Medial parapatellar arthrotomy is the standard exposure · alternatives are midvastus, subvastus and lateral parapatellar (for the valgus knee) · advanced
- End-stage osteoarthritis unresponsive to conservative management (NSAIDs, physiotherapy, activity modification, weight loss, injections) with significant functional limitation affecting quality of life - typical age over 65 years.
- Inflammatory arthritis (rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis) with severe joint destruction despite medical management with DMARDs and biologics, and post-traumatic arthritis following tibial plateau, distal femoral or ligamentous injury, are the other major indications.
- Femoral component rotation is determined using multiple references: posterior condylar axis plus 3 degrees external rotation, the transepicondylar axis (most reliable), and Whiteside's line (the component sits perpendicular to this AP axis). If these conflict, prioritise the epicondylar axis.
- The goal of gap balancing is equal, rectangular flexion and extension gaps with balanced medial and lateral tension - typically 8 to 10mm with the planned component thickness. Dry bone and cement pressurisation are non-negotiable for durable cement fixation.
When & Why
Indications. The dominant indication is end-stage osteoarthritis with Kellgren-Lawrence grade 3 to 4 changes that has failed a minimum of 3 to 6 months of conservative care (NSAIDs, physiotherapy, activity modification, weight loss if BMI over 30, and intra-articular corticosteroid or hyaluronic acid injection), with significant functional limitation - inability to walk more than 1 to 2 blocks, difficulty with stairs, night pain disturbing sleep, and impact on activities of daily living. Other indications: - Inflammatory arthritis (rheumatoid, psoriatic, ankylosing spondylitis) with severe joint destruction despite DMARDs (methotrexate, sulfasalazine) and biologics (TNF inhibitors, IL-6 inhibitors).
- Post-traumatic arthritis following tibial plateau fracture, distal femoral fracture, or chronic ACL or PCL deficiency with secondary degenerative change.
- Osteonecrosis with collapse and secondary degenerative change. Typical patient age is over 65 years (longer implant survival in older patients); younger patients are considered if symptoms are severe and expectations on activity and revision risk are realistic. Contraindications.
- Absolute: active infection (septic arthritis, osteomyelitis, cellulitis), an inadequate soft-tissue envelope with open wounds or ulceration, a non-reconstructable extensor mechanism (quadriceps or patellar tendon rupture), and severe vascular insufficiency precluding healing.
- Relative: age less than 50 to 55 years (higher revision rates - consider HTO or UKA), severe obesity (BMI over 40; increased infection, thromboembolism and mechanical failure), active substance abuse or psychiatric illness limiting rehabilitation, prohibitive anaesthetic comorbidity, and neuropathic (Charcot) arthropathy with severe bone loss and instability. Medical optimisation before listing. Glycaemic control to HbA1c less than 7 percent (ideally less than 6.5 percent; defer if over 8 percent until optimised with endocrinology). Smoking cessation a minimum of 4 to 6 weeks preoperatively. Weight loss toward BMI less than 35 to 40 (bariatric referral if morbidly obese). Nutrition screen (albumin over 35g per L, lymphocyte count over 1500). Dental clearance for active caries or periodontal disease. Treat active skin conditions (psoriasis, eczema, ulceration). Cease anticoagulants and antiplatelets per anaesthetic guidance (warfarin 5 days, clopidogrel 7 days; continue aspirin). Radiographic planning. Weight-bearing films are essential: an AP pelvis-to-ankle mechanical-axis film, standing AP knee, lateral knee, and a skyline (Merchant or sunrise) patellar view. Analyse the deformity - mechanical axis deviation, quantify varus or valgus, and decide if it is fixed or correctable (stress films if uncertain). Template femoral and tibial component sizes, assess the canal if stemmed components are contemplated, and identify bone loss needing augments. Note patellar morphology (Wiberg type, trochlear groove depth), patella alta or baja (Insall-Salvati ratio, normal 0.8 to 1.2), tibial slope (normal 3 to 7 degrees posterior) and osteophytes. CT is reserved for complex deformity, version or prior fracture; MRI is rarely needed. Consent around the documented major risks - infection (including the possibility of staged revision), aseptic loosening and the need for revision surgery, instability, stiffness and manipulation, periprosthetic fracture, venous thromboembolism, and patellar complications - as well as the realistic functional outcome and activity restrictions. Setup. Supine on a standard operating table with a radiolucent extension or foot holder; a leg holder or foot-of-bed flexion allows the knee to flex to 90 degrees or more and is preferred for stable independent positioning. Tourniquet on the proximal thigh with adequate padding. A lateral thigh post prevents external rotation when a leg holder is used. Prepare the entire limb from tourniquet to toes (include the foot for intraoperative alignment assessment).
