Septic arthritis due to Actinomyces naeslundii: report of a case.

In a man with osteoarthritis of the knee, Actinomyces naeslundii septic arthritis developed after intra-articular injection of hyaluronate. Actinomyces is an anaerobic Gram-positive rod. The outcome was favorable after treatment with two antibiotics and arthroscopy. The nature of the organism and its location to a joint are unusual features of this case, which illustrates the need to search for a septic complication before accepting a diagnosis of inflammation related to hyaluronate injection.