The height of the normal intervertebral disc is about 1 4 of the total length of the spine, and the 4th of the chest is the narrowest, only 21mm, waist 5 highest, about 171mm。The total disc height is 32 of the whole vertebral body1%, which accounts for 24 of the total length of the spine3%。Normal intervertebral discs maintain a certain height, so that the facet joints are spaced at a certain distance, and the intervertebral foramen maintains a certain size. The hydrodynamic properties of the nucleus pulposus evenly transmit the upper gravity to the lower vertebral surface, which acts as a cushion during the vertical movement of the body. However, when the intervertebral disc degenerates, especially herniation, it produces morphological and functional disorders, which become the main cause of low back and leg pain.
There are 23 intervertebral discs, which are bounded between cervical 2 and sacrum 1, and there are no intervertebral discs between the neck and sacrococcygeal bones. The intervertebral disc consists of the nucleus pulposus located in **, the fibrous annulus that surrounds it, and the upper and lower cartilage plates. The cartilage plate is actually a component of the upper and lower vertebral bodies, and is often described as a part of the intervertebral disc because it is closely related to the intervertebral disc in clinical practice.
The fibrous ring is composed of collagen fibers and fibrocartilage, arranged in layers on the cross-section, with a total of about 12 layers, each layer is attached to the adjacent vertebral body at a 45° angle with coarse collagen fibers, and intertwined at a 90° angle, so that it can bulge out to the surrounding sides when compressed. The attachment points can be roughly divided into 3 groups: The two ends of the most superficial fibers are attached to the cortical bone of the vertebral body, called sharpay fibers, to increase the firmness of the attachment. The middle layer is an annular epiphysis attached to the upper and lower vertebral bodies. The innermost layer is arc-shaped around the nucleus pulposus, and both ends are attached to the endplate of the vertebral body, the cartilage plate. In the horizontal plane, the anterior and both sides of the annulus fibrous are thick and strong, and the anterior longitudinal ligament is reinforced by a strong and thick anterior longitudinal ligamentThe posterior part is thinner, most of the fibers are attached to the cartilage plate, and the posterior longitudinal ligament is only strip-like in the midline, especially in the lumbar 4, which loses the protective effect of the fibrous annulus, and is a good site for degeneration and protrusion.
With the increase of age, the number of fiber ring layers decreases significantly, the thickness of a single layer increases, and the interval between the middle bundles of a single layer increases. In aging intervertebral discs, the number of fibrous annulus is reduced, the transition zone is thickened, and the organized fibrous structure of the inner layer is gradually reduced. The network width of the fiber loop is not reduced due to the thickening of the remaining layer. Increasing age also causes an irregular distribution of intralamellar bundles: human fiber rings younger than 40 years of age are arranged in a plume form of inclined collagen fibers, and from middle age onwards, the layers undergo progressive degeneration (wear, cracks, loss of collagen fibers). About 10% of the fibrous ring matrix is made up of elastic fibers, and the number of these elastic fibers decreases slightly with age. Injured intervertebral disc in 3It can rupture at 5 kg cm2 pressure, but a normal disc can withstand 70 kg cm2 without damage.
The nucleus pulposus is located in the intervertebral disc** in the thoracic segment and behind the intervertebral disc** in the lower lumbar spine, and is a hyaline semicolloidal body with a network of fine collagen fibers and a small number of chondroblasts and fibroblasts. At birth, the nucleus pulposus is jelly-like, the interwoven fibers in the matrix begin to thicken at the age of 10, the marginal chondroblasts gradually increase at the age of 20, and there is still a boundary between the nucleus pulposus and the fibrous ring, and after the age of 30, the nucleus pulposus is dehydrated, and the fibers and chondroblasts gradually replace the gelatinous nature, and in old age they completely become fibrous structures.
The cartilage endplate is hyaline cartilage, which is the endplate of the vertebral body and the upper and lower boundaries of the intervertebral discs. The cartilage plate is surrounded by cortical bone formed by the epiphysis of the cricoidal ostein. In childhood, the cartilage endplate has blood vessels passing through it, and later it is atresia, leaving only a narrow hole that can protrude into the cancellous bone of the vertebral body when the nucleus pulposus pressure is high, called the Schmorl tubercle, which is often found on lateral radiographs of the lumbar spine. **The cartilage endplate has an osmotic effect, when the pressure in the intervertebral disc is high, the fluid seeps through the cartilage endplate to the vertebral body, and when the pressure is low, it penetrates backwards, and the intervertebral disc relies on this to obtain nutrition. Therefore, the height is slightly higher in the morning than in the evening, and the average height of men is 171mm, female 142mm。
After the age of at least 8 years, the intervertebral disc is no longer vascular**, and the small blood vessels are only distributed to the surface of the annulus fibrous. The intervertebral disc of adults depends on osmotic nutrition, and the penetration between the intervertebral disc and the cancellous bone of the vertebral body is two-way, and the penetration between the intervertebral disc and the surface blood vessels is one-way, that is, it can only penetrate into the blood vessels. Outward penetration can reduce intravertebral disc pressure and protect the intervertebral disc.
A branch of the sinus vertebral nerve, with fibers running up and down behind the vertebral body, distributing to the intervertebral discs. In addition to the posterior longitudinal ligament, periosteum, blood vessels and ventral dura, the nerve fibers of the sinus vertebral nerve fibers can penetrate 1mm deep into the surface of the fibrous annulusIt has also been shown to reach the fibrous annulus thickness of 1 3 and to prove that the anterior branch of the spinal nerve has fibers to the lateral side of the disc.