CALCIUM PYROPHOSPHATE DIHYDRATE CRYSTAL DEPOSITION IN SYNOVIUM - RELATIONSHIP TO COLLAGEN-FIBERS AND CHONDROMETAPLASIA

Objective. Reasons for apparent primary deposition of calcium pyrophos phate dihydrate (CPPD) crystals in some synovial membranes have not be en systematically examined. We undertook the present study to investig ate for and compare possible cellular and matrix factors related to th e presence of these crystals in synovium and cartilage. Methods. Ten s ynovial membrane specimens and 6 cartilage specimens were obtained at the time of joint surgery from 10 patients with CPPD crystal depositio n disease, for light microscopic (LM) and electron microscopic (EM) st udies. Results. In all synovial and cartilage specimens, we found many of the small CPPD crystals aligned on or in parallel to collagen fibe rs, as seen by EM. In 9 of the 10 crystal-containing synovia, we found foci of chondrometaplasia adjacent to CPPD, by LM. In 7 of the synovi a, including the one without LM evidence of chondrometaplasia, we obse rved the presence of chondrocyte-like cells by EM. We did not note any predictable relationship between the crystals and matrix vesicles, ei ther in synovium or in cartilage. Conclusion. Our EM findings provide evidence of the relationship of small CPPD-like crystals, presumably e arly forms, to collagen fibers both in synovium and in cartilage. By L M and EM, we also demonstrate evidence of a close association between chondrometaplasia and CPPD deposits in synovium. We suggest that chond rometaplasia might be responsible for synovial CPPD formation in predi sposed patients. Both the collagen fibers and chondrocyte-like cells s eem to be involved in the primary formation of CPPD deposits in the sy novium as well as in the cartilage.