The four things that make you a TKR candidate

'Am I ready for a knee replacement?' is the question most patients arrive with — and the honest answer is that readiness is determined by four things together, not any one of them in isolation.

The first is a qualifying diagnosis. End-stage osteoarthritis — where cartilage loss has progressed to near-total joint space narrowing and bone meets bone — is the most common reason for total knee replacement (TKR). Rheumatoid arthritis and post-traumatic arthritis, where previous injury has destroyed the joint surface, also qualify.

The second is symptom severity. TKR is considered when knee pain is limiting everyday activities — walking, climbing stairs, moving around the home — and particularly when pain persists at rest or wakes you at night, which signals advanced disease.

The third is documented failure of non-surgical treatment. Physiotherapy, anti-inflammatory medication, walking aids, and intra-articular injections are all explored first. A recommendation for surgery typically follows only when these measures have genuinely stopped providing adequate relief.

The fourth is imaging confirmation. X-ray or MRI findings must support the clinical picture, showing the structural changes consistent with end-stage disease.

These four pillars are assessed together in a structured consultation. Two patients with identical X-rays may reach different conclusions depending on how their symptoms affect daily life and what treatments they have already tried. This is a clinical conversation — not a checklist to complete alone.

Symptoms that signal end-stage disease

The symptom journey in knee osteoarthritis tends to follow a recognisable pattern. Early on, pain is largely mechanical — provoked by activity and eased by rest. Stair-climbing typically becomes effortful before walking distances do, and stiffness after sitting often settles once the joint warms up.

The shift that matters clinically is when rest no longer relieves the pain. When discomfort persists in a chair or wakes a patient repeatedly during the night, it reflects a process that has moved beyond cartilage mechanics into bone involvement and persistent joint inflammation. This is qualitatively different from earlier-stage pain — not simply more of the same — and is one of the clearest flags that disease has reached an advanced stage. Activity-related pain alone, however disabling, does not carry the same clinical weight.

To quantify how symptoms are affecting daily life, clinicians use validated scoring tools such as the WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) and the Oxford Knee Score. These structured instruments measure pain intensity, stiffness, and functional limitation across a range of everyday activities. They form part of a formal clinical assessment rather than a self-screening exercise, and they help establish whether symptom burden has reached the point where surgery is likely to offer meaningful benefit.

One important principle governs how symptoms are interpreted: they must correspond with imaging findings. Severe pain alongside mild radiographic changes — or significant joint space loss with relatively manageable symptoms — prompts further evaluation rather than an immediate surgical recommendation. Neither element alone determines the outcome of the assessment.

When non-surgical options have been exhausted

Before TKR is recommended, a structured course of conservative care should have been tried and found inadequate. That pathway typically moves through several layers: a supervised physiotherapy programme to strengthen the muscles supporting the knee, regular use of analgesics or anti-inflammatory medication, activity modification, weight management where relevant, and walking aids to reduce load through the joint.

If those measures fail to provide sufficient relief, intra-articular injections — corticosteroid or hyaluronic acid — may be appropriate at earlier or moderate stages of osteoarthritis. Orthobiologic treatments follow a similar logic: they may offer benefit when some viable cartilage remains, but their effectiveness falls markedly once cartilage loss is near-total. When imaging confirms bone-on-bone contact and symptoms persist despite injections, the clinical evidence suggests these therapies are unlikely to provide meaningful or durable relief. That is a recognised threshold — not a value judgement on the treatments themselves, but a reflection of the biological reality that there is no longer a cartilage environment for them to support.

It is worth being clear about what 'failure of conservative treatment' actually means. It does not require a fixed number of months, a minimum number of injections, or any particular sequence of steps in rigid order. It means that reasonable options have been adequately trialled — optimised, not merely sampled — and that the patient continues to experience symptoms that limit daily life in a meaningful way. When that point is reached and imaging supports advanced disease, TKR becomes the primary recommended pathway.

What imaging shows and why it matters for TKR candidacy

Imaging sits at the centre of any TKR assessment, but its role is confirmatory rather than decisive.

Weight-bearing X-rays are the starting point. A standing anteroposterior view, taken under load, shows how much joint space remains between the femur and tibia during the activity that actually provokes symptoms. Near-complete narrowing — or bone-on-bone contact visible on that standing view — is the principal radiographic marker of end-stage disease.

