What Happens During Knee Replacement Surgery: A Step-by-Step Look Inside the Operating Room

The pre-op bay is quieter than most people expect. A nurse draws an arrow on the correct leg with a marker, the anesthesiologist asks about loose teeth and old surgeries, and the person on the bed, who has climbed stairs sideways for three years to spare a grinding knee, keeps asking the same thing in different ways: what exactly are they going to do in there?

It is a fair question, and one that rarely gets a full answer in a fifteen-minute clinic visit. Consent forms describe risks. Brochures describe results. Very few explain what happens during knee replacement surgery minute by minute, from the first dose of antibiotic to the moment the surgeon bends the new joint through its range and watches it track.

This piece walks through that sequence in plain language, using only what mainstream guidance and major medical centers describe, so that when your own team explains their approach you can follow every step.

What happens during knee replacement surgery, in plain language

Strip away the instruments and the vocabulary, and the operation comes down to one idea: resurfacing. The knee is a hinge where the end of the thigh bone (femur) meets the top of the shin bone (tibia), with the kneecap (patella) gliding in a groove at the front. In a healthy knee, every one of those surfaces is coated in cartilage, a glassy tissue a few millimeters thick that lets bone slide on bone almost without friction. In advanced osteoarthritis, the cartilage wears through, bone rubs on bone, and the joint stiffens, swells and aches.

A knee replacement does not remove the knee. The surgeon shaves off the ruined cartilage and a thin slice of the underlying bone, then caps the cut surfaces with a metal piece on the femur, a metal tray on the tibia, and a smooth plastic insert between them that does the job the cartilage used to do. Sometimes the back of the kneecap is resurfaced with a plastic button as well. The ligaments, tendons and muscles that hold the knee together mostly stay where they are, which is why the joint feels like your knee afterward and not like a machine attached to your leg.

MedlinePlus describes the procedure in exactly these terms: damaged bone and cartilage are removed and replaced with artificial parts made of metal and plastic. The NHS notes that the operation usually takes 1 to 2 hours. Almost all of that time goes into precision, because the components must sit at the correct angles and tension for the knee to bend fully and stand straight. That precision, rather than the cutting itself, is what the rest of this article is about.

Who is usually offered a knee replacement, and who is asked to wait

Osteoarthritis is by far the most common reason people arrive at this decision, according to the NHS, followed by rheumatoid arthritis and damage from old injuries or fractures. Most people who have the operation are between 60 and 80, although the NHS is clear that age itself is not the deciding factor; the state of the joint and how much it limits daily life are.

Surgeons and guideline bodies tend to look for a similar pattern before recommending surgery. Pain is present most days, often at night, and interferes with sleep. Walking distance has shrunk. Stairs, getting out of a chair and putting on shoes have become planned events. Physical therapy, weight management, walking aids, and simple pain relief have been tried for a reasonable period and no longer hold the line. X-rays show joint space that has narrowed or disappeared. When those things line up, replacement becomes a reasonable option to discuss.

Being asked to wait is common and usually sensible. Someone whose pain is intermittent, or who has not yet given non-surgical measures a fair trial, may be encouraged to continue those first, because an artificial joint has a finite lifespan and cannot be undone. A skin infection near the knee, an active urinary or dental infection, poorly controlled diabetes, or a recent heart event will typically postpone surgery until it is treated, since each raises the risk of a joint infection or a complication under anesthesia. Smoking, very high body weight and thinning bone do not automatically rule surgery out, but teams often ask for a period of preparation.

None of these thresholds is a formula. The decision belongs to the person and the treating team together, weighing how much the knee is costing them now against the risks and the work of recovery.

Is having a knee replacement a big operation? What the morning of surgery looks like

Yes. It is major orthopedic surgery, and it helps to hold two facts at once: it is big, and it is routine. Bone is cut, an implant is fixed in place, and the body has to heal around it. At the same time, it is one of the most frequently performed operations in the world, with every step standardized down to the order in which instruments are laid out.

