Differences in the osteoarthritic synovial fluid composition and rheology between patients with or without flare: a pilot study.

OBJECTIVES

To study the influence of the inflammatory status (flare or not) on hyaluronic acid (HA) and protein composition and on the intrinsic viscosity of the synoviol fluid (SF) from patients with knee osteoarthritis (KOA).

METHODS

Patients with KOA were classified as having flare (F+) when they fulfilled the 4 following clinical criteria: 1) sudden aggravation of knee pain, 2) whose beginning was identifiable, 3) causing nocturnal awakenings 4) with clinical evidence of knee effusion. Patients were classified F- (no flare) if they do not fulfill any of the 3 first criteria. Forty-four SF were obtained by arthrocentesis and assayed using steric exclusion chromatography, which allows HA to be separated from the proteins and to determine both molecular weight (Mw) and concentration (C) of both HA and proteins. SF rheology was determined using a rheometer at 25°C using a cone and plate geometry. Steady-state viscosity was determined in Pa.s, as a function of the shear rate at 1s-1. Correlations between ( Pa.s) and HA and Pr (Mw, C and Mw x C) were calculated.

RESULTS

Among the 44 assayed SF, 25 were classified F- and 19 F+. There were statistically significant differences between F- and F+ for most of the studied variables: HA concentration and Mw (p=0.01 and 0.001 respectively), protein concentration and Mw (p=0.02 and 0.001 respectively), product Mw x C of the proteins (p<0.0001) and viscosity ή (p=0.0005). The product [(Mw xC) HA x (MwxC) proteins] was highly discriminating between F+ and F- (p<0.0001). The steady state viscosity was highly related to HA concentration (p= 0.0002) and HA Mw (p=0.01) and was negatively correlated with (Mw x C) proteins (p=0.0005), protein concentration (p=0.0007) and protein Mw (p=0.03).

CONCLUSIONS

This pilot study shows significant differences of SF composition in patients having a flare-up compared to that of patients who do not have flare. These differences relate to both protein and HA composition and suggest that SF analysis makes possible to distinguish patients with and without flare-up.