MRI adds a different layer of detail: the thickness and integrity of remaining cartilage, changes within the subchondral bone beneath it, and the condition of soft-tissue structures such as the menisci. It is particularly useful when X-ray findings and symptom severity do not quite align, or when the compartmental extent of disease needs clarifying before surgery. AI-assisted MRI analysis — available at Lincolnshire Knee through onMRI™ — can quantify cartilage loss across compartments and detect subchondral involvement with a precision that visual reading alone may not always capture.

Imaging from both modalities also feeds directly into pre-operative planning. Digital templating uses the patient's own joint geometry to determine implant sizing and alignment before the operation begins, supporting a more predictable surgical result.

Total knee replacement vs partial replacement — how the extent of disease decides

Not every knee replacement is the same operation. The label covers a spectrum — and which procedure is right depends almost entirely on how many compartments of the knee are affected by arthritis, not on how severe the pain feels.

The knee has three compartments: medial (inner), lateral (outer), and patellofemoral (between the kneecap and the front of the femur). TKR resurfaces all three with metal and polyethylene components and is indicated when arthritis is widespread across the joint. Where disease is genuinely confined to a single compartment, unicompartmental knee replacement (UKR) — most commonly the medial — may be the more appropriate procedure. It replaces only the damaged surface, preserving the intact ligaments and remaining native cartilage. UKR does, however, require strict patient selection; applied to the wrong candidate it produces predictably poor results.

A third, less common presentation is isolated patellofemoral arthritis — confined to the kneecap joint — for which patellofemoral arthroplasty (PFA) is specifically designed.

Crucially, the choice between these procedures cannot be made from symptoms alone. Pain location does not reliably reflect compartmental extent; imaging and clinical examination together define the pattern. Pre-operative templating — and where appropriate, robotic assistance such as Mako to optimise implant positioning — helps ensure the chosen procedure is executed with precision. Applying an operation that does not match the actual compartmental distribution of disease is a recognised cause of poor outcomes, which is precisely why specialist assessment before any knee replacement is not a formality but a clinical necessity.

Complicating factors and how the assessment works in practice

Several factors can complicate the candidacy picture — but complication is not the same as exclusion, and most of the patients who ask 'does my situation make surgery too risky?' fall into a grey area that warrants assessment rather than a firm no.

Age and activity demand. Patients considering TKR in their 50s face a different set of trade-offs from those in their 70s. Implant durability is well-established, but for someone who has surgery at 52 a revision procedure later in life is a realistic possibility rather than a remote risk. Honest pre-operative discussion about activity goals and long-term expectations is part of responsible surgical practice, not a reason to withhold surgery.

BMI. Higher body weight does not automatically preclude TKR, but it raises perioperative risk and may affect implant longevity. Weight optimisation before surgery is routinely discussed during assessment — the decision remains patient-specific, balancing the degree of functional impairment against an adjusted risk profile.

Deformity and inflammatory arthritis. Significant varus or valgus angular deformity and long-standing rheumatoid arthritis increase operative complexity and perioperative risk. Both remain within the scope of TKR candidacy but require specialist pre-operative planning and templating to achieve reliable alignment and stability.

Absolute contraindications. Active joint infection and the absence of a functional extensor mechanism — the quadriceps-tendon-patella-patellar-tendon chain that straightens the knee — mean TKR is not appropriate regardless of OA severity. Severe peripheral vascular disease affecting the limb may also preclude surgery. These situations are uncommon but are non-negotiable.

At Lincolnshire Knee, the assessment combines clinical history, physical examination, and weight-bearing X-rays, with MRI added where the compartmental picture or soft-tissue status needs clarifying. Objective biomechanical data from MAI Motion® can further quantify how the affected joint is functioning under load. No GP referral is needed: Lincolnshire Knee is part of the MSK Doctors group and accepts patients directly at its Sleaford NG34 and Grantham NG31 sites — book an assessment at lincolnshireknee.co.uk. It is at that consultation that the convergence of structural disease, symptom burden, and failed conservative care can be weighed together — confirming whether TKR is the right next step, or whether an alternative pathway remains open.

1. [1] Knee Replacement – Wikipedia. https://en.wikipedia.org/?curid=2830398 https://en.wikipedia.org/?curid=2830398
2. [2] Knee Replacement – NHS. https://www.nhs.uk/conditions/knee-replacement/ https://www.nhs.uk/conditions/knee-replacement/
3. [3] Osteoarthritis – Wikipedia. https://en.wikipedia.org/?curid=504841 https://en.wikipedia.org/?curid=504841