Partial vs Total Knee Replacement: Which One Do You Need?

Many patients are surprised to learn that “knee replacement” is not a single operation. When a patient comes to me having decided they need their knee replaced, one of the first things I assess is whether they need the whole knee replaced — or just the worn-out part of it.

That distinction — between a total knee replacement and a partial knee replacement — matters a great deal. For the right patient, a partial replacement can mean a smaller operation, a faster recovery, and a more natural-feeling knee. But it is only suitable for a specific group of patients, and choosing it for the wrong knee leads to disappointment. Getting this decision right is one of the more important judgements I make.

Let me explain the difference clearly, and help you understand which one might apply to you.

Understanding the Knee’s Three Compartments

To understand the difference, you need one simple piece of anatomy. The knee is divided into three compartments: the inner (medial) compartment, the outer (lateral) compartment, and the compartment behind the kneecap (patellofemoral).

In many patients with osteoarthritis, all three compartments wear out together. But in a meaningful number of patients, the arthritis is confined to just one compartment — most commonly the inner one — while the other two remain healthy.

This single fact is what determines the choice between partial and total knee replacement.

What Is a Total Knee Replacement?

In a total knee replacement, all of the worn joint surfaces are replaced with an implant. This is the right operation when arthritis affects the whole knee — when two or three compartments are worn out, when there is significant deformity, or when the ligaments and overall structure of the knee require the stability that a total replacement provides.

It is the most common form of knee replacement, it has an excellent long-term track record, and for a knee that is comprehensively arthritic, it is unquestionable the right choice. The great majority of patients who need their knee replaced have a total replacement, and they do very well.

What Is a Partial Knee Replacement?

A partial knee replacement — also called a unicondylar knee replacement — replaces only the single damaged compartment, while leaving the healthy compartments and the patient’s own ligaments completely intact.

The appeal is clear. Because only part of the knee is being replaced, it is a smaller operation. Patients typically experience a quicker recovery, less post-operative pain, and because the natural ligaments and healthy compartments are preserved, the knee often feels more natural — closer to the patient’s own knee. For the right candidate, these are significant advantages.

But — and I cannot stress this enough — the operation is only as good as the patient selection. A partial replacement performed on a knee where the arthritis is not truly confined to one compartment will fail, because the disease in the other compartments continues to progress. The art lies in choosing the right patient.

Who Is a Candidate for Partial Knee Replacement?

In my assessment, a patient may be a good candidate for partial knee replacement when several conditions are met:

• The arthritis must be genuinely confined to a single compartment, confirmed on imaging and clinical assessment.
• The other compartments need to be healthy.
• The ligaments of the knee — particularly the ACL — should be intact and functioning, because the partial implant relies on the knee’s own stability.
• The deformity should be limited and correctable.
• The pattern of pain should match the location of the single-compartment arthritis.

When all of these line up, a partial knee replacement can be an excellent choice that gives the patient a smaller operation and a more natural result. When they do not, a total knee replacement is the safer and more durable answer.

Why Precision Matters Especially in Partial Replacement

Here is where I want to be particularly clear, because it bears directly on outcomes.

Partial knee replacement is technically more demanding than total knee replacement in one specific way: the sizing and positioning of the implant must be extremely accurate. Because the partial implant works alongside the patient’s own healthy compartments and ligaments, even small errors in placement can affect how the knee feels and functions, and can shorten the implant’s life.

This is precisely the situation where robotic assistance offers the clearest benefit. The pre-operative 3D planning and the sub-millimetre execution that robotic surgery provides are especially valuable in partial knee replacement, where there is little margin for error. It is one of the reasons I find robotic technology so useful — it raises the precision of partial replacement to a level that is difficult to achieve consistently by hand.

A Common Misconception

Patients sometimes assume a partial replacement is simply the “lighter” or “easier” option and therefore always preferable. That is not how the decision works.

A partial replacement is not a compromise version of a total replacement — it is a different operation for a different problem. For a knee with single-compartment arthritis and good ligaments, partial is often ideal. For a knee with widespread arthritis, choosing partial just because it sounds less drastic would be a mistake that leads to early failure and the need for further surgery.

The goal is not to do the smallest possible operation. It is to do the right operation for the state of your knee.

What If Both Could Work?

Occasionally a knee sits in a grey area where the decision is genuinely a matter of judgement and discussion. In these cases, I lay out the trade-offs honestly with the patient:

The partial offers a more natural feel and quicker recovery but carries some risk that arthritis may later develop in the other compartments and eventually require conversion to a total replacement; the total is more comprehensive and definitive but is a bigger operation and may feel slightly less natural.

This is a conversation, and the patient’s age, activity, and preferences all feed into it. My job is to give honest, clear guidance so the patient can make an informed choice with confidence.

The Bottom Line

Partial and total knee replacement are both excellent operations — for different knees. A total replacement is the right choice for a comprehensively arthritic knee and is the more common operation. A partial replacement is a smaller, often more natural-feeling option for the specific patient whose arthritis is confined to one compartment with healthy ligaments and limited deformity.

The decision is not about which operation is “better” in the abstract — it is about which one matches the actual state of your knee. That requires careful assessment and honest discussion, and it is exactly the kind of judgement that determines whether you end up with a result you are delighted with.

If you have been told you need a knee replacement, it is worth asking whether you might be a candidate for a partial. Bring your X-rays, and let’s find out together.