Molecular mechanisms of synovial joint lubrication

Cartilage is softer and much rougher than mica, though at these high pressures it may deform affinely.

“Moreover, cartilage is softer and much rougher than mica, though at these high pressures it may deform affinely ( 30 )”

Biological lubrication at synovial joints is not yet well understood at the molecular level.

“Biological lubrication at such synovial joints, despite many decades of study, is not yet well understood at the molecular level ( 29-31 ).”

Recent models of synovial lubrication have focused on the role of pressurized interstitial water and of macromolecules at the outer cartilage surface.

“Recent models have focused on the role of pressurized interstitial water( 31 ) and of macromolecules at the outer cartilage surface( 30 ).”

Articular cartilage consists of a network of collagen fibres permeated with charged, flexible macromolecules, proteins, phospholipids and other components.

“In such joints, layers of articular cartilage (coating the ends of the articulating bones) rub past each other; the cartilage consists of a network of collagen fibres, permeated with a large array of charged, flexible macromolecules, proteins, phospholipids and other components (see review in Ref. [101]); a schematic of a hip joint is shown in Fig. 17.”

Models range from engineering tribology extensions to microscopic models based on molecular components of cartilage and synovial fluid.

“These range from extension of ideas from engineering tribology, to microscopic models based on the known molecular components of cartilage and of synovial fluid.”

The importance of understanding lubrication mechanism in healthy joints has spawned a large number of models.

“The importance of understanding the mechanism of lubrication that leads to such low friction in healthy joints, which has implications both for clinical and biomedical applications, has spawned a large number of models (see Refs. [100] and [101] for reviews of these).”