New knowledge of chondrocalcinosis.

There are three varieties of cartilage-hyaline, elastic, and fibrocartilage. Hyaline cartilage is the precursor of bone. In the adult it is mainly found at bone ends, forming the load-bearing surface of synovial joints. Extra-articular fibrocartilages such as those of the trachea and ribs often calcify with advancing age. Articular cartilage, however, usually remains free from mineral deposits. The term 'chondrocalcinosis' may be defined as a pathological state characterised by the precipitation of insoluble calcium salts in articular and periarticular cartilage. The presence of chondrocalcinosis can be proved only by crystallographic examination. Its presence may be inferred by radiological examination or the discovery of crystals in synovial fluid. In addition, articular chondrocalcinosis is sometimes accompanied by arthritis. There are therefore three separate phenomena associated with chondrocalcinosis-radiological changes, crystals in synovial fluid, and arthritis. These may occur separately or in any combination (Fig. 1). The term 'chondrocalcinosis' was often used loosely in reference to radiological signs, the presence of pyrophosphate crystals in joints, or a characteristic form of arthritis. Recent work has highlighted the fact that many different crystals may be precipitated in cartilage and has led to a questioning of the causal relationship between crystals and arthritis. Further work would be aided by the use of a disciplined nomenclature-referring, for example, to articular pyrophosphate chondrocalcinosis-with a descriptive account of the associated features. Calcium salts positively identified in human articular cartilage are: (1) calcium pyrophosphate dihydrate, Ca2P207.2H20 (pyrophosphate, CPPD); (2) hydroxyapatite, Calo(P04)6.(OH)2 (hydroxyapatite, apatite, HA); and (3) dicalcium phosphate dihydrate, CaHP04.2H20 (brushite, calcium phosphate dihydrate, DCPD). Chondrocalcinosis may be classified according to (1) the nature of the deposit (pyrophosphate, hydroxyapatite, Brushite, or mixtures); (2) the type (familial, metabolic, sporadic, age associated); and (3) the metabolic associations: (a) hydroxyapatite (chronic renal disease); (b) pyrophosphate (hyperparathyroidism, haemachromatosis, hypothyroidism, hypophosphataxia, hypomagnesaemia, gout(?), diabetes mellitus (?), Wilson's disease (?), ochronosis (?)).