The Operation
The goal is to resurface the arthritic knee through a medial parapatellar arthrotomy, make perpendicular, rotationally correct bony resections, balance equal and rectangular flexion and extension gaps, fix the components with pressurised cement onto dry bone, and close a watertight capsule - restoring a neutral mechanical axis, a stable knee through full range and central patellar tracking. The exposure is the heart of the case and is laid out in full as the first steps below.
Choosing the exposure. All four arthrotomies reach the same joint; the standard medial parapatellar is the workhorse.
The default. Splits the quadriceps tendon in line with the VMO fibres medial to the rectus, 5 to 8mm medial to the patella. Best exposure, reliable in almost every knee, but disrupts part of the extensor mechanism.
Splits the VMO in line with its fibres. Less extensor-mechanism disruption and better early recovery, with exposure that is only slightly more limited than the standard approach.
Elevates the VMO from the intermuscular septum, preserving the quadriceps tendon. Most muscle-sparing, but exposure is limited and it is unsuitable for stiff or muscular knees.
Used for the severe valgus knee with contracted lateral structures, allowing lateral soft-tissue balancing from inside-out through the same incision.
Operative sequence
- Supine, leg holder or foot-of-bed flexion so the knee flexes to 90 degrees or more; tourniquet on the proximal thigh with padding; lateral thigh post if a leg holder is used.
- Confirm the knee flexes to 90 degrees and extends fully, and that a sterile alignment rod can assess the mechanical axis intraoperatively.
- Prepare from tourniquet to toes, including the foot for alignment checks.
- Straight longitudinal midline or just medial to it, 12 to 15cm, from 5 to 7cm proximal to the superior pole of the patella to the tibial tuberosity.
- If previous scars exist, use the most lateral usable incision (best blood supply from the lateral genicular artery) and avoid skin bridges less than 5cm wide (necrosis risk).
- Identify the tibial tuberosity, patella and quadriceps tendon before incising; develop full-thickness flaps without excessive undermining; retract gently with skin hooks rather than forceps.
- Incise the medial retinaculum 5 to 8mm medial to the patellar border from superior to inferior pole, extending proximally into the quadriceps tendon in line with the VMO fibres (medial to rectus) and distally along the medial border of the patellar tendon to the tibial tuberosity.
- Carry the incision through the capsule into the joint, confirming entry by visualising synovium and cartilage.
- Stay medial to the patella to preserve the peri-patellar vascular ring and the VMO insertion on the distal medial patella; place stay sutures in the capsular edges to aid later repair.
- Alternative approaches: midvastus (split the VMO in line with its fibres), subvastus (elevate the VMO from the septum), or lateral parapatellar for the severe valgus knee.
- Evert the patella laterally with gentle pressure at 60 to 90 degrees of flexion; if eversion is difficult, extend the quadriceps incision proximally and release adhesions before any lateral release (which risks devascularisation).
- Excise the infrapatellar fat pad flush with the anterior tibia, preserving some for soft-tissue cover; remove the ACL remnant from its tibial and femoral insertions with a curved osteotome.
- Excise the medial and lateral menisci completely; remove peripheral femoral and tibial osteophytes (they falsely tighten the gaps); identify the PCL (preserve in a CR design, may release in a PS design).
- Assess the coronal and sagittal deformity with the knee extended.
- Extramedullary alignment rod along the anterior tibial crest aimed at the centre of the ankle mortise (between the malleoli) or the second metatarsal; set perpendicular to the mechanical axis (0 degrees varus or valgus).
- Posterior slope 3 to 7 degrees (CR often 3 to 5 degrees; PS may accept 5 to 7 degrees) - match native slope or the component design.
- Resect 8 to 10mm from the less-affected plateau (lateral in a varus knee; medial in a valgus knee), with a minimum 2mm of bleeding cancellous bone for cement fixation.
- Cut with an oscillating saw staying on the guide, medial to lateral, protecting the MCL and popliteal vessels with retractors; verify with a trial that alignment, slope and coverage (avoid overhang or underhang) are correct.
- Open the femoral canal at the centre of the trochlear notch with a drill or box cutter and insert the intramedullary rod; set the valgus angle at 5 to 7 degrees (between the mechanical and anatomical axes), individualised from templating.
- Resect 8 to 10mm from the least-worn condyle (lateral in valgus, medial in varus).
