Septic arthritis of the knee

Abstract

The knee is the commonest joint in the body to be affected by septic arthritis. Septic arthritis of the knee is usually caused by Staphylococcus aureus, but there is a wide spectrum of causative organisms, and Gram-negative organisms are implicated in 10-20 % of cases. The gold standard for diagnosis is joint fluid culture, but microscopy and Gram staining can be negative in up to 50 % of cases, and newer assays such as α-defensin and blood tests such as procalcitonin have potential to improve the diagnostic yield in the acute situation. Septic arthritis is serious with a mortality of over 10 % and permanent joint damage in 40 %. Recognition of symptoms, proper interpretation of investigations and prompt treatment are mandatory to achieve a good outcome.