The day usually begins hours before the incision. You will have been asked to fast, typically from midnight, so the stomach is empty under anesthesia. Skin may be washed with an antiseptic wipe the night before and again in the pre-op area. A nurse checks your identity, allergies and which knee is being operated on, and the surgeon marks the leg while you are awake and can confirm it. This surgical site verification is a safety ritual repeated in operating rooms everywhere, and it is not a sign of doubt.

An intravenous line goes into the arm. Through it, a single dose of antibiotic is given shortly before the first cut, timed so that the drug is in the tissues when the skin is opened; the Cleveland Clinic and Mayo Clinic both describe infection prevention as a core part of the procedure rather than an afterthought. Some teams also give a medicine from the antifibrinolytic class, which slows the breakdown of blood clots and reduces bleeding during and after the operation. Whether that is used, and which anesthetic technique is chosen, is decided by the anesthesiologist with you.

Then the pause. Before anything else happens in the room, the whole team stops for a checklist: right patient, right side, allergies confirmed, antibiotic given, equipment ready. Only after everyone agrees does the operation begin.

Anesthesia for knee replacement: spinal, general and nerve blocks

People are often surprised to learn they may not be fully asleep. Mayo Clinic notes that knee replacement is performed under either general anesthesia, which puts you into a controlled unconscious state, or spinal anesthesia, which numbs you from the waist down while you remain awake or lightly sedated. Both are widely used, and the choice depends on your health, your preferences and your anesthesiologist’s judgment.

A spinal anesthetic involves a thin needle placed between the bones of the lower back, delivering local anesthetic into the fluid around the spinal cord. Within minutes the legs become heavy, then numb. Many people are given sedation on top so they drift through the operation without awareness of the sounds. General anesthesia, by contrast, is delivered through the intravenous line and by breathing anesthetic gas through a mask or a breathing tube once you are asleep.

Either way, most teams add a regional nerve block. This is an injection of local anesthetic around a specific nerve, guided by ultrasound, to numb part of the leg for hours after surgery. A common target is the adductor canal on the inner thigh, chosen because it dulls pain from the front of the knee while preserving much of the strength in the thigh muscle, which matters when you try to stand that evening. Some surgeons also inject local anesthetic directly into the tissues around the joint before closing.

Throughout the operation, the anesthesiologist monitors heart rhythm, blood pressure, oxygen level and breathing continuously. If you are having a spinal, you may hear the saw or feel pressure without pain; that is normal and expected. Whatever the plan, it is agreed beforehand, and you can ask for it to be explained until it makes sense.

Total knee replacement procedure steps: what the surgeon actually does

Once you are anesthetized and positioned on your back, the leg is scrubbed with antiseptic and sterile drapes are arranged so that only the knee is exposed. Some surgeons inflate a tourniquet, an air-filled cuff around the upper thigh, to keep the field free of blood; others operate without one. The sequence that follows is remarkably consistent from one operating room to another.

• Incision. A vertical cut is made over the front of the knee. Mayo Clinic describes it as roughly 6 to 10 inches long, though the length varies with the person’s build and the surgeon’s approach.
• Exposure. The surgeon moves the kneecap aside to see the joint, then removes the damaged remnants of cartilage and, in most total replacements, the anterior cruciate ligament.
• Bone preparation. Using cutting guides, or in some centers computer navigation or a robotic arm that holds the saw to a pre-planned angle, the surgeon removes a thin layer of bone from the end of the femur and the top of the tibia. Trial components are fitted to check the size and alignment.
• Balancing. The knee is bent and straightened with the trials in place. The surgeon adjusts soft tissue and component thickness so the ligaments are evenly tensioned and the leg stands straight.
• Fixation. The final metal components are attached, most often with bone cement that hardens in minutes, sometimes with a textured surface designed for bone to grow into. The plastic insert is locked into the tibial tray, and the underside of the kneecap may be resurfaced.
• Closure. The layers are closed with stitches or staples, a dressing is applied, and the leg is often wrapped.

MedlinePlus and Johns Hopkins describe this same order of operations. What differs between surgeons is technique, not the destination.

