In order to understand the function of a facet joint, we need to know a little bit more about the anatomy of the spine. Now I am holding here a model of the lumbar spine. And you can see here, here's the front of the spine. And here's the back of the spine. These are the bony spinous processes that you can feel as you run your hand down the back of someone's spine. And this is the back here. This is the sacrum. Now within the lumbar spine for example– the lower back – you have the vertebral bodies. Usually there's five vertebral bodies in most people. Numbered one, two, three, four, and five. On the back of the spine here; you see as we mentioned the spinous processes here and nestled in between the vertebral body – which are the building blocks of the spine stacked one on top of the other – and the spinous process here at the posterior end you see what's called a facet joint.
The facet joints run in pairs down the entire spine on each side and the facet joints are true synovial joints – they have a synovial membrane and they allow for motion of the spine. The orientation of the facet joint dictates how that facet joint will allow motion. As you can see in the lumbar spine, the orientation is on this plane here where you can have some better flexion and extension of the lumbar spine. In the neck, there's also facet joints, but they're oriented quite differently. You can see — here's the base of the skull. And here's the back of the spine, so we're looking towards the back of somebody here. And these are the facet joints and although they look very different, they serve the same function. They allow for the free movement of the spine, but they also provide support and stability. They also prevent certain motions that would perhaps be detrimental to the spinal cord. The spinal cord is encased within the spine and you can see here. This yellow representation here is the spinal cord running down the central canal with the spinal nerve roots that come out at each level.
Now the facet joints over time are particularly prone to wear-and-tear, to degenerative disease, especially if there is a traumatic incident at some point or points in our life. But, just generally speaking, the facet joints can become very arthritic. It's important to realize that in every person, if you live long enough, you're going to develop facet joint arthropothy – or facet joint arthritis – and that's a normal occurrence. That happens in absolutely everybody pretty much without exception if you live long enough. And that's because the wear-and-tear on a joint is a normal process of aging. It doesn't necessarily mean that you are going to get pain from that joint. However in certain individuals, and oftentimes starting at a very young age, the facet joints themselves – these paired joints in the spine, whether it's the lumbar, thoracic, or cervical – can cause an inflammatory process which causes pain not only in the facet joint and perhaps of the surrounding capsule not pictured here, but also pain that then can be found in the muscles surrounding the facets. The reason for that is that when there is pain in the facet joints, there's a self-protective mechanism that the body uses by sending the surrounding musculature – the perispinal muscles – into spasm to better protect the arthritic joint. But unfortunately, this isn't the best mechanism because oftentimes it leads to decreased function, decreased flexibility, and more pain.
Now in treating facet joint pain, it's often common to do a course of physical therapy, a course of maybe non-steroidal anti-inflammatories, exercise therapy, manipulations, whether it be osteopathic or chiropractic manipulations – can oftentimes be quite helpful in the conservative treatment. When conservative measures fail, then you can employ another form of therapy – injection therapy – to the facet joints or to the nerves leading to the facet joints.