Two things that have to be true before surgery makes sense

Before a consultant recommends total knee replacement, two things need to be established — and both matter equally. The first is a qualifying diagnosis: the knee joint must be failing because of a recognised condition, most commonly osteoarthritis, but also rheumatoid arthritis or post-traumatic arthritis following a previous injury. The second is confirmed failure of non-surgical treatment: the condition must have become chronic, and a structured package of conservative management must genuinely no longer be controlling it.

Neither pillar alone is sufficient. Severe arthritis on an X-ray does not automatically mean surgery is the right next step, and persistent pain does not either — not if the right non-surgical treatments have not yet been properly tried. As the NHS clinical guidance published in March 2025 states, patients should not be considered for knee replacement until their condition is chronic and conservative methods have failed.

So the key question is not simply 'how bad is my pain?' but something more specific: 'have I reached the point where nothing else is working?' The sections that follow unpack what each pillar means in practice — which diagnoses qualify, what conservative treatment failure actually looks like, and which clinical signs tend to prompt a referral for surgical assessment.

Which knee conditions qualify

Four diagnoses account for the vast majority of TKR referrals, with osteoarthritis by far the most common.

Osteoarthritis (OA) qualifies when it has reached end-stage — meaning the protective cartilage has worn away completely, leaving the underlying bones in direct contact. That 'bone-on-bone' state is confirmed on a standing weight-bearing X-ray, not estimated from symptoms alone. Early or mild OA, where meaningful cartilage still remains, does not meet the threshold; the disease must be advanced and causing severe, function-limiting pain.

Rheumatoid arthritis and other inflammatory arthropathies — including juvenile rheumatoid arthritis and osteonecrosis — qualify when the autoimmune or inflammatory process has caused sufficient joint destruction to produce the same degree of functional loss as end-stage OA. Patients in this group are often managed jointly with a rheumatologist before a surgical referral is made, to ensure their systemic disease is as well controlled as possible ahead of any operation.

Post-traumatic arthritis develops after a fracture around the knee, a significant ligament tear, or extensive meniscal loss — injuries that alter joint mechanics and accelerate cartilage wear over subsequent years. The underlying cause differs from primary OA, but the end point — a severely damaged joint confirmed on imaging — is the same qualifying criterion.

In every case, the diagnosis must be established clinically and supported by imaging before surgical candidacy is formally considered.

Clinical signs that suggest your knee has reached a surgical threshold

Five findings, taken together, indicate that a knee may have crossed from a management problem into a surgical one. No single sign is decisive on its own; consultants weigh the overall pattern.

Bone-on-bone change on standing X-ray. A weight-bearing radiograph — taken upright, with the knee under load — is the most objective measure available. When the joint-space gap has disappeared completely, confirming direct bone contact, it provides the structural evidence that symptoms alone cannot.

Chronic joint swelling. Persistent effusion that does not resolve with anti-inflammatory medication signals ongoing joint damage rather than a temporary flare.

Visible deformity. Varus bowing (bow-legged) or valgus collapse (knock-kneed) indicates that the joint surfaces have worn unevenly and that the mechanical axis of the leg has shifted away from normal.

Sleep disturbance. Regular pain at night — arising at rest rather than being triggered by activity — suggests the inflammatory burden has moved beyond what the joint can absorb passively.

Significant functional restriction. Difficulty walking more than a short distance, managing stairs, or rising from a chair represents the clearest day-to-day evidence of surgery-level impairment.

Clinicians often use the WOMAC questionnaire — a validated tool that scores pain, stiffness, and physical function on a standardised scale — to translate these findings into a structured baseline and to track change after treatment.

Mild pain without functional loss does not justify the step to surgery; the risks must be proportionate to the degree of impairment. Individual suitability depends on the full clinical picture, which is why imaging and a consultant assessment remain the definitive step.

Non-surgical treatments you should have tried first

An adequate trial means more than a few GP appointments and a box of ibuprofen. In practice, both NHS and AAOS guidance point to at least three to six months of structured, supervised management — and the pathway has several distinct components that should each be addressed before surgery enters the conversation.

Physiotherapy and exercise. Strengthening the muscles that support the knee — particularly the quadriceps and hamstrings — reduces the load passing through the damaged joint surface. Low-impact activity (swimming, cycling, walking) maintains joint movement and general fitness without the compressive stress of high-impact exercise. A physiotherapist can tailor a programme to what the knee will currently tolerate.

Weight management. Every kilogram of body weight generates roughly three to four kilograms of force across the knee during walking. Even modest weight reduction meaningfully lowers that mechanical load, reduces pain, and — if surgery does become necessary — improves wound healing and anaesthetic risk.

