Short answer
A knee replacement removes damaged joint surfaces and replaces them with metal and plastic parts, either across the whole knee (total) or on one side only (partial).6 It is usually considered when osteoarthritis pain is having a big effect on daily life and non-surgical treatment has not helped enough.13 Its main limitation is that not everyone ends up pain-free: systematic review data suggest that roughly one in five people report an unfavourable long-term pain outcome.9 Because knee pain has several possible causes, the source of the pain needs to be confirmed in person before surgery is discussed.
Decision snapshot
| Question | Snapshot |
|---|---|
| Main reason | Painful, stiff knee from osteoarthritis that has not responded to non-surgical care |
| Types | Total knee replacement (TKR) or partial (unicompartmental) knee replacement |
| Operation | Usually 1 to 2 hours, under spinal or general anaesthesia |
| Hospital stay | Usually 1 to 4 days |
| Driving | At least 6 weeks after a total, 3 weeks after a partial, once fit |
| Long-haul flights | One NHS orthopaedic hospital advises waiting about 3 months |
| Implant survival | About 82% of total knees still in place at 25 years in registry data |
On this page
- What a knee replacement is
- What may be causing the knee pain
- Who may be considered
- Alternatives
- Procedure, preparation and anaesthesia
- Recovery and rehabilitation
- How long a knee replacement lasts
- Pain and comfort
- Risks and complications
- How strong is the evidence?
- Total, partial and red flags
- Cost drivers and quotes
- Frequently asked questions
- Sources
What a knee replacement is
In a total knee replacement (TKR), the worn ends of the thigh bone and shin bone are fitted with metal and plastic parts. It is the most common type. In a partial knee replacement, only the damaged half of the knee is replaced, through a smaller cut.6
The aim is to stop damaged bone surfaces rubbing together. When cartilage is worn by osteoarthritis or damaged by injury, the bones grind against each other and cause pain and stiffness.1
What may be causing the knee pain
Osteoarthritis is the most common reason for a knee replacement, but it is only one of many causes of knee pain.1 Several need entirely different treatment:2
- Sprains, strains and tendonitis after overuse, twisting or repetitive running and jumping.
- Torn ligament, tendon or meniscus, often with giving way, locking or a pop at the time of injury.
- Bursitis, with warmth and redness made worse by kneeling.
- Gout or septic arthritis, with sudden, very bad pain and a hot, red knee. Septic arthritis is an emergency.
- Rheumatoid arthritis or arthritis after injury, less common reasons for replacement.1
Osteoarthritis can usually be diagnosed clinically, without imaging, in people aged 45 or over with activity-related joint pain and no, or only brief, morning stiffness.3 Atypical features call for further tests.
What it may change
- Pain from worn joint surfaces, and the stiffness that comes with it.
- Walking distance and everyday function, as measured by knee scores in trials.5
Who may be considered
The National Institute for Health and Care Excellence (NICE) advises considering referral for joint replacement when symptoms substantially affect quality of life and non-surgical management has not been effective.3 It asks clinicians to use clinical assessment rather than scoring tools, and not to exclude people on age, sex, smoking, other illnesses or body mass index (BMI) alone.
Who may not benefit or may face additional risk
- People whose pain comes mainly from a cause other than joint wear.
- People with clot risk factors such as previous deep vein thrombosis (DVT), obesity, cancer or age over 60, particularly if a long journey follows surgery.11
- People with broken skin, cuts or rashes near the knee, which give bacteria a route in.10
When a responsible clinician may advise against it
- When core non-surgical treatment has not yet been tried properly.3
- When there is an active infection, or the diagnosis is unclear.
- When there is no realistic plan for physiotherapy and follow-up after discharge.
