Total vs Partial Knee Replacement: Which Is Right for You?
Total knee replacement surgery replaces all three compartments of the knee joint. A partial (unicompartmental) replacement resurfaces only the damaged section. The right choice depends on where the wear is, how your leg is aligned under load, and how stable your knee is overall. A standing whole-body scan helps your surgeon see the full picture before deciding.
Key points
- A total replacement suits wear spread across the knee. A partial replacement may be enough when the damage is limited to one compartment.
- Leg alignment, the health of your ligaments and how active you are all affect which operation your surgeon recommends.
- Scans taken lying down can miss alignment problems that only appear when you stand and bear weight.
- An EOS standing scan shows your full leg alignment from hip to ankle. This gives your surgeon the measurements needed to plan accurately.
- ScanAlign is a diagnostic imaging clinic. It does not perform surgery or promise treatment outcomes.
What is the difference between a total and partial knee replacement?
A total knee replacement removes the worn surfaces from all three compartments of the knee. It then caps them with metal and plastic parts. A partial knee replacement, sometimes called a unicompartmental knee replacement, resurfaces only the one compartment that is damaged. It leaves the healthy bone, cartilage and cruciate ligaments untouched.
A partial replacement is a smaller operation. So it usually means a shorter hospital stay and a faster early recovery. However, it is not right for everyone. If wear has spread across the joint, or if the knee is unstable, a total replacement is generally the safer long-term option.
How do you know if you need a total knee replacement?
You might need total knee replacement surgery when arthritis or damage affects more than one compartment, and simpler treatments no longer control your pain. Common signs include the following.
Aching on both the inner and outer sides of the knee, not just in one area.
Your leg alignment has clearly changed when you stand.
Trouble walking, climbing stairs or getting up from a chair, despite medicines and physiotherapy.
The knee feels loose or buckles. This suggests damage to the ligaments or the structure of the knee.
A partial replacement may suit you better if the damage is limited to the inner (medial) compartment, your ligaments are intact and your overall alignment is reasonably good. Your surgeon needs precise imaging to make that decision.
Why does leg alignment matter when comparing knee replacement options?
Leg alignment is one of the most important factors in choosing between a total and a partial knee replacement. If your leg bows inward or outward under your body weight, the load through the knee is uneven. A partial replacement in a badly misaligned leg can wear out quickly. This is because the new surface takes more force than it was designed for.
Your body works as a connected chain. The angle of your hip, the rotation of your thighbone, the tilt of your shinbone and the position of your ankle all affect how force travels through the knee. A problem higher up, such as a slight pelvic tilt, can shift load onto one side of the knee. If the surgeon only looks at the knee on its own, this bigger picture is missed.
That is why whole-leg, weight-bearing imaging matters before any decision on knee replacement. It shows how your joints line up from hip to ankle while you stand, which is exactly how they behave when you walk.
How does a standing scan help plan knee replacement surgery?
A standing scan captures your skeleton under its natural load. When you lie down for a normal X-ray, CT or MRI, gravity no longer presses your joints together, and your muscles relax. So the alignment your surgeon sees on a lying-down scan may not match the alignment you actually walk on.
An EOS scan takes a full-length image of both legs while you stand. It captures the mechanical axis from the centre of your hip to the centre of your ankle in a single exposure, with about 90% less radiation than a standard X-ray, around ten times less. Your surgeon can then measure exactly how much the knee is angled, whether the wear pattern fits a partial or total replacement, and what component positioning would restore balanced loading.
Thinking about a knee replacement? A standing alignment scan gives your surgeon the measurements they need to recommend the right operation.
Book a free video consultationWhen MRI is the better tool. EOS shows bones, joints and alignment clearly. If your surgeon needs to check soft tissue inside the knee, such as cartilage thickness, meniscus tears or ligament damage, MRI is usually the better choice. The two scans work well together. EOS maps the mechanical picture. MRI maps the soft-tissue detail.
What helps you decide between a partial and total knee replacement?
The decision is made by your orthopaedic surgeon, not by a single scan. However, accurate imaging is the foundation of that decision. Here is what your surgical team usually considers.
- Where the wear is. If arthritis affects only the medial compartment and the rest of the knee is healthy, a partial replacement may be suitable.
- Ligament health. A partial replacement relies on intact cruciate ligaments for stability. If those ligaments are damaged, a total replacement is usually recommended.
- Overall leg alignment. Marked bow legs or knock knees may make a partial replacement unsuitable, because the uneven load would remain after surgery.
- Activity level and expectations. Partial replacements can feel more natural and allow a wider range of movement, but they do not suit every knee.
- Age and body weight. These affect how long any replacement is likely to last.
What a standing alignment scan adds is a precise measurement of your mechanical axis under load. This helps your surgeon match the operation to the way your body actually works when upright.
Before you start treatment, or change the one you are on, it is worth getting a detailed diagnosis. Knowing whether the cause sits in the pelvis, the legs or the spine changes what will actually help.
Frequently asked questions
Neither is better in itself. A partial knee replacement keeps more of your natural knee and can feel more natural. But it only works when damage is limited to one compartment and your ligaments are intact. A total replacement is more reliable when wear is widespread.
Most people return to light daily activities within a few weeks, but full recovery can take several months. A partial replacement generally has a shorter early recovery period. Your surgical team will give you a timeline that fits you.
Yes. If a partial replacement wears out, or arthritis spreads to other compartments, it can usually be revised to a total replacement. This is one reason surgeons sometimes prefer a partial option in younger, active patients.
When you lie down, gravity no longer loads your joints, and your alignment can look different. A standing scan shows the true mechanical axis of your leg under body weight. This is exactly how the replacement will work after surgery.
An EOS scan takes a full-length standing image of your skeleton in a single pass, using about 90% less radiation than a standard X-ray, around ten times less. It captures both legs from hip to ankle so your surgeon can measure alignment precisely. You can learn more on the ScanAlign overview page.
Yes. The EOS system uses about 90% less radiation than a standard X-ray, around ten times less. Full safety and preparation details are on the FAQs page.
No. ScanAlign is a private self-pay clinic and you can refer yourself. You start with a free video consultation to check that the scan is suitable for you.
The price for patients travelling from abroad is confirmed during the free video consultation, and more details are on the FAQs and cost page.
An EOS scan shows the alignment and joint spacing of your knee under load. It does not diagnose whether you need surgery. Your surgeon uses the scan together with a clinical examination and other tests to make that recommendation.
ScanAlign is based at 19 Harley Street, London, within The Harley Street Hospital.
See how your knee lines up under your own body weight
A free video consultation lets you talk through your situation from home. You can find out whether a standing alignment scan in London could help your surgical team plan the right operation.
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- National Joint Registry (NJR). Annual reports on knee replacement outcomes in England, Wales, Northern Ireland and the Isle of Man. njrcentre.org.uk
- NHS. "Knee replacement." NHS website, reviewed regularly. nhs.uk/conditions/knee-replacement
- Paley D. Principles of Deformity Correction. Springer, 2002. Widely cited reference on mechanical axis planning and limb alignment.
Written by Abbas Dhami (Specialist Diagnostic Radiographer)
This page is general information and not a diagnosis.
ScanAlign is the trading name of CoreMed Solutions Ltd and operates under The Harley Street Hospital's CQC licence.