Intervertebral disc

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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The intervertebral disc (Discus intervertebralis) is a kind of shock absorber that sits between the individual vertebrae. It is flexible in its shape and thus enables the spinal column to move. Read everything you need to know about the topic: How many discs does a person have? How are the "shock absorbers" constructed? What health problems can the intervertebral discs cause?

What is the intervertebral disc?

The moving part of the spine is made up of 24 vertebrae, between which there are a total of 23 intervertebral discs, the intervertebral discs (Disci intervertebrales). Together they make up about a quarter of the total height of the spine.

Intervertebral disc: structure

Each disc has an outer fibrous ring (annulus fibrosus) and an inner nucleus pulposus (nucleus pulposus). The outer fibrous ring consists of fibrous cartilage - individual cartilage cells surrounded by a halo of cartilage matrix that lie between bundles of collagenous fibers. The structure of this fiber cartilage corresponds to that of a tight connective tissue with similar mechanical properties - above all high tensile strength.

The inner gelatinous nucleus (nucleus pulposus) of every intervertebral disc, which is under great pressure, is soft - if the spine is bent, it can give way to the stretched side. When the disc is injured, the gelatinous nucleus bulges out. The outer fiber ring is intended to prevent this.

Each disc is attached to the end surfaces of the vertebral body above and below by means of a layer of cartilage. Corresponding to the increasing pressure that is exerted on the vertebrae and the shock absorbers in between by the weight of the head and torso, not only the vertebral bodies but also the intervertebral discs increase in height from top to bottom.

In adaptation to the physiological curvature of the spine, the discs are wedge-shaped. In the cervical and lumbar spine, which are curved forward (lordosis), they are higher on the front surface than on the back surface; In the thoracic spine, which is curved backwards (kyphosis), the intervertebral discs are higher on the back surface than on the front surface.

In addition to the intervertebral discs, the stability of the spine is increased by tight ligaments. A broad ligament (ligamentum longitudinale anterius) is attached to the anterior and lateral surfaces of the vertebral bodies, a narrower ligament (ligamentum longitudinal posterius) is attached to the rear of the intervertebral discs.

What is the function of the intervertebral disc?

The function of the intervertebral discs is shock absorption: With a water content of 80 to 85 percent, they act like a pillow of water and evenly distribute the pressure on them. They also allow the spine to bend in all directions.

With an upright posture, each intervertebral disc is pressed together flatter and flatter over the course of the day due to water loss - until at the end of the day the body size is about one to three centimeters smaller than in the morning. When the load is relieved, the shock absorbers absorb water and nutrients again and “swell” again. With increasing age, the water content decreases in all body tissues - also in the intervertebral discs. That is why people get smaller as they age.

Where is the intervertebral disc located?

There is an intervertebral disc between each two vertebrae - exception: there are none between the first and second cervical vertebrae (and also not between the occiput as part of the skull and the first cervical vertebra).

What problems can the intervertebral disc cause?

As a result of aging and water loss, an intervertebral disc degenerates and loses its elasticity. As a result, cracks and also chipping off of the outer fiber ring or the core arise. The shock absorber can then no longer (adequately) fulfill its function.

The degenerative changes can also lead to an intervertebral disc bulging (protrusion) or even falling over (prolapse). The cervical and lumbar spine are particularly susceptible to this. If the incident is more severe, the intervertebral disc may press on the spinal cord or nerves emerging from it. This can cause symptoms such as pain or even symptoms of paralysis.

By violent effects on the intervertebral disc (e.g. in an accident), parts of the inner gelatinous nucleus (nucleus pulposus) can be pressed into the vertebral body (Schmorl's cartilage nodules) or into the vertebral canal (pulposus hernia).

Infection and inflammation of the vertebral shock absorbers are also possible. In addition, cancer cells from tumors (for example in the abdomen) can invade an intervertebral disc.

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