Alternatives
NICE guideline NG226 sets out the non-surgical options for osteoarthritis.3
| Option | What NICE NG226 says |
|---|---|
| Therapeutic exercise | Offer to everyone with osteoarthritis, tailored to their needs |
| Weight loss | Any loss helps; 10% of body weight is likely to be better than 5% |
| Topical NSAID | Offer a topical non-steroidal anti-inflammatory drug for knee osteoarthritis |
| Oral NSAID | Consider if topical treatment is ineffective or unsuitable, with attention to risks |
| Paracetamol, weak opioids | Not routinely, except infrequent short-term use |
| Steroid injection | Consider when other treatments fail; relief is short-term (2 to 10 weeks) |
| Hyaluronan injection | Do not offer |
| Arthroscopic washout or debridement | Do not offer for osteoarthritis |
For arthritis confined to the inner (medial) side, partial replacement is a surgical alternative to total replacement, and NICE says people in that situation should be offered the choice.4
No treatment is a legitimate option
Knee replacement is planned surgery, not an emergency. Continuing with exercise, weight management and pain relief, and revisiting the decision later, is a reasonable choice when symptoms are tolerable.
Procedure, preparation and anaesthesia
Most people go into hospital on the day of the operation, which usually takes 1 to 2 hours. Anaesthesia is either general (asleep) or spinal (awake but numb from the waist down).6
NICE recommends offering a choice of regional or general anaesthesia, each combined with local infiltration analgesia (LIA, numbing medicine injected around the joint during surgery). It also recommends tranexamic acid (a medicine that reduces bleeding) and, for total knee replacement, resurfacing the kneecap.4
Recovery and rehabilitation
Rehabilitation should begin on the day of surgery if possible, and within 24 hours.4 People usually go home after 1 to 4 days, once they can move safely on crutches.7
| Milestone | Typical timing |
|---|---|
| Stitches or clips out | About 10 days |
| Compression stockings | Usually at least 6 weeks |
| Walking without an aid | From about 6 weeks, if ready |
| Driving | At least 6 weeks (total) or 3 weeks (partial) |
| Work | About 6 to 12 weeks, depending on the job |
| Full recovery | Several months or longer |
The home exercise programme matters most. Following it early supports long-term strength and movement.7 NICE recommends supervised outpatient rehabilitation for people who struggle with daily activities, have ongoing functional problems, or find that self-directed exercise is not meeting their goals.4 If surgery happens abroad, that support has to be arranged at home before travelling.
How long a knee replacement lasts
The NHS says most knee replacements last about 25 years.8 A 2019 systematic review of national joint registries estimated that 82.3% of total knee replacements and 69.8% of partial (unicompartmental) replacements were still in place at 25 years; at 15 years the figures were 93.0% and 76.5%.14
These figures count revision surgery, not satisfaction. The 20- and 25-year data came from the Finnish registry, and UK data were not included. The UK National Joint Registry (NJR) reports that knee revision estimates have fallen since 2009.15
Pain and comfort
The operation itself is not felt: patients are either asleep or numb from the waist down.6 Local infiltration analgesia, and sometimes a nerve block that does not weaken the leg muscles, helps with pain in the first hours and days.4
Pain, swelling and stiffness are expected for weeks, and the exercises are uncomfortable at first. Pain relief is given in hospital and continued at home.
Risks and complications
Expected temporary effects: pain, swelling, bruising, stiffness and reliance on walking aids for several weeks.7
Recognised complications:
- Persistent pain. A systematic review of prospective studies found that 10% to 34% of people reported an unfavourable long-term pain outcome after total knee replacement, about 20% in the best-quality studies. The authors considered these likely underestimates.9
- Stiffness and instability, including difficulty bending the knee.8
- Wound infection, usually treated with antibiotics.8
- Blood clots (DVT), reduced by stockings or blood-thinning medicines.8
- Damage to a nearby nerve, blood vessel or ligament, which is uncommon.8
Rare serious complications: deep infection of the joint, which may need further surgery. Treatment ranges from washout with implant retention to one- or two-stage revision, and infection can appear months or years later.10 A clot that travels to the lungs (pulmonary embolism, PE) can be life-threatening.11
Urgent warning signs
The NHS advises urgent medical advice for throbbing or cramping leg pain; a high temperature or feeling hot, cold or shivery; oozing or pus from the wound; or knee redness, swelling or pain that is worsening. Leg pain and swelling with difficulty breathing or chest pain needs emergency care.8
How strong is the evidence?
