Knee Replacement Surgery

Introduction

Knee replacement surgery is an operation that resurfaces a worn or damaged knee joint with artificial parts so that the knee can move with less pain. It is one of the most commonly performed orthopaedic operations in the world, and for many people with severe knee arthritis it offers a real change in how they walk, sleep, and live day to day.

If you are reading this, you most likely already know that your knee pain is not improving with the treatments you have tried so far, and a doctor has raised the possibility of surgery, or you are weighing it as the next step. This article walks through what knee replacement surgery is, the different types and approaches, what happens before, during, and after the operation, and what life looks like in the months and years that follow.

The decision to have a knee replaced is a personal one. It depends on how much your pain affects your life, what other options have been tried, your overall health, and what you hope to do after surgery. The information here is meant to help you have a fuller conversation with your orthopaedic surgeon — not to replace that conversation.

What Is Knee Replacement Surgery?

The knee is the joint where the thigh bone (femur) meets the shin bone (tibia), with the kneecap (patella) sitting in front. The ends of these bones are normally covered by smooth cartilage, which allows the joint to glide. When that cartilage wears away usually from osteoarthritis, but sometimes from inflammatory arthritis, injury, or other causes — bone rubs on bone. This causes pain, stiffness, swelling, and over time, loss of function.

Knee replacement surgery, also known as knee arthroplasty, removes the damaged cartilage and a thin layer of bone from the surfaces of the knee joint and replaces them with implants made of metal alloys and a hard, durable plastic called polyethylene. The implants are designed to recreate the smooth, gliding surfaces of a healthy knee.

The operation does not actually replace the whole knee. It resurfaces the parts of the joint that are worn. Many ligaments and soft tissues around the knee are kept in place to maintain stability and movement.

Why Is Knee Replacement Surgery Performed?

The most common reason for knee replacement is severe osteoarthritis that has not responded to other treatments. Other reasons include:

• Rheumatoid arthritis — an inflammatory condition in which the body's immune system attacks the joint lining
• Post-traumatic arthritis — arthritis that develops years after a serious knee injury or fracture
• Avascular necrosis — loss of blood supply to part of the bone, causing it to collapse
• Severe knee deformity — such as bow-leg or knock-knee deformity that affects walking
• Failed previous knee surgery — where earlier treatments have not relieved pain or have worsened the joint

Surgery is generally considered when knee pain limits daily activities such as walking, climbing stairs, getting in and out of a chair, or sleeping, and when a reasonable trial of non-surgical treatments has not given enough relief.

Who Is a Candidate?

There is no single test that determines who is a candidate for knee replacement. The decision combines the severity of the joint damage seen on X-ray, the level of pain and disability, the impact on quality of life, and overall health.

Major orthopaedic societies, including the American Academy of Orthopaedic Surgeons (AAOS), describe knee replacement as appropriate when severe arthritis is confirmed on imaging, when pain and functional limitation are significant, and when non-surgical treatments have been tried. There is no strict age cut-off. Most people who have knee replacement are between 50 and 80 years old, but younger and older patients also have the procedure when their situation calls for it.

Factors that surgeons typically weigh when assessing candidacy include:

• The pattern and severity of cartilage loss
• Knee alignment and stability
• Range of motion in the knee
• Body weight, because higher weight places more load on the implant
• Diabetes control, heart and lung health, and other conditions that affect surgical risk
• Smoking status, which affects wound healing
• Skin condition around the knee
• Bone strength
• Activity goals and expectations after surgery

Knee replacement is rarely performed in children or adolescents. In young adults, surgeons often try to delay replacement when possible, because the implant has a finite lifespan and revision surgery later in life is more complex.

Alternatives to Consider

Before recommending surgery, doctors typically go through a series of non-surgical and joint-preserving options. Major guidelines, including those of the AAOS and the American College of Rheumatology, describe a stepwise approach. The right combination depends on the underlying cause, severity, and individual factors.

Lifestyle and physical measures

• Weight loss — even modest weight reduction can reduce load on the knee and improve symptoms
• Exercise and physiotherapy — strengthening the muscles around the knee, especially the quadriceps, often improves pain and function
• Activity modification — replacing high-impact activities with lower-impact ones such as cycling or swimming
• Walking aids — a cane or walking stick used in the opposite hand can offload the affected knee
• Bracing — an offloader brace may help in certain patterns of arthritis

Medications

• Paracetamol for mild pain
• Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or naproxen, taken under medical guidance because of stomach, kidney, and heart-related considerations
• Topical NSAID gels, which deliver medication to the knee with fewer whole-body side effects
• Disease-modifying drugs for inflammatory forms of arthritis such as rheumatoid arthritis

