Background/Purpose

The presence of calcium crystals (CC) in synovial fluid (SF) of osteoarthritis (OA) is a well known and frequent feature (1). However, their role in the pathogenesis of OA is still unclear and matter of discussion, in particular as regard the local inflammation (2). The objective of the study was to evaluate the presence of the most common CC, calcium pyrophosphate (dehydrate) (CPP) and basic calcium phosphate (BCP), in SF of the symptomatic knee OA (KOA, particularly in early disease stage (<1year) and to investigate their association with local infiammation, disease activityand severity.We performed an ultrasensitive analysis of SF crystals using the scanning electron microscopy (SEM) and the routinary method by compensated polarized ligth microscopy (CPLM) and alizarin red staining.

Methods

Seventy-four (48 F, mean age 64.85±9.33 yrs, range 50-89 yrs) consecutive outpatients attending theRheumatology Unit, University of Padova with symptomatic KOA (according to the American College of Rheumatology criteria) underwent knee arthrocentesis. After optical and CPLM,  the SF was analysed by SEM. Total white blood cell (WBC) count was performed and a cut-off of total WBC was established in < 1000/mm³. Patients’ medical history, clinical features (WOMAC, Lequense and VAS) X-ray findings (Kellgren & Lawrence), ultrasound and power Doppler (PD) signal values were also assessed. 

Results

CPP crystals were identified in 32.4% by CPLM and in 31.1% by SEM. Alizarin  was positive in 36.5% of the samples. BCP were found in 13.5% by SEM. CPP and BCP crystals were simultaneously positive in 8.1% of the samples by SEM.

The study population was divided into three groups depending on disease duration (group A <1 yr; group B 1-5 yrs; group C > 5 yrs). The SF volume (p=0.0008) was significantly different in the group A with respect to B and C groups. The SF WBC was higher during the early stages of disease (group A), although not significant, with respect to B and C groups. Moreover,  the presence of CC  in group A correlated significantly with SF WBC (p=0.048) and % of PMN (p=0.033) with respect to those without CC in the same group.

PD resulted positive in 43.24% of all the patients, 62.5% of these were CC+  according to SEM (p<0.0001).

Conclusion

The presence of CC in SF,  also when detected in early OA stages,  was associated with a higher degree of local inflammation, so suggesting that they may  play a role of in eliciting an inflammatory reaction, which may be crucial in OA pathogenesis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/relationships-between-inflammation-disease-severity-and-synovial-fluid-calcium-crystals-detected-by-scanning-electronic-microscopy-in-early-osteoarthritis/