Supravital staining of synovial fluid with Testsimplets

Inflammatory and Noninflammatory Synovial Fluids Exhibit New and Distinct Tribological Endotypes

Inferior synovial lubrication is a hallmark of osteoarthritis (OA), and synovial fluid (SF) lubrication and composition are variable among OA patients. Hyaluronic acid (HA) viscosupplementation is a widely used therapy for improving SF viscoelasticity and lubrication, but it is unclear how the effectiveness of HA viscosupplements varies with arthritic endotype. The objective of this study was to investigate the effects of the HA viscosupplement, Hymovis®, on the lubricating properties of diseased SF from patients with noninflammatory OA and inflammatory arthritis (IA). The composition (cytokine, HA, and lubricin concentrations) of the SF was measured as well as the mechanical properties (rheology, tribology) of the SF alone and in a 1:1 mixture with the HA viscosupplement. Using rotational rheometry, no difference in SF viscosity was detected between disease types, and the addition of HA significantly increased all fluids' viscosities. In noninflammatory OA SF, friction coefficients followed a typical Stribeck pattern, and their magnitude was decreased by the addition of HA. While some of the IA SF also showed typical Stribeck behavior, a subset showed more erratic behavior with highly variable and larger friction coefficients. Interestingly, this aberrant behavior was not eliminated by the addition of HA, and it was associated with low concentrations of lubricin. Aberrant SF exhibited significantly lower effective viscosities compared to noninflammatory OA and IA SF with typical tribological behavior. Collectively, these results suggest that different endotypes of arthritis exist with respect to lubrication, which may impact the effectiveness of HA viscosupplements in reducing friction.

Intracellular and extracellular CPPD crystals are a regular feature in synovial fluid from uninflamed joints of patients with CPPD related arthropathy

OBJECTIVES

To determine whether calcium pyrophosphate dihydrate (CPPD) crystals can be found in the synovial fluid of non-inflamed joints in patients with CPPD related arthropathy; if so, to determine whether they interact with cells and produce subclinical inflammation in this setting.

METHODS

74 synovial fluid samples were obtained from non-inflamed knees of 74 patients with CPPD related arthropathy. Identification of CPPD crystals and synovial fluid cell counts were done manually in undiluted samples using a haematocytometric chamber. A supravital stain (Testsimplets, Boehringer Mannheim) was used to carry out differential counts and to assess the presence of intracellular crystals.

RESULTS

All 74 samples contained CPPD crystals. The mean cell count was 301.4 cells/microl (95% confidence interval (CI), 216.6 to 386.4; range 22 to 2302.5). Mononuclear cells accounted for 83.2% (95% CI, 80.4% to 86.1%; range 43% to 99%), the rest being polymorphonuclear (PMN) cells (16.8% (95% CI, 13.9% to 19.6%; range 1% to 57%)). All the samples contained intracellular CPPD crystals, which were found in 24.0% of all the cells (95% CI, 20.1% to 27.9%; range 1% to 78%). Most of the intracellular crystals were inside mononuclear cells (22.2% of all the cells (95% CI, CI 18.5% to 25.9%)), although some PMN also contained them (1.8% of all the cells (95% CI, 1.1% to 2.4%)).

CONCLUSIONS

CPPD crystals are normally found in synovial fluid of non-inflamed joints of patients with CPPD related arthropathy, and they interact with cells. The raised cell counts and percentage of PMN suggest mild subclinical inflammation in these joints.

Processing of noninflammatory synovial fluids with hyaluronidase for cytospin preparations improves the accuracy of differential counts

Differential leukocyte counts on noninflammatory synovial fluids (NISF) are not widely reported or used in research, apparently due to technical difficulties related to either high viscosity or low numbers of cells. We describe an evaluation of a technique using hyaluronidase and cytospin preparations to study NISF. Twenty-three consecutive synovial fluids (SF) with less than 2,000 white blood cells (WBC)/mm3 were studied either by the usual smear of a single drop or by adding two drops of hyaluronidase (150 USP units/ml) to 0.25 cc of SF and cytocentrifuging at 800 rpm for 10 min. Both preparations were stained with Wright's stain. Cytospin preparations gave better morphology, and in 22/23 specimens we could count 100 cells on one slide. Smeared preparations gave dark cells and required 2-3 slides to count 100 cells. Differential counts on the cytospin preparations consistently showed higher percentages of monocytes, suggesting that these cells were underdetected and misinterpreted as lymphocytes on the routine smears. Polymorphonuclear leukocytes (PMN) were significantly less frequent (P 0.005) in osteoarthritis (OA) fluids than in the other diseases with NISF. Relatively more PMN may suggest consideration of a diagnosis other than OA. Cytospin preparations of hyaluronidase-treated NISF may open up an important area for investigation of the role of SF cells in less inflammatory diseases.