Research » Partial vs Total Knee Replacement (TOPKAT)

Partial vs Total Knee Replacement: What the TOPKAT Trial Found at 10 Years

The TOPKAT trial (Total Or Partial Knee Arthroplasty Trial) is one of the most important recent studies in knee replacement surgery, and its 10-year results were published in The Lancet Rheumatology in 2026. I was not involved in this trial, but its findings are highly relevant to my practice, because I offer both partial and total knee replacement and patients often ask which is better. This page explains what the trial found and what it means for choosing the right operation.

What is partial knee replacement, and how does it differ from total?

The knee has three main compartments. In many people with osteoarthritis, the wear is concentrated in just one of them – most often the inner (medial) side. A partial (unicompartmental) knee replacement resurfaces only that worn compartment, leaving the healthy parts of the knee and the natural ligaments intact. A total knee replacement resurfaces the whole joint.

Partial replacement is a smaller operation, but it has long been debated whether it lasts as well as a total replacement, because registry data have shown higher revision rates for partial knees. The question that mattered was whether that reflects the implant itself, or how often the surgeon performs the procedure – and how the two operations compare over the long term.

What the TOPKAT trial set out to do

TOPKAT was a multicentre, pragmatic randomised controlled trial – the most reliable type of study for comparing treatments – carried out across 27 NHS hospitals in the UK. It enrolled 528 patients with late-stage arthritis confined to the inner (medial) compartment of the knee, and randomly assigned them (1:1) to either a partial or a total knee replacement. The main measure was the Oxford Knee Score, a well-validated patient questionnaire, assessed up to 10 years after surgery, alongside a detailed analysis of cost-effectiveness.

What did the trial find at 10 years?

Knee function and satisfaction

At 10 years, partial knee replacement matched total knee replacement for knee function and pain – patients did just as well on the Oxford Knee Score, despite partial being the smaller operation that keeps the healthy compartments and cruciate ligaments of the knee. Earlier in the trial there had in fact been small clinical differences that favoured partial replacement – it was modestly ahead at around the 5-year mark – and these evened out by 10 years, while partial retained its advantages in complications, quality of life and value. Patient satisfaction was high in both groups (around 85% for partial and 82% for total replacement).

Complications, reoperations and revisions

This is where partial replacement showed clear advantages. It had significantly fewer complications overall, while reoperation and revision rates were no higher than for total replacement (revisions were around 5% in each in the main analysis) – directly addressing the long-standing concern that partial knees might need revising more often. The trial also noted that when a partial replacement does need revising, it tends to be a relatively straightforward operation, whereas revising a total replacement is usually more complex.

Cost-effectiveness

Partial knee replacement was more cost-effective for the NHS, with lower overall health-care costs and quality-of-life gains (quality-adjusted life years) over the 10 years that favoured partial replacement.

Why does this matter, and is partial knee replacement right for me?

The headline from TOPKAT is genuinely encouraging for partial knee replacement: for arthritis confined to the inner compartment of the knee, it matched total replacement for knee function and pain at 10 years while delivering fewer complications, better value, and simpler revision if it is ever needed – all from a smaller operation that preserves more of the natural knee. On the strength of these results, the trial's authors recommended that, in experienced hands, partial knee replacement be offered as the treatment of choice for this pattern of arthritis.

That last point is important. The excellent results in TOPKAT came from surgeons who regularly perform partial knee replacement, and the trial was careful to include only patients whose arthritis was genuinely limited to one compartment. A partial replacement is not suitable for everyone – if the arthritis involves more of the knee, a total replacement remains the right operation.

In my own practice I offer both partial and total knee replacement, including robotic-assisted surgery, and I take time to work out which is best for you based on the pattern of your arthritis, your symptoms, your X-rays and scans, and your goals. For the right patient, the evidence now strongly supports partial knee replacement as a durable, effective choice.

Frequently asked questions

What is a partial (unicompartmental) knee replacement?

A partial knee replacement resurfaces only the damaged part of the knee, most commonly the inner (medial) compartment, while keeping the rest of the natural knee and its ligaments. It is suited to arthritis that is confined to one compartment of the knee, whereas a total knee replacement resurfaces the whole joint.

Is a partial knee replacement as good as a total knee replacement?

For arthritis confined to the inner compartment of the knee, partial replacement is an excellent option. In TOPKAT's 10-year results it matched total replacement for knee function and pain, while having significantly fewer complications, reoperation and revision rates that were no higher, better cost-effectiveness, and a simpler operation if revision is ever needed. On this basis the trial's authors recommended it as the treatment of choice for this pattern of arthritis when performed by an experienced surgeon.

Does a partial knee replacement last as long as a total knee replacement?

At 10 years in TOPKAT, revision rates were similar, at around 5% in both groups in the main analysis. When performed by experienced surgeons for suitable patients, partial replacement was durable, and if a partial replacement does need revising it tends to be a simpler operation than revising a total replacement.

Who is suitable for a partial knee replacement?

Generally, people whose arthritis is confined to one compartment of the knee, most often the inner (medial) side, with intact ligaments. Not everyone is suitable; the right choice depends on the pattern of arthritis, which is assessed with examination and X-rays or scans.

Why isn't partial knee replacement used for everyone?

A partial replacement only treats one compartment, so it is not suitable if arthritis affects more of the knee. Results also depend on surgeon experience: the strong outcomes in TOPKAT came from surgeons experienced in the procedure, and registry data show higher revision rates when surgeons perform it infrequently.

Is partial or total knee replacement more cost-effective?

In TOPKAT, partial knee replacement was more cost-effective for the NHS, with lower overall costs and at least as good health outcomes over 10 years.

Read the Full Paper

This trial is published open access in The Lancet Rheumatology under a Creative Commons licence (CC BY 4.0). You can read the full text below, or on the Lancet Rheumatology website.

Full citation: Beard DJ, Davies LJ, Cook JA, et al; TOPKAT Study Group. Assessing clinical and cost effectiveness of total versus partial knee replacement (TOPKAT): 10-year follow-up of a multicentre, randomised controlled trial. The Lancet Rheumatology. 2026;8(2):e116–e126. doi:10.1016/S2665-9913(25)00250-4

This summary is written for general information and explains the research in patient-friendly terms. It does not replace individual medical advice. If you have questions about knee arthritis or knee replacement, please get in touch to arrange a consultation.

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