Anatomy of the Lumbar Spine

The lumbar spine is the lower back that starts below the last thoracic vertebra T12 and ends at the top of the sacral spine or sacrum S1. Each lumbar spinal level is numbered from top to bottom, L1 to L5, or L6. The low back bodies are larger, and thicker structures of dense bone. From the front or anterior, the vertebral body has a rounded shape.

The posterior bony structure is a different lamina, which is a thin bony plate that shields and protects access to the spinal canal. There are vertebral arches that create the hollow spinal canal for lumbar nerve structures and the cauda equina.

 

Lumbar Structure Strong Joint Complex

One intervertebral disc together with the facet joints forms a strong joint complex that allows the spine to bend and twist. One pair of facet joints from the top or superior vertebral body connects the lower or inferior set of facet joints. The facet joints are synovial joints, which means they are lined with cartilage and the capsule holds synovial fluid that enables joints to glide during movement. Think of it as hydraulics with smooth fluid motion.

Facet joint syndrome can develop from aging and degenerative spinal changes causing low back pain. The lumbar discs are secured in place by the fibrous endplates of the superior and inferior vertebral bodies.

The jelly/gel center of each disc called the nucleus pulposus is surrounded by the annulus fibrosis, which is a tough layer of fibrocartilage that you can think of as a radial tire.

Discs are integral to the joint complex and function to:

1. Hold the superior and inferior vertebrae together
2. Take the weight
3. Absorb and distribute shock and forces when moving about
4. Create an open nerve passageway called foramen or neuroforamen

The neuroforaminal spaces on either side of the disc allow nerve roots to exit the spinal canal and leave the column.

Lumbar disc herniation is a common cause of low back pain that can spread out into one or both legs. This is called lumbar radiculopathy. This condition can develop when the nerves are compressed.

 

Low Back Support

• Lumbar Ligaments
• Tendons
• Muscles

Systems of strong fibrous bands of ligaments hold the vertebrae and discs together and stabilize the spine by helping to prevent over/excessive movements.

The 3 major spinal ligaments are the:

1. Anterior longitudinal ligament
2. Posterior longitudinal ligament
3. Ligamentum flavum.

Spinal tendons attach muscles to the vertebrae and together work to limit excessive movement.

Lumbar Spine Nerves

The spinal cord comes to an end between the first and second lumbar vertebrae (L1-L2). Below this is the remaining nerves that form the cauda equina which is a bundle of nerves that looks like a horse’s tail. These nerves send messages between the brain and the lower body structures, including the:

• Large intestine
• Bladder
• Abdominal muscles
• Perineum
• Legs
• Feet

Protect Your Back

Around 80% of adults will see a doctor for low back pain at some point. Therefore take care of your lumbar spine to help avoid painful, unnecessary wear-and-tear. You can minimize the risk of a low back injury/pain by:

1. Losing weight. Even a loss of 5 pounds can help reduce back pain.
2. Strengthening the core/abdominal muscles. The abdominal and low back muscles work together to form a supportive band around the waist and low back. Stronger muscles help stabilize the low back and reduce the risk of injury.
3. Stopping smoking. Nicotine reduces blood flow to the spine’s structures. This includes the lumbar discs and accelerates age-related degeneration.
4. Proper posture and proper body mechanics. When lifting objects keep your spine erect and use your legs. Ask for help with heavy objects. The lumbar spine is can bend and twist simultaneously, try to avoid doing this, as it is a perfect setup for a strain or sprain.

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NCBI Resources