How does synovial fluid lubricate and nourish joints?

Synovial fluid is a viscous, thixotropic substance secreted by synovial lining cells within the synovial tissue. It plays two critical roles in maintaining joint health:

Lubrication
The fluid’s thixotropic nature—meaning it is both viscous and elastic—allows it to form elastohydrodynamic lubricant films between the moving surfaces of a joint. Its viscosity decreases as the speed of joint movement increases, while its elasticity increases, ensuring smooth motion. Additionally, fatty pads within the joint cavity contribute to this process by "streamlining" the space and helping maintain the fluid at the proper thickness and consistency between articulating surfaces.12

Nutrition
Because articular cartilages, disks, and menisci lack a direct blood supply, they rely on synovial fluid for nourishment. As a dialyzate of blood plasma, the fluid contains essential nutrients that are distributed over the surface of the cartilage through joint movement. From the surface, these nutrients slowly pass into the interior of the cartilage to support the metabolic needs of chondrocytes.31