize femur. Midflexion instability suggests gap mismatch.'

Dangers at this step

Over-resection to balance gaps = worsens bone loss, may escalate to Type 3 defects
Under-constraining = instability postop, reoperation
Maltracking patella = anterior knee pain, patellar complications, patient dissatisfaction
Flexion contracture accepted = poor function, patient dissatisfaction
Midflexion instability (loose in midflexion) = cam-post problems or gap mismatch requiring revision
Overstuffing joint (poly too thick) = stiffness, limited ROM; understuffing = instability

Step 11: Cementation Technique & Final Components

Cementation Technique & Final Components: METICULOUS CEMENTATION CRITICAL: Clean and dry all bone surfaces. Pulse lavage entire field. Dry with suction and sponges. Apply cement restrictors in canals if needed. High-viscosity antibiotic-loaded cement (gentamicin or tobramycin). CEMENT APPLICATION: Pressurize into sclerotic bone with cement gun. Paint onto back of augments. Fill metaphyseal defects. For cones/sleeves: cement component onto cone, press-fit cone into metaphysis (do NOT cement cone-bone interface - needs osseointegration). STEM FIXATION STRATEGY: HYBRID (cement component/augments, press-fit stem - most common) or FULLY CEMENTED (cement component AND stem if press-fit inadequate). If cementing stem, centralize in canal, avoid stem-in-cement-in-bone (weak), want stem-cement interdigitation. Remove excess cement especially POSTERIORLY (impingement) and from cam-post mechanism. INSERTION SEQUENCE: (1) Insert tibial component with stem, cement onto cone if used, remove excess cement. (2) Insert femoral component with stem, cement onto augments, remove excess cement. (3) While cement curing, insert TRIAL POLY to compress interfaces and remove excess cement extruding into joint. (4) After cement cured, remove trial poly, insert FINAL POLY (modular locking poly - ensure locked). CHECK FINAL STABILITY: repeat stability testing, confirm ROM, check tracking.

Clinical Pearl

Technical Tip: EXAM KEY: 'Cement technique is absolutely critical in revision with poor bone quality. I use high-viscosity antibiotic cement, pressurize with cement gun into sclerotic bone. Pulse lavage and dry bone first. Cones/sleeves: DO NOT CEMENT bone-cone interface - press-fit only for osseointegration. Cement component onto cone. Stems: hybrid fixation most common - cement component and augments, press-fit stem into diaphysis. If cannot achieve press-fit (poor bone, wide canal), fully cement stem. Cemented stems: avoid stem-in-cement-in-bone technique (weak) - want cement interdigitated with bone and stem. Remove ALL excess posterior cement - causes impingement and pain. Critical sequence: tibia first, femur second, TRIAL poly while cement cures to compress interfaces and extrude excess cement, then final poly after curing. Ensure final poly locked securely - dissociation is a complication.'

Dangers at this step

Poor cement penetration in sclerotic bone = early loosening (most common failure mode)
Posterior cement extrusion = impingement, pain, limited flexion, may need reoperation
Cementing cone-bone interface = prevents osseointegration, failure
Stem-in-cement-in-bone technique = weak construct, failure
Components not fully seated = proud component, subsidence, early failure
Cam-post mechanism cement = catching, dissociation, instability
Polyethylene not locked = dissociation (sudden instability and pain)
Cement on articulating surfaces = rapid poly wear

Step 12: Closure & Tibial Tubercle Fixation

Closure & Tibial Tubercle Fixation: If TTO performed: Carefully reduce tibial tubercle to anatomic position. FIX WITH 2-3 bicortical screws (4.5mm cortical screws) placed in lag fashion through tubercle into posterior cortex. Add CERCLAGE WIRE or HEAVY SUTURE (Fiberwire #5) around proximal tibia for rotational control and compression. Test fixation stability with gentle traction. Close periosteum over TTO if possible. CAPSULAR CLOSURE: Repair capsule and arthrotomy in layers with interrupted 0-Vicryl. If quad snip performed, repair with interrupted 0-Vicryl sutures. Ensure extensor mechanism continuity - no gaps. PATELLAR CLOSURE: Repair retinaculum if possible. If tissue deficient, may need synthetic mesh (Marlex) reinforcement. TEST FINAL ROM passive - should maintain 0-110° achieved during trialing. SUBCUTANEOUS: Close in layers, 2-0 Vicryl to deep tissue. SKIN: Staples or interrupted nylon sutures. DRAIN: controversial - many use deep drain (12-24hr removal). DRESSING: Compressive but not circumferential. KNEE IMMOBILIZER or hinged brace if instability concerns or TTO performed.

