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Resurfacing a worn knee joint with metal and plastic, so it carries weight without grinding. For arthritis that has stopped responding to everything else, it is one of the most reliable operations in orthopaedics — and not always the whole knee.
In an arthritic knee the smooth cartilage covering the ends of the bones wears away, until bone rubs on bone — see knee osteoarthritis. Knee replacement surgery removes the worn surfaces and caps them: a metal shell on the end of the thigh bone, a metal tray on the shin bone, and a hard-wearing plastic insert between them that does the job the cartilage used to do.
The bone underneath, and the ligaments and muscles around the knee, are kept wherever possible. That is why the operation is better described as resurfacing than as replacing the joint.
It is an operation for pain, not for an X-ray. Severe wear on a scan with tolerable symptoms is not a reason to operate. Pain that wakes you at night, limits how far you can walk, or stops you doing what matters to you — despite proper treatment — is.
The knee has three compartments. If only one is worn, only one may need replacing.
| Total knee replacement | Partial (unicompartmental) | |
|---|---|---|
| What is replaced | All the worn surfaces of the joint | One compartment only |
| Suits | Wear across the knee, inflammatory arthritis, significant deformity or unstable ligaments | Wear limited to one side, with good movement and intact ligaments |
| Recovery | Steady over weeks to months | Usually quicker, with more of the natural knee kept |
| Track record | The longest, and the most predictable for advanced arthritis | Excellent in well-chosen patients, with a slightly higher chance of further surgery later |
| If it wears out | Revision surgery | Can usually be converted to a total replacement |
Which suits you is decided by where the wear is, the alignment of the leg, and how stable the knee is — on examination and X-ray, not by preference.
On the left, both worn surfaces are capped and a plastic bearing sits between them. On the right, only one side has been resurfaced: the other condyle keeps its own cartilage, and the ligaments in the middle of the knee are left in place.
What the picture cannot show is which one suits you. That depends on where the wear is, how the leg lines up and whether the ligaments are intact — which is what the examination and X-rays are for.
Age matters less than it used to, but it still matters. Implants last longer than they once did, though a knee replaced at 55 is more likely to need revision in a lifetime than one replaced at 75. That is weighed against years of pain, not used as a reason to wait indefinitely.
A robotic arm or a navigation system does not perform the operation. It plans the cuts from a three-dimensional model of your knee and helps the surgeon place the implant to that plan, within finer tolerances than the eye and a jig allow.
What that reliably improves is the accuracy of implant position and alignment. Whether it also means less pain or a longer-lasting knee is still being studied, and honest answers should say so. It is used routinely here, including for partial knee replacement, where precise positioning matters most.
X-rays, and a CT scan if the operation is robot-assisted. Blood tests, an anaesthetic review, and dental or skin infections treated first. Exercises beforehand help: a stronger knee going in recovers faster coming out.
Usually one to two hours, under spinal or general anaesthetic. The worn surfaces are removed and the components fitted, with the knee balanced through its range of movement before closing.
Enhanced Recovery After Surgery is a set of protocols before, during and after the operation designed to reduce complications and get people moving sooner: standing and walking the same day, pain relief that does not flatten you, and a shorter stay without cutting corners.
Home after one to two days, walking with a frame or sticks. Daily exercises to regain bend and straightening, which is the part that decides the result. Swelling and bruising are expected.
Driving at around four to six weeks; desk work about the same; physical work later. Most of the improvement is in the first three months, and the knee keeps settling for up to a year.
Most people get substantial pain relief and walk further than before, and the majority say they would have it done again. Not everyone is fully satisfied: a knee replacement feels different from a natural knee, kneeling is often uncomfortable, and a minority still have pain afterwards. Knowing that beforehand is part of choosing well.
Knee replacement here is performed by Dr Kelvin Tan Guoping, an orthopaedic surgeon specialising in hip and knee replacement. He is a Fellow of the Royal College of Surgeons of Edinburgh, holds a Master of Medicine in orthopaedics, and is an Adjunct Assistant Professor at NUS. He consults in English, Mandarin, Teochew and Hokkien.
Not necessarily. The question is how much the knee is costing you now, weighed against the chance of needing a revision later. Implants last longer than they used to, and a partial replacement can be converted to a total one if the rest of the knee wears.
Most knee replacements are still working 15 to 20 years after surgery. Weight, activity and how well the implant is positioned all affect that.
Some people can, many find it uncomfortable even when the knee is working well. It is not harmful to try.
It places the implant more accurately and consistently. Whether that means less pain or a longer-lasting knee is still being studied, so it is offered as a better-controlled way of doing the operation rather than a different operation.
Driving at around four to six weeks, once you can control the car safely and are off strong painkillers. Desk work about the same; physical work later.
No. Bring any knee X-rays or scan reports, and a note of the treatments you have already tried.
Knee osteoarthritis · Knee pain · Torn meniscus · Knee fracture · Knee bursitis · Hip pain
Bring your X-rays if you have them. The first conversation is usually about whether you need a replacement yet, and whether it would be partial or total.
