Fig. 2

Synovial fluid viscosity and the correlation between viscosity and HA concentration. A Synovial fluid viscosity was measured by multiple particle-tracking microrheology (MPTM) and reported in centipoise (cP; n = 18 healthy, n = 17 OA). Data are displayed as box-and-whisker plots representing the first and third quartiles, median, and range of the viscosity values for healthy and OA samples. B A strong correlation between synovial fluid viscosity and HA concentration measured via a sandwich ELISA was observed in OA joints (R² = 0.9, P < 0.0001, n = 17, equation: y = 1 + 434 × x²), but not in healthy joints (R² = 0.1, P = 0.02, n = 18, equation: y = 1 + 256 × x²). C The synovial fluid viscosity was also found to have higher correlation with HA concentrations determined with competitive HA ELISA in OA joints (R² = 0.8, P < 0.0001, n = 17, equation: y = 1 + 69 × x²) than in healthy joints (R² = 0.2, P = 0.01, n = 18, equation: y = 1 + 93 × x²)