| Claim | Vireon assessment | What supports it | Important limitation |
|---|---|---|---|
| Exercise and weight loss help knee osteoarthritis | Strong | NICE NG2263 | Benefit depends on keeping it up |
| Partial and total replacement give similar function for medial arthritis | Moderate | TOPKAT randomised trial, 528 patients, 5 years5 | Experienced surgeons only; longer follow-up pending |
| About 82% of total knees last 25 years | Moderate | Registry meta-analysis14 | Older implants; long-term data from one country |
| About one in five report unfavourable long-term pain | Moderate | Systematic review9 | Pain measures varied; missing data |
| Deep infection after knee replacement | Uncertain incidence | NHS and AAOS patient guidance810 | No verified rate given here |
| Best timing for long-haul flights after surgery | Mixed | Hospital and society advice1213 | Advice differs; individual clot risk varies |
Survival figures describe implants put in years ago, and a knee can be painful or stiff without being revised. TOPKAT found 6% of the partial group and 8% of the total group needed further surgery, but the trial may have been too small to show differences in reoperation reliably.5
Total, partial and treatment-specific red flags
Partial replacement suits arthritis confined to one compartment. In TOPKAT, function was similar, hospital stay was shorter (3.2 versus 4.3 days on average) and revision was 4% in both groups at five years.5 Registry data show lower 25-year survival for partial knees.14
Red flags include surgery offered without examining the knee in person, no named implant, no rehabilitation plan, and a long-haul flight home planned within days without a discussion of clot prevention.12 See medical travel red flags.
Cost drivers and what a quote should include
Cost depends on whether the replacement is total or partial, the implant, the anaesthetic, length of stay and the amount of physiotherapy included. A written quote should list:
- Pre-operative tests, imaging and professional fees.
- The implant manufacturer and model, and whether the kneecap will be resurfaced.
- Nights in hospital, clot-prevention medicine and stockings.
- Inpatient and outpatient physiotherapy sessions, and follow-up review.
- What happens, and who pays, if a complication or re-operation occurs.
More on this in what a treatment quote should include.
If you are travelling for treatment
- Diagnosis and fitness for surgery need in-person examination; scans alone do not settle the cause of pain.
- Journeys over 4 hours raise clot risk.11 The Royal Orthopaedic Hospital advises about 3 months after knee replacement before journeys over 4 hours; the American Association of Hip and Knee Surgeons says many people travel within weeks with a clot-prevention plan.1213
- On any long journey, move about every hour, drink water and avoid alcohol.11
- Book physiotherapy at home before leaving, and carry the operation note and implant details. See aftercare at home and DVT and travel.
Questions worth asking a clinician
- What is causing my pain, and how sure are you?
- Am I suitable for a partial replacement, and why or why not?
- Which implant will you use, and what does registry data show for it?
- How will my clot risk be managed, including the journey home?
- Who do I contact if I develop warning signs after I return?
Frequently asked questions
Does knee replacement hurt?
The operation is done under anaesthesia, but recovery is painful for several weeks and is managed with pain relief.67 A minority have pain that persists long term.9
When can I drive and go back to work?
Driving usually waits at least 6 weeks after a total and 3 weeks after a partial replacement; work usually resumes after 6 to 12 weeks.7
When can I fly?
Advice varies, so it should be agreed with the surgical team. One NHS orthopaedic hospital advises about 3 months before journeys over 4 hours after knee replacement.12
Will I need another operation one day?
