Revision Total Knee Arthroplasty

Revision TKA is technically demanding, and compared with the primary operation it brings higher complication rates, longer operative times and inferior functional outcomes. National registries record over 100,000 primary TKAs annually in high-income settings, with far greater volumes worldwide, so the burden of revision surgery is substantial.

Who is revised. The mean age at revision is 65-70 years, younger than at primary TKA, and women outnumber men 2:1, the same ratio as for the primary. Revision comes a mean of 7-10 years after the index operation.

How it compares with a primary. Every measure is worse:

• Complication rate 20-30%, against 5-10% after a primary
• Operative time 2-3 hours, against 1-1.5 hours
• Functional scores 70-80% of those after primary TKA
• Survivorship 85-90% at 10 years, against 95% for a primary
• Re-revision risk 15-20% within 5 years

Aseptic loosening is the most common indication, about half of all revisions, with instability and infection behind it. Technical error is a further reason to revise: malrotation, malalignment or a component size mismatch.

Metaphysis and diaphysis. The metaphysis, the wide flared bone at the joint, gives the components their primary support, and it is the region that revision bone loss compromises; the AORI classification grades that damage. The diaphysis, the narrow shaft below, is where stems gain fixation.

The collateral ligaments. The MCL prevents valgus instability and the LCL prevents varus instability, so their integrity determines how much constraint the revision needs. Intraoperative stress testing settles it: one deficient collateral means a CCK, both mean a hinge.

The Anderson Orthopaedic Research Institute (AORI) classification is the gold standard for grading bone loss in revision TKA, and it guides the choice of augments, stems and structural grafts. Each grade maps to a reconstruction. Type 1 defects can be managed with standard components, Type 2 needs augmentation, and Type 3 demands structural support from a metaphyseal sleeve, cone or bulk allograft.

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The painful TKA. A painful TKA is not automatically a loose TKA. Up to a quarter of painful TKAs have no identifiable intra-articular cause, and revising these blindly worsens outcomes. Before committing to revision, systematically exclude infection (always first), then the intrinsic and extrinsic causes.

History. Localise the pain and characterise it as start-up, activity-related or constant, then correlate it with imaging and aspiration. Ask about the onset, mechanical symptoms such as locking and catching, prior infections and previous surgeries.

Examination. Record the range of motion, varus-valgus and AP drawer stability, any extensor lag, the integrity of the wound and the neurovascular status.

Excluding infection. Serum ESR and CRP come first; an elevated value suggests infection. The knee is then aspirated for a synovial WBC, PMN% and culture (aerobic, anaerobic and fungal). The diagnostic findings for PJI on aspiration:

• Synovial WBC greater than 3000 cells/µL
• PMN greater than 80%
• Positive culture

When the answer is unclear. Alpha-defensin or synovial CRP is added if clinical suspicion is high, and alpha-defensin is confirmatory if the aspiration is equivocal. Consider aspiration biopsy if imaging shows loosening. If infection is suspected but the aspiration is negative, nuclear medicine imaging (Tc-99m, Indium-111 WBC) is used.

Imaging.

• AP and lateral radiographs for component position, alignment, radiolucent lines and osteolysis
• Long-leg alignment films for the mechanical axis
• CT if severe bone loss is suspected, to quantify the defects and plan the reconstruction

Planning. From the imaging, estimate the AORI grade, set the constraint level from bone loss and ligament integrity, and plan augments and stems for Type 2 and 3 defects. Make sure CCK and hinge implants, sleeves and cones are available.

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The ladder. Start with the least constraint possible, PS if feasible. Escalate to a CCK if one collateral ligament is deficient or there is moderate bone loss, and use a rotating hinge only for massive bone loss (AORI Type 3) or global instability. Over-constraining increases interface stress and loosening risk; under-constraining risks instability.

What decides it. Cruciate-retaining implants need an intact PCL and are rarely used in revision. The constraint decision, made finally at trialling, rests on:

• Bone loss (AORI grade)
• Collateral ligament integrity (MCL and LCL competence)
• Flexion-extension gap balance
• Extensor mechanism function

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Posterior-stabilised. Indicated for AORI Type 1 bone loss with intact MCL and LCL, balanced flexion-extension gaps and simple aseptic loosening or polyethylene wear. It needs adequate metaphyseal bone stock, no significant instability and a good extensor mechanism, and it may need stems for fixation.

• Lowest constraint, so the least interface stress
• Better preservation of range of motion
• Lower revision rate than a hinge, and a familiar implant
• Unsuitable for moderate to severe bone loss, and risks instability if mis-selected

In practice PS revision is rarely used; most revisions require at least CCK constraint.

Constrained condylar knee. Indicated for AORI Type 2A/2B bone loss, insufficiency of the MCL or the LCL, flexion-extension gap imbalance and moderate instability. A taller post and deeper cam give more constraint than a PS, and a wider tibial baseplate adds stability; it is compatible with modular augments and accepts modular stems for fixation. The CCK is the most commonly used implant in revision TKA, balancing constraint with survivorship.

Rotating hinge. Indicated for AORI Type 3 bone loss, insufficiency of the MCL and the LCL (global instability), massive bone loss requiring structural grafts, and extensor mechanism disruption (with repair). The mechanical hinge allows flexion-extension only, and a rotating bearing reduces torque at the interfaces. Long cemented stems are mandatory, and it accepts metaphyseal sleeves and cones.