- Set femoral rotation from multiple references and verify they agree: posterior condylar axis plus 3 degrees external rotation (simple but unreliable in valgus), the transepicondylar axis (most reliable, lateral prominence to medial sulcus), and Whiteside's line (perpendicular to the AP axis from trochlear groove to intercondylar notch). If they conflict, prioritise the epicondylar axis.
- Size the component to fill the AP dimension without anterior notching (a stress riser for supracondylar fracture) or posterior overhang (impingement); complete anterior, posterior and chamfer cuts with a 4-in-1 block; add the box cut for a PS design, centred and avoiding posterior cortex perforation.
- Place spacer blocks between the resected surfaces in full extension; target 8 to 10mm (matching the planned component including polyethylene).
- The knee should extend fully to 0 degrees with balanced medial and lateral tension and no lift-off.
- Tight medially (varus knee): release the deep MCL incrementally by pie-crusting, remove remaining osteophytes, and preserve the superficial MCL (the primary stabiliser).
- Tight laterally (valgus knee): release the ITB from Gerdy's tubercle, the posterolateral capsule, popliteus and LCL incrementally, protecting the common peroneal nerve.
- Globally tight: resect more distal femur (increases both flexion and extension gaps equally).
- Place spacer blocks at 90 degrees flexion; the gap should equal the extension gap and be rectangular (equal medial and lateral tension), with the femoral component parallel to the tibial cut.
- Tight in flexion: downsize the femoral component, or increase distal femoral resection (increases the flexion gap more than extension), or release the posterior capsule or PCL in a CR design. Loose in flexion: upsize the femur or use a thicker polyethylene.
- Asymmetric tightness usually reflects a femoral rotation error (internal rotation tightens the medial flexion gap).
- Insert the tibial trial aligned with the tibial tuberosity and centred (or 1 to 2mm medial), the trial polyethylene, and the femoral trial; reduce and assess systematically - alignment via an EM rod, varus or valgus stability in extension and flexion, ROM (full extension, flexion at least 110 degrees), and patellar tracking with the "no-thumb test" (centralisation by 30 to 40 degrees flexion without manual pressure).
- Remove all trials; pulsatile lavage with at least 3L (preferably 6L), clearing debris from the posterior capsule, gutters and suprapatellar pouch.
- Gently curette sclerotic bone to expose bleeding cancellous surface; dry the bone thoroughly with suction, sponges and compressed air - wet bone prevents interdigitation and causes early loosening.
- Insert intramedullary canal plugs if stemmed components are used.
- Mix antibiotic-loaded cement per protocol (typically gentamicin 1g per 40g, or tobramycin); apply at the dough phase (no longer sticky, does not adhere to the glove) as a 2 to 3mm layer onto the BONE (not the component), and pressurise into cancellous bone to create macro-interlock.
- Tibia: cement the cut surface, impact the baseplate aligned with the tuberosity and centred or 1 to 2mm medial, and remove excess cement while still viscous (especially posteriorly near the popliteal vessels); maintain pressure until polymerisation is complete.
- Femur: cement all surfaces (distal condyles, anterior, posterior, chamfers, box), impact in the verified rotation, re-check rotation against the landmarks before the cement sets (inadvertent internal rotation during impaction is the commonest error), and remove excess from the posterior condyles, intercondylar area and trochlea.
- Patella: cement onto a prepared bleeding bed with fixation holes drilled; centre the component (avoid medialisation or lateralisation); keep total patellar thickness (bone remnant plus component) equal to or 1 to 2mm less than native to avoid overstuffing.
- Select the polyethylene insert (typically 8 to 12mm) from the gap assessment and confirm the locking mechanism is fully engaged (visual check, tactile click, tug test) - an unlocked insert can dislocate catastrophically.
- Final pulsatile lavage of the whole joint (3 to 6L), removing all cement and bone debris (third-body wear shortens longevity); inspect the posterior capsule, gutters, suprapatellar pouch, intercondylar notch and undersurface of the patella.
- Reduce and verify: alignment via an EM rod through the mechanical axis, full extension (a flexion contracture is not acceptable) with flexion goal of 110 degrees or more, stability with a soft endpoint and less than 5 degrees opening on varus or valgus stress, and central patellar tracking through full range without subluxation.
- A lateral release is performed ONLY if maltracking persists after verifying component rotation and position - sequential, lateral retinaculum first then ITB, avoiding extensive release.
