The knee joins the lower end of the thighbone, the femur, to the upper shinbone, the tibia. The kneecap, or patella, moves against the front of the femur. Smooth articular cartilage covers their joint surfaces. The lining makes synovial fluid, which helps lubricate the joint as it bends and straightens.

Two menisci, curved wedges between the thighbone and shinbone, help cushion the joint. Ligaments help hold the bones together and stabilise movement, while the thigh muscles supply strength. For walking, stairs or getting out of a chair, these structures work together: a replacement changes joint surfaces but muscles and remaining soft tissues still matter.

Surgeons describe three compartments: the inner, or medial; outer, or lateral; and the patellofemoral compartment behind the kneecap. Osteoarthritis can involve one or several. Cartilage damage and other changes in the joint can accompany pain, stiffness and reduced function, but a scan alone does not describe how much the knee affects a person’s life.

Most knee replacements are offered for osteoarthritis. Other reasons can include rheumatoid arthritis or arthritis following an injury. Pain at rest or during walking, difficulty with stairs, stiffness and changes in leg alignment can make ordinary tasks harder. Tell the team what you can no longer do, what you have tried and what outcome would matter most.

NICE recommends considering referral for hip, knee or shoulder replacement for osteoarthritis when symptoms substantially affect quality of life and non-surgical management is ineffective or unsuitable. Referral is a chance to discuss the options, not a commitment to surgery. NICE says age, smoking, other conditions or body mass index alone should not exclude someone from referral, while acknowledging that these factors can influence surgical risk.

The surgeon takes a history, examines movement, strength, stability and alignment, and may use X-rays to assess the pattern of damage. NICE notes that osteoarthritis is often diagnosed clinically without imaging. An X-ray showing arthritis does not automatically mean replacement is required: the decision brings together symptoms, examination, alternatives and your priorities.

For osteoarthritis, NICE recommends tailored therapeutic exercise, such as strengthening and aerobic activity, as a core treatment. Supervised sessions can be considered. Pain can increase when exercise begins, so discuss how to build a manageable programme and when to review it. For someone living with overweight or obesity, weight management may also improve pain and function; support should be tailored to the person.

A walking stick or other walking aid may help with mobility. NICE recommends offering a topical non-steroidal anti-inflammatory drug, or NSAID, for knee osteoarthritis if medicine is needed. If topical treatment is ineffective or unsuitable, an oral NSAID may be considered with attention to stomach, kidney, liver and cardiovascular risks and other medicines. Ask a clinician or pharmacist what is appropriate for you.

A corticosteroid injection into the joint can be considered when other medicines are ineffective or unsuitable, or to support exercise. NICE describes its benefit as short term. It advises against hyaluronan injections for osteoarthritis and against arthroscopic washout or debridement for osteoarthritis. Other operations may suit particular circumstances; ask what is relevant to your diagnosis rather than assuming all knee pain has the same options.

Choosing to continue non-surgical care is an active plan. Agree how you will manage symptoms, when to review function and what changes need earlier assessment. Replacement is usually elective, so ask how long you can take to decide and whether waiting has particular consequences for your knee or health.

In a total knee replacement, damaged cartilage and a small amount of underlying bone are removed from the ends of the thighbone and shinbone. Metal components cover the prepared surfaces, with a medical-grade plastic spacer between them. The operation resurfaces the joint rather than replacing the entire leg. Depending on the plan, the undersurface of the kneecap may also receive a plastic component.

A partial, or unicompartmental, replacement resurfaces only the affected compartment and preserves the other surfaces and ligaments. It can be an option when arthritis is confined to one area. The examination of ligaments and motion, imaging and the pattern of symptoms all matter. Significant stiffness, ligament damage or inflammatory arthritis can make a partial replacement unsuitable.

NICE recommends offering a choice of partial or total replacement to people with isolated medial compartment osteoarthritis, with a discussion of benefits and risks. Partial replacement often involves a faster recovery and preserves more of the knee; arthritis can later develop in an unreplaced compartment and further surgery may be needed. A total replacement treats more of the joint but is a larger resurfacing procedure. Neither choice guarantees a particular outcome.

The plan can change if the surgeon finds more extensive damage during the operation. Before consent, ask whether conversion from partial to total is possible, under what circumstances and what you would agree to. NICE recommends offering patella resurfacing with primary elective total knee replacement; ask whether it is planned and why.

The metal components may be fixed to bone with bone cement, or designed for bone to grow onto a press-fit surface. Implant design and fixation depend on the planned operation and the individual. Ask which materials and fixation are proposed, whether an allergy is relevant, and how the implant choice fits your knee.

The new surfaces glide against a plastic bearing. The replaced cartilage does not grow back as a natural joint surface, and the implant can wear or loosen over time. The kneecap remains, even if its underside is resurfaced. Some surrounding tissues and ligaments are retained, but exactly what is removed or retained depends on the operation and implant design.

The knee can feel different from before. Numbness around the scar and some stiffness are possible, and full natural movement is not assured. Kneeling can be uncomfortable. Ask what range of movement is realistic given your knee before surgery and how this might affect work, prayer, gardening or other activities important to you.

