Partial vs Total Knee Replacement: How to Decide What's Right for You

One of the questions I hear most often from patients who have been told they need a knee replacement is: "Do I need the whole knee done, or just part of it?" It is a genuinely important question, and the answer is not always straightforward. It is probably why so many patients arrive at their first consultation having read conflicting things online and feeling more confused than when they started.

So let me try to give you the clearest, most honest version of how I think about this decision.

The Knee Has Three Compartments, and That Matters

To understand the difference between a partial and a total knee replacement, it helps to understand how the knee is structured. The knee joint has three distinct compartments: the medial compartment on the inner side of the knee, the lateral compartment on the outer side, and the patellofemoral compartment at the front, between the kneecap and the thigh bone.

Osteoarthritis (the wear-and-tear kind that most people are dealing with) does not always affect all three compartments equally. In a significant number of patients, the damage is concentrated in one area, most commonly the medial (inner) compartment. The rest of the knee joint is relatively healthy.

This is the starting point for the whole partial versus total conversation.

What Is a Partial Knee Replacement?

A partial knee replacement (also called a unicompartmental knee replacement) replaces only the damaged compartment. The healthy cartilage and ligaments in the rest of the knee are left completely intact. The procedure is less invasive than a total replacement, the incision is smaller, and the recovery is generally faster.

The implant I use most frequently for partial knee replacement is the Zimmer Persona, which allows for a high degree of precision in fitting the components to the individual anatomy of the patient's knee. That precision matters: a partial replacement only works well if it is positioned correctly and sized accurately, because it has to integrate with the remaining natural knee mechanics.

What Is a Total Knee Replacement?

A total knee replacement resurfaces all three compartments of the knee. The damaged ends of the femur and tibia are removed and replaced with metal components, with a plastic spacer between them that acts as the new cartilage. The back of the kneecap may also be resurfaced.

It is a more extensive procedure than a partial replacement, but it is also the more versatile one. It can address arthritis across the whole joint, including deformity, and it removes the possibility of arthritis developing in the remaining compartments later on, because there are no remaining compartments.

So How Do I Decide Which One Is Right for a Patient?

When I look at a patient's knee, I am considering several things simultaneously.

First: Where is the arthritis? X-rays tell me how the joint space has narrowed and in which compartments. If the damage is clearly isolated to one area, typically the medial compartment, and the rest of the joint looks healthy on imaging and feels stable on examination, then a partial replacement is firmly on the table.

If the arthritis is widespread, affecting two or three compartments, then a total replacement is almost certainly the right answer.

Second: Are the ligaments intact? A partial knee replacement relies on the cruciate ligaments being functional, as they are what maintains the stability and natural movement of the knee after only one compartment is replaced. If the anterior cruciate ligament is absent or significantly damaged, a partial replacement is not appropriate regardless of how localised the arthritis appears on imaging.

Third: What does the patient's knee look like on examination? X-rays do not tell the whole story. I examine the knee: how it moves, whether there is any angular deformity, where the pain is most pronounced, and how the joint feels under load. A knee that looks borderline on imaging might reveal itself as clearly unsuitable for partial replacement when examined properly.

Fourth: The patient's age, weight, and activity level These factors influence the decision, though perhaps not in the way people expect. Partial knee replacements were traditionally thought of as a procedure for older, less active patients, but that thinking has largely shifted. Modern partial knee components perform well across a range of activity levels, and younger patients who are good candidates can achieve excellent results.

What the Recovery Looks Like and How It Differs

This is where the difference between the two procedures is most tangible for patients.

After a partial knee replacement, most patients are up and walking the same day. Hospital stay is typically one to two nights. Many people are driving within two to three weeks and back to normal daily activity within four to six weeks. The range of motion tends to feel more natural more quickly, because so much of the original knee structure is preserved.

After a total knee replacement, the recovery is a longer commitment. Walking begins early (usually on the day of or morning after surgery), but the knee works hard in the weeks that follow. Achieving full range of motion takes time and consistent physiotherapy. Most patients are functioning well at six weeks, driving by six to eight weeks, and experiencing the full benefit of the surgery at three to six months.

The important caveat: a total replacement, done well, gives extremely durable results. National joint registry data consistently shows over 90% of total knee replacements still functioning well at 15 years. Partial knee replacements have a slightly higher revision rate over time, largely because the remaining compartments can continue to develop arthritis. Patients should understand this going in.

The Honest Trade-Off

If someone is an ideal candidate for a partial knee replacement, I will usually recommend it. The recovery is faster, the feel of the knee is often more natural, and if a revision is ever needed years down the line, converting a partial replacement to a total is a straightforward procedure.

But I would rather perform an excellent total knee replacement than a partial one that the patient was not quite right for. The selection criteria genuinely matter: a partial replacement placed in a knee with widespread arthritis or a compromised ligament will not perform well, and the patient will be left worse off than if they had simply had the total in the first place.

The decision is never made on imaging alone. It is made in the clinic, with the full picture in front of me: X-rays, examination, and a proper conversation about what the patient needs from their knee and what they are prepared to go through.

What I Tell Patients Who Ask Which One They Are Having

My honest answer, until I have examined them and reviewed their imaging, is: I do not know yet, and anyone who tells you before seeing your scans and examining your knee is guessing.

What I can tell you is that if you are a candidate for partial knee replacement, I will tell you clearly. And if total knee replacement is the right option for you, I will explain exactly why, in a way that makes sense.

If you are weighing up your options and want a clear, unhurried conversation about which procedure might be right for your specific situation, I would be glad to see you.

Book a consultation → | Call 01978 268065

You might also find it useful to read about knee arthritis treatment options or the Zimmer Persona partial knee system in more detail.

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This article is written for general information and does not replace individual medical advice. The right surgical decision for your knee depends on a full clinical assessment, which should always be carried out by a qualified orthopaedic surgeon.