- Close the medial parapatellar arthrotomy with interrupted or continuous absorbable sutures (1-0 or 0 Vicryl) to a watertight seal; repair any proximal quadriceps extension and confirm the patellar tendon insertion is intact.
- Use interrupted sutures where tissue is friable or under tension (continuous risks dehiscence if one loop breaks); consider non-absorbable reinforcement in poor tissue.
- Close subcutaneous tissue in layers (2-0 or 3-0 Vicryl) then skin (staples, subcuticular absorbable, or sutures); apply an absorptive inner and compressive outer dressing.
- A drain is optional (consider for oozing, early anticoagulation, or high haematoma risk) and removed at 24 to 48 hours if used.
The popliteal artery and vein lie only 10 to 15mm posterior to the tibial cortex at the joint line, tethered by geniculate branches. Protect them with retractors during the posterior tibial cut, use a careful saw technique and never plunge posteriorly, visualise the blade exit, remove posterior cement extrusion gently under direct vision, and avoid hyperextension during closure (which stretches the artery). Confirm pulses before and after tourniquet release. If the artery is injured it is an emergency: release the tourniquet, flex the knee, decompress any haematoma, and call vascular surgery immediately - delay beyond 6 hours threatens the limb.
Internal rotation of the femoral component causes patellar maltracking AND flexion-gap asymmetry (medial tightness) with flexion instability. Use all three landmarks - posterior condylar axis plus 3 degrees external rotation, the transepicondylar axis, and Whiteside's line - plus a functional rectangular flexion-gap check. If they disagree, trust the epicondylar axis. In the valgus knee with a hypoplastic lateral condyle, do NOT rely on the posterior condylar axis - it over-externally rotates the reference and causes maltracking.
Wet bone prevents cement interdigitation and causes early aseptic loosening. Lavage with at least 3L (preferably 6L), curette sclerotic bone to a bleeding surface, then dry thoroughly with suction, sponges and compressed air immediately before applying the cement. Pressurise the cement into cancellous bone to create the macro-interlock that gives long-term fixation.
Aftercare & Complications
Rehabilitation | Phase | Timing | Focus | ROM goal | |-------|--------|-------|----------| | 1 | 0 to 24 hours | Multimodal analgesia (regional block or local infiltration), early mobilisation day 0 or 1, mechanical VTE prophylaxis | Full extension immediately | | 2 | 1 to 7 days | Walking frame or crutches, quadriceps and ROM exercises, stairs; discharge at 3 to 5 days when safe | 90 degrees flexion by day 3 to 5 | | 3 | 2 to 6 weeks | Wound review and suture removal at 10 to 14 days; progressive strengthening and gait; driving from 4 to 6 weeks (right TKA, off opioids, safe emergency stop) | 0 degrees extension, 110+ degrees flexion by 6 weeks | | 4 | Long term | Low-impact activity (walking, swimming, cycling; avoid running, jumping, contact sport), weight management, report pain, swelling or fevers early | Expect 0 to 120 degrees | Thromboprophylaxis. Every patient is risk-stratified and treated per national guidance (AAOS, NICE NG89, or equivalent). Aspirin 81 to 100mg once daily is now first-line in standard-risk patients (comparable VTE protection and lower bleeding than LMWH or DOACs). High-risk patients (age over 75, BMI over 35, prior VTE, thrombophilia, cancer, immobility) receive LMWH (enoxaparin 40mg subcutaneously daily), rivaroxaban 10mg daily, or apixaban 2.5mg twice daily. Duration is a minimum of 10 to 14 days, extended toward 28 to 35 days in high-risk patients. Antibiotics. A single weight-based preoperative dose within 60 minutes of incision is the global standard (cefazolin 2g IV, or vancomycin 15 to 20mg per kg if MRSA-colonised or beta-lactam allergic). Routine postoperative continuation beyond 24 hours is NOT recommended (WHO and major society SSI guidance). Routine antibiotic prophylaxis before dental procedures is NO longer recommended for most prosthetic-joint patients (AAOS or ADA and NICE) - selective use only in immunocompromised or high-risk individuals after shared decision-making. Complications
- Recognition
- Superficial: wound erythema, drainage, dehiscence, cellulitis. Deep: persistent pain, warmth, effusion, fevers, CRP over 100 and ESR over 30, sinus tract. Acute (less than 3 weeks) is obvious; chronic (over 3 weeks) may be subtle, with pain alone. MSIS criteria - major: sinus tract, purulent fluid, or same organism on two cultures; minor: synovial WCC over 3000, PMN over 70 percent, raised CRP and ESR
- Prevention
