Septic arthritis is an infection in a joint. It is most commonly a bacterial infection. Joints affected are usually leg joints such as hips, knees and ankles.

Septic arthritis is usually caused by bacteria entering the joint through the bloodstream, or following infection of a surrounding bone. Occasionally it can follow a penetrating injury (where skin was broken), but often the cause is unknown. In rare cases septic arthritis can be caused by a fungus.

The infection causes the build-up of pus within the joint, which makes the joint swollen and painful.

Signs and symptoms of septic arthritis

The symptoms of septic arthritis can vary. If your child has septic arthritis, they will usually become unwell rapidly. They may be generally unwell, and have:

• a painful joint – the pain may be present when they move the joint themselves, or if it is moved passively during an examination
• tenderness in the surrounding area 
• a hot, swollen, red joint
• decreased movement and use of joint
• a fever more than 38°C.

In newborns and young babies, the only obvious symptoms of septic arthritis may be irritability or fever. Commonly the hip is affected, and your baby may have swelling in the buttock or thigh, an inability to move the hip (especially during nappy changes) and they may hold their leg in an unusual posture.

Pain and decreased movement in the hip are also signs of another common condition called transient synovitis (also known as irritable hip). See our fact sheet Transient synovitis (irritable hip).

A condition with similar symptoms affecting bones is osteomyelitis. See our fact sheet Osteomyelitis.

When to see a doctor

If you think your child has septic arthritis, you should take your child to the nearest emergency department. The doctor will make a diagnosis by looking at and assessing the joint, and asking questions about your child's symptoms and recent history (e.g. recent injury to the area, if they have had other infections).  Your child will usually also need an X-ray, ultrasound, and some blood tests.

If your child has recently had an injury and they are showing signs of septic arthritis in the injured area, return to your treating hospital.

Treatment for septic arthritis

• Your child may need to be admitted to hospital for treatment, including antibiotics given directly into a vein through a drip (intravenous or IV therapy). In the rare cases where the cause of the infection is a fungus, different medication will be given.
• Pain relief medicine will be given.
• Your child will usually need to have a surgical procedure where the joint is washed out, to clean the infection out of the joint. This is performed under a general anaesthetic (while your child is asleep), and it may need to be done more than once.
• They may need a plaster, traction or splint on the joint to stop it from moving.
• Your child will need regular blood tests to check their progress and recovery from the infection while in hospital. Their temperature will also be checked frequently.

The IV antibiotic treatment will continue until your child shows signs of improvement, through their blood tests and temperature checks. In some cases, long-term IV antibiotics can be given after your child has gone home from hospital, with nurses visiting you at home to help. Your child may need to keep taking oral (by mouth) antibiotic liquid or tablets for another three to six weeks.

Each child recovers at a different speed.  It is difficult to know how long they will need to stay in hospital, but most children will be able to go home once their temperature has been normal for 24 hours.

Care at home

It is very important to make sure your child keeps taking every dose of their oral antibiotics. This will ensure they recover from the infection, and prevent the infection from coming back. Your child must take the entire course of antibiotics.

Keep an eye out for an increase in your child's temperature or any of the other signs and symptoms listed above. If any of these symptoms develop, go to the hospital emergency department or contact your treating doctor.

Follow-up

Your child will have a follow-up appointment after they leave hospital. It is important to keep this appointment, even if your child seems well. Regular follow-up will be arranged to ensure that there has not been any damage to the joint. Blood tests may also be arranged, which should be performed prior to your child's appointment.

Key points to remember

• Septic arthritis is a bacterial infection in a joint, which causes swelling and pain. In rare cases it can be caused by a fungus.
• The symptoms may vary greatly. If your child has a rapid onset of fever, with a reluctance or inability to use a limb, take them to a hospital emergency department.
• Treatment often involves a stay in hospital where intravenous (IV) antibiotics are given.
• Regular blood tests are sometimes needed to monitor your child's progress – even after going home.
• It is essential your child takes the entire course of all antibiotics after going home. This is usually for three to six weeks.

For more information

• Kids Health Info fact sheet: Plaster cast care
• Kids Health Info fact sheet: Wound care
• Kids health Info fact sheet: Transient synovitis (irritable hip).
• Kids Health Info fact sheet: Osteomyelitis

Developed by The Royal Children's Hospital Orthopaedic department. We acknowledge the input of RCH consumers and carers.

Reviewed June 2018.

This information is awaiting routine review. Please always seek the most recent advice from a registered and practising clinician.

Kids Health Info is supported by The Royal Children’s Hospital Foundation. To donate, visit  www.rchfoundation.org.au.