A 35-year-old man with a hot swollen knee where septic arthritis is suspected.
A This is a medical emergency and urgent Gram staining and culture are indicated. Staphylococcus aureus is the most common infecting pathogen in septic arthritis. Intravenous benzylpenicillin plus flucloxacillin is the preferred treatment until sensitivities are known. Remember the possibility of opportunistic infection if the patient is immunocompromised, e.g. HIV positive.