ABSTRACT
Crystal-associated arthritis usually connotes either monosodium urate mono-
hydrate (MSU) or calcium pyrophosphate dihydrate (CPPD) crystals. These two
crystals are easily detected and identified by polarized light microscopy. Less
common crystals, such as cholesterol and oxalate, may also be visualized by
polarized light microscopy. Basic calcium phosphate (BCP) crystals, on the other
hand, found in up to 60% of cases of knee osteoarthritis, usually can not be
identified by this technique (1). The failure of polarized light microscopy to
detect BCP crystals relates to the very small size of the crystals and the random
orientation of crystals within a crystal mass. In rare cases, BCP crystals may be
visualized with the light microscope as refractile “shiny coins” which represent
laminations of crystals in a globular mass (2). Thus, other means have been
necessary to identify BCP crystals.
