When Does a Knee Replacement Need to Be Revised?
The vast majority of knee replacements function well for many years without any problems. However, a small proportion will eventually fail — either through a definable mechanical process or, in some cases, for reasons that are not yet fully understood. When failure occurs, revision surgery may be required.
Revision knee replacement — the partial or complete replacement of one or more components of a knee arthroplasty — is significantly more complex than the original primary procedure. It is typically longer, involves greater blood loss, carries higher rates of complication, and produces less predictable outcomes. Bone loss from the primary implant and the biological changes that have occurred around it make reconstruction considerably more technically demanding.
For these reasons, the decision to revise a knee replacement requires careful thought, a thorough investigation of the underlying cause of failure, and an honest discussion between surgeon and patient about the realistic goals of surgery and the risks involved. Revision surgery should never be undertaken lightly — and critically, it should only be undertaken when a clear, identifiable cause for the failure has been established.
Mr. Lodge has a specialist interest and considerable experience in revision knee surgery, including complex cases referred from other centres. He works within a multidisciplinary framework — including specialist microbiologists and radiologists — to ensure that every revision decision is robustly investigated and carefully planned before proceeding.
The single most important principle in revision knee surgery is this: establish the cause of failure before operating. Surgery undertaken without a clear understanding of why the original replacement has failed is unlikely to address the underlying problem — and may leave the patient no better off, or in some cases worse.
Why Do Knee Replacements Fail?
There are several well-recognised reasons why a knee replacement may require revision. Understanding the mechanism of failure is essential — both because different failure modes require different surgical solutions, and because the expected outcome of revision surgery differs significantly depending on the indication.
Aseptic Loosening
Loosening in the absence of infection is the most common cause of late revision knee surgery. Over time, wear particles from the polyethylene bearing can trigger a chronic inflammatory response in the surrounding bone — a process called osteolysis — leading to progressive bone loss and eventual failure of the implant-bone interface. On X-ray this appears as lucent lines around the components, often progressing to visible subsidence or migration of the implant. Loosening may cause deep aching pain at rest and with activity, often with a mechanical quality. CT scanning and nuclear medicine bone scans help confirm the diagnosis and quantify bone loss in advance of planning revision.
Clear indication for revisionInstability
Instability — where the knee feels insecure, gives way, or collapses during activity — is one of the most common early indications for revision, accounting for approximately 20% of all revision procedures. It typically results from imbalance of the collateral ligaments at the time of primary surgery, or from subsequent stretching or attenuation of the ligamentous structures. Patients describe a sense of the knee buckling, particularly on stairs or uneven ground, often accompanied by recurrent swelling. Careful clinical assessment and stress X-rays under fluoroscopy help characterise the type and degree of instability — coronal (side-to-side), sagittal (front-to-back), or flexion-gap instability — each of which requires a different surgical response.
Clear indication for revisionPeriprosthetic Joint Infection (PJI)
Infection of a knee replacement is one of the most serious and surgically challenging complications in orthopaedics. PJI may present acutely — with fever, wound breakdown and rapid joint destruction — or in a more indolent, chronic form with persistent low-grade pain, stiffness and elevated inflammatory markers. Diagnosis requires a combination of blood tests (CRP, ESR, D-dimer), joint aspiration with microbiological culture and cell count, and in some cases nuclear medicine imaging. Treatment almost always requires surgical intervention — either a single-stage or two-stage revision exchange, depending on the organism involved, chronicity of infection and patient factors. The eradication of infection must be confirmed before a new implant is reintroduced.
Clear indication — requires specialist pathwayOsteolysis (Periprosthetic Bone Loss)
Osteolysis refers to the progressive loss of bone around an implant, driven by the biological response to wear debris — most commonly polyethylene particles. It may occur with or without visible clinical loosening and can remain asymptomatic for a considerable period, making regular radiographic follow-up essential. If detected early, bone loss can sometimes be managed with revision of the polyethylene bearing alone — a more limited procedure that preserves well-fixed metal components and the remaining bone stock. Left unaddressed, progressive osteolysis will eventually compromise the structural integrity of the bone sufficiently to make future reconstruction significantly more complex and the outcome less predictable.
