title: The mechanism of synovial fluid retention in pressurized joint cavities.
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.
authors.affiliation: Medical Engineering Division, Department of Engineering, Queen Mary, University of London, London, UK.
authors.forename: Y
authors.initials: Y
authors.lastname: Lu
authors.forename: J R
authors.initials: JR
authors.lastname: Levick
authors.forename: W
authors.initials: W
authors.lastname: Wang
mesh_terms: D000818:Animals; D006801:Humans; D006820:Hyaluronic Acid / Q000378:metabolism*; D007596:Joints / Q000502:physiology*; D008960:Models, Psychological; D011312:Pressure; D013582:Synovial Fluid / Q000502:physiology*; D013583:Synovial Membrane / Q000502:physiology*
chemical_list: D006820:Hyaluronic Acid