Injections

• Corticosteroid injections can reduce inflammation and pain for weeks to months
• Hyaluronic acid injections are used in some settings, although guideline support varies
• Platelet-rich plasma (PRP) and other biologic injections are offered in some centres; evidence is still evolving and guidelines are cautious

Joint-preserving surgery

• Arthroscopy is generally not recommended as a treatment for osteoarthritis alone, but may be used for specific mechanical problems
• Osteotomy — cutting and realigning the bone to shift weight away from a damaged part of the knee — can be considered in younger patients with arthritis limited to one side of the joint
• Cartilage repair procedures may be considered for focal cartilage defects, particularly in younger, more active patients, although they are not a treatment for established widespread arthritis

When these options no longer give enough relief and arthritis continues to limit life, knee replacement enters the conversation. Whether and when to move from non-surgical to surgical treatment is a clinical decision made with your surgeon.

Types of Knee Replacement Surgery

Total knee replacement

Total knee replacement, also called total knee arthroplasty, is the most common type. The surgeon resurfaces all three compartments of the knee: the inner (medial), the outer (lateral), and the joint between the kneecap and thigh bone (patellofemoral). Metal components are attached to the end of the femur and the top of the tibia, with a plastic spacer in between. The back of the kneecap may or may not be resurfaced depending on the surgeon's assessment.

This is typically chosen when arthritis affects more than one compartment of the knee, or when there is significant deformity.

Partial (unicompartmental) knee replacement

Partial knee replacement, also called unicompartmental knee replacement, resurfaces only one damaged compartment of the knee. The other parts of the joint, including the cruciate ligaments and the healthy cartilage, are kept intact.

For appropriately selected patients, partial knee replacement can offer a smaller operation, quicker recovery, and a knee that often feels more natural than after total replacement. It is suitable when arthritis is limited to one compartment and the ligaments and remaining cartilage are healthy. If arthritis later develops in another compartment, the partial replacement can be converted to a total replacement.

Patellofemoral replacement

This is a less common form of partial replacement that resurfaces only the joint between the kneecap and the thigh bone. It is used in the rare cases where arthritis is confined to that part of the knee.

Bilateral knee replacement

When both knees have severe arthritis, both can be replaced. This can be done in two stages a few months apart (staged bilateral) or both at the same time (simultaneous bilateral). Simultaneous replacement means a single anaesthetic and a single recovery period, but it places a larger load on the body and is generally reserved for patients with good overall health. Staged replacement spreads the demand over time and is more common.

Revision knee replacement

Revision surgery is performed when a previous knee replacement has worn out, loosened, become infected, or otherwise stopped working well. It is a more complex operation than the first replacement because of scarring, bone loss, and the need for specialised implants. Recovery is often longer. Revision surgery is typically performed by surgeons with specific experience in this area.

Surgical Approaches and Techniques

Within each type of knee replacement, surgeons use different approaches and tools.

Conventional (standard) approach

In the conventional approach, the surgeon makes an incision in the front of the knee, moves the kneecap to one side, and works directly on the joint. Bone cuts are guided by mechanical instruments. This is a well-established approach with long track records of outcomes.

Minimally invasive knee replacement

Minimally invasive techniques use a smaller skin incision and aim to disturb less of the surrounding muscle and tendon tissue. They may be associated with somewhat quicker early recovery in selected patients. Long-term outcomes are similar to standard techniques. Not all patients are suitable, and the approach depends on the surgeon's training and the anatomy of the knee.

Computer-assisted and robotic-assisted knee replacement

Computer navigation and robotic-assisted systems are used in some centres to help with planning bone cuts and aligning the implant. The surgeon remains in control; the technology assists with precision. Studies suggest these systems can improve the accuracy of implant positioning. Whether this translates into clearly better long-term outcomes is still being studied. Major societies describe these as useful tools rather than essential ones.

Cemented, cementless, and hybrid fixation

The implants are held to the bone either with bone cement (a fast-setting acrylic), without cement (where the bone grows into a textured implant surface), or with a combination of the two. The choice depends on bone quality, implant design, age, and surgeon preference.

Preparing for Knee Replacement Surgery

Preparation usually begins several weeks before the operation. Good preparation tends to improve recovery.