Early intervention improves outcomesMalalignment & Malposition
If the components of a knee replacement are not correctly positioned or aligned at the time of primary surgery, the forces transmitted through the joint will be uneven — accelerating wear, producing instability, and causing pain that is often difficult to characterise. Malalignment may affect the rotational position of the femoral component, the tibial slope, or the overall coronal alignment of the limb. It is identified on weight-bearing X-rays, CT scans and gait analysis. Malposition is a correctable mechanical cause of failure — revision to restore correct alignment typically produces good outcomes when it is the primary driver of symptoms.
Correctable cause — revision appropriatePeriprosthetic Fracture
Fracture of the bone around a knee replacement — most commonly above the femoral component — can occur following a fall, or occasionally without a clear traumatic event in the context of osteolysis or osteoporosis. Treatment depends on the fracture pattern, the stability of the underlying implant and the quality of the remaining bone. Where the implant is still well-fixed, the fracture may be amenable to fixation with plates or nails. Where the implant has been compromised by the fracture, revision to a longer-stemmed implant capable of bypassing the fracture site is required. These cases require careful pre-operative planning and, where complex, are best managed in specialist centres.
Case-by-case decision with specialist inputRevision for Pain Alone — Why a Clear Cause Must Be Found
Revision surgery for unexplained pain alone carries a high risk of a poor outcome
As discussed on the total knee replacement page, approximately 4–5% of patients continue to experience pain following a technically successful knee replacement — without any identifiable mechanical cause such as loosening, infection, malalignment or instability. This represents one of the most challenging problems in knee arthroplasty, and it is important to be completely clear about the evidence regarding revision surgery in this context.
Revision surgery undertaken for pain alone — in the absence of a clearly identifiable and correctable mechanical failure — is associated with very high rates of patient dissatisfaction and poor functional outcomes. The evidence is consistent and unambiguous on this point. Operating on a knee that is mechanically functioning correctly, in the hope that changing components will alleviate unexplained pain, does not reliably produce improvement — and carries all of the additional risks and complexity of revision surgery without addressing an underlying structural problem.
The reason for this is straightforward: if the pain does not arise from a correctable mechanical cause, revising the implant will not remove the source of that pain. The altered pain processing, sensitisation, psychological factors or neurological changes that may be contributing to the patient's experience cannot be addressed by surgery.
This does not mean that patients with a painful knee replacement should be dismissed or told nothing can be done. It means that the evaluation of the painful knee replacement must be thorough, systematic and unhurried before any surgical decision is made. If, after comprehensive investigation, a specific correctable cause — such as a low-grade infection, subtle malposition or a discrete mechanical problem — is identified, revision surgery directed at that cause may be highly effective.
Mr. Lodge is transparent and direct with patients facing this difficult situation. Where no clear cause is found, he will be honest that revision surgery is unlikely to be of benefit, and will work with colleagues — including pain specialists, physiotherapists and psychologists — to explore alternative strategies for improving quality of life.
What the Evidence Shows
Studies consistently report that revision knee replacement for unexplained pain produces the worst outcomes of any revision indication — with patient satisfaction rates significantly lower than revision for infection, loosening or instability. In contrast, revision surgery directed at a well-characterised mechanical failure — where the cause is clearly identified and the revision specifically targets it — can produce good to excellent outcomes, with meaningful improvement in pain and function.
This disparity underlines why the assessment of the painful or failing knee replacement is as important as the surgery itself. Getting the diagnosis right before the revision is the most powerful determinant of outcome.
Investigating the Failing Knee Replacement
Before any revision decision is made, a thorough and systematic work-up is undertaken to identify the mechanism of failure. This process may take several weeks and involves a combination of clinical assessment, blood tests, imaging and — where infection is suspected — joint aspiration.