Total vs partial knee replacement: what changes inside the room

Not every arthritic knee is worn evenly. The joint has three compartments: the inner (medial) side, the outer (lateral) side and the space behind the kneecap. When damage is confined to one, usually the inner side, a partial replacement can resurface just that compartment and leave the rest of the joint, including both cruciate ligaments, untouched. The NHS describes partial replacement as an option for a minority of people with limited disease, and notes that the recovery tends to be quicker because less tissue is disturbed. A total replacement, by contrast, resurfaces all three compartments and is the standard choice when arthritis is widespread.

Feature	Total knee replacement	Partial (unicompartmental) replacement
Surfaces replaced	Femur, tibia, often the kneecap	One compartment only
Cruciate ligaments	Anterior usually removed; posterior kept or substituted	Both preserved
Incision	Longer, full exposure	Shorter, limited exposure
Typical candidates	Arthritis in two or more compartments, significant deformity	Arthritis limited to one compartment with intact ligaments
Usual recovery pace	Standard timeline	Often somewhat faster (NHS)
Later revision	Possible if components wear or loosen	May be converted to a total replacement if arthritis spreads

Two other terms come up in consent discussions. A cruciate-retaining implant keeps the posterior cruciate ligament, which runs through the center of the knee and stops the shin sliding backward. A posterior-stabilized implant removes that ligament and builds a small post and cam into the components to do the same job. Both are long established; the choice usually reflects the condition of the ligament and the surgeon’s training. Cemented and uncemented fixation, likewise, are both mainstream. If your surgeon uses one particular design, asking why is a good use of a clinic visit.

How painful is a full knee replacement?

Honest answer: the knee hurts afterward, sometimes considerably, and the discomfort is real work to manage in the first two weeks. Anyone who tells you otherwise is selling something. The good news is that the pain is expected, planned for and, for most people, follows a recognizable arc.

During the operation itself you feel nothing, whether under general or spinal anesthesia. The first hours afterward are usually the easiest, because the nerve block placed before surgery is still working and the knee feels heavy and numb rather than painful. As the block wears off, typically overnight, a deep ache sets in around the front and sides of the knee, along with a tight, swollen feeling and soreness in the thigh where the tourniquet sat.

Pain control is layered rather than dependent on a single drug. Mayo Clinic and the Cleveland Clinic describe combinations of scheduled anti-inflammatory and acetaminophen-type medicines, short courses of stronger analgesics where needed, ice, elevation and early movement, each addressing a different part of the pain pathway. Your team chooses the specific plan based on your kidneys, stomach, heart and other medications; nothing here should be adjusted without them.

The character of the pain matters as much as its intensity. Sharp pain when the physical therapist bends the knee is expected and settles when you stop. A constant ache at rest that improves as swelling comes down over the first fortnight is also typical. What is not typical is pain that steadily worsens after the first week, pain paired with fever, or calf pain unrelated to the knee. Those belong in the red-flag section further down.

Most people describe the second and third nights as the low point, and the second and third weeks as the turn.

Knee replacement recovery timeline: the first 24 hours and the following weeks

Recovery begins before the anesthetic has fully worn off. In the recovery area, nurses check circulation in the foot, the dressing and your pain level, and the physical therapist often appears the same day. Mayo Clinic notes that people are usually encouraged to stand and take steps with a walker or crutches within hours of surgery, because early movement reduces stiffness and lowers the risk of blood clots. Compression stockings or an inflatable calf device and a preventive blood-thinning medicine, prescribed by your team, are standard for the same reason.

How long you stay depends on how you are moving, not on a fixed number. The NHS gives a typical range of 1 to 3 days, and Mayo Clinic observes that many people go home the same day or the day after. Before discharge, most teams want to see you walk a set distance, manage a few stairs if you have them at home, and demonstrate the exercises you will continue there.

The first fortnight is about swelling, sleep and range of motion. The knee is often warm and puffy, bruising spreads down the shin, and bending past a right angle is hard. Regular icing, keeping the leg elevated when resting, and the exercise sheet from your therapist are the daily routine. Stitches or staples are usually removed around the two-week mark.

