Knee Replacement Surgery Explained: The Operation, Implants, and Hospital Stay

A knee replacement resurfaces the worn ends of your knee rather than removing the joint: the surgeon caps the bottom of the thigh bone and the top of the shin bone (and usually the back of the kneecap) with metal and a smooth plastic spacer, in an operation that takes about 1 to 2 hours and is most often done under a spinal anaesthetic. The word “replacement” makes people picture the whole knee being lifted out, so the first thing worth knowing is how much of your own knee stays.

The day I understood it was resurfacing, not removal, the operation stopped sounding like something done to a machine and started sounding like something done to a knee that was still mine. Below is what actually happens, in the order it happens, with the bits I had to ask three times before anyone explained.

What the surgeon actually does

The surgeon removes only a few millimetres of damaged surface and replaces it with implant components shaped to glide smoothly. Knee osteoarthritis is the gradual loss of the cartilage that lets the joint move freely, and the knee is the large joint most often disabled by it worldwide ¹. A total knee replacement (TKR) addresses that worn cartilage and the rough bone beneath by trimming the very ends of the femur (thigh bone) and tibia (shin bone) and fitting precise metal caps over them, with the back of the kneecap usually resurfaced too.

Crucially, your ligaments, your kneecap tendon, the surrounding muscle, and almost all of your bone remain. This is why orthopaedic surgeons talk about “resurfacing” the joint. Knee replacement is offered when symptoms are severe and persistent and good non-surgical care no longer helps, which is why international guidance puts exercise, weight management, and other alternatives before knee surgery first ². It is elective and driven by quality of life, never an emergency.

Anaesthesia: awake or asleep

Most knee replacements are done under spinal anaesthesia, with general anaesthesia as the common alternative. A spinal numbs you from roughly the waist down while you stay awake, usually with sedation so you feel calm and drowsy and remember little. A general puts you fully asleep. Spinal anaesthesia is often preferred for knee surgery because it can mean less sickness afterwards and a clearer head, but the choice is individual and made with the anaesthetist after reviewing your health.

I chose to be awake under a spinal, which sounded alarming until I understood I would feel pressure and movement at most, not pain. For many women, that small piece of control over an otherwise daunting day matters more than they expect.

The operation, step by step

The operation itself usually takes about 1 to 2 hours. After the anaesthetic takes effect, the surgeon opens the front of the knee, moves the kneecap aside, and exposes the worn joint surfaces. Using cutting guides, they remove the damaged ends of the femur and tibia, trim the bone to match the implant shape, and trial the components to check the knee straightens, bends, and feels stable. Once the fit and tension are right, the final implants go in, the kneecap is resurfaced if needed, and the knee is closed in layers.

You then move to a recovery area while the anaesthetic wears off and your observations settle, so the day stretches well beyond the surgical hour or two. Range of motion work begins early, because the goal over the coming weeks is roughly a fully straight knee out to about 115 to 120 degrees of bend, and early movement protects against stiffness.

The implant: metal, plastic, and how it stays put

The implant is a set of metal alloy components with a polyethylene (medical plastic) bearing between them that lets the surfaces slide almost frictionlessly. The metal is typically a cobalt-chromium or titanium alloy. The plastic spacer sits where your cartilage used to be and does the gliding work.

Fixation comes in two main forms. Cemented implants are held with a fast-setting bone cement, a long-established and very common method. Cementless implants have a textured surface that your own bone grows into over weeks. Both are well proven, and your surgeon weighs your bone quality and their own experience when choosing. For women, this is one place where bone health matters: the chance of lower bone density rises after about age 50, so a bone-density (DEXA) scan and good bone health are worth raising before surgery ³. It is also worth knowing the difference between a partial and total knee replacement, since a partial resurfaces only one worn compartment and suits fewer people.

Hospital stay and going home

Hospital stay now ranges from same-day home to a few days, depending on country, health system, and how you recover. Many modern programmes aim to get you upright and taking a few steps within hours, and discharge once you can walk safely with aids, manage any stairs you have at home, control pain with tablets, and pass the practical checks the team set. Some go home the same day; others stay one to three nights. Neither is better or worse on its own; it reflects local practice and your individual progress.

What no one quite captured for me was how ordinary the leaving felt: not triumphant, just steady, with a frame, a sheet of exercises, and a knee that already bent more than the one I walked in on. The real work was the weeks that followed, which is its own story in the recovery timeline.

What this surgery is, and is not

A knee replacement is a reliable, durable operation, not a miracle reset. Long-term registry and review data suggest around 8 to 9 in 10 total knee replacements last 20 years or more ⁴, which is reassuring, though it is still major surgery with real recovery and a small set of risks. Understanding the operation honestly, as resurfacing under a spinal with a short hospital stay, takes a lot of the fear out of the decision without pretending it is small.

This article is general information, not medical advice, and cannot account for your own knee, imaging, or health. Talk to a qualified clinician or orthopaedic surgeon before making any decision about surgery.