Clinical & Radiographic Assessment
First-line evaluation
- Detailed history — character, timing and distribution of pain; any history of wound healing problems, infections or antibiotic courses after primary surgery
- Clinical examination — stability testing, range of movement, patellar tracking, wound assessment, any signs of infection
- Weight-bearing X-rays — assessing component position, joint line, radiolucent lines, subsidence and bone loss
- Long-leg alignment films — measuring overall coronal alignment of the limb
- CT scan — detailed assessment of rotational alignment of components, bone stock and implant position
Laboratory & Microbiological Tests
Ruling out — or confirming — infection
- Blood tests: CRP, ESR, white cell count, fibrinogen and D-dimer — elevated in PJI but also in other inflammatory states
- Joint aspiration under fluoroscopic guidance — synovial fluid white cell count, differential and culture; the single most informative test for ruling in or out periprosthetic joint infection
- Extended microbiological culture — samples held for a minimum of two weeks to detect slow-growing organisms, including Propionibacterium acnes
- Nuclear medicine imaging — white cell-labelled scintigraphy or SPECT/CT to assess for occult infection where aspiration is equivocal
- Alpha-defensin assay — a synovial fluid biomarker with high sensitivity and specificity for PJI, used where diagnosis remains uncertain
Infection must be excluded before any aseptic revision is undertaken. Proceeding with revision for apparent loosening or instability in a knee that is in fact infected will almost certainly result in failure of the revision — with significant consequences for the patient and greatly increased complexity of any subsequent treatment. Where doubt exists, aspiration is mandatory before operating.
What Does Revision Surgery Involve?
Revision knee replacement surgery is tailored to the individual patient's failure mode, the degree of bone loss, the condition of the soft tissues and the ligamentous stability available. No two revision procedures are the same — and this is part of what makes it one of the most technically demanding areas of orthopaedic surgery.
Scope of Revision
In some cases, only one component needs to be addressed — for example, isolated polyethylene bearing exchange where the metal components remain well-fixed and the failure is due to wear or a discrete bearing problem. This is a relatively limited procedure with faster recovery and lower risk.
More commonly, a full revision involving removal and replacement of all components is required. This is a substantially larger operation — typically taking two to four hours — and involves carefully removing the primary implants while preserving as much bone as possible, addressing any bone defects with augments, bone graft or tantalum cones, and reimplanting a new reconstruction that is specifically designed for the revision setting.
Revision Implant Design
Revision knee implants differ fundamentally from primary implants. They use longer stems that extend into the femoral and tibial canals to achieve fixation beyond any compromised metaphyseal bone. They incorporate modular augments and wedges to fill bone defects. And they use more constrained bearing designs — such as varus-valgus constrained (VVC) or rotating hinge constructs — to compensate for the ligamentous deficiency that is often present following a failed primary replacement.
The degree of constraint chosen must be carefully matched to the degree of instability present. Excessive constraint transfers stress to the implant-bone interface and increases the risk of aseptic loosening; insufficient constraint risks recurrent instability. This balance is one of the key surgical judgements in revision knee surgery.
Two-Stage Revision for Infection
Where periprosthetic joint infection is confirmed, the standard of care in the UK remains a two-stage revision in the majority of cases. In the first stage, all implants and cement are removed, the joint is thoroughly debrided and washed out, and an antibiotic-loaded cement spacer is inserted to maintain the joint space and deliver high local concentrations of antibiotic to eradicate residual infection. The patient then undergoes a prolonged course of targeted intravenous antibiotics, guided by the specific organism identified.
Once infection has been confirmed as eradicated — through clinical assessment, resolution of inflammatory markers and repeat aspiration — the second stage is performed: full revision reimplantation using the definitive revision construct. The interval between stages is typically six weeks to three months, depending on the organism involved and the pace of biological recovery. This two-stage approach gives the best chance of durable infection eradication, though it requires significant patient commitment and carries its own risks at each stage.
A note on one-stage revision for infection: In carefully selected patients — particularly where the organism is known, sensitive to antibiotics, the soft tissues are in good condition and the patient is medically fit — a single-stage revision exchange (where new implants are placed at the same sitting after thorough debridement) may be considered. This avoids the period with a spacer and reduces overall surgical burden. Mr. Lodge will discuss which approach is most appropriate at consultation, guided by the microbiology, clinical factors and current evidence.
What Can You Expect from Revision Surgery?
