Joint Lubrication Aided by Flexing

Joint Cartilage Gets Slippery During Flex Time describes how the production of molecules, which lubricate and protect joints, is induced by shear forces on cartilage. The molecule is proteoglycan 4 and it is chondrocyte cells that produce it. Proteoglycan is a glycoprotein i.e. a protein with a carbohydrate attachment. It is found in connective tissue throughout the body. There are different forms of proteoglycan. Some provide rigidity to cartilage but proteoglycan-4 has a lubrication function. It is primarily secreted into joint fluid.

To quote the article "Sah’s team attached bovine stifle joints, which are similar to human knee joints, to a bio-reactor that provided continuous irrigation with sterile nutritional fluids under normal physiological conditions. Immobile joints were compared to joints that were flexed 24 hours in a way that mimicked walking motions. The flexing was provided by a specially designed continuous passive motion device."

Results showed a direct relationship between proteoglycan 4 production and the amount of shear forces created by opposing bones sliding against each other. Much sliding led to greater production. Immobility was linked to less production. An intermediate amount of sliding caused intermediate production levels.

It is hoped that researchers will be able to generate proteoglycan 4 in a lab by stimulating chondrocytes in cartilage tissue; smooth, well-lubricated cartilage surface being the goal.