[Suppurative arthritis caused by Gemella morbillorum in a patient with rheumatoid arthritis of the knee].

Rheumatoid arthritis of the knee is a common disease, but suppurative arthritis caused by Gemella morbillorum in the same joint is rare. We report a case of suppurative arthritis caused by Gemella morbillorum in a patient with rheumatoid arthritis. Because the infection symptoms was not typical, the diagnosis was delayed, and the delayed diagnosis and therapy led to a poor outcome of the patient.