Septic arthritis is inflammation of a joint caused by a bacterial infection. It is also known as infectious or bacterial arthritis.

The condition is most commonly caused by staphylococcal or streptococcal bacteria. These bacteria may have entered a wound and travelled through your bloodstream to the affected joint, or may have infected your joint directly following an injury or during surgery.

Any joint can be affected by septic arthritis – and more than one joint can be affected at a time – but the condition is most common in the knees and hips.

You should see your GP or visit your local accident and emergency (A&E) department as soon as possible if you think you or your child may have septic arthritis.

The sooner the infection is picked up and treated, the better the outlook. If the condition is left untreated, it can become life-threatening and can lead to permanent joint damage.

Signs and symptoms

Septic arthritis typically causes severe pain, swelling, redness and heat in affected joints. These symptoms tend to develop quickly over a few hours or days.

You may also have difficulty moving the affected joint and some people have a high temperature (fever).

Young children with septic arthritis will generally be irritable and may cry whenever the infected joint is moved (for example, during nappy changing). They may also try to avoid using or putting any weight on affected joints.

Who's at risk?

Septic arthritis can be seen at any age, including in babies and infants, although it is less common in older children, teenagers and young adults.

The following factors can increase your risk of septic arthritis:

• having an artificial joint implant, such as a knee replacement or hip replacement
• having a bacterial infection somewhere else in your body
• having a long-term condition such as diabetes or rheumatoid arthritis
• using injected drugs
• taking medication that suppresses your immune system
• recently injuring a joint
• recently having joint surgery or injections into your joints

Diagnosis septic arthritis

If your symptoms suggest septic arthritis, your GP will refer you to your nearest A&E department immediately for an assessment.

You may have a blood test and a sample of fluid removed from your affected joint with a needle to look for signs of inflammation and infection, and to identify any bacteria.

If you have septic arthritis, there may be high numbers of white blood cells (a sign of infection) in your blood and joint fluid. However, in many cases these tests come back normal, so they cannot be relied upon to rule out the infection.

Treating septic arthritis

Septic arthritis is treated with antibiotics. You will normally need to stay in hospital for at least two weeks to have antibiotics given to you intravenously (directly into a vein).

You may need to rest in bed for a few days to take pressure off the affected joint and you will be given medication to relieve the pain.

You might also have the fluid drained from your infected joint using a needle and syringe, or during a procedure called an arthroscopy (where a fine, metal tube is inserted through a small incision near the affected joint). This will normally be done by the orthopaedic surgeon.

After you finish the course of intravenous antibiotics, you'll probably need to take antibiotic tablets at home for at least another four weeks.

You should completely recover after antibiotic treatment, although some people still experience persistent limited movement in the affected joint.