Mayo Clinic notes that light daily activities such as shopping and housework are usually manageable 3 to 6 weeks after surgery. The NHS suggests many people can drive again around 6 to 8 weeks, once the leg is strong enough for an emergency stop and the surgeon agrees. Full recovery of strength and stamina, the NHS says, can take up to a year. These are typical ranges from those sources, not targets or promises.

What is the hardest part of knee replacement recovery?

Ask a room of people who have been through it and you will hear the same three answers, in roughly this order: sleep, the first two weeks of physical therapy, and patience in months two to six.

Sleep is disrupted for several reasons at once. The knee aches more lying down because swelling pools when the leg is level. Rolling over requires moving a heavy, stiff limb. Some analgesics disturb normal sleep patterns. Cleveland Clinic guidance on recovery emphasizes elevation, regular icing and a consistent evening routine, and many therapists suggest a pillow under the calf rather than under the knee, so the joint is not held bent for hours.

Physical therapy is hard because the goal in the early weeks is range of motion, and the only way to regain it is to bend a swollen, sore knee further than it wants to go, repeatedly. The reason is mechanical: as the tissues heal, scar forms, and scar that is never stretched sets stiff. Therapists watch for a specific problem called arthrofibrosis, a dense scarring inside the joint that can limit bending permanently if motion is not regained early. That is why they are insistent, and why the discomfort has a purpose.

The later stretch is a different kind of hard. By eight or ten weeks the crutches are gone and the wound has faded, and people around you assume you are done. Yet the knee still swells after a long day, clicks when you climb stairs, and tires before you do. Mayo Clinic and the NHS both describe improvement continuing for many months. The hardest part here is trusting that a joint that already feels better than the arthritic one will keep improving without a visible milestone each week.

What can you never do after knee replacement?

The list is shorter than most people fear, and it is mostly about loads rather than positions. A replacement knee is a bearing made of metal and a highly durable plastic. Every step wears the plastic by a microscopic amount; every hard landing wears it more. The design goal is to make that wear so slow that the joint outlasts its owner, and the surgeon’s advice afterward is about keeping the odds in your favor.

Mayo Clinic advises against higher-impact activities such as jogging, downhill skiing and sports that involve jumping or sudden pivoting. Walking, swimming, cycling, golf, doubles tennis, hiking on reasonable terrain and most gym work are generally encouraged once the knee has recovered. The distinction is repeated impact and twisting under load, not exercise itself.

Kneeling deserves its own paragraph because so many people ask about it. Mayo Clinic notes that kneeling is often uncomfortable after a replacement but is not harmful to the implant. Many people find it easier over time, especially with a cushion; some never like it. Deep squats past a right angle are similar: often possible eventually, sometimes never comfortable, rarely dangerous.

Two genuinely permanent habits matter more than any activity ban. First, treat infection anywhere in the body seriously. Bacteria in the bloodstream from a neglected tooth abscess, skin wound or urinary infection can settle on an artificial joint, and a deep joint infection is one of the most serious complications of the operation. Tell every dentist and doctor you have an implant, and ask your surgeon about their advice on antibiotics before dental work, as recommendations vary. Second, keep your follow-up appointments even when the knee feels perfect, because loosening or wear can begin silently and is far easier to manage when caught on an X-ray.

Risks and alternatives, in neutral terms

Every consent form for this operation lists the same core risks, and it is worth knowing why each appears. Infection can involve the skin around the wound, which usually responds to antibiotics, or the joint itself, which may require further surgery to wash out or replace components. Blood clots can form in the deep veins of the calf or thigh and, rarely, travel to the lungs; this is the reason for early walking, compression and preventive blood thinners. Nerve or blood vessel injury near the knee is uncommon but possible. Fracture of the bone around the implant, stiffness that limits bending, persistent pain, loosening of the components over years, and the ordinary risks of anesthesia complete the standard list, as set out by Mayo Clinic, the NHS and MedlinePlus.

Implants do not last forever. Mayo Clinic reports that most replaced knees are still functioning well 15 years after surgery, and revision surgery is available when a component wears or loosens, though it is a larger operation with a longer recovery than the first. Younger, heavier or very active people place more demand on the joint, which is one reason surgeons sometimes advise waiting.