Algorithm

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Every revision follows the same sequence, whatever the failure mode:

1. Rule out infection first, by aspiration and ESR/CRP
2. Assess bone loss by AORI grade, from imaging and then the intraoperative findings
3. Evaluate the soft tissues: collateral ligament integrity and the extensor mechanism
4. Select the constraint, PS to CCK to hinge, from the bone loss and the instability
5. Plan the reconstruction: augments for Type 2, sleeves or cones for Type 3, stems for stability

Chronic PJI goes down the two-stage pathway described in its own section below.

Aseptic LooseningInstability

Confirming it. Radiolucent lines greater than 2mm that progress, with component subsidence, indicate loosening. Infection is still excluded by aspiration (WBC, PMN%, culture); ESR and CRP are normal or mildly elevated. Assess collateral ligament integrity from the examination and prior radiographs.

Reconstruction by grade. Remove the loose components and cement, and make the final assessment of bone loss at that point.

• Type 1: standard components (PS or CCK), cement fill, short stems
• Type 2: metal augments, modular stems, CCK constraint
• Type 3: metaphyseal sleeve or cone, long cemented stems, hinge constraint

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Reading the pattern. Varus-valgus laxity means MCL or LCL insufficiency and requires a CCK or a hinge. A flexion-extension gap imbalance, a mismatch between the extension and 90° flexion gaps, may need thicker polyethylene or more constraint. Global instability, both varus-valgus and AP, requires a hinge.

Testing it. Apply varus-valgus stress in extension and at 90° flexion. An intact MCL with a deficient LCL takes a CCK with varus-valgus constraint (5-10°); if both collaterals are deficient, a rotating hinge (0° laxity).

Matching the implant to the severity.

• Mild (less than 5mm): increase polyethylene thickness, consider a CCK
• Moderate (5-10mm): CCK with stems and augments as needed
• Severe (greater than 10mm, or global): rotating hinge with long stems (14-16cm diaphyseal fixation)

Balance the gaps by adjusting component sizing, augments or polyethylene thickness. Instability is a soft tissue problem, but it is usually solved with implant constraint rather than ligament reconstruction: collateral reconstruction is rarely successful, and increasing constraint is the better answer.

Consent. Consent covers the complications tabulated under Complications (infection, which is higher than after a primary, aseptic loosening, periprosthetic fracture, which is higher with stems, stiffness and neurovascular injury, with the popliteal artery at risk), the risk of re-revision, and DVT/PE, for which standard prophylaxis is required.

Equipment. Revision is not the day to discover a missing tray:

• Revision implant system with CCK and hinge options
• Metal augment blocks (5mm, 10mm, 15mm)
• Modular stems in various lengths (50-150mm)
• Metaphyseal sleeves and cones for Type 3 defects
• Component removal and cement removal sets
• C-arm, essential for alignment and stem placement
• Pulse lavage for high-volume irrigation

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A stable, well-fixed revision can still function poorly if the joint line is not restored. In revision TKA the joint line is easily elevated (proximalised), because distal femoral bone is lost or resected and the temptation is to "build down" the tibia or under-augment the distal femur.

What an elevated line does. The collaterals are only isometric about the native joint line, so an elevated line leaves them non-isometric and lax in mid-flexion: mid-flexion instability. By lowering the patella relative to the trochlea it also produces patella baja, with anterior knee pain, impingement and lost flexion.

Bringing it back. Restore the joint line to its native level using bony landmarks, and prefer distal femoral augments, which restore distal femoral offset, over building up the tibia.

Why stems. Modular stems provide rotational stability and load sharing, protecting the metaphyseal bone-implant interface. They reduce stress at that interface and improve survivorship, and in most revisions they are not optional.

• AORI Type 1: short stems, 50-75mm, press-fit or cemented
• AORI Type 2: 75-100mm, press-fit in the metaphysis and cemented in the diaphysis
• AORI Type 3: 100-150mm, fully cemented in the diaphysis (14-16cm fixation length)
• Rotating hinge: long cemented stems, always

Cemented or cementless. The diaphyseal stem can be fixed cemented or cementless (press-fit), a genuine, frequently examined controversy; the metaphyseal cone and sleeve hardware itself is covered in the dedicated bone-loss topic.

The compromise. Neither is universally superior. The contemporary compromise endorsed by current reviews is dual-zone (hybrid) fixation: biological metaphyseal fixation with a cone or sleeve, combined with a relatively short fully cemented stem.

Two-stage revision is the gold standard for chronic periprosthetic joint infection (PJI) in the knee, with infection control rates of 85-90%.

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Criteria for reimplantation. Before Stage 2 the aspiration and markers should show:

• Synovial WBC less than 3000 cells/µL
• PMN less than 80%
• Negative culture (or a low virulence organism with biofilm coverage)
• ESR and CRP trending down (not necessarily normal)

Fracture at the stem tip. Periprosthetic fractures often occur at the stem tip, a stress riser in osteoporotic bone. When the stem is stable, ORIF is with a plate and strut allograft; a loose stem is revised to a longer one.

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Most revisions weight-bear as tolerated from the start and begin range of motion immediately, aiming for 0-110° by 6 weeks. A tibial tubercle osteotomy changes that: the tubercle must heal, and weight-bearing is protected until it does.