An acutely painful hot swollen knee

A woman in her 90s presented to the emergency department with shortness of breath, fever, and pulmonary oedema, and was admitted for treatment of community acquired pneumonia and heart failure syndrome with doxycycline, furosemide, and oxygen. She had a medical history of respiratory infections, knee osteoarthritis, and gout (for which she was taking allopurinol). She had no joint replacements.

Two days later, her temperature spiked at 38.3°C on the ward. Examination revealed an acutely warm, tender, and swollen left knee with moderately limited flexion and extension and an effusion. No trauma had occurred on the ward. She was otherwise systemically well. Blood tests showed raised inflammatory markers compared with admission (table 1), but normal renal and liver function, and no derangement of electrolytes. Table 1 also shows the results of the microbiological investigation of the 25 mL of yellow, viscous fluid removed by diagnostic joint aspiration and blood culture.

A …