The outcomes of revision knee replacement are generally less predictable than those of primary surgery, and vary considerably depending on the indication, the degree of bone loss, the complexity of reconstruction required and — crucially — whether a clear cause of failure was identified and specifically addressed.
When revision is undertaken for a well-characterised mechanical failure — loosening, instability or malalignment — with a healthy soft tissue envelope and good residual bone stock, outcomes can be very good, with meaningful improvement in pain and function. Registry data shows that carefully selected revision cases can achieve high rates of implant survival at five and ten years when infection has been definitively excluded.
Recovery from revision knee replacement is typically slower than from primary surgery. Hospital stay is longer, physiotherapy requirements are more intensive, and the time to achieve maximum function may extend to twelve to eighteen months. Patients should approach revision surgery with realistic expectations and a clear understanding that the trajectory of recovery is likely to be harder work than the primary procedure.
Infection (Re-infection or New Infection)
Higher than primary surgeryThe risk of infection following revision knee replacement is higher than after primary surgery — estimated at two to three times the primary rate. In patients undergoing revision for infection specifically, reinfection rates of around 10–15% are reported even after thorough two-stage exchange. The larger surgical exposure, longer operative time, poorer soft tissue quality and compromised host biology all contribute to this elevated risk. Meticulous infection prevention measures — extended antibiotic cover, careful wound management and prompt treatment of any remote infection — are essential.
Blood Loss & Transfusion
Greater than primary surgeryRevision knee surgery involves more extensive bone preparation, a larger surgical field and longer operative time than primary replacement — all of which contribute to greater blood loss. Cell salvage, tranexamic acid and careful surgical technique are used to minimise this, but the requirement for blood transfusion is more likely than in primary surgery. Pre-operative assessment of haemoglobin and iron stores, and optimisation of anaemia before the operation, reduces this risk.
Stiffness & Restricted Range of Movement
Common; intensive physiotherapy requiredAchieving adequate range of movement after revision is more challenging than after primary surgery. Scar tissue from previous surgery, compromised soft tissues and the larger reconstruction required all impair the flexibility of the knee. Intensive, committed physiotherapy — started early and continued consistently — is essential to maximise the functional range achieved. Manipulation under anaesthetic (MUA) may be required in some cases if flexion remains inadequate at six weeks post-operatively.
Nerve & Vessel Injury
Higher risk than primary surgeryThe common peroneal nerve, the popliteal artery and vein are all at increased risk during revision surgery — particularly where scar tissue from previous procedures has distorted normal tissue planes. Careful intraoperative identification and protection of these structures is essential, but the risk of nerve injury is higher in revision surgery than in primary replacement, and patients should be counselled accordingly.
Re-revision & Further Failure
Higher than after primary surgeryThe risk of requiring further revision surgery after an initial revision is considerably higher than the risk of revising a primary replacement. Published data from large revision series reports re-revision rates of 14–20% at two to five years. Each successive revision is associated with greater bone loss, more complex reconstruction and poorer outcomes. This reinforces the importance of ensuring that revision is undertaken for the right indication, at the right time, and with a level of surgical planning and expertise commensurate with the complexity of the case.
Overall perspective: Revision knee replacement is a highly specialised undertaking with outcomes that are less predictable and a complication profile that is substantially higher than primary surgery. When undertaken for the right reasons — a clear, identifiable and correctable cause — revision can be transformative. When undertaken without that clear cause, the evidence strongly predicts a poor outcome. The value of careful pre-operative assessment cannot be overstated.
Concerned About Your Knee Replacement?
If you are experiencing problems with a knee replacement — whether recently implanted or several years old — the first step is a thorough specialist assessment to understand what, if anything, has gone wrong.
Mr. Lodge sees patients with problematic primary knee replacements from across North Yorkshire, West Yorkshire and East Yorkshire. Not every painful or underperforming knee replacement requires further surgery — and in many cases, reassurance, physiotherapy or simple non-operative measures may be all that is needed. But where revision is indicated, having the assessment done by a surgeon with specific experience in revision arthroplasty is important.
To arrange a consultation — whether for a second opinion on an existing knee replacement or for assessment of a potentially failing implant — please contact us using the details below.