When comparing total knee replacement and partial knee replacement, start by identifying where your arthritis is. If the damage is confined to one compartment of your knee, a partial replacement may suit you. More widespread arthritis usually favours a total replacement. [2]
Partial replacement can preserve more of your knee and allow an easier early recovery. [2] The trade-off is a higher chance of further surgery in national registry data. [1] Choosing well means considering both your symptoms now and what another operation might involve later.
At a Glance
- Partial replacement may suit arthritis confined to the inner compartment, with functioning ligaments.
- More widespread arthritis usually favours total replacement.
- Partial replacement may offer an easier early recovery, but national registry data show a higher revision risk.
- Your symptoms, arthritis pattern and the implications of further surgery all help guide the decision.
On this page
- What is the difference between total and partial knee replacement?
- Can you have a partial knee replacement instead of a total replacement?
- Is partial knee replacement less painful than total replacement?
- What do robotic assistance and a fixed-bearing implant change?
- How long do partial and total knee replacements last?
- Why does your surgeon's experience matter?
- Summary
What is the difference between total and partial knee replacement?
Your knee has three compartments: the inner, or medial, compartment; the outer, or lateral, compartment; and the patellofemoral compartment behind your kneecap.
A medial unicompartmental knee replacement resurfaces the worn inner compartment with metal and plastic components. It preserves the other compartments and the cruciate ligaments, which help control how your knee moves.
Total knee replacement surgery resurfaces both the inner and outer compartments. The undersurface of the kneecap may also be replaced.
Other partial replacements treat different patterns of arthritis. Lateral unicompartmental replacement treats isolated outer-compartment wear. Patellofemoral replacement treats isolated arthritis between the kneecap and thighbone. This article focuses on medial partial replacement, the more common comparison with total replacement.
Can you have a partial knee replacement instead of a total replacement?
The ideal candidate has anteromedial osteoarthritis: full-thickness cartilage loss, often described as bone-on-bone wear, in the inner part of the knee. [2]
The ligaments should function normally, with well-preserved cartilage in the outer compartment and relatively well-preserved cartilage behind the kneecap. [2] Dr Vishal Pai generally looks for less than 10 degrees of correctable varus, or bow-legged alignment. This is a selection preference rather than a universal boundary.
Examination and imaging help establish whether the remaining knee is suitable. Pre-surgery long limb alignment X-rays and an MRI scan are often organised. Significant arthritis elsewhere or unsuitable ligament function generally makes total replacement the better option.
Even if your anatomy suits partial replacement, your symptoms should justify knee replacement surgery. Exercise, physiotherapy, weight management where appropriate and suitable pain relief remain options before deciding on an operation. [9]
Is partial knee replacement less painful than total replacement?
Often, the early recovery is easier. A Finnish randomised trial involving 143 patients found better pain and activity scores two months after partial replacement, although the differences largely disappeared by two years. [2]
Partial replacement may also provide better movement and a more natural-feeling knee. Preserving the ligaments may contribute, but neither operation guarantees a pain-free knee or a return to every activity.
Longer-term results can be similar. The TOPKAT trial followed 528 patients allocated to partial or total replacement and found no clinically meaningful difference in knee pain and function at ten years. [3]
Both operations require rehabilitation, and a full recovery can take 12 months following surgery. Risks include infection, blood clots, stiffness, and persistent pain. Osteoarthritis in a partial knee replacement can also progress to involve the other compartments, and this is termed disease progression. This may require revision surgery.
What do robotic assistance and a fixed-bearing implant change?
Dr Vishal Pai uses the fixed-bearing Stryker Restoris MCK implant with Mako robotic assistance. Its plastic insert is secured to the tibial component, avoiding the dislocation mechanism associated with a mobile bearing prosthesis. [6]
Mako robotic assistance supports surgical planning and accurate bone cuts while preserving bone. It also allows the assessment of ligament balance throughout movement. [4] [6]
One aim is to avoid overcorrecting a bow-legged knee into valgus, or knock-knee alignment, which can overload the preserved outer compartment. Accurate positioning and balance support that aim, but robotic assistance cannot guarantee that arthritis will not progress or that revision will never be needed. [8] [4]
How long do partial and total knee replacements last?
