To practice a history and physical exam for acute mono-arthritis, with focus on knee joint examination. To review can’t miss diagnoses for acute inflammatory monoarthritis. To review NEJM Clinical Video on Knee Arthrocentesis: https://www.nejm.org/doi/full/10.1056/NEJMvcm051914. To practice using likelihood ratios from the JAMA Rational Clinical Exam Article Does This Adult Patient Have Septic Arthritis to formulate a post-test probability of septic arthritis in this case. To discuss initial next steps in management including investigations in workup for acute inflammatory monoarthritis, and empiric antibiotics for septic arthritis