The lumbar spine contains a total of 5 intervertebral discs situated between the vertebral bodies.

The primary functions of these discs are to ¹ Cramer GD. General Characteristics of the Spine. In: Clinical Anatomy of the Spine, Spinal Cord, and Ans. Elsevier; 2014:15-64. doi:10.1016/b978-0-323-07954-9.00002-5 :

Distribute compressive loads placed on the spine, providing shock absorption properties
Maintain the distance between the vertebral bodies during movement
Provide flexibility to the spine and prevent excessive movements
Create and maintain the lordotic (backward C-shaped) curve of the lumbar spine

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A spinal disc consists of two main parts: the jelly-like nucleus pulposus in the disc's center and the outer-most layers, collectively called the annulus fibrosus. These two components facilitate the spine's movement and provide support for the vertebrae.

Disc degeneration or trauma can cause the nucleus to herniate through the weakened layers of the outer disc and leak out of the annulus fibrosus into the spinal canal.

In the case of a lumbar herniated disc, the weak spot in the annulus fibrosus is directly underneath the spinal nerve root, so a herniation in this area can put direct pressure on the nerve.

The nerve root extends down the leg, and any type of pinching or pressure on the nerve in the lower spine can cause pain, numbness, tingling, or weakness to radiate along the path of the nerve down the leg. However, many people have shown a herniated disc on MRI scans yet have no associated pain, so not all herniated discs will cause symptoms.

The discs are typically named based on the vertebrae above and below it, for example, the L4-L5 disc.

Characteristics of the Lumbar Discs

Illustration of lumbar disc from above and from the side view with anatomical labels.

The lumbar discs undergo changes in shape and size based on posture and activity level.

The lumbar intervertebral discs have the following distinguishing features ² Cramer GD. The Lumbar Region. In: Clinical Anatomy of the Spine, Spinal Cord, and Ans. Elsevier; 2014:246-311. doi:10.1016/b978-0-323-07954-9.00007-4 :

Size. The lumbar intervertebral discs are the thickest compared to other spinal regions. The discs are also thicker in front than the back.
Height. The lumbar discs become shorter during the day due to the weight of the upper body. It is estimated that sleeping for a minimum of 5 hours helps the discs regain their original shape.
Shape. The form of the lumbar disc changes with movement. When the spine bends forward, the height in the front of the disc decreases while the posterior height increases. The opposite occurs while bending backward.

The discs are secured in place by the anterior (front) and posterior (back) longitudinal ligaments. ¹ Cramer GD. General Characteristics of the Spine. In: Clinical Anatomy of the Spine, Spinal Cord, and Ans. Elsevier; 2014:15-64. doi:10.1016/b978-0-323-07954-9.00002-5

Composition of the Lumbar Discs

Top down view of the nucleus pulposus and annulus fibrosus of a vertebral disc.

Spinal discs are composed of a tough outer layer and soft inner core.

While the overall composition of the lumbar discs is similar to other discs in the spine, there are a few differences.

The lumbar disc typically consists of ¹ Cramer GD. General Characteristics of the Spine. In: Clinical Anatomy of the Spine, Spinal Cord, and Ans. Elsevier; 2014:15-64. doi:10.1016/b978-0-323-07954-9.00002-5 :

Annulus fibrosus. The outer shell of a lumbar disc is called the annulus fibrosus. This shell is thick and consists of several layers of tough collagen protein fibers, as opposed to a single layer seen in the discs of the neck. The annulus fibrosus provides the main shock-absorbing properties delivered by the disc.
Nucleus pulposus. A softer type of collagen protein fills the central part of the lumbar disc, called the nucleus pulposus. The nucleus pulposus contains 70% to 90% of water and reaches its peak hydration between the ages of 20 to 30 years, following which, dehydration and degeneration begin to occur.

As age advances, the discs may get calcified (deposition of calcium) and hardened, reducing their flexibility. ¹ Cramer GD. General Characteristics of the Spine. In: Clinical Anatomy of the Spine, Spinal Cord, and Ans. Elsevier; 2014:15-64. doi:10.1016/b978-0-323-07954-9.00002-5

Vertebral Endplates of the Lumbar Discs

Cross sectional view of a lumbar vertebra and disc.

