- Type
- Unicompartmental arthroplasty
- Bone removed
- Less than a total knee replacement
- Ligaments
- Both cruciates preserved
- Hospital stay
- 0 to 2 nights
- Driving
- About 3 to 4 weeks
- Revision rate
- Higher than total knee replacement (AOANJRR)
The knee's three compartments
The knee has three compartments: medial (inside), lateral (outside), and patellofemoral (behind the kneecap). Arthritis can affect one, two, or all three.
A total knee replacement resurfaces the whole knee. A partial (unicompartmental) knee replacement resurfaces only the arthritic compartment and leaves the rest untouched, most often the medial compartment, since that's where arthritis usually starts.
Benefits and trade-offs
Because the ligaments and unaffected compartments are preserved, a partial knee tends to feel more natural, with quicker recovery, less blood loss, and a smaller operation. For the right patient, there's some evidence it gives better function than a total knee.
The trade-off is longevity: the Australian joint replacement registry consistently shows partial knees are revised at a higher rate than total knees, partly due to patient selection and partly because arthritis can progress in the compartments left untouched. Revision rates are also strongly linked to how often a surgeon performs the procedure, this is an operation where selection and experience both matter.
Why age matters
Partial knees are often more appropriate in younger patients. They may wear out after 10 to 15 years, but revising a partial knee to a total knee is usually more straightforward than revising a total knee and that total knee is then likely to last 20+ years. For a younger patient, that staged approach can mean two reliable operations across a lifetime instead of one complex revision late in life.
Who's a good candidate
A partial knee works best when the arthritis is confined to a single compartment, the ACL is intact, any deformity is mild and correctable, and the knee still has good range of motion, Professor Rodda assesses all of this on examination and imaging.
If more than one compartment is affected, the ACL is deficient, or the deformity is significant, a partial knee is likely to fail early and a total knee is the more reliable option. Some patients ask for a partial knee simply because it's a smaller operation, that's true, but not everyone is a candidate.
How it's planned
As with total knees, partial knee replacements are planned using detailed pre-operative imaging and patient-specific instrumentation, so implant position is matched to the patient's own anatomy.
The bottom line
This choice should be made on your anatomy and imaging, not on marketing. It's a discussion Professor Rodda is always happy to have in consultation.
Questions worth asking at your consultation
Every one of these is a fair question and none of them should be awkward to ask. Print them or bring them on your phone.
- Am I a good candidate for unicompartmental (partial) knee replacement, and what would make me a poor one?
- What are the alternatives, including doing nothing for now?
- How many of these do you perform in a year?
- What does the Australian registry say about the implant you would use for someone my age?
- What does a realistic result look like for me specifically, and what will I still not be able to do?
- What is your plan if it does not go well?
Frequently asked questions.
Is a partial knee replacement better than a total?
Not better, different. In the right knee it gives a more natural feeling joint, better movement and a faster recovery. It also has a higher revision rate over time. It is the right operation for a minority of arthritic knees and the wrong one for the majority, so selection matters more than preference.
Who is suitable?
Someone whose arthritis is confined to one compartment, whose anterior cruciate ligament is intact, whose deformity corrects passively, and whose other compartments are genuinely preserved. This is assessed on weight-bearing and stress radiographs and confirmed during the operation.
What happens if it wears out?
It is usually converted to a total knee replacement. That conversion is generally a more straightforward operation with better results than revising a failed total knee replacement, because less bone was removed the first time.
Will I need a total knee replacement eventually?
Some people will and some will not. Arthritis can progress into the other compartments over time, and that is the most common reason a partial is later converted. Age at surgery is the main factor: the younger you are, the more years of exposure there are.
Is the recovery really faster?
Usually yes, and this is consistently reported. Less bone is removed, less soft tissue is disturbed and the cruciate ligaments are intact, so swelling is less and range returns sooner. Many patients are off crutches within two weeks.
References.
- Australian Orthopaedic Association National Joint Replacement Registry. Annual Report. Adelaide: AOA.
- 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. Lancet. 2014;384(9952):1437-1445.
- Liddle AD, Pandit H, Judge A, Murray DW. Effect of surgical caseload on revision rate following total and unicompartmental knee replacement. J Bone Joint Surg Am. 2016;98(1):1-8.
This page provides general information about a medical condition and a surgical procedure. It is not individual medical advice and does not replace consultation with a qualified practitioner. Outcomes vary between individuals and all surgery carries risk. A referral is needed for a consultation with Professor Daevyd Rodda; without one, you can start with the practice nurse practitioner, who can provide it.