What would you do? Case challenges in knee surgery: Four knee arthroplasties presenting with effusions

Four total knee arthroplasty patients present with effusions from excess synovial fluid, pus, or blood. “Which fluid” and “why” are the important questions. Recent Guidelines for Diagnosis of Periprosthetic Infection from the American Academy of Orthopedic Surgeons provide a useful diagnostic algorithm. Leukocyte counts and differential, plus culture, are emphasized. Suspected inflammatory arthropathy led to an “anchoring bias” in the first case. Unsuspected bone loss posed a challenge in our second case, and the final cases suffered effusions from instability, often a difficult diagnosis to establish.