Clinical Pearl

Technical Tip: EXAM KEY: 'If TTO: Fixation absolutely critical - 2-3 bicortical screws in lag fashion plus cerclage wire around proximal tibia for rotation control and compression. Test stability. Postop protocol for TTO: NWB or toe-touch weight bearing for 6 weeks, NO active SLR for 6 weeks (protects TTO and extensor mechanism), passive ROM only initially. TTO union takes 8-12 weeks - X-ray surveillance. Quad snip heals without special precautions - just repair well. I close capsule and arthrotomy meticulously in layers - extensor mechanism integrity critical. Test final passive ROM - should maintain trial ROM. Drain controversial - I use for 12-24 hours. Compression dressing, immobilizer if TTO or instability concern.'

Dangers at this step

TTO inadequate fixation = non-union or displacement (early weight-bearing or active SLR causes this)
TTO screws too anterior = fracture through tubercle; too posterior = intraarticular
Early active extension with TTO = avulsion, failure, extensor lag
Poor capsular repair = extensor lag, weakness
Hematoma formation = arthrofibrosis, infection risk
Drain left >48 hours = increased infection risk
Circumferential tight dressing = compartment syndrome in this higher-risk population

Step 13: Confirm Final Assessment & Documentation

Confirm Final Assessment & Documentation: Before leaving OR: FINAL CHECKS - (1) Stability throughout ROM, (2) Alignment under image intensifier if available, (3) ROM documented (extension/flexion), (4) All sponges and instruments accounted for, (5) Hemostasis adequate. INTRAOPERATIVE X-RAYS: AP and lateral to confirm component position, stem seating, alignment. OPERATIVE NOTE DOCUMENTATION critical: (1) Findings (AORI bone loss grade, ligament status, removed implant details), (2) Reconstruction (augments used, cone/sleeve sizes, stem lengths and fixation method, constraint level, poly thickness), (3) Final alignment and ROM, (4) Complications if any, (5) Implant stickers in chart. IMPLANT TRACKING: Record all lot numbers, register the implant with the relevant national joint registry (e.g. NJR, AJRR, AOANJRR, NZJR, Nordic registries), document for future reference.

Clinical Pearl

Technical Tip: EXAM KEY: 'Before closing, systematic final check: stability throughout arc, alignment verified, ROM measured and documented, all counts correct, hemostasis adequate. Intraop X-rays confirm component position and stem seating - especially important in revision. Operative note documentation is medico-legally critical and helps future surgeons if re-revision needed: record AORI grade, ligaments, implants removed, new implants used with all specifics (stem lengths, augment sizes, cone types, constraint), final alignment and ROM. Register implants with the relevant national joint registry - registries track revision outcomes worldwide. Implant stickers in medical record. This documentation may be crucial years later.'

Dangers at this step

Inadequate final stability check = missed instability requiring immediate reoperation
Poor documentation = medical-legal issues, future surgeons unable to identify implants
Not registering implants = cannot identify for future revision
Missed intraoperative fracture or malposition = poor outcome

Complications

Revision TKR Complications: Recognition, Prevention, Management

Post-operative Care

TTO or structural graft: NWB or TTWB 6 weeks, no active SLR 6 weeks, passive ROM only. Otherwise: WBAT immediately, active ROM day 1-2. Brace if instability concerns. Aggressive physiotherapy to prevent stiffness. Chemical DVT prophylaxis (LMWH or factor Xa inhibitor) for 14 days minimum. TTO X-rays at 2, 6, 12 weeks to assess union. Full clinic follow-up: 2wk (wound), 6wk (X-rays, progress weight-bearing if TTO), 3mo (X-rays, assess ROM and function), 6mo, 1yr, then annually. National joint registry reporting where applicable.

Clinical Decision Scenarios

Use these scenarios to practise clinical reasoning and management decisions

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"A 68-year-old woman presents with painful TKR 3 years post-primary surgery. X-rays show radiolucent lines around both tibial and femoral components. How do you approach this case?"

PRACTICAL APPROACH

This patient has a failed TKR with possible loosening. My systematic approach begins with mandatory infection workup - this is CRITICAL and cannot be bypassed. I would obtain ESR and CRP - values greater than 30 and 10 respectively suggest infection. I would perform joint aspiration under sterile conditions, sending for cell count (greater than 3000 WCC concerning), differential (greater than 80% PMNs highly suggestive), culture (held 14 days for low-virulence organisms), and alpha-defensin testing which has high sensitivity and specificity. If infection is confirmed, I would proceed with TWO-STAGE REVISION: Stage 1 involves complete explantation of all components, aggressive debridement of all infected tissue, and placement of antibiotic-loaded cement spacer (static or articulating containing 3-6g vancomycin plus aminoglycoside per 40g cement). This is followed by 6 weeks of IV organism-specific antibiotics. After antibiotics completed and inflammatory markers normalized, I would re-aspirate to confirm infection clearance before Stage 2 reimplantation. If infection is ruled out (aseptic loosening), I would obtain CT with metal artifact reduction to classify bone loss using AORI system - Type 1 intact, Type 2A one side involved, Type 2B both sides, Type 3 deficient metaphysis. I would identify the existing implant brand and arrange appropriate extraction equipment. I would template for reconstruction including stem lengths (typically 100-150mm for 4-6cm diaphyseal fixation), augment sizes, and cone/sleeve options. Intraoperatively, I would assess ligament status to determine constraint level needed.

