Chylous joint effusion is a rare condition in which synovial fluids containing large amounts of lipids take on a milky appearance as a result. We report on a 19-year-old male patient with posttraumatic chylous knee effusion. Several days after striking his knee against the ground because of a traffic accident, his left knee showed obvious swelling. Aspiration of his knee was performed, yielding 70ml of purulent-appearing fluid. To distinguish this condition from purulent or tuberculosis arthritis, arthroscopic biopsy and debridement were performed. Arthroscopic examination visualized distinctive yellow-white soft lesions covering much of the joint capsule, resembling a cobweb. Tissue cultures for bacteria were negative. Pathologically, we identified clusters of xanthoma cells with fibrin exudation due to disruption of the synovium and intra-articular fat pad necrosis. Centrifuging the aspiration fluid yielded a thick creamy lipid layer as the supernatant. A fresh drop preparation showed that the specimen contained innumerable fat globules, which stained red with oil red O stain. The patient was able to walk without difficulty or further swelling of his knee at the end of the second postoperative week. Posttraumatic chylous effusion is self-limited. Purulent arthritis or tuberculosis arthritis, however, should still be the presumptive diagnosis in such cases. Arthroscopic irrigation and debridement should be considered for these traumatic cases to confirm diagnosis and to speed up recovery.
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