Most people do not; registry data suggest about 82% of total knees are still in place at 25 years.14
Bottom line
Knee replacement is a well-established operation for painful osteoarthritis, with long-lasting implants for most people. It works on joint wear, not every kind of knee pain, and a meaningful minority still have pain afterwards. Rehabilitation and clot prevention decide much of the outcome, so they need a plan that continues at home.
Related reading
Sources
- NHS. Knee replacement: why it’s done. NHS website; 2024. https://www.nhs.uk/tests-and-treatments/knee-replacement/why-its-done/ Accessed 5 November 2026.
- NHS. Knee pain. NHS website. https://www.nhs.uk/conditions/knee-pain/ Accessed 5 November 2026.
- National Institute for Health and Care Excellence. Osteoarthritis in over 16s: diagnosis and management (NG226). NICE; 2022. https://www.ncbi.nlm.nih.gov/books/NBK588843/ Accessed 5 November 2026.
- National Institute for Health and Care Excellence. Joint replacement (primary): hip, knee and shoulder (NG157). NICE; 2020. https://www.ncbi.nlm.nih.gov/books/NBK561385/ Accessed 5 November 2026.
- NIHR Evidence. Partial knee replacement could be first choice for suitable patients with osteoarthritis (summary of Beard D, et al. Lancet 2019;394:746-56). NIHR; 2019. https://evidence.nihr.ac.uk/alert/partial-knee-replacement-could-be-first-choice-for-suitable-patients-with-osteoarthritis Accessed 5 November 2026.
- NHS. Knee replacement: how it’s done. NHS website. https://www.nhs.uk/tests-and-treatments/knee-replacement/how-its-done/ Accessed 5 November 2026.
- NHS. Knee replacement: recovery. NHS website. https://www.nhs.uk/tests-and-treatments/knee-replacement/recovery/ Accessed 5 November 2026.
- NHS. Knee replacement: complications. NHS website. https://www.nhs.uk/tests-and-treatments/knee-replacement/complications/ Accessed 5 November 2026.
- Beswick AD, Wylde V, Gooberman-Hill R, Blom A, Dieppe P. What proportion of patients report long-term pain after total hip or knee replacement for osteoarthritis? A systematic review of prospective studies in unselected patients. BMJ Open; 2012;2:e000435. doi:10.1136/bmjopen-2011-000435. https://bmjopen.bmj.com/content/2/1/e000435 Accessed 5 November 2026.
- American Academy of Orthopaedic Surgeons. Infection after joint replacement. OrthoInfo. https://www.orthoinfo.org/diseases–conditions/joint-replacement-infection Accessed 5 November 2026.
- NHS. DVT (deep vein thrombosis). NHS website. https://www.nhs.uk/conditions/deep-vein-thrombosis-dvt/ Accessed 5 November 2026.
- The Royal Orthopaedic Hospital NHS Foundation Trust. Travel, surgery and deep vein thrombosis. ROH. https://roh.nhs.uk/services-information/other-info/before-surgery/travel-surgery-and-dvt Accessed 5 November 2026.
- American Association of Hip and Knee Surgeons. What precautions should I take when traveling with my joint replacement? AAHKS. https://hipknee.aahks.org/?p=1155 Accessed 5 November 2026.
- Evans JT, Walker R, Evans JP, Blom AW, Sayers A, Whitehouse MR. How long does a knee replacement last? A systematic review and meta-analysis of case series and national registry reports with more than 15 years of follow-up. Lancet; 2019;393:655-63. doi:10.1016/S0140-6736(18)32531-5. https://research-information.bris.ac.uk/en/publications/how-long-does-a-knee-replacement-last-a-systematic-review-and-met/ Accessed 5 November 2026.
- National Joint Registry. 22nd Annual Report 2025, chapter 3: Outcomes after joint replacement 2003 to 2024. NJR; 2025. https://www.ncbi.nlm.nih.gov/books/NBK618761/ Accessed 5 November 2026.
Article history
- — First published.