[Apatite rheumatism].

Acute periarthritis is a typical example of apatite arthropathy related to intratendinous calcifications. The attack may be followed by virtually complete radiological disappearance of the calcification. Within the joint one may exceptionally demonstrate the presence of hydroxyapatite crystals in the synovial fluid during a fluxional flare-up of arthrosis or in the fluid withdrawn from the humeral joint following rupture of calcification in the glenohumeral cavity. More frequently, the crystals are detected in the synovial fluid from joints damaged by advanced destructive arthrosis. These crystals are sometimes associated with calcium pyrophosphate crystals (mixed pyrophosphatic and apatitic arthropathy).