Second: The Intervertebral Discs
Normal discs (Figure 7) serve as shock absorbers for the spine, occupy space between vertebrae (intervertebral disc space) (Figure 8) that keep the holes (intervertebral foramen) (Figure 4) where the nerve roots exit open, and provide nutrition to the vertebral body above and the vertebral body below it. So all efforts should be aimed at preserving this shock absorber. Disc degeneration can result from many factors. A few of these include prolonged altered spinal curves/posture, trauma, age, genetics, and pathologies that can progress due to repetitive and improper body mechanics during common activities that include sitting, lifting, and bending with rotation. These motions are commonly repeated during normal activities that may be conducted at work or home.
Figure 7. Normal Discs.
Figure 8. Intervertebral Disc Space.
Pathological consequences emerge from prolonged repetitive positioning in biomechanically unsound positions. We will now pictorially review a few of those degenerative conditions (Figure 9) that typically can be seen at various stages of a dental professionals career.
Figure 9. Degenerative Conditions.
In our 20s, 30s, and 40s, the disc’s water content is the highest producing a normal disc signal on a magnetic resonance image (MRI) (Figure 7). This high water content also increases our vulnerability for a disc injury. During this stage of life, the development of disc pathology can be seen to include disc bulges, disc herniations and disc extrusions. These generally develop from excessive prolonged lumbar flexion. Now let’s look at the progression that can occur with disc lesions. In the early stages of disc injury, the outer wall of the disc bulges various amounts possibly putting pressure on a nearby nerve root (Figure 10).
Figure 10. Diffuse Disc Bulges.
A more severe form of a disc bulge is a disc herniation (Figure 11) followed by a disc extrusion (Figure 12). The outer layer of the disc actually fractures allowing the gelatinous content of the disc to extrude outside of the disc. This nuclear material then sits outside the disc, possibly on the nerve root itself, and can block part of the foramen where the nerve root exits.
Figure 11. Disc Herniation.
Figure 12. Disc Extrusion.
Into our 50s and beyond the disc will lose water content causing the disc height to shrink. This loss of water from the disc, otherwise known as disc desiccation (Figure 13), causes the disc to become thin. This thin disc no longer provides adequate shock absorption causing more friction and shearing, creating degenerative changes in the vertebral bodies above and below it with the formation of osteophytes. This can be called osteophytosis (Figure 14).
Figure 13. Disc Desiccation.
Figure 14. Osteophytosis.
This growth of bone additionally limits the joints in the spine from moving thus further contributing to arthritis. Now, review pictorially the degenerative disc disease progression and the associated pathologies that may result from thin or thinning discs: degenerative joint disease (Figure 15), degenerative disc disease (Figure 16), stenosis of the intervertebral foramen (Figure 5), and osteophyte formation (Figure 14) on the vertebral bodies or in the intervertebral foramen.
Figure 15. Degenerative Joint Disease.
Figure 16. Degenerative Disc Disease.