- Optimise diabetes to HbA1c less than 7 percent, stop smoking 4 to 6 weeks, BMI less than 40, treat active infections and eradicate MRSA. Single weight-based dose within 60 minutes of incision (cefazolin 2g, or vancomycin 15 to 20mg per kg if MRSA or beta-lactam allergic), normothermia, laminar flow, pulse lavage over 3L, antibiotic-loaded cement in high-risk patients. Routine dental prophylaxis is NO longer recommended
- Management
- Superficial: oral antibiotics and wound care. Acute deep with well-fixed components: DAIR with polyethylene exchange plus 6 weeks IV then oral suppression. Chronic or failed DAIR: two-stage revision with antibiotic spacer, 6 to 12 weeks organism-specific IV antibiotics, reimplant when markers normalise. One-stage revision for selected low-virulence organisms. Suppressive oral antibiotics if surgery declined
- Recognition
- Start-up pain progressing to constant pain with activity, effusion, restricted ROM. Radiographs show progressive radiolucent lines over 2mm, migration or subsidence, cement mantle fracture and osteolysis; compare serial films. Aspiration is MANDATORY to exclude infection before any revision
- Prevention
- Meticulous cement technique (dry bone, pressurisation, macro-interlock). Correct alignment (tibia perpendicular to mechanical axis, femur 5 to 7 degrees valgus) and rotation. Polyethylene at least 8mm, preferably highly cross-linked. Remove all debris. Avoid the very young and very obese
- Management
- Exclude infection (CRP, ESR, aspirate, nuclear imaging if uncertain). Revision TKA: explant loose components, assess bone stock (often deficient), use stems bypassing defects by 50 to 100mm, augments or metaphyseal sleeves and cones, allograft for large defects. Choose constraint by ligament integrity (CR or PS, then CCK, then rotating hinge)
- Recognition
- Patient reports giving way, looseness or hyperextension; over 5 degrees opening on stress, recurvatum. Distinguish pattern and timing (early technical versus late wear or attenuation). Standing and stress films, CT for component rotation; aspirate if revising
- Prevention
- Equal, rectangular flexion and extension gaps (8 to 10mm with planned component). Correct femoral rotation. Appropriate polyethylene thickness from gap assessment. Preserve collaterals with incremental releases. Proper cam-post engagement in PS designs; avoid over-release
- Management
- Determine timing and pattern. Early and well-positioned: exchange to a thicker polyethylene. Malrotation: revise the femur to correct rotation. Late wear: exchange the polyethylene if isolated. Ligament attenuation: revise to higher constraint (PS, then CCK, then rotating hinge). Step up constraint only as needed - over-constraint increases loosening
- Recognition
- Maltracking: grinding and giving way on stairs, a J-sign, failure to centralise by 30 to 40 degrees flexion. Clunk: a palpable clunk at the flexion-extension transition from a suprapatellar nodule. Fracture: acute pain and loss of active extension. Skyline view for tracking, lateral view for height or fracture, CT for rotation
- Prevention
- Correct femoral rotation (internal rotation is the commonest cause), align the tibia with the tuberosity, centre the patellar component, preserve the patellar blood supply with the medial arthrotomy, keep the patellar remnant 12 to 15mm, and avoid overstuffing. Resurfacing practice varies by region (see Background)
- Management
- Maltracking: obtain a CT rotation study; if malrotation is present revise the component and do NOT simply perform a lateral release. If components are correct: sequential lateral release (retinaculum, then ITB), then a Fulkerson anteromedialisation if severe. Fracture: non-operative if non-displaced with an intact mechanism; ORIF if displaced; revision patellar component or patelloplasty if loose or thin. Clunk: arthroscopic or open debridement
- Recognition
- Limited ROM, difficulty sitting, with stairs and getting in or out of a car; flexion less than 90 degrees (less than 75 severe), a fixed flexion contracture, firm endpoint, pain on passive stretch. Exclude component malposition (excessive slope, a flexed femoral component, patellar overstuffing) and low-grade infection
- Prevention
- Avoid overstuffing; ensure an adequate flexion gap (test to at least 110 degrees with trials); start day-one physiotherapy; use multimodal analgesia for pain-free therapy; identify high-risk patients (diabetes, young males, prior stiffness)
- Management
- Early (under 6 weeks): aggressive physiotherapy and analgesia. Persistent at 6 to 12 weeks: manipulation under anaesthesia (best before 12 weeks, performed gently to avoid fracture). Late or failed MUA: arthroscopic or open arthrolysis. If component malposition is present: revise. ALWAYS aspirate to exclude infection before MUA or arthrolysis
