What is the lubrication of diarthrodial joints
Diarthrodial (synovial) joints serve as mechanical bearings with coefficients of friction lower than the friction an ice skate generates as it glides over ice. The three major sources of lubrication are:
• Hydrodynamic lubrication: loading of the articular cartilage causes compression that forces water out of the cartilage. This fluid forms an aqueous layer that separates and protects the opposing cartilage surfaces.
• Boundary layer lubrication: a small glycoprotein called lubricin (proteoglycan 4), which is produced by synovial lining cells and chondrocytes, binds to the superficial zone of articular cartilage where it retains a protective layer of water molecules.
• Hyaluronic acid: produced by synovial lining cells and lubricates the contact surface between synovium and cartilage. It does not contribute to cartilage on cartilage lubrication.