Alternatives exist at every stage. Supervised exercise programs strengthen the muscles that unload the joint. Weight management reduces the force through the knee with every step. Walking aids, braces and footwear changes redistribute load. Anti-inflammatory medicines and injections of corticosteroid into the joint can ease flares for weeks or months, though evidence for repeated injections is mixed and the decision rests with the prescribing clinician. For some, an osteotomy, which realigns the shin bone to shift weight onto a healthier compartment, is an option before replacement. None of these repairs worn cartilage, but each can delay or avoid surgery for people whose symptoms are manageable.

What people often get wrong about knee replacement

The whole knee is cut out. It is not. Only the worn surfaces and a thin layer of bone are removed. The ligaments on either side, the tendons, the muscles and most of the bone remain, which is why the joint feels like yours.

You will be asleep no matter what. Many people have a spinal anesthetic and sedation rather than a general anesthetic. Both are standard, and Mayo Clinic describes both as routine options.

Rest is the fastest way to heal. The opposite is closer to the truth. Early movement, described by Mayo Clinic as beginning within hours, reduces stiffness and clot risk. Prolonged bed rest after this operation is a risk, not a comfort.

Robotic surgery means the robot operates. Where robotic systems are used, they hold or guide the cutting tool to a plan the surgeon has made from a scan. The surgeon controls every step. The evidence on whether this improves how the knee feels or lasts is still developing, and major guidance does not currently favor one method over another.

Once the wound heals, you are recovered. The skin heals in weeks; the NHS notes that full recovery can take up to a year. Swelling, clicking and fatigue in the leg during that period are ordinary.

You must wait until the pain is unbearable. Guideline bodies suggest surgery when symptoms substantially limit life despite non-surgical care. Waiting until muscles have wasted and the joint is badly deformed can make the operation and recovery harder, though the timing is always individual.

New knees are for older people only. The NHS notes most recipients are 60 to 80, but candidacy rests on the joint and the person’s function, with the finite lifespan of the implant weighed carefully for younger patients.

Questions to ask your care team before knee replacement

A good consultation leaves you knowing not just what will happen, but why your surgeon has chosen each element for you. These questions tend to open that conversation, and no competent team will mind being asked.

• Which compartments of my knee are damaged, and is a partial replacement an option for me? If not, what rules it out?
• Will you keep my posterior cruciate ligament or substitute it with the implant design? How do you decide?
• Do you use cement to fix the components, a press-fit surface, or a combination, and why for my bone?
• Will my kneecap be resurfaced? What guides that choice?
• What anesthetic do you recommend for me, and will I have a nerve block? What should I expect as it wears off?
• How do you prevent infection and blood clots in your patients, and what will I need to do at home?
• Roughly how long do your patients usually stay, and what do you need to see before I go home?
• What will my pain plan look like in the first two weeks, and who do I call if it is not working?
• When will physical therapy start, how often, and can I do most of it at home?
• Which of my current medicines should be paused or continued around surgery? (Never change these on your own.)
• What are your specific criteria for driving, returning to work and returning to my particular sport?
• What signs would make you want to see me urgently after discharge?
• How will you follow the implant over the years, and how often will I need X-rays?

Write the answers down, or bring someone who will. Consent conversations cover a great deal, and the calm you feel walking into the operating room is often in direct proportion to how many of these you had answered the week before.

When to call your doctor after knee replacement surgery

Most of what you feel in the weeks after surgery is expected: aching, swelling, bruising that travels down the shin, warmth around the joint and stiffness in the mornings. A handful of signs are different in kind, and Mayo Clinic, the Cleveland Clinic and the NHS agree they should prompt a same-day call to your surgical team, or emergency care where noted.

• Signs of infection: fever or chills; increasing redness, heat or spreading swelling around the wound; cloudy, foul-smelling or persistent drainage; a wound edge that opens.
• Signs of a blood clot in the leg: new pain or tenderness in the calf or thigh, especially on one side; swelling of the calf or ankle that is worse than the knee swelling; skin that is warm and reddened over the calf.
• Signs of a clot in the lung (emergency): sudden shortness of breath, chest pain that worsens with breathing, coughing up blood, a racing heart or feeling faint. Call emergency services rather than the clinic.
• Pain that is escalating rather than settling after the first week, or pain that is not controlled by the plan you were given.
• Loss of movement or sensation: numbness, tingling or weakness in the foot, or a knee that suddenly cannot bear weight or bend after previously managing both.
• A fall onto the operated leg, even without obvious injury.
• Bleeding, black stools or vomiting while taking a blood-thinning medicine.