The UK TOPKAT randomised trial studied 528 people suitable for either partial or total replacement for isolated medial compartment osteoarthritis. At five years, the groups had similar improvement in the Oxford Knee Score, a measure of pain and function. Some participants received a different operation from the one assigned, including when findings at surgery changed the plan.

In that trial, revision and other re-operation rates were similar over five years, but further operations were uncommon and the study may not have been large enough to detect differences in them. The trial also discusses registry studies that observed more revisions after partial replacement, although such observational comparisons have limitations. These findings do not establish an individual’s lifetime risk and may not apply to arthritis elsewhere in the knee. A surgeon’s experience and your individual findings matter when applying the evidence.

Pre-assessment checks your health and may include blood tests and blood pressure. Bring a list of prescribed medicines, over-the-counter products and supplements, and tell the team about allergies, blood thinners, previous anaesthetic problems and changes in your health. Ask exactly which medicines to continue, pause or restart, and follow your hospital’s eating and drinking instructions.

NICE recommends advice on exercise before and after replacement, diet, weight management and stopping smoking. Ask for a plan suited to your abilities and any other conditions. If you become unwell while waiting, inform the hospital. Discuss your goals, the benefits, risks, alternatives and the likely need for help before giving consent.

Arrange transport and help with shopping, meals, washing or caring duties if needed. Move frequently used items within easy reach, clear trip hazards and consider stairs, a supportive chair and bathroom access. Tell the team if you live alone or have accessibility needs so discharge planning and equipment can be considered early.

NICE recommends offering people having primary elective knee replacement a choice of regional anaesthesia with local infiltration analgesia, or general anaesthesia with local infiltration analgesia. Regional anaesthesia may involve a spinal injection that numbs the lower body; general anaesthesia means you are asleep. Local infiltration puts pain-relieving medicine around the operation site. A suitable nerve block may also be considered. Discuss your health, preferences and the benefits and risks with the anaesthetic team.

The surgeon makes a cut at the front of the knee, accesses the joint, prepares the surfaces and fits the planned components. The knee is checked and the wound closed with stitches or clips and dressed. In recovery, staff monitor you and provide pain relief. Ask what was done and whether anything found during surgery changed the plan.

The aim is to reduce pain and improve everyday function. Many people find daily life improves, but some have ongoing pain, stiffness, difficulty bending or instability. Recovery can take months, and replacement does not guarantee a pain-free knee or the ability to return to every activity. Ask which of your symptoms the operation is expected to help and which may have another cause.

A blood clot may form in a leg vein and can travel to the lungs. Your team will assess prevention, which may include medicines and compression stockings, as well as early movement. Ask how long to use any prescribed prevention, what side effects to report and what to do if you miss a dose. Do not stop or change a blood thinner without advice.

A wound infection may be treated with antibiotics; infection deep around the joint can need further surgery. Infection can occur later as well as soon after surgery. Other possible complications include bleeding, injury to nerves, blood vessels or ligaments, and anaesthetic or other medical problems. Individual risk depends on health and the procedure. The urgent signs at the start of this guide explain when to seek help.

Stiffness, persistent pain, instability, wear or loosening may require assessment and sometimes further treatment. Pain after replacement can have more than one cause, so new or worsening symptoms should not simply be assumed to be normal healing or implant failure. NICE recommends referral to an orthopaedic service for new or worsening pain, limp or loss of function related to a replacement.

In hospital, nurses and physiotherapists help you get moving, usually with crutches or a frame at first. NICE recommends rehabilitation on the day of surgery if possible, and within 24 hours, including mobilisation and advice on daily activities and home exercises. Discharge depends on your safety and progress. Ask about wound care, medicines, clot prevention, follow-up and a number to call.

At home, exercises prescribed by your physiotherapist support strength and movement. Build walking gradually and use your walking aid until the team says you can progress. Swelling and soreness are expected, but worsening symptoms need assessment. Ask how to manage pain and side effects so you can exercise and rest. If the exercises or daily tasks are not manageable, ask for a review rather than trying to push through.

NICE recommends supervised group or individual outpatient rehabilitation when someone has difficulty with daily activities, ongoing functional needs or self-directed rehabilitation is not meeting their goals. Ask for help with stairs, washing, dressing or getting in and out of a car if these are difficult. A useful plan includes clear goals and someone to contact between appointments.

Recovery commonly takes several months or longer and is often shorter after partial replacement. NHS England suggests work may be possible around six to twelve weeks, depending on the work and the person. It advises waiting at least six weeks to drive after a total replacement or three weeks after a partial replacement, and checking with your doctor that you are fit to drive. You must be able to control the car and perform an emergency stop; check your insurer and follow your own team’s advice.

Longer term, many people can return to activities such as walking, swimming and cycling. Discuss high-impact sport, kneeling and physically demanding work with your team. A replacement can last many years, but no individual lifespan is guaranteed. Wear, loosening, infection or arthritis in a remaining compartment can lead to revision, an operation replacing some or all implant components. Revision and other re-operations are not the same thing, and the treatment depends on the cause.