The detection of calcium pyrophosphate crystals in sequential synovial fluid examinations of patients with osteoarthritis: once positive, always positive.

The aim of this study was to investigate whether calcium pyrophosphate dihydrate (CPPD) crystals are constantly detectable in sequential synovial fluid (SF) examinations of patients with initially CPPD-positive osteoarthritis (OA). For this purpose, we searched our SF database for CPPD-positive patients, who had two or more SF analyses between 2008 and 2012 to get sequential information. The database contains SF data determined by a standardised procedure.