Septic Arthritis
Bacteria in the joint space trigger a neutrophil response whose enzymes digest articular cartilage within days, so the inflammation destroys the joint faster than the organism does.
Definition
Septic arthritis is infection within a native or prosthetic joint space, almost always bacterial. No single test confirms it. The diagnosis rests on a short history of a hot, swollen, painful joint with restricted movement, turbid synovial fluid, and an organism grown from joint fluid or blood. It is treated before it is confirmed.
First principles
A short history of a hot, swollen joint is septic arthritis until proven otherwise
The standing UK guideline sets a deliberately low threshold: a short history of a hot, swollen, tender joint with restricted movement is septic arthritis until proven otherwise. If clinical suspicion is high, treat for it even in the absence of fever. The reason is the cost of being wrong. Case fatality is about 11%, and up to a third of survivors keep permanent joint damage. Normal inflammatory markers do not change that.
This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.