Generally, the pain associated with degenerative disc disease is thought to stem from two main factors:
The proteins contained within the disc space can cause a lot of inflammation, and as a general rule inflammation will cause pain.
- In the lumbar disc space, the low back pain can radiate into the hips. The associated pain can also travel down the back of the leg (also called sciatica, or radiculopathy), and possibly into the foot and toes.
- In the cervical disc space, the neck pain may be local or may radiate into the arm, shoulder and possibly into the hand (a cervical radiculopathy).
- Abnormal micromotion instability
If the annulus - the outer rings of the intervertebral disc - degenerates and wears down, it is not as effective in resisting motion in the spine. This condition has been termed "micromotion" instability because it is usually not associated with gross instability (such as a slipped vertebral body or spondylolisthesis).
Both the inflammation and micromotion instability can cause lower back or neck muscle spasms. The muscle spasm is the body's attempt to stabilize the spine. It is a reflex, and although the body's response of muscle spasm is not necessary for the safety of the nerve roots, it can be quite painful.
The muscle spasms associated with the instability are thought to cause the flare-ups of intense pain often associated with degenerative disc disease.
Symptomatic Degenerative Disc
The two findings most correlated with a pathological disc - a degenerating disc that is painful - are:
- Cartilaginous end plate erosion
- Disc space collapse
Like other joints in the body, each vertebral segment is a joint that has cartilage in it. In between the vertebral body and the disc space is a layer of cartilage, which is known as the cartilaginous end plate.
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The cartilaginous end plate is the source of disc nutrition. If it becomes eroded, it is thought that the disc is likely to go through a degenerative cascade leading to the inflammation and micromotion instability, which in turn causes pain. As it goes through the process, the disc space will collapse.
MRI findings of spinal degeneration are not specific causes of back pain. Typical MRI findings may include:
- Disc dehydration, also called disc desiccation, and often referred to as a dark disc or black disc, because a disc with less water in it looks dark on an MRI scan
- Annular tears
- Disc bulges
These findings may or may not be the cause of the patient's low back pain. It is well known that the results of surgically fusing a spine with these findings will be less reliable than fusing a disc space that has disc space collapse and cartilaginous end plate erosion.