Synovial Fluid Analysis to Identify Osteoarthritis

Synovial fluid analysis under transmitted, polarized, and compensated light microscopy is used to evaluate the inflammatory or non-inflammatory nature of a sample through simple steps. It is particularly useful in osteoarthritis to detect calcium crystals and identify a more severe subset of osteoarthritis.

Synovial fluid (SF) analysis is important in diagnosing osteoarthritis (OA). Macroscopic and microscopic features, including total and differential white blood cell (WBC) count, help define the non-inflammatory nature of SF, which is a hallmark of OA. In patients with OA, WBC in SF samples usually does not exceed 2000 cells per microliter, and the percentage of inflammatory cells, such as neutrophils, is very low or absent. Calcium crystals are frequent in SF collected from OA patients. Although their role in the pathogenesis of OA remains unclear, they have been associated with a mild inflammatory process and a more severe disease progression. Recently, calcium crystals have been described in both the early and late stages of OA, indicating that they may play a vital role in diagnosing different clinical subsets of OA and pharmacological treatment. The overall goal of SF analysis in OA is two-fold: to ascertain the non-inflammatory degree of SF and to highlight the presence of calcium crystals.

Osteoarthritis (OA) is a complex and multifactorial chronic joint disease, with an estimated pooled global prevalence of 16% in subjects aged 15 and over, and 23% in subjects aged 40 and over¹. The incidence of OA is expected to increase due to an aging population and an increase in risk factors, such as obesity and metabolic syndrome².

Among the major issues associated with OA are the difficulty in diagnosing the disease in its early stages and currently available treatments limited to pain management and symptomatic slow-acting drugs (SYSADOAs) such as glycosaminoglycans. The diagnosis of OA....

The present protocol complies with the guidelines of the Ethics committee of Padova University Hospital. SF was collected with patient consent from the knee joints of patients receiving therapeutic arthrocentesis for joint effusion at their initial presentation to the clinic or in response to an arthritic flare. Contraindications to the procedure were: coagulopathy, anticoagulant medications, skin lesions, dermatitis, or cellulitis overlying the joint. All SF samples were deidentified.

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Large joints affected by OA are often swollen and produce significant amounts of SF, which are drained via arthrocentesis¹⁵. The macroscopic characteristics of SF evaluated immediately after arthrocentesis essentially include the quantity, color, clarity, and viscosity¹⁷. Despite their low specificity, they provide preliminary data on the degree of inflammation. The color depends on SF cellularity and the degree of fragmentation of extracellular matrix macromolecul.......

In OA, SF analysis helps define disease characteristics through simple steps: total and differential leukocyte counts and searching for crystals, including CPP and BCP. Furthermore, the detection of MSU crystals may highlight important comorbidities.

Despite low costs and simple execution, the sensibility of the tests and reliability of the results may be affected due to inexperienced analysts-mainly as it pertains to crystal identification. Training and experience of the analyst are crucial i.......

The Authors wish to acknowledge Professor Leonardo Punzi for his precious mentorship in the field of synovial fluid analysis and Padova University Hospital for its support.