[Lipid microcrystals and other rare crystals in the joints]

Although not strictly of crystalline nature, various formations can be observed in joint fluids and be responsible for "microcrystalline" arthritis. They can consist of lipidic structures (cholesterol crystals, fatty lobules, liposomes) or calcium crystalline structures such as calcium oxalate crystals detected in fluids of dialyzed chronic renal failure patients, reflecting primary or secondary oxalosis. Other phosphate calcium crystals have been identified, associated to apatite or pyrophosphate crystals, but their pathogenic role is uncertain. Charcot-Leyden crystals reflect eosinophilic arthritis. A phylogenic role may be played by corticoid suspension crystal or prosthetic debris. Lastly, some crystals can be artefacts, resulting from sampling conditions and storage of joint fluids.