An unusual case of knee pain: pseudogout and Abiotrophia defectiva infection.

A 90-year-old man was diagnosed with monoarticular arthritis due to pseudogout and Abiotrophia defectiva infection. A. defectiva is recognized as a cause of endocarditis, but is rarely described in septic arthritis. To our knowledge, this is one of the few case reports of septic arthritis due to this organism, and the first in association with pseudogout. This report supports the routine culture of synovial fluid and is further evidence for the role of A. defectiva in septic arthritis.