Pseudoseptic inflammatory knee effusion caused by phagocytosis of sickled erythrocytes after fracture into the knee joint

A 57-year-old black man with sickle cell disease was admitted to the hospital because of a painful crisis. After a fall with a fracture into the right knee joint, he developed an acutely painful, swollen knee. Synovial fluid from the right knee showed leukocyte counts of up to 154,000/mm3 and was negative for urate and calcium pyrophosphate dihydrate crystals. Gram stains and cultures were negative. Some sickled red cells were seen by light microscopy; electron microscopy revealed crystal-like arrays of sickled hemoglobin tactoids in erythrocytes which were enfolded and phagocytized by the cells of the synovial fluid. We suggest that this phagocytosis of sickled red cells is the likely cause for the otherwise unexplained inflammation.