Partial Knee Replacement
Partial or unicompartmental knee replacement resurfaces only the worn part of the knee. Who it suits, what it offers over a total replacement, and its limits.
The knee has three compartments. A partial, or unicompartmental, replacement resurfaces only the worn one and leaves the rest of the joint alone, including your own cruciate ligaments.
Why it is attractive when appropriate
- Less bone removed
- Own ligaments preserved, so the knee’s natural mechanics are largely intact
- Faster and generally less painful early recovery
- Knee frequently described as feeling more natural
- Can be converted to a total replacement later if needed
Why it is not offered more often
Because most arthritic knees do not qualify. Suitability requires:
- Arthritis genuinely confined to one compartment on weight-bearing imaging
- Intact and functioning anterior cruciate ligament
- Deformity that is limited and passively correctable
- Reasonable range of movement
- Absence of inflammatory arthritis
It becomes unsuitable with multi-compartment wear, significant fixed deformity, ligament instability, or inflammatory disease.
What the operation involves
A smaller incision than a total replacement, resurfacing of the affected compartment only, and implant positioning that is less forgiving of error than in a total replacement, which is one reason robotic assistance is sometimes used here.
Risks
The same categories as a total replacement: infection, blood clots, stiffness, persistent pain, and eventual wear. There is an additional consideration specific to partial replacement, which is progression of arthritis in the compartments that were left alone, and which can lead to conversion to a total replacement in due course.
How to decide
The partial or total comparison sets out the trade-offs in full, including what to ask if only one option was offered to you.
Common questions
Am I suitable for a partial knee replacement?
Broadly, if the arthritis is genuinely confined to one compartment of the knee, your cruciate ligaments are intact and working, deformity is limited and correctable, and the knee moves reasonably well. Only a minority of arthritic knees meet these criteria, which is why most patients are appropriately offered a total replacement. It is still a fair question to ask about your own imaging.
Is recovery faster than a total replacement?
Generally yes. Less bone is removed, your own ligaments are preserved, and the early recovery tends to be quicker and less painful. Many patients describe the knee as feeling more like their own. That said, the rehabilitation still matters and the difference is one of degree rather than kind.
What happens if it wears out?
A partial replacement can usually be converted to a total replacement later, which is a more straightforward proposition than revising a failed total. This is one of the arguments for a partial in a younger patient with isolated arthritis.
Related reading
Partial or Total Knee Replacement: How to Decide
How surgeons choose between a partial and a total knee replacement, what each involves, how long they last, and the questions to ask if only one was offered.
Total Knee Replacement
What a total knee replacement involves, who it suits, what recovery asks of you, and the risks and alternatives worth understanding before deciding.