Venous thromboembolism. Without prophylaxis DVT occurs in 40 to 60 percent and PE in 1 to 3 percent (fatal PE 0.1 to 0.5 percent); appropriate prophylaxis cuts DVT to 1 to 5 percent and PE to less than 1 percent. Suspect DVT with calf swelling, pain and erythema (confirm with compression ultrasound; D-dimer if negative) and PE with chest pain, dyspnoea, hypoxia and haemoptysis (CTPA is the gold standard). Treat with therapeutic LMWH or a DOAC for at least 3 months; massive PE with haemodynamic instability needs thrombolysis or embolectomy, and an IVC filter only if anticoagulation is absolutely contraindicated. Neurovascular injury. Popliteal artery injury is rare (less than 0.1 percent) but devastating - protect the vessels during the posterior tibial cut and posterior cement removal, avoid hyperextension, and monitor pulses; injury is an emergency (see the safety alert above). Common peroneal nerve injury (0.5 to 2 percent, up to 5 percent in valgus correction) presents with foot drop and dorsal foot numbness - prevent it with incremental valgus releases, padding and avoiding compression; most are neurapraxia that recover over 6 to 12 months with an AFO, so observe with serial EMG unless a sharp transection is suspected. Wound complications (2 to 5 percent; higher with obesity, diabetes, vascular disease and multiple previous incisions) range from superficial dehiscence (local wound care, secondary intention if small, delayed closure or skin graft if larger) through skin necrosis (debridement and plastic cover with a medial gastrocnemius flap for proximal defects) to persistent drainage beyond 5 to 7 days (aspirate and consider washout - do not let a wound drain externally for over 1 to 2 weeks). Periprosthetic fracture (0.5 to 2 percent; commonest in the supracondylar femur, then tibia, then patella) is prevented by avoiding anterior femoral notching, keeping a 12 to 15mm patellar remnant, gentle impaction, and treating osteoporosis. The critical distinction is whether the component is stable or loose.
- Classification
- Lewis and Rorabeck
- Key types
- Type I non-displaced with a stable component; Type II displaced with a stable component; Type III loose component
- Classification
- Felix et al
- Key types
- Types I to IV based on anatomical location and component stability
- Classification
- Ortiguera and Berry
- Key types
- Type I stable component with an intact extensor mechanism; Type II component disruption; Type III inferior pole avulsion; Type IV comminuted
Viva & Exam Focus
BALANCEDBALANCED - gap-balanced TKA
WEPT 3WEPT 3 - femoral rotation references
10 to 15mm posterior to the tibial cortex at the joint line, tethered by geniculate branches. Protect with retractors during the posterior tibial cut, careful saw technique, gentle posterior cement removal under direct vision, and avoid hyperextension on closure. Confirm pulses before and after tourniquet release.
Wraps the fibular neck, 20 to 30mm distal to the lateral joint line, vulnerable in valgus correction (up to 5 percent). Use incremental lateral releases, padding, avoid compression from haematoma or tight dressings, and monitor foot dorsiflexion postoperatively.
Deep layer inserts at the joint line; superficial layer 5 to 7cm distal on the medial tibia. Release only the deep MCL incrementally by pie-crusting, preserve the superficial MCL (primary stabiliser), and remove osteophytes first.
The peri-patellar ring (dominant lateral genicular artery at the mid-lateral border) is preserved by an arthrotomy 5 to 8mm medial to the patellar border, avoiding extensive lateral release, gentle handling, and retaining some fat pad.
At risk in the posterior femoral and box cuts (PS design). Visualise the posterior cortex, protect with a retractor, avoid plunging the saw, size the component to avoid notching or overhang, and respect box-chisel depth.
Tight extension: release deep MCL medially (varus), ITB laterally (valgus), or resect more distal femur (equal increase of both gaps). Tight flexion: downsize the femur or increase distal femoral resection. Patellar maltracking: check femoral rotation first (commonest cause), then tibial rotation and patellar position before any lateral release.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“How do you determine femoral component rotation in TKA and why is this so critical? Walk me through your systematic approach.”
“What are the main complications of cemented TKA and how do you prevent them? Focus on the three commonest causes of revision.”
“A patient has persistent patellar maltracking despite what you believe is optimal component positioning. Walk me through your systematic approach to troubleshooting and management.”
