Acute pseudoseptic arthritis after intraarticular sodium hyaluronan.

A 70-year-old woman with a history of knee osteoarthritis was admitted for acute arthritis 9 days after a second intraarticular injection of sodium hyaluronan (Ostenil). The joint fluid was purulent, with no crystals, and laboratory tests showed marked inflammation, leading to antibiotic treatment for suspected septic arthritis. Incapacitating symptoms persisted, prompting surgical lavage of the knee, which failed to relieve the severe pain.