Apatite deposition disease. A new arthropathy.

A method for identifying particles of crystalline calcium hydroxyapatite in synovial fluids and biopsy material has been developed with high-resolution scanning electron microscopy and an energy-dispersive micro-analytical system. Particles of hydroxyapatite were identified in the joints of six patients diagnosed as having osteoarthritis, three of whom had acute inflammatory episodes with effusions into the joints. Apatite was not identified in joints affected by rheumatoid arthritis and other types of arthropathy. Animal studies showed that hydroxyapatic crystals can cause an acute inflammatory reaction, and this has been confirmed by experimental studies in man. It is suggested that a third type of crystal-deposition disease should be recognised--namely, calcium-hydroxyapatite crystal-deposition disease.