Total Knee Replacement: What the Operation Actually Involves

If you have been told you may need a total knee replacement, it helps to know, in plain terms, what actually happens to your knee. This article walks through what is removed, what is put in its place, what the implant is made of, and what the day of surgery and the days after typically look like. It is general information, not advice for your particular knee — that decision belongs in a consultation.

What is actually removed, and what replaces it

Despite the name, a total knee replacement does not remove the whole knee or the whole leg bone. The surgeon removes a thin layer of worn cartilage and a small amount of bone from the end of the thigh bone (femur) and the top of the shin bone (tibia) — usually only a few millimetres, shaped precisely to fit the new implant. Depending on the case, the back surface of the kneecap (patella) may also be resurfaced. The ends of the bones are then capped with the artificial components, with a smooth spacer between them standing in for the cartilage that has worn away. The ligaments and muscles around the knee are, in most cases, kept and worked around rather than removed, since they help hold the new joint stable.

What the implant is made of

A standard knee implant has three working parts. The femoral component, which caps the thigh bone, and the tibial component, which caps the shin bone, are made of a metal alloy — commonly cobalt-chromium or titanium alloys, chosen for their strength and their long history of use inside the body. Between them sits a spacer made of medical-grade polyethylene, a durable plastic that lets the joint glide smoothly. If the kneecap is resurfaced, a small plastic button is fixed to its underside. The components may be fixed to the bone with bone cement, or made with a textured surface that allows bone to grow onto it directly — which approach is used depends on bone quality and the surgeon's assessment, and is something to discuss directly rather than assume.

Anaesthetic, in general terms

Total knee replacement can be done under general anaesthetic, where you are fully asleep, or under spinal or regional anaesthetic, where the lower body is numbed and you remain awake or lightly sedated. Many patients also receive a nerve block around the knee to help with pain in the hours after surgery. Which option is used depends on your general health, any other medical conditions, and a conversation with the anaesthetist beforehand — this is a decision made jointly with you, not something fixed in advance.

What happens on the day

You will usually be admitted on the day of surgery or the day before, with checks on your health and final questions answered. In the operating theatre, the leg is cleaned and draped, and anaesthesia is given. The surgeon makes an incision at the front of the knee to reach the joint, then shapes the ends of the femur and tibia to receive the implant. Trial components are often fitted first to check movement and alignment before the final implants are seated. The wound is then closed in layers, a dressing is applied, and in some cases a small drain is left in place temporarily. You are then moved to a recovery area for monitoring as the anaesthetic wears off.

How long the operation takes

The surgery itself usually takes somewhere in the region of one to two hours, though this varies with the individual knee, whether it is a first-time or revision procedure, and other factors specific to the case. The total time away from the ward is longer than this, since it includes anaesthetic preparation beforehand and monitoring in recovery afterwards. If you are having both knees done, whether in one session or two, this changes the overall timeframe, and is something to plan with your surgeon in advance.

The first hours after surgery

Once you are back on the ward, nurses monitor your blood pressure, wound, and pain levels closely. Pain relief is given regularly rather than only when asked for, since staying ahead of pain generally makes early movement easier. If you had a spinal anaesthetic, sensation and movement in the leg return gradually over a few hours. Many units encourage patients to begin gentle ankle and foot movements early, to support circulation. Some patients are helped to stand or take a few steps with support on the same day, while others begin the following morning — this depends on how you are recovering and on the physiotherapy routine at the hospital.

The first few days in hospital

Physiotherapy is a central part of the early days. A physiotherapist will usually work with you on standing, walking with a frame or crutches, and bending and straightening the knee within a comfortable range. Pain and swelling are managed with medication, ice, and elevation of the leg when resting. The wound is checked regularly, and you may be given medication to reduce the risk of blood clots, particularly if your mobility is still limited. Staff will also look at practical things before you go home, such as managing stairs and getting in and out of a chair safely. The length of the hospital stay varies from patient to patient and is decided based on how you are progressing, not on a fixed schedule.

When to seek urgent care

A small number of symptoms after knee surgery need urgent attention rather than waiting for a scheduled appointment. These include numbness or weakness in the leg or foot, loss of bladder or bowel control, a fever together with a hot, swollen joint, or fluid or pus discharging from the wound. Sudden calf pain, swelling, or breathlessness can also be a sign of a blood clot and should not wait. If any of these occur, contact the surgical team immediately or go to an emergency department — do not wait for your next follow-up visit.

Every knee and every recovery is different, and the details above are general patterns rather than a plan for your case. If you have been told you may need a total knee replacement, or you are trying to understand whether it is the right option for your knee, the next step is a consultation, where your X-rays, symptoms, and general health can be looked at together and your questions answered directly.