There are 5 intervertebral discs in the lumbar spine. These discs are located between the adjacent vertebrae.
They enable the highly mobile lumbar spine to move in all directions while supporting the upper body. They also protect the vertebrae by acting as shock absorbers and distributing forces throughout the spine.
A typical lumbar disc is wedge-shaped. It is approximately 7 to 10 millimeters thick and 4 centimeters in diameter. It is made of a tough outer layer called the annulus fibrosus, which encapsulates a soft gel-like interior called the nucleus pulposus.
The annulus fibrosus is composed of 15 to 20 concentric rings1, made of fibrocartilage, which distribute heavy loads placed on the disc.
The nucleus pulposus is mainly composed of water and a loose network of collagen and elastin fibers suspended in a mucoprotein gel, which gives the disc cushioning and flexibility.
A vertebral endplate forms the transition between the disc and the vertebra. It is made up of two layers – a bony layer, which attaches to the vertebral body, and a cartilaginous layer, which attaches to the intervertebral disc. The endplate facilitates the transport of nutrients to the discs and protects the vertebrae and discs from compressive loads on the spine.
When an endplate becomes damaged, pain signals are transmitted from the endplate to the brain through the basivertebral nerve fibers. This pain is called vertebrogenic pain and occurs in the area surrounding the injured endplate.
The lumbar discs experience some degree of degenerative changes with age, becoming flatter and less flexible.
These changes result in a condition called degenerative disc disease, which may cause a variety of disc problems, such as
- Disc herniation – a condition where the inner gel-like core of a spinal disc pushes through the tough outer layer
- The leaking of inflammatory proteins onto a nearby spinal nerve, OR
- Degenerative spondylolisthesis – a condition where one vertebra slips forward
These conditions increase the risk of low back pain and sciatica symptoms such as pain that radiates down the leg and into the foot.
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