What causes reactive arthritis?
Unlike septic arthritis, reactive arthritis isn’t caused by an active infection within your joints. With reactive arthritis the inflammation in your joints is a reaction to an infection elsewhere in your body. Reactive arthritis is diagnosed if you suddenly develop arthritis, especially in your knees or ankles, just after suffering an infection. Sometimes the infection may have been so mild that you didn't notice it.
Reactive arthritis most commonly develops after infections of the bowel or genital tract.
It's not known exactly why this happens. One theory is that once your immune system has dealt with the original infection, fragments of bacteria may be carried through your bloodstream and deposited in the lining of your joints. This could trigger an inflammatory reaction.
Chlamydia, the most common sexually transmitted infection (STI) in the UK, can trigger bouts of reactive arthritis. It often doesn’t have any symptoms (especially in women), but it may cause pain on passing urine or discharge from your vagina or penis. If you experience these symptoms, or have had unprotected sex and are worried, see your GP or visit a sexual health clinic.