Anatomy of Rheumatoid Arthritis
Rheumatoid arthritis usually starts in the neck (cervical spine), so we'll start there, too.
Cervical Spine Joints
At the top of your spine, where your spine and skull come together, you have the atlas vertebra. It's called that as a reference to Atlas from Greek mythology, who had to support the weight of the world on his shoulders. The atlas in the cervical spine is the first vertebra, the one that supports the weight of the head.
Below the atlas, you have the axis vertebra. It got that name because it helps the atlas rotate, giving the neck incredible mobility.
On the axis, there is a special bony projection called the odontoid process or the dens (that's what it's labeled in the drawing below); that's the pivot point for the C1 vertebra, or the atlas. The odontoid process is a tooth-like structure that rises from the body of the axis, and the joint space between the axis and the atlas is termed atlantoaxial. That is a joint that can be affected by RA.
The cervical spine also includes the lateral (side) joints termed zygapophyseal or facet joints. These joints (like all joints in your body) help facilitate movement and are very important to your flexibility.
The facet joints (again, like all joints in your body) are covered by cartilage that protects your bones as you move. The cartilage also makes it easier for your bones to move.
The whole joint—cartilage and all—is covered by a thin membrane called the synovium. The synovium produces synovial fluid, which is what truly helps your joints move well. The synovial fluid lubricates the cartilage and bone.
In rheumatoid arthritis, white blood cells can turn against the synovium and cause inflammation. That inflammation can then lead to the release of certain chemicals that thicken the synovium. The thickened synovium is what causes swollen joints.
Thoracic and Lumbar Spines
It's rare for rheumatoid arthritis to affect the thoracic (upper or mid-back) or lumbar (low back) spines). It is possible, though. Those spinal regions also have facet joints, just like the cervical spine, so those joints can be affected by RA.
You can test your rheumatoid arthritis knowledge with this quiz.