Indications
- End-stage OA (Kellgren-Lawrence 3 to 4, failed conservative care 3 to 6 months, functional limitation, pain affecting quality of life)
- Inflammatory arthritis (RA, PsA, AS) with severe destruction despite DMARDs and biologics
- Post-traumatic arthritis and osteonecrosis; typical age over 65 years, younger only if severe with realistic expectations
Femoral rotation (critical)
- Multiple references: PCA plus 3 degrees ER (unreliable in valgus), transepicondylar axis MOST RELIABLE (lateral prominence to medial sulcus), Whiteside's line (perpendicular), balanced flexion gap (functional)
- If references conflict, prioritise the transepicondylar axis
- Internal rotation causes patellar maltracking and flexion instability (medial tightness)
- Verify with visual landmarks, trial tracking (centralise by 30 to 40 degrees), and a rectangular flexion gap
Gap balancing
- Extension gap at 0 degrees, 8 to 10mm, balanced medial and lateral, tibia perpendicular to mechanical axis
- Flexion gap at 90 degrees equal to extension, rectangular, femoral rotation determines it
- Tight extension medially: incremental deep MCL release, remove osteophytes, preserve superficial MCL
- Tight flexion: downsize femur, resect more distal femur, check PCL tension (CR design)
Cement technique
- Dry bone MANDATORY (wet bone prevents interdigitation and causes early loosening); lavage 3 to 6L then dry
- Pressurise cement into cancellous bone (macro-interlock); apply to the bone not the component
- Sequence: tibia first (patella everted), femur second (verify rotation), patella third (centred)
- Remove excess cement while viscous, especially posteriorly near the popliteal vessels
Danger zones
- Popliteal vessels (10 to 15mm posterior to tibia): retractors, careful saw, gentle posterior cement removal
- Common peroneal nerve (fibular neck): incremental valgus releases, padding, monitor foot dorsiflexion
- MCL (deep at joint line, superficial 5 to 7cm distal): controlled incremental release, preserve superficial layer
- Patellar blood supply (lateral genicular dominant): arthrotomy 5 to 8mm medial, avoid extensive lateral release
Intraoperative troubleshooting
- Tight extension: deep MCL medially (varus), ITB laterally (valgus), or more distal femur (equal increase both gaps)
- Tight flexion: downsize femur, more distal femoral resection, check PCL (CR design)
- Patellar maltracking: check femoral rotation FIRST, then tibial rotation and patellar position; avoid routine lateral release
- Difficult eversion: extend the quadriceps incision proximally before any lateral release
Complications - the big 3 causes of revision
- Infection: prevent (HbA1c less than 7 percent, smoking cessation, single dose cefazolin 2g, lavage 3 to 6L, antibiotic cement if high risk); manage (DAIR if acute less than 3 weeks, two-stage if chronic)
- Aseptic loosening: prevent (dry bone, pressurisation, correct alignment and rotation, remove debris); manage (revision with stems, augments, exclude infection first)
- Instability: prevent (gap balancing, correct femoral rotation, preserve collaterals); manage (revise malrotation, increase constraint PS to CCK to hinge only as needed)
Postoperative essentials
- VTE prophylaxis for all per national guidance (AAOS or NICE NG89): aspirin 81 to 100mg once daily first-line in standard risk; LMWH or DOAC if high risk; 10 to 14 days minimum, 28 to 35 days high risk
- Physiotherapy from day 1; goal 0 degrees extension and 110+ degrees flexion by 6 weeks
- Stiffness: MUA if less than 90 degrees and before 12 weeks (best results); arthrolysis if MUA fails or after 12 weeks
- Routine dental antibiotic prophylaxis NO longer recommended for most patients (AAOS or ADA, NICE); selective use only in high-risk individuals
Background & Evidence
Epidemiology and demand. Knee osteoarthritis is the leading indication for TKA. Demand is rising steeply in the developed world - US modelling (Kurtz, 2009) projected substantial growth in both primary and revision joint replacement from 2010 to 2030, with the revision burden growing fastest, which underpins the emphasis on durable fixation and correct technique. Implant longevity. The best global benchmark is the systematic review and meta-analysis of Evans and colleagues (2019), which pooled national-registry data and estimated 25-year all-cause survival of total knee replacement at 82.3 percent (95 percent CI 81.3 to 83.2) - the figure to quote when counselling patients and the evidence basis for offering TKA to suitably selected younger patients. Registry estimates are more reliable than case-series data, which tend to overstate survival. Patellar resurfacing - an unresolved debate. Whether to resurface the patella varies by region and remains contested.
