MSK: Anatomy Of The Lumbar Spine

Anatomy Of The Lumbar Spine

The anatomy of the lower back includes the lumbar spine and many surrounding structures.  

Your lower back supports the weight of your upper body and maintains your upright position. At the same time, it is flexible, allowing you to bend, straighten, twist, and turn from side to side.

Lower Back Anatomy

The lower back is a common site for musculoskeletal problems. Certain parts of the lower back are affected, depending on the specific condition. For example:

  • Arthritis involving facet joints

  • A strain of a muscle or tendon

  • A displaced or herniated disc

  • A sprain of a ligament

  • Spinal stenosis involving narrowed spinal canal

Since you have a problem with your lower back, it may be helpful to better understand its structure. 

Lumbar Vertebrae

The lumbar vertebrae are the bones of the lower back. There are five bones that make up this part of the spine. From top to bottom, they’re L1 (lumbar vertebra one), L2, L3, L4, and L5. 

Vertebra

One bone of the back is called a vertebra. Each lumbar vertebra has the following parts:

  • Vertebral body -  main part

  • Vertebral foramen - opening in the center of each vertebra through which the spinal cord passes

  • Pedicles - attach several small projections (processes) in the back of the vertebrae to the vertebral body

  • Transverse process - two small projections on either side of each vertebra; site where the lateral intertransversarii muscles (see below) attach

  • Facet joints - connections between the back parts of vertebrae as they stack on top of each other

Intervertebral Discs

Intervertebral means between the vertebrae, so the discs are the cushions of fibrocartilage located between the bodies of the vertebrae. 

Ligaments 

Ligaments are fibrous tissue that attach bones to other bones to help keep them stable. There are several pairs of ligaments that help support the lumbar vertebrae.

Muscles

The back has layers of muscles. Some are closer to the surface (superficial muscles). Moving deeper into the body, there are intermediate and deep muscles.

Tendons

Tendons attach muscles to bones or joints. When a muscle contracts, the tendon transmits that force to the attached bone.  

Fasciae

Fasciae is a thin layer of tissue that helps keep body structures in place. The thoracolumbar fascia covers part of the muscles of the lower back and helps support the lumbar spine. 

Spinal Canal And Cord, Nerve Roots, And Spinal Nerves 

The spinal canal is the passage formed by the opening in the center of each vertebra. The spinal cord is located within the spinal canal. The spinal cord, the link between the brain and the body,  starts at the base of the brain and ends at the top part of the lumbar spine. The covering of the brain and spinal cord is the dura mater. The spinal cord passes through the vertebral foramen of each vertebra.

Nerve roots branch off of the spinal cord on both sides and continue through the body as the 31 pairs of spinal nerves. There are 5 pairs of spinal nerves in the lumbar region, corresponding to the 5 lumbar vertebrae.

The spinal cord ends at the cauda equina, a bundle of nerves and nerve roots located at the level of the second lumbar vertebra. 

Summary

  • Your lumbar spine is quite complex and is made up of vertebrae, intervertebral discs, muscles, ligaments, tendons, fasciae, spinal canal and cord, nerve roots, and spinal nerves.

  • The lower back is a common site for musculoskeletal problems. Certain parts of the lower back are affected, depending on the specific condition.

  • The lumbar vertebrae are the bones of the lower back. There are five bones that make up this part of the spine. One bone of the back is called a vertebra

  • The intervertebral discs are the cushions of fibrocartilage located between the bodies of the vertebrae. 

  • The lower back muscles support the lumbar spine, other parts of the musculoskeletal system, and certain body functions. 

  • Ligaments are fibrous tissue that attach bones to other bones, tendons attach muscles to bones or joints, and fasciae is a thin layer of tissue that helps keep body structures in place.

  • The spinal canal, containing the spinal cord, is the passage formed by the opening in the center of each vertebra. 

  • Nerve roots branch off of the spinal cord on both sides and continue through the body as the spinal nerves. 

For More Information

National Institute of Arthritis and Musculoskeletal and Skin Diseases. Back Pain (2019). Retrieved 6-1-2022 from https://www.niams.nih.gov/health-topics/back-pain.

National Institute of Neurological Disorders and Stroke. Low Back Pain Fact Sheet (2020). Retrieved 6-1-2022 from https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Low-Back-Pain-Fact-Sheet.