Knee Replacement Surgery: Procedure, Types, Risks and Recovery
Key takeaways
- A knee replacement resurfaces a worn knee joint with metal and plastic parts, most often to relieve the pain of osteoarthritis.
- It is a successful operation, but with around 80 to 90% satisfied it is honestly lower than hip replacement: about 1 in 5 feel the knee is never quite normal.
- Modern implants typically last 15 to 20+ years, and around 90 to 95% are still in place at 10 years.
- Most people return to normal activities within about 3 months, with full recovery taking 6 to 12 months, sometimes longer.
- Serious complications are uncommon: infection affects about 1 to 2 in 100 people.
By Margaret Doyle | Medically reviewed by Mr Paul Henderson, FRCS (Tr&Orth)
Updated May 11, 2026 · 5 min read
A knee replacement is surgery to resurface a worn knee joint with artificial metal and plastic parts, called a prosthesis or implant. It is most often performed to relieve pain and restore movement when osteoarthritis has worn away the joint. It is a successful operation, but I want to be honest from the first line: with around 80 to 90% of people satisfied, it has lower satisfaction than hip replacement, and about 1 in 5 feel the new knee is never quite “normal”1. Modern implants typically last 15 to 20+ years2.
When I was facing my own knee replacement, the plain-English clinical facts were the part I most wanted, and the honesty about recovery was the part I could not find. So here is both, checked by a consultant orthopaedic surgeon: how the procedure works, the types available, the real risks, the demanding recovery, and what it costs. If you are still deciding, start with the signs you may need a knee replacement.
What is a knee replacement?
A knee replacement resurfaces the worn ends of the bones that meet at the knee, capping them with smooth metal and a plastic spacer so the joint glides again. The knee is where the thigh bone (femur), shin bone (tibia), and kneecap (patella) meet, and in a healthy joint smooth cartilage lets these surfaces move freely. When that cartilage wears away, usually through osteoarthritis, bone rubs on bone, which causes the pain, stiffness, and swelling.
In a total knee replacement (also called total knee arthroplasty), the surgeon resurfaces all three compartments of the knee with metal and plastic components. In a partial (unicompartmental) knee replacement, only the one damaged compartment is resurfaced, keeping the healthy bone and ligaments. We compare these in partial vs total knee replacement.
Who needs a knee replacement?
Surgery is usually considered when knee pain limits everyday activities such as walking, climbing stairs, and sleeping, and when non-surgical treatments no longer help. Common underlying conditions include:
- Osteoarthritis: by far the most common reason, the “wear and tear” that accounts for the large majority of knee replacements.
- Rheumatoid arthritis: an inflammatory joint disease.
- Post-traumatic arthritis: arthritis that follows a serious knee injury or fracture.
I delayed my own surgery for the best part of a decade, partly fear and partly because nobody could tell me plainly when “bad enough” was. We cover symptoms, candidacy, and what to try first in signs you need a knee replacement and alternatives to knee replacement.
Types of knee replacement
There are three main types, matched to how much of the joint is worn:
| Type | What is resurfaced | Typically used for |
|---|---|---|
| Total knee replacement | All three compartments | Most patients with widespread arthritis |
| Partial (unicompartmental) replacement | Only the one damaged compartment | Wear confined to one side, usually the inner |
| Kneecap (patellofemoral) replacement | Only the joint behind the kneecap | A less common option for isolated kneecap wear |
The implant is made of metal (commonly cobalt-chromium and titanium) with a medical-grade polyethylene plastic spacer that the surfaces glide against. Your surgeon chooses the type and whether to fix the implant with bone cement, based on your pattern of wear, age, and bone quality. See types of knee replacement for the options in full.
How is knee replacement surgery performed?
The operation takes about 1 to 2 hours under general or spinal anaesthetic. The surgeon opens the front of the knee, removes the worn cartilage and a few millimetres of bone, then fits and tests the metal and plastic parts for stability and a good range of bend. Most patients stand and take a few steps with a frame, helped by a physiotherapist, the same day or the day after surgery, and stay in hospital 1 to 3 days (some centres do day-case surgery in selected patients)3.
Physiotherapy and daily exercises begin the day of or the day after surgery and continue for months; bending the knee is the key early goal. In my own recovery the bending was the hardest, most important thing I did, and far more uncomfortable than I had been led to expect.