Pre-operative assessment

You will typically have a thorough check before surgery, which may include:

• Blood tests
• Heart tracing (ECG) and sometimes echocardiogram
• Chest X-ray
• Detailed knee X-rays and sometimes MRI or CT for planning
• Review of medications, including blood thinners, diabetes medications, and arthritis drugs
• Dental check, since untreated dental infection can affect joint surgery outcomes
• Screening for skin infections around the knee

Optimising your health

Before surgery, doctors generally recommend:

• Stopping smoking well before the operation, as smoking slows wound healing and increases complications
• Controlling diabetes, with HbA1c often targeted to a level your surgical team agrees on
• Managing weight where possible, since very high body weight is associated with higher rates of complications
• Building up strength with pre-operative physiotherapy, sometimes called “prehab”
• Reviewing medications — some drugs need to be stopped or adjusted before surgery
• Treating any active infections, including in the urinary tract, skin, or teeth

Practical preparation at home

Because you will have limited mobility for a few weeks, simple changes at home make recovery smoother:

• Clearing walking paths and removing loose rugs
• Setting up a chair with arms, a firm seat, and a footrest nearby
• Arranging a bed on a single level if you live in a multi-storey home
• Installing grab bars in the bathroom and a raised toilet seat
• Stocking easy-to-prepare food
• Arranging help with daily tasks for at least the first one to two weeks

What Happens During Knee Replacement Surgery

On the day of surgery, you will be admitted to hospital and prepared for the operating theatre.

Anaesthesia

Knee replacement can be done under:

• Spinal anaesthesia — an injection in the back that numbs the lower half of the body, often combined with mild sedation. This is widely used in modern knee replacement.
• General anaesthesia — in which you are fully asleep
• Regional nerve blocks are often added to reduce pain after surgery

1. The skin is cleaned and an incision is made in the front of the knee
2. The surgeon moves the soft tissues aside to expose the joint
3. Damaged cartilage and a thin layer of bone are removed from the ends of the femur and the top of the tibia
4. The bone surfaces are shaped to fit the implants
5. Trial components are placed to check fit, stability, and movement
6. The final implants are fixed in place with or without bone cement
7. The kneecap may be resurfaced
8. The knee is checked through a range of motion
9. The wound is closed in layers and a dressing applied

In hospital

Many patients now stand and take a few steps with help on the same day as surgery or the day after. Hospital stays vary but are often two to four days, and shorter in some programmes. During this time, the team focuses on:

• Pain control with a combination of medications
• Starting physiotherapy — getting the knee bending and straightening, and practising walking with a frame or crutches
• Preventing blood clots with medication, compression devices, and early movement
• Wound care
• Checking that you can manage stairs and basic tasks before discharge

The first few weeks at home

The first two weeks at home are typically the most demanding. Pain and swelling are still present, sleep can be disrupted, and physiotherapy exercises require effort. During this period, most people:

• Walk short distances at home with a walker or crutches
• Do daily exercises to improve bending, straightening, and strength
• Use ice and elevation to manage swelling
• Take pain medication as prescribed, gradually reducing over time
• Continue blood-thinning medication for several weeks

By around six weeks, many people can walk without aids on flat ground, climb stairs, and resume light daily activities. Driving is usually possible somewhere between four and eight weeks for a right knee replacement, and earlier for a left knee in countries where cars are right-hand drive, but only when reflexes and strength have returned. The exact timing is decided with the surgeon.

Months three to twelve

Strength and confidence continue to build over months. Most improvement happens within the first three to six months, but small gains often continue up to a year and sometimes longer. Swelling, warmth, and a sense of stiffness can persist for several months, even when the knee is healing well.

Physiotherapy

Physiotherapy is central to recovery. The goals usually include:

• Restoring straightening and bending of the knee
• Strengthening the quadriceps and other muscles around the knee
• Improving balance and walking pattern
• Gradually increasing activity

How well a knee replacement turns out depends not only on the surgery but on the work done in rehabilitation. People who engage actively with their exercises tend to recover function more fully.

Risks and Complications

Knee replacement is a generally safe operation, but like any major surgery it carries risks. Most patients do well, and serious complications are uncommon. Possible risks include:

General surgical risks

• Infection — either at the wound or, more seriously, deep around the implant. Deep infection may require further surgery and prolonged antibiotics.
• Blood clots — in the leg veins (deep vein thrombosis) or, rarely, the lungs (pulmonary embolism). Blood-thinning medication and early movement reduce this risk.
• Bleeding requiring transfusion in some cases
• Anaesthetic reactions
• Heart or lung complications, particularly in patients with other medical conditions

Knee-specific risks

• Stiffness — if the knee does not bend or straighten enough during recovery, a procedure to manipulate the knee under anaesthesia may be needed
• Persistent pain — a small proportion of patients experience ongoing pain even after a technically successful operation
• Nerve or blood vessel injury — rare, but possible
• Fracture around the implant during or after surgery
• Implant loosening or wear over many years
• Instability if the soft tissue balance is not ideal
• Numbness around the scar, which is common and usually improves over time

Late complications

Years after surgery, implants can wear out, loosen, or, rarely, become infected through bacteria carried in the bloodstream. These problems may require revision surgery. Patients are usually advised to seek prompt treatment for any infection elsewhere in the body, including dental infections, because of the small risk of bacteria spreading to the implant.