The 2025 Australian joint replacement registry reports an estimated 4.1% revision rate at five years for Restoris MCK, approximately four in 100. That estimate comes from 6,792 procedures with varying follow-up. [1]
Across modern implants used for osteoarthritis, the registry's ten-year revision estimates are 11.3% for unicompartmental replacement and 4.7% for total replacement. [1]
These are population averages across different patients and implants, rather than a direct Restoris comparison or a prediction for your knee. TOPKAT found similar revision numbers at ten years, showing that results in selected patients treated within a trial can differ from national averages. [1] [3]
Why does your surgeon's experience matter?
Dr Vishal Pai regularly performs partial knee replacement surgery. Familiarity with patient selection and surgical technique affects implant survival. [5]
Research involving Oxford mobile-bearing implants found lower revision rates when partial replacements accounted for at least 20% of a surgeon's knee replacements. [5]
A smaller Restoris study compared 37 robotic procedures with 72 manual Oxford procedures by one surgeon. Operating time stabilised sooner with robotic assistance, but the study did not prove a reduction in revision risk. [6]
Summary
A medial unicompartmental knee replacement may suit isolated inner-compartment arthritis with functioning ligaments. Weigh its recovery benefits against revision risk, using your arthritis pattern and symptoms to guide the decision. [2] [1]
If you would like to discuss how this applies to your knee, you can book a consultation with Dr Vishal Pai.
References
Show all 9 referencesHide references
- Australian Orthopaedic Association National Joint Replacement Registry. 2025. Annual report. Tables KP17, KP18 and KT12. AOANJRR.
- Knifsund J et al. 2021. Functional results of total-knee arthroplasty versus medial unicompartmental arthroplasty: two-year results of a randomised, assessor-blinded multicentre trial. BMJ Open.
- Beard DJ et al. 2026. 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.
- Robinson PG et al. 2019. A systematic review of robotic-assisted unicompartmental knee arthroplasty: prosthesis design and type should be reported. The Bone & Joint Journal.
- Mohammad HR, Judge A, Murray DW. 2023. The influence of surgeon caseload and usage on the long-term outcomes of mobile-bearing unicompartmental knee arthroplasty: an analysis of data from the National Joint Registry for England, Wales, Northern Ireland, and the Isle of Man. The Journal of Arthroplasty.
- Clement ND et al. 2026. Learning curve of robotic arm-assisted versus manual unicompartmental knee arthroplasty: accuracy, theatre time, complications, patient-reported outcome measures, and implant survival. Bone & Joint Open.
- Levy KH et al. 2023. Unicompartmental knee arthroplasty revised to total knee arthroplasty versus primary total knee arthroplasty: a meta-analysis of matched studies. The Knee.
- Huang Z et al. 2025. The influence of severe knee varus and patellofemoral joint degeneration on outcomes following fixed-bearing medial robotic-assisted unicompartmental knee arthroplasty: a minimum of 18-month follow-up. Journal of Orthopaedic Surgery and Research.
- National Institute for Health and Care Excellence. 2022. Osteoarthritis in over 16s: diagnosis and management (NG226). NICE.
Frequently Asked Questions
Can a partial replacement be converted to a total replacement?
Yes, although conversion can be more complex than a first total replacement. Standard primary components may be suitable when enough bone remains, and the ligaments provide adequate stability. Bone loss may require a graft, metal augments or stems. This helps explain why preserving bone during the original operation is useful. [7]
Does mild wear behind the kneecap rule out a partial replacement?
Not necessarily. Mild changes may be acceptable, depending on their location and symptoms. More extensive damage needs careful assessment. [8]
What could make a partial replacement need further surgery?
Arthritis can progress in the retained compartments, or the implant can loosen. [1] Increasing pain or instability warrants assessment, although neither symptom alone proves that revision is needed.
See whether partial knee replacement may suit your knee
Dr Vishal Pai assesses knee arthritis and performs partial and total knee replacement. You can arrange a consultation to discuss your symptoms, arthritis pattern and treatment options.
Written by Dr Vishal Pai
Vishal is an experienced knee surgeon based in Bayside, Melbourne. He consults at Sandringham Orthopaedic Specialists and operates at The Avenue Hospital and Calvary Holmesglen Private Hospital. His practice focuses on sports knee surgery, including ACL reconstruction and meniscal repair, as well as robotic knee replacement.