Facet Arthrosis (degeneration)
The facet joints are in the back of the spine, about a half inch from the bump that you can feel in the middle of your back (the spinous process). These joints are indicated in the picture on the right by the asterisk (*).
These joints slide apart or together, depending on whether the patient is bending forward or backward, as indicated in the picture below.
While the disc is the cushion in the front, the facet joints in the back part of the spine glide over each other as the spine moves, with the center of rotation in the region of the disc.
The wear and tear or degeneration that can occur in a joint is often referred to as arthrosis. The facet joints in the back part of the spine, which are joints that normally have a smooth cartilage surface, can wear out. The xray appearance of this wearing out is more calcium deposit in the joints, making them look more white, as is apparent in the lower lumbar joints on these xrays below.
In this cross sectional view, normal appearing facet joints are seen. Notice that it appears that the two sides fit nicely together.
In this view of a level with facet degeneration, it can be seen that extra bone is seen forming on one side, and extra fluid is seen onthe other. Clearly, these joints don't seem like they'd have smooth motion as the spine flexes and extends.
On this view, the facets have overgrown to a point where they are compressing the nerves in the spinal canal. This condition is called spinal stenosis
Here in various CT scans, which highly bony details better than an MRI, the joint space can be seen as being almost the same thickness throughout at a level without wear and tear of the facet joints on this cross sectional view.
In this image, however, the facet joints can be seen as irregular and rougher appearing, and on the right side, there is extra bone growth, referred to as osteophytes, which are a sign of arthritis of these joints.
The facet joints can also wear out in the neck, where these joints have a different shape, overlapping like shingles on a roof, and can also develop arthritis with the cartilage worn away.
Since this cartilage is invisible to the xray beam, when cartilage is present, a joint space will be visible. When the cartilage is worn away, there will be a thinner or missing space between the bones. With further progression, there can be bone on bone contact.