Medication. Oral and topical NSAIDs remain the mainstay for inflammatory pain. Simple analgesics (paracetamol) are commonly used in combination. Neither addresses the underlying joint damage, but adequate pain control supports participation in physiotherapy.

Injection therapies. Corticosteroid injections offer short-to-medium-term anti-inflammatory relief and serve a secondary diagnostic function: a knee that responds well suggests the inflammatory component is significant; one that fails to respond at all provides useful clinical information. Viscosupplementation (hyaluronic acid) aims to restore some of the joint's natural lubrication and cushioning. Evidence for viscosupplementation is moderate and varies by patient profile.

Walking aids and unloader bracing. A walking stick or frame redistributes load away from the most damaged compartment. Varus or valgus unloader braces can reduce medial or lateral compartment stress in appropriate patients.

Emerging options. Genicular artery embolisation (GAE) and radiofrequency ablation (RFA) of the genicular nerves are beginning to appear as adjuncts or delaying strategies in selected patients. Platelet-rich plasma (PRP) injections are similarly being used in this context. None of these is yet standard of care, and evidence continues to develop; they are best discussed with a specialist rather than pursued independently.

Working through this pathway thoroughly matters for the patient as much as for any clinical checklist — it identifies what still helps, documents what does not, and ensures that any surgical decision is grounded in genuine need.

Factors that raise surgical risk or rule it out

Not everyone who meets the indication criteria will be an uncomplicated surgical candidate. Understanding where the boundaries lie — and how firm they are — helps patients approach a consultant conversation with realistic expectations.

Absolute contraindications

A small number of conditions make TKR unsafe regardless of symptom severity:

• Active infection — either within the knee joint itself or elsewhere in the body (sepsis). Implanting metalwork into an infected field carries an unacceptable risk of catastrophic failure.
• Severe untreated peripheral arterial disease — insufficient blood supply to the lower limb compromises healing and dramatically raises the risk of serious post-operative complications.
• Extensor mechanism deficiency — rupture of the quadriceps or patellar tendon means the patient cannot extend the knee; without that function, rehabilitation is not viable.
• Neuropathic (Charcot) joint — a joint whose nerve supply is severely disrupted cannot provide the sensory feedback needed to protect an implant from rapid mechanical failure.

Relative contraindications

These are factors that raise risk rather than rule surgery out — the balance of benefit versus risk requires individual clinical judgement:

• Morbid obesity (BMI above 40) increases the risk of delayed wound healing and peri-operative infection. Weight loss before surgery meaningfully reduces these risks and is worth pursuing as a concrete preparatory step rather than a barrier.
• Poorly controlled systemic disease — significant cardiac or pulmonary conditions that have not been optimised raise anaesthetic and recovery risk.
• Severe cognitive impairment may limit a patient's capacity to engage with post-operative rehabilitation, which is central to achieving a good outcome.
• Poor skin quality around the knee can complicate wound closure.

Advanced age alone is not a contraindication. NHS guidance is explicit on this point: chronological age does not exclude a patient from consideration.

Where any of these factors are present, the consultant's role is to weigh the individual risk-benefit picture — factoring in deformity severity, ligament integrity, bone quality, and overall medical fitness — rather than applying a blanket rule.

What a formal candidacy assessment involves

Knowing what to expect at a candidacy consultation takes most of the anxiety out of the appointment. The assessment has four distinct components, each serving a specific purpose.

Standing, weight-bearing X-rays are taken with the patient upright so the joint carries full body weight — the same loading it experiences during walking. Images taken lying down can underestimate joint-space loss; standing films reveal the true extent of compartmental narrowing and confirm whether bone-on-bone contact is present.

Structured clinical history. The consultant will ask how long symptoms have been present, which activities are affected, and — critically — which non-surgical treatments have been tried and what each achieved. This maps the conservative-management pathway already covered in section four and establishes that surgery is genuinely the next step rather than a premature one.

Medical fitness review. Cardiovascular status, current medications, diabetes control, and anaesthetic risk are all assessed. Where a comorbidity is sub-optimally managed, a referral for further optimisation before any surgical date is set is standard practice.

Patient-reported outcome measures. Validated tools such as the WOMAC index and the Oxford Knee Score give the knee pain and functional limitation a numerical baseline. These scores also serve as the benchmark against which post-operative improvement is measured — making them as useful to the patient as to the surgeon.

Shared decision-making runs through each element. The consultation is a two-way conversation about personal goals, expected activity level, and realistic outcomes — not a conveyor belt towards a pre-determined surgical plan.