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"You are performing a revision TKR and after removing the components, you find AORI Type 2B bone loss on both femur and tibia with an attenuated MCL. The patella everts with significant difficulty. Describe your reconstruction strategy."

PRACTICAL APPROACH

This is a challenging revision TKR requiring extensile exposure, substantial bone defect reconstruction, and increased constraint. Let me address each issue systematically. EXTENSILE EXPOSURE: Given difficulty with patellar eversion, I would perform a TIBIAL TUBERCLE OSTEOTOMY (TTO) - this is my preferred approach as it provides excellent exposure while preserving the extensor mechanism. Technique involves a 5-7cm osteotomy of the tibial tubercle, 1cm thick, hinged laterally on periosteum and lateral soft tissues. I would later fix this with 2-3 bicortical screws (4.5mm) in lag fashion plus cerclage wire for rotational control. Postoperatively this requires NWB for 6 weeks and NO active SLR for 6 weeks. BONE DEFECT RECONSTRUCTION: For Type 2B loss affecting both condyles/plateaus bilaterally, I would use METAPHYSEAL CONES on both femur and tibia. These are highly porous tantalum or titanium cones that press-fit into the metaphyseal defects and osseointegrate over time. Key technical point: I would NOT cement the bone-cone interface - this must remain press-fit for biologic ingrowth. I would then cement the tibial tray and femoral component ONTO the cones. If augments needed for fine-tuning, I would use 5-10mm blocks in addition. Both femoral and tibial stems are mandatory - 100-150mm length to achieve 4-6cm diaphyseal fixation, bypassing the compromised metaphyseal bone. CONSTRAINT SELECTION: With an attenuated MCL showing 5-10mm varus-valgus opening, I would use a CONSTRAINED CONDYLAR KNEE (CCK). This provides inherent varus-valgus constraint within ±8° while still allowing 5-6° of axial rotation. CCK is the most commonly used constraint in revision TKR and provides an appropriate balance - rotating hinge would be over-constraining with an attenuated (not absent) MCL.

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"During revision TKR component removal, you hear a crack as the tibial component comes out. You identify a medial tibial plateau fracture. How do you manage this and what changes to your reconstruction plan?"

PRACTICAL APPROACH

An intraoperative periprosthetic fracture during revision TKR requires immediate recognition and management adjustment. This is not uncommon during component extraction, especially in osteoporotic bone. IMMEDIATE ASSESSMENT: I would carefully assess the fracture pattern - is it a simple split of the medial plateau or more comminuted? Does it extend into the metaphysis or diaphysis? Is the lateral plateau intact? This assessment will guide both immediate fixation and implant selection. FRACTURE MANAGEMENT: For a medial plateau fracture, I would reduce the fragment anatomically and provisionally fix with K-wires. Definitive fixation would involve a medial buttress plate (often a small fragment 3.5mm LCP or specific periarticular plate) with screws placed to avoid the planned tibial stem trajectory. Alternatively, I may use multiple 4.5mm lag screws if the fragment is large enough. For smaller fragments or comminution, I may accept some bone loss and address with augmentation. RECONSTRUCTION PLAN CHANGES: This fracture fundamentally changes my reconstruction strategy: 1. BONE LOSS: The fracture effectively converts this to at least AORI Type 2A (if previously Type 1) or worsens existing bone loss classification. I would now plan for a METAPHYSEAL CONE on the tibial side to provide stable fixation despite compromised medial plateau. 2. STEM FIXATION: I would use a LONGER TIBIAL STEM (150mm minimum) to bypass the fracture site and achieve fixation in healthy diaphyseal bone. The stem must extend at least 2 cortical diameters beyond the distal extent of any fracture. 3. CEMENTED vs PRESS-FIT: Given the fracture, I would strongly consider a FULLY CEMENTED tibial stem rather than press-fit to avoid further stress on the compromised bone during press-fit impaction. 4. WEIGHT-BEARING: Postoperatively I would restrict to PROTECTED WEIGHT-BEARING or NWB for 6-12 weeks until fracture union, rather than standard WBAT. 5. SURVEILLANCE: Close radiographic follow-up at 2, 6, and 12 weeks to monitor fracture healing.