In the longer term, a knee that becomes newly painful, swollen or unstable months or years after surgery, or a fever that follows dental work or another infection, should also be reported promptly. Artificial joints can become infected at any point in their life, and early assessment makes a real difference to the options available. When in doubt, call. Surgical teams would far rather answer a question that turns out to be nothing than hear about a complication late.

Frequently asked questions

How long does knee replacement surgery take?

The operation itself usually takes 1 to 2 hours, according to the NHS. Add preparation, anesthesia and time in the recovery area, and you should expect to be away from your family for several hours in total. Partial replacements are often at the shorter end, while knees with severe deformity or previous surgery can take longer.

Is knee replacement a major surgery?

Yes, it is major orthopedic surgery that involves cutting bone, fixing an implant and a recovery measured in months. It is also one of the most commonly performed operations worldwide, with highly standardized steps and safety checks. Both facts are true at once, which is why teams take preparation and infection prevention so seriously.

Are you awake during knee replacement surgery?

You may be. Mayo Clinic describes two standard options: general anesthesia, where you are fully unconscious, and spinal anesthesia, where you are numb from the waist down and usually sedated so you are drowsy and unaware. Neither involves feeling pain. Your anesthesiologist recommends one based on your health and preferences.

How painful is a full knee replacement?

Pain during surgery is fully blocked by anesthesia, and a nerve block often keeps the knee numb for the first hours afterward. Once it wears off, most people describe a deep ache and tightness that peaks in the first few days and eases over two to three weeks. Teams manage it with layered medicines, ice, elevation and early movement, adjusted to each person.

What is the hardest part of knee replacement recovery?

People most often name disrupted sleep in the first weeks, the discomfort of early physical therapy needed to regain bending, and the patience required in months two to six when improvement slows but continues. Therapists push range of motion early because scar tissue that is never stretched can set the knee stiff.

How long do you stay in the hospital after a knee replacement?

Typically 1 to 3 days, according to the NHS, and Mayo Clinic notes many people now go home the same day or the day after. Discharge depends on walking safely with an aid, managing stairs if needed, having pain under control and knowing your home exercises, rather than on a fixed number of nights.

What can you never do after knee replacement?

Mayo Clinic advises avoiding higher-impact activities such as jogging, skiing and jumping or pivoting sports, because repeated impact wears the plastic bearing. Walking, swimming, cycling and golf are generally encouraged. Kneeling may be uncomfortable but does not harm the implant. Lifelong vigilance about infections anywhere in the body matters more than any single activity.

What are the total knee replacement procedure steps?

After anesthesia and antiseptic preparation, the surgeon makes a vertical incision at the front of the knee, moves the kneecap aside, removes damaged cartilage and a thin layer of bone from the femur and tibia, fits trial components to check alignment and ligament balance, fixes the final metal parts with cement or a press-fit surface, inserts the plastic bearing, and closes the wound.

What does the knee replacement recovery timeline look like?

Walking with support usually starts within hours, hospital stays run 1 to 3 days, stitches come out around two weeks, light daily activities are commonly manageable at 3 to 6 weeks according to Mayo Clinic, driving is often reconsidered around 6 to 8 weeks per the NHS, and full strength can take up to a year. These are typical ranges, not promises.

How long does a knee replacement last?

Mayo Clinic reports that most replaced knees are still functioning well 15 years after surgery. Wear depends on activity level, body weight and time. If a component loosens or wears, revision surgery is possible, though it is a larger operation than the first. Regular follow-up X-rays help catch problems before they cause symptoms.

References

• NHS: Knee replacement
• MedlinePlus: Knee joint replacement
• Cleveland Clinic: Knee replacement

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.