Intervertebral disc

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Intervertebral disc
716 Intervertebral Disk.svg
Intervertebral disc
Details
Part of Vertebral column
System Musculoskeletal system
Function Fibrocartilaginous joint between spinal vertebrae
Identifiers
Latin discus intervertebralis
MeSH D007403
TA98 A03.2.02.003
TA2 1684
FMA 10446
Anatomical terminology

An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to hold the vertebrae together, and to function as a shock absorber for the spine.

Contents

Structure

Cervical vertebra with intervertebral disc Cervical vertebra english.png
Cervical vertebra with intervertebral disc

Intervertebral discs consist of an outer fibrous ring, the anulus (or annulus) fibrosus disci intervertebralis, which surrounds an inner gel-like center, the nucleus pulposus. [1] The anulus fibrosus consists of several layers (laminae) of fibrocartilage made up of both type I and type II collagen. Type I is concentrated toward the edge of the ring, where it provides greater strength. The stiff laminae can withstand compressive forces. The fibrous intervertebral disc contains the nucleus pulposus and this helps to distribute pressure evenly across the disc. This prevents the development of stress concentrations which could cause damage to the underlying vertebrae or to their endplates. The nucleus pulposus contains loose fibers suspended in a mucoprotein gel. The nucleus of the disc acts as a shock absorber, absorbing the impact of the body's activities and keeping the two vertebrae separated. It is the remnant of the notochord. [2]

There is one disc between each pair of vertebrae, except for the first cervical segment, the atlas . The atlas is a ring around the roughly cone-shaped extension of the axis (second cervical segment). The axis acts as a post around which the atlas can rotate, allowing the neck to swivel. There are 23 discs in the human spine: 6 in the neck (cervical) region, 12 in the middle back (thoracic) region, and 5 in the lower back (lumbar) region. [3] Discs are named by the vertebral body above and below. For example, the disc between the fifth and sixth cervical vertebrae is designated "C5-6". [4]

Development

During development and at birth, vertebral discs have some vascular supply to the cartilage endplates and the anulus fibrosus. These quickly deteriorate leaving almost no direct blood supply in healthy adults. [5]

Intervertebral disc space

The intervertebral disc space is typically defined on an X-ray photograph as the space between adjacent vertebrae. In healthy patients, this corresponds to the size of the intervertebral disc. The size of the space can be altered in pathological conditions such as discitis (infection of the intervertebral disc).[ medical citation needed ]

Function

The intervertebral disc functions to separate the vertebrae from each other and provides the surface for the shock-absorbing gel of the nucleus pulposus. The nucleus pulposus of the disc functions to distribute hydraulic pressure in all directions within each intervertebral disc under compressive loads. The nucleus pulposus consists of large vacuolated notochord cells, small chondrocyte-like cells, collagen fibrils, and aggrecan, a proteoglycan that aggregates by binding to hyaluronan. Attached to each aggrecan molecule are glycosaminoglycan (GAG) chains of chondroitin sulfate and keratan sulfate. Increasing the amount of negatively charged aggrecan increases oncotic pressure, resulting in a shift of extracellular fluid from the outside to the inside of the nucleus pulposus. The amount of glycosaminoglycans (and hence water) decreases with age and degeneration. [6]

Clinical significance

Anything arising from the intervertebral disc may be termed discogenic in particular when referring to associated pain as discogenic pain. [7]

Herniation

Stages of spinal disc herniation Disc Herniation.JPG
Stages of spinal disc herniation

A spinal disc herniation, commonly referred to as a slipped disc, can happen when unbalanced mechanical pressures substantially deform the anulus fibrosus, allowing part of the nucleus to obtrude. These events can occur during peak physical performance, during traumas, or as a result of chronic deterioration (typically accompanied with poor posture), and has been associated with a Propionibacterium acnes infection. [8] Both the deformed anulus and the gel-like material of the nucleus pulposus can be forced laterally or posteriorly, distorting local muscle function and putting pressure on the nearby nerve. This can give symptoms typical of nerve root entrapment, which can vary between paresthesia, numbness, chronic and/or acute pain, either locally or along the dermatome served by the entrapped nerve, loss of muscle tone and decreased homeostatic performance. The disc is not physically slipped; it bulges, usually in just one direction.

