Abstract
Objective: Hyaluronan (HA) in synovial fluid is vital to fluid retention in joint cavities. This study aims to evaluate a HA concentration polarization hypothesis and to examine, quantitatively, the agreement between theoretical predictions and experimental results.
Methods: A non-steady-state model was developed for HA ultrafiltration and concentration polarization on the synovial surface. The Kedem-Katchalsky equation was used to calculate the trans-synovial filtration rate Q as the HA concentration polarization layer built up. Model parameters were based on data from experiments. Effects of parameters on fluid filtration were investigated.
Results: The HA osmotic pressure at the synovial surface was found to approach the intra-articular pressure, P, during fluid infusion. The model simulated the experimentally observed decay in Q with the time at constant P, and predicted nonlinear P-Q relations in good agreement with experimental results over a range of bulk HA concentrations, from pathological (0.2 g L− 1) to physiological (4.0 g L−1). It gave quantitative insights into the development of the osmotic pressure and the significance of the HA reflection coefficient.
Conclusions: The osmotic pressure of a HA concentration polarization layer on the synovial surface leads to outflow buffering. This provides the mechanism by which the vital lubricating synovial fluid is retained in a joint cavity under pressure.
The study was supported in part by the Wellcome Trust (056983/Z/99).