Abstract
A 47-year-old patient presented with a chylous knee effusion and traumatic infected skin lacerations. The diagnosis of septic arthritis was considered because of purulent looking joint fluid, spuriously high synovial fluid white cell count, and signs of acute knee synovitis. Synovial fluid lipid analysis showed increased total lipids due to high concentration of neutral lipids, mainly triglycerides, and repeated knee radiographs showed a small fracture of the tibial spine. Joint trauma with subchondral fracture can be associated with frank chylous effusion, which may mimic acute septic arthritis.