Vertebral endplates are made of bone and cartilage that provide stability and structural connection between the lumbar discs and vertebral body.

A bi-layered vertebral endplate made of cortical bone and hyaline cartilage is attached to the upper and lower surfaces of the disc and binds the disc to the vertebral body. The bony portion of the endplate is attached to the vertebral body and helps resist compressive loads on the spine. The cartilaginous portion of the endplate helps contain the annulus fibrosus and nucleus pulposus within their normal anatomic borders. ¹ Cramer GD. General Characteristics of the Spine. In: Clinical Anatomy of the Spine, Spinal Cord, and Ans. Elsevier; 2014:15-64. doi:10.1016/b978-0-323-07954-9.00002-5

The disc receives a majority of its nutrition through these endplates by absorbing fluids (similar to the action of a sponge) during spinal movements. Excessive forces and high-pressure postures, such as prolonged standing and sitting, can inhibit disc nutrition. ¹ Cramer GD. General Characteristics of the Spine. In: Clinical Anatomy of the Spine, Spinal Cord, and Ans. Elsevier; 2014:15-64. doi:10.1016/b978-0-323-07954-9.00002-5

While the lumbar discs provide significant flexibility and protective functions, they are also highly susceptible to injury. In general, the front part of the disc is the strongest and the back and sides are weaker and susceptible to herniation and other disc disorders. ¹ Cramer GD. General Characteristics of the Spine. In: Clinical Anatomy of the Spine, Spinal Cord, and Ans. Elsevier; 2014:15-64. doi:10.1016/b978-0-323-07954-9.00002-5 Research indicates that 90% of lumbar disc herniations occur at the L4-L5 or the L5-S1 disc space. ³ Donnally III CJ, Butler AJ, Varacallo M. Lumbosacral Disc Injuries. [Updated 2019 Apr 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK448072/

Read more about Causes of Lower Back Pain

Infographic of 5 Tips for Lumbar Pain Relief

View this 5 Tips for Lumbar Pain Relief Infographic in our Infographic Center.

Sharp, burning, or radiating pain from a herniated disc is a call for immediate pain relief, but effective pain relief methods look different for everyone. Here are 5 little-known tips for lumbar herniated disc pain.

Heat and cold therapy help relieve muscle tension and pain. Heat can loosen muscle tightness, reduce muscle spasms, increase blood flow, and improve elasticity. Cold can decrease the local tissue temperature, providing an analgesic and anti-inflammatory effect.
Physical activity releases endorphins. Staying moderately active can provide relief of pain from a lumbar herniated disc. When you exercise, the body releases endorphins, which naturally improve your mood and reduce your perception of pain.
Certain sleep positions help relieve pain. You may find comfort sleeping in a position that relieves tension in the lower back. Try using a pillow under your knees, or lie on your side with a pillow between your knees to keep your spine straight and hips balanced.
The McKenzie Method can help shift sciatica pain. The McKenzie Method is a type of physical therapy that involves a specific approach to exercise. For lumbar herniated disc pain, the goal is to shift pain away from your leg (sciatica) and centralize it more in your lower back.
Myofascial release may help reduce pain. Myofascial pain from a lumbar herniated disc can be worsened by poor posture and inactivity. Myofascial release is a form of manual therapy that has been shown to improve low back pain.

This information is not intended or implied as a substitute for medical advice, diagnosis or treatment. All content, including text, graphics, images or other information provided is intended for general information purposes only. Always consult with your physician for diagnosis or treatment.

Dr. Kara Beasley is a neurosurgeon practicing at Boulder Neurosurgical & Spine Associates, where she has several years of experience specializing in spine and brain surgery.

1 Cramer GD. General Characteristics of the Spine. In: Clinical Anatomy of the Spine, Spinal Cord, and Ans. Elsevier; 2014:15-64. doi:10.1016/b978-0-323-07954-9.00002-5
2 Cramer GD. The Lumbar Region. In: Clinical Anatomy of the Spine, Spinal Cord, and Ans. Elsevier; 2014:246-311. doi:10.1016/b978-0-323-07954-9.00007-4
3 Donnally III CJ, Butler AJ, Varacallo M. Lumbosacral Disc Injuries. [Updated 2019 Apr 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK448072/