Pseudoseptic arthritis due to acute lipoarthrosis in a systemic lupus erythematosus patient with osteonecrosis.

Introduction Acute unexplained monarthritis from which purulent-appearing but sterile synovial fluid is obtained has been dubbed pseudoseptic arthritis (1). A number of entities have been described that can present in this manner. Empirical therapy for septic arthritis is still indicated in these presentations, but can be discontinued when an alternative explanation for the acute condition is identified. We encountered a patient with acute knee monarthritis from which we obtained seemingly purulent synovial fluid, but in whom we ultimately demonstrated a process illustrating an unusual mechanism by which such a presentation might develop.