Basic calcium phosphate and pyrophosphate crystals in early and late osteoarthritis: relationship with clinical indices and inflammation.

The current study aimed to investigate the association of calcium pyrophosphate (CPP) and basic calcium phosphate (BCP) crystals in synovial fluid (SF) of patients with osteoarthritis (OA) with disease severity, clinical symptoms, and synovial inflammation. One-hundred-and-ten patients with knee OA completed the Western Ontario and McMaster Universities Arthritis Index (WOMAC) self-assessment questionnaire, the Lequesne algofunctional index survey, and the visual analogic scale forms; they also underwent power Doppler ultrasonography (PDUS) to assess synovial inflammation. Scanning electron microscopy (SEM) was used to detect SF crystals. SEM analyses uncovered CPP crystals in 26 patients (23.6%), BCP crystals in 24 patients (21.8%), and both types of crystals in 7 patients (6.3%). Categorizing patients according to SF crystal type, a strong association between BCP crystal presence, and higher WOMAC and Lequesne index scores has been uncovered. Classifying our patients according the severity Kellgre-Lawrence score, we found that the prevalence of CPP alone (27.8%) or in combination with BCP (11.1%) was higher in the late stage group with respect to the early one (CPP 21.6% and CPP + BCP 4.1%, respectively). The prevalence of BCP crystals alone was, instead, higher in the early (23%) with respect to the late group (19.4%). No association between the presence of crystals and the radiographic scores has been observed. Considering the growing evidence supporting a role of low-grade inflammation in OA pathogenesis, the results of this study suggest a role for calcium crystals in the development of the disease.

Detection of Calcium Crystals in Knee Osteoarthritis Synovial Fluid: A Comparison Between Polarized Light and Scanning Electron Microscopy.

BACKGROUND: The identification of calcium crystals in synovial fluid (SF) of patients with osteoarthritis (OA) represents an important step in understanding the role of these crystals in synovial inflammation and disease progression. OBJECTIVES: This study aimed to investigate the presence of calcium pyrophosphate (CPP) and basic calcium phosphate (BCP) crystals in SF collected from patients with symptomatic knee OA by scanning electron microscopy (SEM) coupled to x-ray energy dispersive spectroscopy, compensated polarized light microscopy (CPLM), and alizarin red staining. METHODS: Seventy-four patients with knee OA were included in the study. Synovial fluid samples were collected after arthrocentesis and examined under CPLM for the assessment of CPP crystals. Basic calcium phosphate crystals were evaluated by alizarin red staining. All the samples were examined by SEM. The concordance between the 2 techniques was evaluated by Cohen κ agreement coefficient. RESULTS: Calcium pyrophosphate and BCP crystals were found, respectively, in 23 (31.1%) and 13 (17.5%) of 74 OA SFs by SEM analysis. Calcium pyrophosphate crystals were identified in 23 (31.1%) of 74 samples by CPLM, whereas BCP crystals were suspected in 27 (36.4%) of 74 samples. According to κ coefficient, the concordance between CPLM and SEM was 0.83 for CPP, and that between alizarin red and SEM was 0.68 for BCP. CONCLUSIONS: The results of our study showed a high level of concordance between the 2 microscope techniques as regards CPP crystal identification and a lower agreement for BCP crystals. Although this finding highlights the difficulty in identifying BCP crystals by alizarin red staining, the use of SEM remains unsuitable to apply in the clinical setting. Because of the in vitro inflammatory effect of BCP crystals, further work on their analysis in SF could provide important information about the OA process.

Evidence of silicon dioxide crystals in synovial fluid of patients with osteoarthritis.

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.