Partial vs Total Knee Replacement: Comparing the Outcomes That Matter to Patients
Key points
- This was a large systematic review bringing together 60 studies that compared partial (unicompartmental) and total knee replacement, focusing on the outcomes that matter most to patients.
- Across many of those outcomes, partial replacement came out ahead: shorter hospital stay, fewer serious medical complications, lower risk of blood clots and infection, better movement and function, and a quicker return to work and sport.
- The one area where total replacement did better was revision: partial knee replacements were more likely to need revising, particularly in the early years.
- That higher revision rate is strongly linked to surgeon experience – it is much lower when the operation is done by surgeons who perform it regularly.
- Both are good operations; the review supports giving patients this full picture so they can choose with their surgeon.
What was this review comparing?
For arthritis affecting only one part of the knee – most commonly the inner (medial) compartment – there are two well-established operations. A partial (unicompartmental) knee replacement resurfaces only the worn compartment, keeping the rest of the natural knee and its ligaments, while a total knee replacement resurfaces the whole joint. Around a quarter to a half of people needing a knee replacement could potentially be suitable for a partial, yet only about 8% of knee replacements in the UK are partial – in part because of long-standing uncertainty about how the two compare.
In this review, my colleagues and I set out to give patients and surgeons a clear, comprehensive picture by comparing partial and total knee replacement across the outcomes that patients themselves told us mattered most – not just how long the implant lasts, but recovery, complications, movement, function and getting back to normal life.
How the review was done
This was a systematic review and meta-analysis, which is the most rigorous way of bringing together existing evidence. Rather than relying on clinical trials alone, we drew on three types of study side by side – randomised controlled trials, large national joint registries and databases, and large cohort studies – so that we could compare the operations across far more patients and more outcomes than previous reviews. We searched the major medical databases for studies published between 1997 and 2018, and included 60 studies in the final analysis.
What did the review find?
Recovery and hospital stay
Partial knee replacement was consistently associated with a shorter hospital stay than total replacement, and with a quicker return to work and to sport. As a smaller operation that preserves more of the natural knee, it tended to allow a faster recovery.
Complications and safety
Partial replacement had fewer serious medical complications. Across the studies, it was associated with lower rates of heart attack, stroke, blood clots (venous thromboembolism) and deep infection, and with lower early mortality, compared with total replacement.
Movement and function
Partial replacement was associated with a better range of movement and better functional scores on patient questionnaires, as well as better kneeling ability. Pain relief was similar between the two operations – both are very effective at relieving the pain of arthritis.
Revision and reoperation
This was the area where total replacement performed better. Partial knee replacements were more likely to need revision surgery, particularly within the first five years. Importantly, the need for other (non-revision) reoperations was similar for both. The review also examined why the partial revision rate is higher: registry data show it is closely tied to how often a surgeon performs the operation, with much lower revision rates in experienced, higher-volume hands – and there is also a lower threshold to revise a partial knee, because doing so is generally more straightforward than revising a total replacement.
What does this mean for choosing between partial and total knee replacement?
The review concluded that both partial and total knee replacement are good, viable operations for arthritis confined to one compartment of the knee. When compared directly, partial replacement offered advantages across several outcomes that matter to patients – faster recovery, fewer serious complications, and better movement and function – while total replacement had the lower risk of needing revision surgery in the future.
The key message is that patients deserve this full picture when deciding. The right choice depends on the pattern of your arthritis and on what matters most to you – for example, weighing a quicker recovery and better function against a lower chance of future revision. Surgeon experience matters too: the strong results for partial replacement are most reliably achieved by surgeons who perform it regularly. These findings sit alongside the TOPKAT randomised trial, which later showed similar long-term knee scores and revision rates for the two operations, with partial being more cost-effective.
In my own practice I offer both partial and total knee replacement, including robotic-assisted surgery, and I take time to discuss which suits you best based on your scans, symptoms and goals.
Frequently asked questions
What is the difference between a partial and a total knee replacement?
A partial (unicompartmental) knee replacement resurfaces only the worn part of the knee, most often the inner (medial) compartment, keeping the rest of the natural knee and its ligaments. A total knee replacement resurfaces the whole joint. Partial replacement suits arthritis confined to one compartment.
Which has fewer complications, partial or total knee replacement?
In this review, partial knee replacement had fewer serious medical complications than total replacement, including lower rates of heart attack, stroke, blood clots and deep infection, as well as lower early mortality and a shorter hospital stay.
Do partial knee replacements need replacing more often?
The review found that partial knee replacements had a higher revision rate than total replacements, particularly in the earlier years. However, this is strongly linked to how often the surgeon performs the operation: revision rates are considerably lower when partial replacement is carried out by experienced, higher-volume surgeons.
Is recovery faster after a partial knee replacement?
Generally yes. In the review, partial knee replacement was associated with a shorter hospital stay and a quicker return to work and to sport compared with total knee replacement.
Which gives better movement and function?
The review found better range of movement and better functional (patient-reported) scores after partial knee replacement, while pain relief was similar between the two operations.
How do I decide between a partial and a total knee replacement?
It is a shared decision with your surgeon, based on the pattern of your arthritis, your priorities (for example faster recovery and function versus a lower chance of future revision), and the surgeon's experience with partial replacement. Both are good operations when used for the right patient.
Read the Full Paper
This systematic review is published open access in The BMJ under a Creative Commons licence (CC BY-NC 4.0). You can read the full text below, or on the BMJ website.
Full citation: Wilson HA, Middleton R, Abram SGF, Smith S, Alvand A, Jackson WF, Bottomley N, Hopewell S, Price AJ. Patient relevant outcomes of unicompartmental versus total knee replacement: systematic review and meta-analysis. BMJ. 2019;364:l352. doi:10.1136/bmj.l352
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.
