How many lumbar intervertebral discs are there?

There are many reasons that may lead to lumbar disc disease. For example, some people suffer from long-term constipation, which can make defecation difficult. Patients will squat in the toilet and strain to defecate, which can damage the lumbar spine. In addition, many people now sit at their desks for a long time to work. Long-term improper sitting posture can cause lumbar pain, and severe cases can cause lumbar disease. Many people don't know how many segments the lumbar disc has. Let's learn about this below.

How many lumbar intervertebral discs are there?

The nucleus pulposus is a viscous, transparent, gelatinous substance that accounts for approximately 50% to 60% of the cross-sectional area of ​​the intervertebral disc. In children, the boundary between the nucleus pulposus and the annulus fibrosus is obvious, but in old age, the water content of the nucleus pulposus decreases, the collagen thickens, and the boundary between the annulus fibrosus and the nucleus pulposus is not obvious. The nucleus pulposus is wrapped in the annulus fibrosus and radially disperses the pressure transmitted by the vertebral body through deformation. It acts like a bearing when the lumbar spine moves. The height of a normal person changes within a day, which is related to the change in the water content of the nucleus pulposus. The height at night is 1.5cm to 2.4cm shorter than that in the morning, and the change is less in the elderly.

In addition, the nucleus pulposus plays a role in fluid exchange between the vertebral body and the cartilage endplate. The fluid in its contents can diffuse into the vertebral body by osmotic pressure. The nutrition of the nucleus pulposus depends on the penetration of the cartilage endplate, which is closely connected with the spongy bone. The spongy bone of the vertebral body has rich blood supply and there is no interstitial bone separating the cartilage endplate. Changes in pressure can cause the fluid in the vertebral body to be exchanged.

The annulus fibrosus is divided into three layers: outer, middle and inner. The outer layer is composed of collagen fiber bands, and the inner layer is composed of fibrous cartilage bands. The anterior and lateral parts of the annulus fibrosus are the thickest, almost twice as thick as the posterior part. The posterior part is the thinnest, but generally also has 1-2 layers of fibers. The annulus fibrosus is arranged in tight and oblique layers, surrounding the nucleus pulposus and forming the outer part of the intervertebral disc, like a coiled spring, connecting the upper and lower vertebrae to each other, maintaining the liquid component of the nucleus pulposus, and maintaining its position and shape. The annulus fibrosus may become loose due to long-term improper posture or external impact. Once the annulus fibrosus becomes loose, the nucleus pulposus will shift and stimulate the nerves, which is commonly known as lumbar disc herniation. The cartilage plate is a transparent, avascular cartilage tissue. There is one above and below the vertebral body. Its average thickness is 1 mm. It is thinner and more translucent in the central area and is located within the posterior bone ring. There is no nerve tissue in the cartilage endplate, so when the cartilage endplate is damaged, it neither produces pain symptoms nor can it repair itself. The avascular cartilage plates above and below the vertebrae are like the cartilage in the knee and hip joints. They can withstand pressure, protect the vertebrae, buffer pressure, and connect the vertebrae and intervertebral discs for nutrient exchange. In early childhood, this is the growth area of ​​vertebral bone.

Before the age of 20, the lumbar intervertebral disc has blood vessels, which gradually disappear and its water content decreases year by year. In the fetus, the water content of the annulus fibrosus and nucleus pulposus is 80% and 90% respectively. At the age of 30, these figures drop to 60% and 75% respectively.