Short answer
A total knee replacement resurfaces the whole joint, while a partial (unicompartmental) replacement resurfaces only the one worn section and keeps the rest of the knee, including its ligaments.12 For people whose arthritis is limited to one compartment, a large UK trial found similar function at five years, with partial replacement giving a quicker, lower-risk recovery but registry data showing a higher chance of revision surgery later.34 The deciding factor is whether the damage really is confined to one area and the ligaments are intact.2
Key points
- The knee has three compartments; a partial replacement treats one of them.
- Only people with arthritis confined to one compartment and stable ligaments are candidates.
- Partial replacement usually means a faster recovery and fewer early complications.
- In the TOPKAT trial, knee function scores at five years did not differ between the two.
- Registry data show partial replacements are about twice as likely to be revised.
How the two operations differ
The knee has three compartments: the inner (medial) side, the outer (lateral) side, and the area behind the kneecap (patellofemoral).2 Osteoarthritis, the wear-related loss of the smooth cartilage lining the joint, can affect one, two or all three.
A total knee replacement resurfaces the whole joint.1 A partial, or unicompartmental, knee replacement resurfaces just one section with metal and plastic parts, leaving the healthy bone, cartilage and ligaments in the other compartments untouched.2 The NHS notes that which type is used depends on the damage to your knee.1
| Feature | Partial knee replacement | Total knee replacement |
|---|---|---|
| What is replaced | One compartment | All joint surfaces |
| Who it suits | Arthritis in one compartment, intact ligaments | Wider range of arthritis patterns |
| Recovery | Usually faster; NHS driving guidance from 3 weeks | Usually slower; NHS driving guidance from 6 weeks |
| Early complications | Lower rates of clots, heart attack, stroke and readmission in registry data | Higher than partial in registry data |
| Function at 5 years (TOPKAT) | No significant difference in Oxford Knee Score | |
| Revision surgery | About twice the revision rate at 8 years in registry data | Lower revision rate |
Who may be considered for a partial replacement
The American Academy of Orthopaedic Surgeons (AAOS) states that arthritis must be limited to one compartment for a partial replacement to be an option. Pain is typically concentrated on one side, and the ligaments should be intact.2 People with inflammatory arthritis (such as rheumatoid arthritis), marked stiffness or ligament damage may not be suitable.2
In the TOPKAT trial, people with late-stage arthritis limited to the inner compartment were recruited, and 45% of those assessed were excluded for various reasons, which gives a sense of how selective the criteria can be.3
What the evidence says
Function. TOPKAT was a UK randomised controlled trial of 528 people with medial compartment osteoarthritis. At five years, there was no difference between groups in the Oxford Knee Score (a questionnaire measuring knee pain and function), and the two operations had a similar incidence of reoperations and complications.3 Partial replacement was more cost-effective, and the authors suggested it should be considered the first choice for suitable patients.3 The evidence that the two give similar medium-term function in suitable patients is Moderate, since it rests mainly on one well-run trial.
Safety and revision. A study of over 100,000 matched patients in the National Joint Registry for England and Wales found that after partial replacement, deaths, blood clots, heart attacks, strokes, readmissions and length of stay were all lower than after total replacement.4 Revision rates at eight years, however, were about twice as high after partial replacement. The authors estimated that for every 100 people given a partial rather than a total replacement, there would be around one fewer death and three more reoperations in the first four years.4
Registry data cannot fully explain why partial replacements are revised more often. One recognised reason is that arthritis can progress in the compartments left untouched, which may lead to conversion to a total replacement.2
How recovery differs
The AAOS lists a faster recovery, less pain after surgery, less blood loss and a lower chance of infection and blood clots as advantages of partial replacement.2 Many people also report that a partial replacement feels more natural, because more of the original knee is kept.2
The NHS advises waiting at least 3 weeks before driving after a partial knee replacement, compared with at least 6 weeks after a total one, and notes that partial replacements usually recover faster.5 The general timeline is covered in the recovery timeline after knee replacement.
Common questions
Can a partial knee replacement be converted to a total one later?
Yes. The AAOS notes that if arthritis develops in the parts of the knee that were not replaced, a total knee replacement may be needed.2
Is a partial knee replacement a smaller operation?
Generally, yes. Less of the joint is replaced, and registry data show fewer serious early complications and shorter hospital stays than after total replacement.4
Why might a surgeon recommend a total replacement when I asked about a partial?
Usually because the arthritis affects more than one compartment, or the ligaments are damaged or the knee is very stiff.2 It is reasonable to ask which X-ray or examination findings led to the recommendation.
Does robotic surgery change the choice?
Robotic assistance is a separate question from which operation suits your knee. The evidence is covered in whether robotic knee replacement is better.
Bottom line
For people whose arthritis is confined to one compartment, a partial knee replacement offers similar medium-term function with an easier recovery and fewer early complications. The trade-off is a higher chance of further surgery later. The first question is not which operation is better, but whether your knee meets the criteria for a partial one.
Related reading
- Knee replacement: what it involves, risks and recovery
- What Is the Recovery Timeline After Knee Replacement?
- How Long Do Knee and Hip Replacements Last?
- Is Robotic Knee Replacement Better?
Sources
- NHS. What is a knee replacement? NHS website. https://www.nhs.uk/tests-and-treatments/knee-replacement/what-is-a-knee-replacement/ Accessed 5 November 2026.
- American Academy of Orthopaedic Surgeons. Unicompartmental knee replacement. OrthoInfo. https://www.orthoinfo.org/treatment/unicompartmental-knee-replacement Accessed 5 November 2026.
- Beard DJ, Davies LJ, Cook JA, et al; TOPKAT Study Group. The clinical and cost-effectiveness of total versus partial knee replacement in patients with medial compartment osteoarthritis (TOPKAT): 5-year outcomes of a randomised controlled trial. The Lancet; 2019;394(10200):746–756. https://doi.org/10.1016/S0140-6736(19)31281-4
- Liddle AD, Judge A, Pandit H, Murray DW. Adverse outcomes after total and unicompartmental knee replacement in 101,330 matched patients: a study of data from the National Joint Registry for England and Wales. The Lancet; 2014;384:1437–1445. https://doi.org/10.1016/S0140-6736(14)60419-0
- NHS. Knee replacement: recovery. NHS website. https://www.nhs.uk/tests-and-treatments/knee-replacement/recovery/ Accessed 5 November 2026.
Article history
- — First published.