Spine's Facet and Sacroiliac Joints
Like other joints in the body, facet joints are subject to repetitive stress injuries and degenerative diseases such as osteoarthritis. Also, the joint capsule can rupture and form cysts that pinch nerves, but most of the time, they just flare up.
- Cartilage is basically smooth, rubbery tissue. Your nose is composed of it, as are your ears. Cartilage caps the ends of bones, providing cushion and slipperiness, enabling bones to move easily. When cartilage wears away, bone grinds on bone, causing pain and deterioration. Osteoarthritis and rheumatoid arthritis are two common diseases that damage joint cartilage. In the spine, facet joints are covered with cartilage.
- Ligaments are strong fibrous bands that connect bone-to-bone. Their main job is to stabilize bones, holding them in place. They do, however, have a little flexibility.
- Joint capsules lie between the joints. A fluid, called synovial fluid, is produced in the capsule. Because there is a lot of sliding at these joints, the lubricating fluid is very important in helping prevent grinding. (Cartilage also helps.)
Sacroiliac (SI) Joints
The sacroiliac (SI) joints link your sacrum to your pelvis, specifically to your iliac bones. You can easily feel your iliac bones; they're the bones at the top of your hips. Strong ligaments stabilize and attach your sacrum to your hip bones. Some motion is possible through these joints, but it's very limited. Pregnancy, for example, can loosen these joints, and if they don't return to normal, they can cause instability issues later in life.
The SI joint can be an overlooked source of back pain; it's subject to the same things that can happen to other joints, such as osteoarthritis. Also keep in mind the weight this lowest part of your spine bears. Excessive body weight and lifting injuries can negatively affect these joints. Because lots of muscles attach to the sacrum, muscular weakness or imbalances can misalign joints and be possible sources of pain.
Jason Highsmith, MD is a practicing neurosurgeon in Charleston, NC and the author of The Complete Idiot's Guide to Back Pain. Click here for more information about the book.