Another kind of herniation, of the nucleus pulposus, can happen as a result of the formation of Schmorl's nodes on the intervertebral disc. [9] This is referred to as vertical disc herniation.

Degeneration

Micrograph showing a fragment of an intervertebral disc demonstrating degenerative fibrocartilage with loss of nuclei and nests of chondrocytes, as seen in degenerative disc disease. HPS stain. Degenerative disc disease - high mag.jpg
Micrograph showing a fragment of an intervertebral disc demonstrating degenerative fibrocartilage with loss of nuclei and nests of chondrocytes, as seen in degenerative disc disease. HPS stain.

Before age 40, approximately 25% of people show evidence of disc degeneration at one or more levels. Beyond age 40, more than 60% of people show evidence of disc degeneration at one or more levels on magnetic resonance imaging (MRI). [10] These degenerative changes are a normal part of the ageing process and do not correlate to pain. [11]

3D medical animation still shot of scoliosis 3D Medical Animation scoliosis Intervertibral Disc.jpg
3D medical animation still shot of scoliosis

One effect of aging and disc degeneration is that the nucleus pulposus begins to dehydrate and the concentration of proteoglycans in the matrix decreases, thus limiting the ability of the disc to absorb shock. This general shrinking of disc size is partially responsible for the common decrease in height as humans age. The anulus fibrosus also becomes weaker with age and has an increased risk of tearing. In addition, the cartilage endplates begin thinning, fissures begin to form, and there is sclerosis of the subchondral bone. [5] Since the fissures are formed in the anulus fibrosus due to osteo-arthritic bones or degeneration in general, the inner nucleus pulposus can seep out and put pressure on any number of vertebral nerves. [12] A herniated disc can cause mild to severe pain such as sciatica and treatment for herniated discs range from physical therapy to surgery. [13] (see also: Intervertebral disc arthroplasty) Other degeneration of the vertebral column includes diffuse idiopathic skeletal hyperostosis (DISH) [14] which is the calcification or ossification of the ligaments surrounding the vertebrae. This degeneration causes stiffness and sometimes even curvature in the lumbar and thoraco-lumbar spinal region. Burgeoning evidence suggests that long-term running may mitigate age-related degeneration within lumbar intervertebral discs [15]

Scoliosis

While this may not cause pain in some people, in others it may cause chronic pain. Other spinal disorders can affect the morphology of intervertebral discs. For example, patients with scoliosis commonly have calcium deposits (ectopic calcification) in the cartilage endplate and sometimes in the disc itself. [16] Herniated discs are also found to have a higher degree of cellular senescence than non-herniated discs. [5] In addition to scoliosis, which is the lateral 'S' curvature of the spine, the fused vertebrae can also experience other abnormalities such as kyphosis [12] (hunchback) which shows in old age, or lordosis [12] (swayback), which is often present in pregnancy and obesity.

Etymology

The Latin word anulus means "little ring"; it is the diminutive of anus ("ring"). However, modern English also spells the word more phonetically annulus, as with the term annular eclipse, where the moon blocks the sun except for a bright ring around it. [17]

Additional images

See also

Related Research Articles

<span class="mw-page-title-main">Lumbar vertebrae</span> Five vertebrae between the pelvis and the rib cage

The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse process and by the absence of facets on the sides of the body. They are designated L1 to L5, starting at the top. The lumbar vertebrae help support the weight of the body, and permit movement.

<span class="mw-page-title-main">Sciatica</span> Lower back pain that extends down leg

Sciatica is pain going down the leg from the lower back. This pain may go down the back, outside, or front of the leg. Onset is often sudden following activities like heavy lifting, though gradual onset may also occur. The pain is often described as shooting. Typically, symptoms are only on one side of the body. Certain causes, however, may result in pain on both sides. Lower back pain is sometimes present. Weakness or numbness may occur in various parts of the affected leg and foot.

