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.