Rheology of synovial fluid

Area of Science:

• Rheology
• Biomaterials Science
• Orthopedics

Background:

• Synovial fluid is crucial for joint lubrication and function.
• Understanding the rheological properties of synovial fluid is key to diagnosing joint diseases.

Purpose of the Study:

• To investigate the rheological differences between normal and pathological synovial fluids.
• To elucidate the relationship between synovial fluid rheology and its molecular structure.
• To propose a theory explaining synovial fluid's rheological performance and deterioration.

Main Methods:

• Rheological measurements including shear stress and first normal stress difference as a function of shear gradient.
• Calculation of apparent shear viscosity (eta 1), apparent normal viscosity (psi 7), and apparent shear modulus (G').
• Analysis of zero shear viscosity (eta 0), shear modulus (G'), and characteristic time (theta 1).

Main Results:

• All measured rheological parameters deteriorated in pathological synovial fluids.
• Significant changes were observed in zero shear viscosity (eta 0), shear modulus (G'), and characteristic time (theta 1).
• Hyaluronic acid molecular mass of at least 10(7) g.mol-1 is necessary for optimal synovial fluid function.

Conclusions:

• Pathological changes in synovial fluid lead to a significant deterioration of its lubricating and rheological properties.
• The observed rheological decline is linked to alterations in the solute structure, particularly hyaluronic acid.
• A theoretical framework for understanding normal synovial fluid rheology and its pathological changes has been proposed.