<span class="mw-page-title-main">Discectomy</span> Surgical removal of an intervertebral disc

A discectomy is the surgical removal of abnormal disc material that presses on a nerve root or the spinal cord. The procedure involves removing a portion of an intervertebral disc, which causes pain, weakness or numbness by stressing the spinal cord or radiating nerves. The traditional open discectomy, or Love's technique, was published by Ross and Love in 1971. Advances have produced visualization improvements to traditional discectomy procedures, or endoscopic discectomy. In conjunction with the traditional discectomy or microdiscectomy, a laminotomy is often involved to permit access to the intervertebral disc. Laminotomy means a significant amount of typically normal bone is removed from the vertebra, allowing the surgeon to better see and access the area of disc herniation.

<span class="mw-page-title-main">Schmorl's nodes</span> Medical condition

Schmorl's nodes are protrusions of the nucleus pulposus of the intervertebral disc through the vertebral body endplate and into the adjacent vertebra.

<span class="mw-page-title-main">Back injury</span> Damage or wear to bones, muscles or other tissues of the back

Back injuries result from damage, wear, or trauma to the bones, muscles, or other tissues of the back. Common back injuries include sprains and strains, herniated discs, and fractured vertebrae. The lumbar spine is often the site of back pain. The area is susceptible because of its flexibility and the amount of body weight it regularly bears. It is estimated that low-back pain may affect as much as 80 to 90 percent of the general population in the United States.

<span class="mw-page-title-main">Spondylosis</span> Degeneration of the vertebral column

Spondylosis is the degeneration of the vertebral column from any cause. In the more narrow sense it refers to spinal osteoarthritis, the age-related degeneration of the spinal column, which is the most common cause of spondylosis. The degenerative process in osteoarthritis chiefly affects the vertebral bodies, the neural foramina and the facet joints. If severe, it may cause pressure on the spinal cord or nerve roots with subsequent sensory or motor disturbances, such as pain, paresthesia, imbalance, and muscle weakness in the limbs.

<span class="mw-page-title-main">Degenerative disc disease</span> Medical condition

Degenerative disc disease (DDD) is a medical condition typically brought on by the normal aging process in which there are anatomic changes and possibly a loss of function of one or more intervertebral discs of the spine. DDD can take place with or without symptoms, but is typically identified once symptoms arise. The root cause is thought to be loss of soluble proteins within the fluid contained in the disc with resultant reduction of the oncotic pressure, which in turn causes loss of fluid volume. Normal downward forces cause the affected disc to lose height, and the distance between vertebrae is reduced. The anulus fibrosus, the tough outer layers of a disc, also weakens. This loss of height causes laxity of the longitudinal ligaments, which may allow anterior, posterior, or lateral shifting of the vertebral bodies, causing facet joint malalignment and arthritis; scoliosis; cervical hyperlordosis; thoracic hyperkyphosis; lumbar hyperlordosis; narrowing of the space available for the spinal tract within the vertebra ; or narrowing of the space through which a spinal nerve exits with resultant inflammation and impingement of a spinal nerve, causing a radiculopathy.

<span class="mw-page-title-main">Spinal fusion</span> Immobilization or ankylosis of two or more vertebrae by fusion of the vertebral bodies

Spinal fusion, also called spondylodesis or spondylosyndesis, is a surgery performed by orthopaedic surgeons or neurosurgeons that joins two or more vertebrae. This procedure can be performed at any level in the spine and prevents any movement between the fused vertebrae. There are many types of spinal fusion and each technique involves using bone grafting—either from the patient (autograft), donor (allograft), or artificial bone substitutes—to help the bones heal together. Additional hardware is often used to hold the bones in place while the graft fuses the two vertebrae together. The placement of hardware can be guided by fluoroscopy, navigation systems, or robotics.

Congenital vertebral anomalies are a collection of malformations of the spine. Most, around 85%, are not clinically significant, but they can cause compression of the spinal cord by deforming the vertebral canal or causing instability. This condition occurs in the womb. Congenital vertebral anomalies include alterations of the shape and number of vertebrae.

