Human Body: What's Inside a Joint?

It’s true that a joint is the place where two bones meet, but a joint involves more than just bones.  Most joints in the body are moveable and consist of:

Cartilage—This is the white, shiny material on the ends of bones.  Cartilage allows bones to glide smoothly against each other so that it doesn’t hurt to move a joint.

Synovium—This tissue lines the joint and seals it into its own little capsule.

Synovial fluid—This is the clear, sticky fluid inside a joint.  It is produced by the synovial membrane and is the consistency of oil.  The synovial fluid lubricates the joint and provides nourishment and oxygen to cartilage cells.

Ligaments—These tough, elastic bands of connective tissue surround a joint to give it support and to keep it from bending too far the wrong way.

Tendons—Similar to ligaments, tendons are tough cords of connective tissue.  Tendons attach to muscles on each side of a joint and help control the movement of the joint.

Bursas—These are fluid-filled sacs that sit between bones and ligaments.  Each bursa acts like a cushion and prevents excess friction in  a joint.