Get help now
- Go to A&E or call 999 if a joint suddenly becomes hot, swollen and very painful, you cannot move it or bear weight, and you have a fever, shivers or feel unwell.
- Go to A&E the same day if you have a joint replacement and it becomes newly painful, red, swollen or starts leaking fluid, or if a joint flares up soon after an injection or operation.
- If you are not sure, call NHS 111 now and describe your symptoms. If you take medicines that affect your immune system, such as methotrexate, biologics or steroids, say so.
- Do not wait for it to settle, and do not treat it with leftover antibiotics at home.
Quick answer: Septic arthritis is an infection inside a joint, usually caused by bacteria. It typically causes one hot, swollen, very painful joint that is hard to move, often with a fever. It is a medical emergency because the infection can damage the joint within days and spread to the blood. Go to A&E or call 999 if you think you might have it.
What is septic arthritis?
Septic arthritis happens when germs, most often bacteria, get into the fluid and lining of a joint. The body reacts with intense inflammation. Pus can build up inside the joint, and the infection can quickly start to damage cartilage and bone. It can also spread into the bloodstream and cause sepsis, which is life-threatening.
Germs can reach a joint through the bloodstream from an infection elsewhere, such as the skin, urine or chest. They can also get in directly, through a wound, an animal bite, a joint injection or an operation. The knee is the joint most often affected, followed by the hip, shoulder, ankle and wrist, but any joint can be involved.
Warning signs
Septic arthritis usually comes on over hours to a couple of days. Typical signs are:
- Severe pain in one joint, often so bad that you cannot bear to move it or have it touched.
- Swelling, warmth and sometimes redness over the joint.
- Being unable to walk or put weight on the leg, if a hip, knee or ankle is affected.
- A high temperature, shivering or feeling generally unwell. Not everyone has a fever, particularly older people and those taking steroids or other medicines that dampen the immune system.
In babies and young children, the signs can be less obvious. A child may refuse to use a limb, cry when a nappy is changed or be very irritable with a temperature. Seek urgent help if you notice this.
Who is most at risk?
Anyone can get septic arthritis, but the risk is higher for people who:
- Already have joint damage, for example from rheumatoid arthritis, osteoarthritis or gout.
- Have an artificial joint, such as a hip or knee replacement.
- Take medicines that lower the immune system, such as steroids, DMARDs or biologics.
- Have diabetes, kidney disease or liver disease.
- Are older, particularly over 80.
- Have recently had a joint injection or joint surgery.
- Have broken or infected skin, such as leg ulcers or cellulitis.
- Inject drugs.
Is it septic arthritis or a flare?
This is a very common worry for people who already live with inflammatory arthritis or gout, because a flare can look similar. Clues that point towards infection are one joint that is much worse than your usual flares, pain that is severe and getting worse quickly, a fever or feeling unwell, and symptoms that do not respond to your usual flare plan. A gout attack and an infection can even happen together.
You cannot reliably tell the difference at home, and doctors often cannot tell without testing fluid from the joint. If one joint is suddenly much worse than usual, especially with a fever, get checked the same day. Our guides to what to do in a flare and gout versus pseudogout explain more about typical flares.
What happens in hospital
Doctors will examine you and ask about recent infections, injuries, injections and your medicines. The most important test is to draw off fluid from the joint with a needle, called joint aspiration. This relieves pressure and lets the lab look for bacteria and crystals. You will also usually have:
- Blood tests, including inflammation markers and blood cultures to check for infection in the bloodstream.
- An X-ray or ultrasound, and sometimes an MRI, to look at the joint.
Where possible, the joint fluid sample is taken before antibiotics start, but if you are very unwell treatment will not be delayed.
Treatment
Septic arthritis is treated with antibiotics, usually given through a drip at first and then as tablets. The course often lasts several weeks. The exact antibiotic depends on the germ found and local hospital guidance.
Most people also need the infected fluid removed from the joint. This may be done by repeated needle drainage or by an operation to wash out the joint, either through keyhole surgery or an open procedure. If an artificial joint is infected, the orthopaedic team may need to carry out more surgery, sometimes in stages, to clear the infection.
If you take medicines that affect your immune system for arthritis, your team will usually advise pausing some of them while the infection is treated. Only change or stop your arthritis medicines on the advice of your own team.
Recovery and getting moving again
Once the infection is under control, gentle movement and physiotherapy help to stop the joint stiffening and rebuild strength. Recovery can take weeks to months. Some people are left with stiffness or later wear and tear in the joint, which is why early treatment is so important. Ask your team for a clear plan covering:
- How long to take antibiotics and when to finish them.
- Which symptoms mean you should come back straight away, such as fever or pain returning.
- When and how to restart any arthritis medicines that were paused.
- A graded exercise programme. Our guide to rebuilding after time off your feet may help.
Lowering your risk
- Look after your skin. Keep cuts clean and covered, and get infected skin or leg ulcers treated promptly.
- Keep diabetes as well controlled as you can.
- Stay up to date with vaccines your team recommends. See our guide to vaccines on DMARDs and biologics.
- If you have a joint replacement, tell dentists and other clinicians, and seek advice promptly for any infection.
- Know the signs of infection that your rheumatology team has asked you to watch for if you take immune-suppressing medicines.
Frequently asked questions
Is septic arthritis an emergency?
Yes. It can damage a joint within days and spread to the blood. Go to A&E or call 999 if you have a hot, swollen, very painful joint, especially with a fever or feeling unwell.
Can you have septic arthritis without a fever?
Yes. Older people and those taking steroids, DMARDs or biologics may not develop a high temperature. A suddenly very painful, swollen joint still needs urgent checking.
How long does it take to recover from septic arthritis?
Antibiotics usually continue for several weeks, and getting full movement and strength back can take weeks to months with physiotherapy. Some people have lasting stiffness.
Can septic arthritis come back?
It can, particularly in a damaged or artificial joint. Finish the full antibiotic course and return promptly if pain, swelling or fever come back.
Should I stop my methotrexate or biologic if I think I have an infection?
Contact your rheumatology team or the doctor treating you for advice. Many teams recommend pausing some medicines during a serious infection, but do not stop or change doses without advice.
Can a steroid injection cause septic arthritis?
It is a rare complication of any joint injection. Seek urgent advice if a joint becomes increasingly hot, swollen and painful in the days after an injection, especially with a fever.
Sources and further reading
This guide is for general education and is not a substitute for personal medical advice. Everyone's situation is different, so always follow the advice of your own GP, pharmacist or rheumatology team. If you feel very unwell, call 999 or go to A&E. For urgent advice, contact NHS 111.