This week we discuss a common E.D presentation- acute monoarthritis! First: rule out septic arthritis. Then: consider other diagnoses such as gout, seronegative arthritis and hemarthrosis. We go through the pathophysiology, diagnostic techniques and management of these common conditions. Written by: Dr. Teresa Semalulu (Internal Medicine Resident) and Dr. Deborah Koh (Internal Medicine Resident) Reviewed by: Dr. John Neary (General Internist), Dr. Mark Matsos (Rheumatology)Infographic by: Rachel Ahle (Physician Assistant Student)