- Typical practice
- Predominates in North America and Australasia
- Evidence
- Meta-analyses show it reduces reoperation for anterior knee pain
- Typical practice
- Common in the UK and Europe
- Evidence
- Registry data show comparable overall revision rates
Registry evidence. Large national arthroplasty registries - the National Joint Registry (NJR, UK), the American Joint Replacement Registry (AJRR, US), the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), and the Swedish Knee Arthroplasty Register - report cemented TKA implant survivorship and revision rates and form the global evidence base for implant and technique selection. Why the technique matters. Component malrotation, imperfect cement technique and unbalanced gaps are not theoretical concerns - they translate directly into the commonest failure modes (patellar complications, loosening, instability). The clinical studies referenced below establish each of these links, and are exactly what an examiner expects a candidate to quote.
References
How long does a knee replacement last? Systematic review and meta-analysis with 15+ years follow-up
- Pooled national-registry data (14 registries, 299,291 TKRs) showed 25-year all-cause survival of total knee replacement of 82.3 percent (95 percent CI 81.3 to 83.2).
- Registry estimates were considered more reliable than case-series data, which tend to overstate survival.
- Provides the best global benchmark for counselling patients on implant longevity, the majority of which are cemented designs.
Malrotation causing patellofemoral complications after total knee arthroplasty
- Combined (femoral plus tibial) internal component rotation correlated directly with severity of patellofemoral complications on CT.
- Small internal rotation (1 to 4 degrees) caused tilt or lateral tracking; moderate (3 to 8 degrees) caused subluxation; large (7 to 17 degrees) caused dislocation or patellar component failure.
- The transepicondylar axis and tibial tubercle are reproducible CT landmarks for assessing component rotation.
Gap balancing versus measured resection technique for total knee arthroplasty
- Fluoroscopic deep-knee-bend analysis of 60 TKAs: condylar lift-off over 1mm occurred in 45 to 60 percent of measured-resection knees versus none of the gap-balanced knees.
- Setting femoral rotation by the flexion gap (gap balancing) produced superior coronal-plane stability.
- Improved stability is proposed to reduce polyethylene wear and improve function.
The anteroposterior axis for femoral rotational alignment in valgus total knee arthroplasty
- In valgus knees, using the posterior condylar axis as the rotation reference required intraoperative tibial tubercle transfer in several knees and led to recurrent patellar instability.
- Switching to the anteroposterior (Whiteside's) axis in 107 valgus knees significantly reduced patellar tracking problems, with no patellar instability at 2 years.
- Defines Whiteside's line: deepest part of the trochlear groove to the centre of the intercondylar notch.
Long-term results of the total condylar knee arthroplasty: a 15-year survivorship study
- 112 consecutive cemented Total Condylar knee arthroplasties: 94.1 percent clinical survivorship at 15 years (90.9 percent when radiographic failures included).
- Heavier patients (over 80kg) had the lowest survivorship, establishing body weight as a loosening risk factor.
- Only 2 of the tibial components were truly loose despite radiolucencies around 72 percent - distinguishing benign lucent lines from loosening.
The unstable total knee arthroplasty: causes and cures
- Classifies instability by direction: varus-valgus, recurvatum, flexion, and global.
- Isolated polyethylene exchange and ligament reconstruction generally fail - revision must eliminate the deforming force, most often correcting coronal alignment.
- Only collateral ligament failure typically mandates a constrained implant; constraint is not a substitute for diagnosis and surgical technique.
Total knee arthroplasty
- Classic description of the principles of total knee arthroplasty that underpin modern technique.
- Establishes the rationale for the measured-resection approach to component positioning.
Future young patient demand for primary and revision joint replacement: national projections from 2010 to 2030
- US primary and revision joint replacement demand projected to rise substantially through 2030.
- The revision burden is projected to grow the fastest of any segment.
Proceedings of the International Consensus on Periprosthetic Joint Infection
- Establishes consensus diagnostic criteria and management principles for periprosthetic joint infection.
- Underpins the MSIS-based definition of PJI used for diagnosis and treatment decisions.
Management of patients with orthopaedic implants undergoing dental procedures - clinical practice guideline
- Concludes that routine antibiotic prophylaxis before dental procedures is NOT indicated for the majority of patients with a prosthetic joint.
- NICE guidance concurs, advising against routine dental prophylaxis.
National arthroplasty registry reports (cemented TKA survivorship and revision rates)
- Large national registries report cemented TKA implant survivorship and revision rates.
- Provide the comparative implant- and technique-level evidence used to guide selection.