Risks and complications
Knee replacement is generally safe, but no surgery is risk-free. The most relevant complications, with roughly how common they are:
- Infection: about 1 to 2 in 100; uncommon but serious, and sometimes needing further surgery1.
- Blood clots (deep vein thrombosis and pulmonary embolism): risk reduced with blood thinners, compression, and early movement.
- Stiffness that will not improve: occasionally needs a manipulation under anaesthetic (MUA) to free the knee up.
- Ongoing or unexplained pain: about 1 in 5 people have some residual pain or stiffness, and a smaller number have persistent troublesome pain.
- Implant wear or loosening over many years, which may eventually need a revision knee replacement.
For most people with severe arthritis, the pain relief outweighs these risks. But that 1 in 5 figure is real, and I think it deserves to be said plainly rather than buried.
Recovery after knee replacement
Most people return to normal activities within about 3 months, though full recovery, with the swelling settled and strength and confidence back, takes 6 to 12 months, sometimes longer4. You will need walking aids (a frame, then crutches or a stick) for 2 to 6 weeks, and most people resume driving around 6 weeks, once they can control the car safely and are off strong painkillers. Physiotherapy is the single biggest factor in a good outcome. It is normal for the new knee to feel stiff, swollen, and “not yours” for months; that does not mean anything has gone wrong.
How long does a knee replacement last?
A modern knee replacement typically lasts 15 to 20+ years, and registry data shows around 90 to 95% are still in place at 10 years2. Younger, heavier, or more active patients tend to wear implants faster. When an implant does eventually wear out, loosen, or become infected, it can be redone in a revision knee replacement.
How much does a knee replacement cost?
Cost depends on where you live and how care is funded:
- Public health systems (such as the UK’s NHS): free at the point of use. I had mine on the NHS.
- UK private / self-pay: broadly £12,000 to £16,000.
- United States: broadly $30,000 to $50,000 for self-pay, though insured costs and hospital list prices vary widely.
Always confirm what an estimate includes: the surgeon’s fee, the implant, the hospital stay, and follow-up physiotherapy.
Is a knee replacement worth it?
For most people, yes. Around 80 to 90% are satisfied, the great majority get real, lasting relief from arthritis pain, and most say they would do it again1. But satisfaction is honestly lower than for a hip, recovery is harder, and a meaningful minority are left with a knee that works well but never feels completely natural. I am very glad I had mine; I also think you deserve to go in knowing both halves of that truth.
References
- Total Knee Replacement (OrthoInfo), American Academy of Orthopaedic Surgeons. ↩
- How long does a knee replacement last?, National Joint Registry. ↩
- Knee replacement, NHS. ↩
- Knee replacement surgery, Versus Arthritis. ↩
Common questions
How long does a knee replacement last?
Modern knee replacements typically last 15 to 20+ years, and registry data shows around 90 to 95% are still in place at 10 years. Implant survival depends on your age, weight, and activity level. Younger, heavier, or more active patients wear implants faster and are more likely to need a revision.
Is a knee replacement major surgery?
Yes. It is performed under general or spinal anaesthetic and takes about 1 to 2 hours. Most people stay in hospital 1 to 3 days, take their first steps with a frame the same day or the day after surgery, and need walking aids for 2 to 6 weeks.
How painful is a knee replacement?
There is real pain in the first days and weeks, usually controlled with regular medication, and the bending exercises are uncomfortable. The knee stays stiff and swollen for months. Most people find the arthritis pain they had before surgery is gone once they heal, but about 1 in 5 have some residual ache or stiffness.
What is the satisfaction rate for a knee replacement?
Around 80 to 90% of people are satisfied with their knee replacement, which is honestly lower than hip replacement. About 1 in 5 feel the knee is never quite normal: some stiffness, difficulty kneeling, clicking, or a weather-change ache can persist. Most people are still very glad they had it.
What is the best age for a knee replacement?
There is no single best age. It is most common between 60 and 80, but the right time depends on pain, loss of function, and how much the knee limits daily life rather than age alone. Surgeons weigh implant lifespan against quality of life when advising younger patients.
How much does a knee replacement cost?
In a public health system such as the NHS it is free at the point of use. UK private or self-pay is broadly £12,000 to £16,000. In the United States, self-pay is broadly $30,000 to $50,000, though insured costs and hospital list prices vary widely.
Written by Margaret Doyle. Medically reviewed by Mr Paul Henderson, FRCS (Tr&Orth).
Our guides are written from personal experience and reviewed by a qualified clinician for accuracy. Read our editorial policy.