Life After Knee Replacement Surgery

Activities

After full recovery, the following are generally encouraged:

• Walking
• Swimming
• Cycling
• Golf
• Light hiking
• Doubles tennis or other low-impact recreational sports
• Yoga and most gentle exercise classes, with care for deep kneeling positions

High-impact activities such as running, jumping sports, and contact sports are generally discouraged, because they place heavy loads on the implant and can shorten its lifespan. Many surgeons advise against repeated deep squatting and kneeling, although some people are able to kneel comfortably.

The new knee — what it feels like

A replaced knee is not a normal knee. It is a very functional knee, but most patients can feel that it is different. Common sensations include:

• A feeling of tightness or pressure, especially in the first year
• Occasional clicking sounds, which are usually harmless
• Numbness in a patch of skin around the scar
• Mild swelling after long activity, particularly during the first year

Most people adjust to these sensations and report a clear improvement in quality of life.

How long does a knee replacement last?

Modern implants are designed to last many years. Available evidence suggests that most knee replacements continue to function well at 15 to 20 years, and many last longer. Lifespan depends on the patient's age, weight, activity level, bone quality, and the implant itself. Younger and more active patients are more likely to need revision surgery at some point in their lives, simply because they place more years of use on the implant.

Follow-up

Most surgeons see patients several times in the first year after surgery and then periodically afterwards, often with X-rays at long intervals to check the implant. Reporting any new pain, swelling, fever, or wound problem early is important. So is treating any infection elsewhere in the body promptly.

Frequently Asked Questions

How painful is knee replacement surgery?

The first few days after surgery are typically the most painful, but modern pain management combines several methods — nerve blocks, spinal anaesthesia, oral medications, ice, and movement — to keep pain manageable. Most people find that the pain decreases steadily over the first few weeks. Pain that suddenly worsens, with fever or wound discharge, should be reported to the surgical team.

How long will I need to be off work?

Return to work depends on the type of work. People with desk-based work often return in four to six weeks, sometimes part-time at first. Work that involves standing, walking, or lifting may require three months or more before full duties resume. Your surgeon and physiotherapist help judge readiness.

Will I be able to bend my knee fully?

Most patients regain enough bend to walk, climb stairs, get into a car, and rise from a chair comfortably. Many achieve bend close to that of the pre-surgery knee. Deep bending such as full squatting may or may not be possible depending on the implant, soft tissue, and individual factors.

Can both knees be replaced at the same time?

Yes, in selected patients. Simultaneous bilateral knee replacement means one anaesthetic and one recovery period, but places a larger load on the body. Staged surgery, where each knee is done some months apart, is more common. The decision depends on overall health and is made with the surgical team.

What is the difference between total and partial knee replacement?

Total knee replacement resurfaces all parts of the joint. Partial knee replacement resurfaces only the damaged section and keeps the rest of the joint, including the ligaments. Partial replacement requires that arthritis be limited to one part of the knee. When suitable, it can offer a smaller operation and a knee that often feels more natural, but not everyone is a candidate.

What is robotic-assisted knee replacement?

Robotic-assisted knee replacement uses a computer-guided system to help the surgeon plan and execute the bone cuts and implant positioning. The surgeon stays in control of the operation. Studies suggest the technology can improve precision of implant placement. Whether this leads to noticeably better long-term outcomes is still being studied.

How do I know if it is time for surgery?

This is a decision shared with your surgeon. It is generally considered when knee pain limits everyday activities such as walking, sleeping, or climbing stairs, when non-surgical treatments have not given enough relief, and when imaging shows significant joint damage. The decision is rarely urgent — it is about quality of life.

Are there age limits for knee replacement?

There is no strict age cut-off. Surgeons consider overall health and fitness for surgery rather than age alone. Older patients in good health do well with knee replacement. Younger patients are sometimes advised to delay surgery when possible, because they may outlive the implant and need revision later.

Will I need another operation later?

Most modern knee replacements last 15 to 20 years or longer. Some patients, particularly younger and more active ones, will eventually need revision surgery. Revision is more complex but is a well-established operation.

Can I travel by air after knee replacement?

Long flights soon after surgery raise the risk of blood clots. Most surgeons advise avoiding long flights in the first few weeks. After that, travel is generally possible with sensible precautions such as walking during the flight and staying well hydrated. Metal in the implant may set off airport scanners; most modern systems handle this without difficulty.

Conclusion

Knee replacement surgery is one of the most consistently effective operations in modern medicine for severe knee arthritis that has not responded to other treatments. It offers most patients meaningful relief from pain and a return to activities they had given up. It is also major surgery, with a recovery measured in months rather than weeks, and a small but real risk of complications.

The choice of whether and when to have a knee replaced, which type and approach is appropriate, and what to expect afterwards is best made through detailed conversation with an orthopaedic surgeon who has examined your knee, reviewed your imaging, and understood what matters most to you. The information in this article is meant to help that conversation go further, not to take its place.