In a healthy joint, there is a natural cycle of "wear and repair."1
The joint capsule has two distinct layers: an outer fibrous layer and an inner synovial membrane.
The synovial membrane contains synoviocytes, which make and secrete synovial fluid, and consists of two layers: a connective tissue layer that contains nerves, blood vessels and lymphatics in addition to a thin lining that allows passage of blood components from the vascular layer into the joint.
Synovial (joint) fluid acts as the boundary lubricant of the joint capsule and synovial membrane to keep unwanted cells out of the joint cavity. It also removes waste and nourishes the cartilage.
Articular cartilage is a connective tissue that covers the ends of bones that is critical to the performance of joints. Dense fibers and a water-rich matrix give it “coil spring” resistance to pressure and shear forces (much like a shock absorber), and the ability to distribute loads evenly into subchondral bone. Cartilage cells repair and replace matrix components subjected to normal “wear and tear”.
Subchondral bone absorbs the forces of movement and carries away waste from the joint. It contains sensory nerves and blood vessels.