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Updated: Aug 15, 2026

A Friction Testing-Bioreactor Device for Study of Synovial Joint Biomechanics, Mechanobiology, and Physical Regulation
Published on: June 2, 2022
The mechanism of synovial fluid retention in pressurized joint cavities
Y Lu1, J R Levick, W Wang
1Medical Engineering Division, Department of Engineering, Queen Mary, University of London, London, UK.
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.
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