Septic arthritis is inflammation of a joint caused by a bacterial infection. It's also known as infectious or bacterial arthritis.
Septic arthritis 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.
The most common joints to become infected are the knee and hip. In infants under the age of 3, septic arthritis usually affects the hip.
The sooner the infection is picked up and treated, the better the outlook. If septic arthritis is left untreated, it can cause severe illness and can be life-threatening.
Symptoms of bacterial arthritis
Septic arthritis typically causes swelling, redness and heat in the affected joint. These symptoms usually come on over a period of 1 to 2 weeks after the infection.
Newborns and infants with septic arthritis will generally be irritable and may cry whenever the infected joint is moved (for example, during nappy changing).
Who's at risk?
Septic arthritis can be seen at any age, including in babies and infants, although it's uncommon between infancy and adolescence.
The following factors will increase your risk of septic arthritis:
- having an artificial joint implant
- having a bacterial infection somewhere else in your body
- having a long-term illness or disease such as diabetes or rheumatoid arthritis
- injecting drugs
- taking medication that suppresses your immune system
- recently injuring a joint
- recently having joint surgery
How is bacterial arthritis diagnosed?
If septic arthritis is suspected because you have the above symptoms, your doctor may take a blood test and a sample of fluid from your affected joint.
If you have septic arthritis, there would usually be high numbers of white blood cells (a sign of infection) in your blood and fluid. However, in some cases of septic arthritis, these tests come back normal, so they cannot be relied upon to rule out the infection.
How is bacterial arthritis treated?
Septic arthritis is treated with antibiotics such as flucloxacillin. You'll need to stay in hospital for at least 2 weeks to have antibiotics given to you intravenously (injected directly into your vein). After that, you'll need to take antibiotic tablets for at least the following 4 weeks.
Meticillin-resistant staphylococcus aureus (MRSA) infection is a potential problem. If the joint is infected with MRSA, these bacteria will be harder to treat as they are resistant to a number of widely used antibiotics.
You may also need to have fluid drained from your infected joint using a needle and syringe. This will normally be done by an orthopaedic surgeon.
You should completely recover after you've finished your course of antibiotic treatment.