Knee Replacement Risks and Complications, and How Common They Are
Key takeaways
- Knee replacement is generally safe, but no operation is risk-free, so it helps to know the real rates.
- Infection affects about 1 to 2 in 100 people and is a serious complication that can need further surgery.
- Blood clots are a recognised risk, reduced with blood thinners, compression stockings, and early movement.
- About 1 in 5 people have some ongoing pain or stiffness, and a smaller number have persistent troublesome pain.
- Stiffness that will not bend far enough may need a manipulation under anaesthetic, a recognised early complication.
By Margaret Doyle | Medically reviewed by Mr Paul Henderson, FRCS (Tr&Orth)
Published May 8, 2026 · 3 min read
Knee replacement is generally a safe operation, but no surgery is risk-free: the most relevant complications are infection (about 1 to 2 in 100), blood clots, stiffness, and ongoing pain (about 1 in 5). Serious complications are uncommon, and hospitals take specific steps to prevent each one. Knowing the real rates, rather than vague reassurance, is how you weigh up the operation properly1.
When I was consenting to surgery, a long list of risks was read out fast and it frightened me more than it informed me. What I needed was the honest likelihood of each. So here it is, checked by a consultant orthopaedic surgeon, with the numbers attached. For the operation in full, see knee replacement surgery.
How risky is a knee replacement overall?
A knee replacement is generally safe and routine, performed in huge numbers every year, with most people recovering well. National guidance such as NICE NG226 supports it as an effective treatment for severe osteoarthritis when other measures no longer help2. But it is major surgery, so the sensible question is not “is it risky?” but “how likely is each specific problem?” The rest of this article answers that, complication by complication.
Infection
Infection affects about 1 to 2 in 100 people having a knee replacement. It is uncommon but serious, because a deep infection around the implant can need further surgery and a prolonged course of antibiotics1. Hospitals lower the risk with sterile theatre technique, antibiotics given around the time of surgery, and careful wound care afterwards. Tell your team promptly about a fever or a wound that becomes hot, red, swollen, or leaks.
Blood clots (DVT and PE)
Blood clots are a recognised risk after any major lower-limb surgery. A clot in the leg is a deep vein thrombosis (DVT); one that travels to the lungs is a pulmonary embolism (PE), and together these are called VTE. The risk is reduced with blood thinners, compression, and early movement, often getting you up the same day3. Report new calf pain or swelling, or any breathlessness, straight away.
Stiffness and manipulation under anaesthetic
Stiffness is one of the defining challenges of a knee, far more than a hip. If the knee will not bend far enough in the early weeks despite physiotherapy, the surgeon may perform a manipulation under anaesthetic (MUA), moving the joint through a fuller range while you are asleep. It is a recognised early complication and treatment, and it is exactly why bending the knee is the key early goal from the day of or day after surgery. The bending exercises were the hardest part of my recovery, and dreading an MUA was what made me keep doing them. See regaining knee bend and avoiding stiffness.
Ongoing or unexplained pain
About 1 in 5 people have some ongoing pain or stiffness after a knee replacement, and a smaller number have persistent troublesome pain that needs investigation1. Some ache for months as the knee heals is normal and not a complication. Lasting pain can come from stiffness, ongoing swelling, or, less often, infection or a problem with the implant. This honest reality is covered fully in knee replacement success rates.
Less common complications
Some complications are genuinely uncommon:
- Nerve or blood-vessel injury: uncommon, and most nerve issues settle.
- Fracture of bone around the implant: uncommon.
- Wound-healing problems: more likely with smoking, diabetes, or extra weight.
- Implant wear or loosening over many years, which may eventually need a revision; remember around 90 to 95% of implants are still in place at 10 years4.
How to reduce your risk
You have real influence over the odds. Reaching a healthy weight, stopping smoking, controlling diabetes, doing your prehab, taking your blood thinners, and following wound-care advice all lower your risk. Reporting warning signs early lets problems be treated before they grow. Good preparation does a lot of this work, which is why we cover it in preparing for knee replacement surgery.
References
- Total Knee Replacement (OrthoInfo), American Academy of Orthopaedic Surgeons. ↩
- Osteoarthritis in over 16s: diagnosis and management (NG226), NICE. ↩
- Knee replacement, NHS. ↩
- How long does a knee replacement last?, National Joint Registry. ↩
Common questions
What are the risks of a knee replacement?
The main risks are infection (about 1 to 2 in 100), blood clots, stiffness that may need a manipulation under anaesthetic, ongoing pain or stiffness (about 1 in 5), and, uncommonly, nerve or blood-vessel injury or fracture. The implant can also wear or loosen over many years. Serious complications are uncommon, and steps are taken to prevent them.
How common is infection after a knee replacement?
Infection affects about 1 to 2 in 100 people having a knee replacement. It is uncommon but serious, because a deep infection around the implant can need further surgery and a long course of antibiotics. Hospitals reduce the risk with sterile technique, antibiotics around the time of surgery, and careful wound care.
How likely are blood clots after knee surgery?
Blood clots in the leg (deep vein thrombosis) or lungs (pulmonary embolism) are a recognised risk after knee replacement. The risk is reduced with blood thinners, compression stockings, and getting you moving early, often the same day. Tell your team straight away about new calf pain, swelling, or breathlessness.
Why does my knee still hurt after a replacement?
Some ache and stiffness is normal for months as the knee heals, and about 1 in 5 people have some ongoing pain or stiffness longer term. A smaller number have persistent troublesome pain that needs investigation. Causes can include stiffness, ongoing swelling, or, less often, infection or a problem with the implant.
What is a manipulation under anaesthetic?
If the knee will not bend far enough in the early weeks despite physiotherapy, the surgeon may move it through a fuller range while you are asleep, called a manipulation under anaesthetic (MUA). It is a recognised early complication and treatment for stiffness, and it is why the bending exercises matter so much from day one.
How can I reduce my risk of complications?
Reaching a healthy weight, stopping smoking, controlling conditions such as diabetes, doing your prehab and post-op exercises, taking your blood thinners, and following wound-care advice all lower your risk. Reporting warning signs early, such as fever, a hot red wound, or calf swelling, lets problems be treated quickly.
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.