To better understand osteoarthritis, you need to understand what makes up a joint. Some of the components of a joint include cartilage, synovial fluid, tendons, ligaments, and muscles. In a joint with osteoarthritis, cartilage breaks down and wears away. This can cause pain, swelling, and loss of motion of the joint. The joint can also lose its shape over time, and can develop small growths called osteophytes on its edges.
Understanding the Normal JointMost joints -- the place where two moving bones come together -- are designed to allow smooth movement between the bones and to absorb shock from movements like walking or repetitive movements.
The joint is made up of:
- Cartilage: This is a hard but slippery coating on the end of each bone. Healthy cartilage allows bones to glide over one another. It also absorbs energy from the shock of physical movement. Cartilage, which breaks down and wears away in people with osteoarthritis, is described in more detail in the following section.
- Joint capsule: This is a tough membrane sac that holds all the bones and other joint parts together.
- Synovium: This is a thin membrane inside the joint capsule.
- Synovial fluid: This fluid lubricates the joint and keeps the cartilage smooth and healthy.
- Ligaments, tendons, and muscles: As a group, these tissues keep the bones stable and allow the joint to bend and move. Ligaments are tough, cord-like tissues that connect one bone to another. Tendons are tough, fibrous cords that connect muscles to bones. Muscles are bundles of specialized cells that contract to produce movement when stimulated by nerves.