<span class="mw-page-title-main">Intervertebral foramen</span> Foramen between spinal vertebrae

The intervertebral foramen is an opening between two pedicles of adjacent vertebra in the articulated spine. Each intervertebral foramen gives passage to a spinal nerve and spinal blood vessels, and lodges a posterior (dorsal) root ganglion. Cervical, thoracic, and lumbar vertebrae all have intervertebral foramina.

<span class="mw-page-title-main">Spinal disc herniation</span> Injury to the connective tissue between spinal vertebrae

A spinal disc herniation is an injury to the intervertebral disc between two spinal vertebrae, usually caused by excessive strain or trauma to the spine. It may result in back pain, pain or sensation in different parts of the body, and physical disability. The most conclusive diagnostic tool for disc herniation is MRI, and treatment may range from painkillers to surgery. Protection from disc herniation is best provided by core strength and an awareness of body mechanics including good posture.

<span class="mw-page-title-main">Anterior cervical discectomy and fusion</span> Surgical procedure

Anterior cervical discectomy and fusion (ACDF) is a surgical procedure to treat nerve root or spinal cord compression by decompressing the spinal cord and nerve roots of the cervical spine with a discectomy, followed by inter-vertebral fusion to stabilize the corresponding vertebrae. This procedure is used when other non-surgical treatments have failed.

Artificial disc replacement (ADR), or total disc replacement (TDR), is a type of arthroplasty. It is a surgical procedure in which degenerated intervertebral discs in the spinal column are replaced with artificial disc implants in the lumbar (lower) or cervical (upper) spine. The procedure is used to treat chronic, severe low back pain and cervical pain resulting from degenerative disc disease. Disc replacement is also an alternative intervention for symptomatic disc herniation with associated arm and hand, or leg symptoms.

<span class="mw-page-title-main">Spinal decompression</span> Relief of pressure on the spinal cord or compressed nerve roots

Spinal decompression is the relief of pressure on the spinal cord or on one or more compressed nerve roots passing through or exiting the spinal column. Decompression of the spinal neural elements is a key component in treating spinal radiculopathy, myelopathy and claudication.

<span class="mw-page-title-main">Lumbar provocative discography</span>

Lumbar provocative discography is an invasive diagnostic procedure for evaluation for intervertebral disc pathology. It is usually reserved for persons with persistent, severe low back pain (LBP) who have abnormal spaces between vertebrae on magnetic resonance imaging (MRI), where other diagnostic tests have failed to reveal clear confirmation of a suspected disc as the source of pain, and surgical intervention is being considered.

<span class="mw-page-title-main">Disc protrusion</span> Medical condition in which spinal cartilage bulges outward under pressure but remains intact

A disc protrusion is a medical condition that can occur in some vertebrates, including humans, in which the outermost layers of the anulus fibrosus of the intervertebral discs of the spine are intact but bulge when one or more of the discs are under pressure.

Modic changes are pathological changes in the bones of the spine, the vertebrae. These changes are situated in both the body of the vertebrae and in the end plate of the neighboring disc. Clinically, Modic Changes are often associated with constant lower back pain during the day, with peak pain occurring during the night and in the morning, coupled with back stiffness.

<span class="mw-page-title-main">Vertebral column</span> Bony structure found in vertebrates

The vertebral column, also known as the backbone or spine, is the core part of the axial skeleton in vertebrate animals. The vertebral column is the defining characteristic of vertebrate endoskeleton in which the notochord found in all chordates has been replaced by a segmented series of mineralized irregular bones called vertebrae, separated by fibrocartilaginous intervertebral discs. The dorsal portion of the vertebral column houses the spinal canal, a cavity formed by alignment of the neural arches that encloses and protects the spinal cord.

Astronauts have expressed an increased incidence of back pain during spaceflight and herniated intervertebral discs (IVD) have been diagnosed upon return of Skylab and Shuttle spaceflight participants.

<span class="mw-page-title-main">Vertebra</span> Bone in the vertebral column

Each vertebra is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal segment and the particular species.

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