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Evidence of Silicon Dioxide Crystals in Synovial Fluid of Patients with Osteoarthritis

FRANCESCA OLIVIERO, PAOLA FRALLONARDO, LUCA PERUZZO, ROBERTA RAMONDA, PAOLO SFRISO, ANNA SCANU, LEONARDO TAURO, FRÉDÉRIC LIOTÉ, and LEONARDO PUNZI

ABSTRACT.

Objective. Synovial fluid (SF) may contain a number of crystals that optical microscopy is unable to identify with certainty. Scanning electron microscopy (SEM) was utilized in this study to characterize SF crystals in the context of knee osteoarthritis (OA).

Methods. SF was collected from the knees of 25 patients with OA and examined under optical light microscopy. Calcium pyrophosphate dihydrate (CPPD) crystals were assessed by means of compensated polarized light microscopy, while alizarin red S staining was performed to identify apatite (BCP) crystals. All the specimens were also analyzed by SEM and x-ray diffractometry, as gold standards.

Results. CPPD crystals were found in 32% and BCP in 24% of the SF examined by SEM. The degree of concordance between polarized light microscopy and SEM was 0.83 for CPPD and 0.46 for BCP (kappa statistic). The secondary and backscatter electron SEM observations allowed identification of silicon dioxide (SiO₂) crystals in 8 out of 10 patients in whom polarized light microscopy revealed irregular and polymorph crystals.

Conclusion. SiO₂ crystals cannot be readily identified by their morphology or polarization properties under optical microscopy. Their presence, nevertheless, did not lead to misclassification. (J Rheumatol First Release April 15 2008)

Key Indexing Terms:

SYNOVIAL FLUID
OSTEOARTHRITIS
CALCIUM PYROPHOSPHATE
CALCIUM PHOSPHATE
SILICON DIOXIDE

From the Rheumatology Unit, Department of Clinical and Experimental Medicine, University of Padova, Padova, Italy.

F. Oliviero, PhD; P. Frallonardo, MD, Rheumatology Unit, Department of Clinical and Experimental Medicine, University of Padova; L. Peruzzo, PhD, Institute of Geosciences and Georesources, CNR Padova; R. Ramonda, MD, PhD; P. Sfriso, MD, PhD; A. Scanu, PhD, Department of Clinical and Experimental Medicine, University of Padova; L. Tauro, Department of Geosciences, University of Padova; F. Lioté, MD, PhD, Rheumatology Federation, Viggo Petersen Center, INSERM U606, Lariboisière Teaching Hospital, Paris, France; L. Punzi, MD, PhD, Rheumatology Unit, Department of Clinical and Experimental Medicine, University of Padova.

Address reprint requests to F. Oliviero, Rheumatology Unit, Department of Clinical and Experimental Medicine, University of Padova, Via Giustiniani 2, 35128 Padova, Italy. E-mail: francesca.oliviero@unipd.it

Accepted for publication January 4, 2008.