Chalky joint effusion. The result of massive synovial deposition of calcium apatite in progressive systemic sclerosis.

A patient with long-standing progressive systemic sclerosis developed calcification of the suprapatellar pouch. Chalky white synovial fluid from the knee joint contained many crystals that were characterized as apatite by X-ray diffraction. In this case massive amounts of cystals were presumably shed into the fluid from the heavily calcified synovium.