The lumbar spine is the lower back that begins below the last thoracic vertebra (T12) and ends at the top of the sacral spine, or sacrum (S1). Most people have 5 lumbar levels (L1-L5), although it is not unusual to have 6. Each lumbar spinal level is numbered from top to bottom – L1 through L5, or L6.
The low back vertebral bodies are larger, thicker, block-like structures of dense bone. From the front (or anterior), the vertebral body appears rounded. However, the posterior bony structure is different – lamina, pedicles and bony processes project off the back of the vertebral body. These processes and vertebral arches create the hollow spinal canal for lumbar nerve structures and the cauda equina.
Fig. 1. Detailed views of the lumbar spinal column and bony anatomy. Photo source: Shutterstock.com.
Lumbar Structures Create Strong Joint Complex
A single intervertebral disc separates 2 vertebral bodies, and together with the facet joints, forms a strong joint complex that enables the spine to bend and twist. One pair of facet joints from the top (or superior) vertebral body connects to the lower (or inferior) pair of facet joints. The facet joints are true synovial joints, meaning they are lined with cartilage and the joint’s capsule encases synovial fluid that enables joints to glide during movement.
- Facet joint syndrome may develop as a consequence of aging and degenerative spinal changes and cause lower back pain.
Lumbar intervertebral discs are secured in place by the fibrous endplates of the superior and inferior vertebral bodies. The gel-like centre of each disc, called the nucleus pulposus, is encased, or surrounded, by the annulus fibrosis – a tough layer of fibrocartilage that could be likened to a radial tyre.
Discs are integral to the joint complex and function to (1) hold the superior and inferior vertebrae together, (2) bear weight, (3) absorb and distribute shock and forces during movement, and (4) create open nerve passageways called foramen or neuroforamen. The neuroforaminal spaces at either side of the disc level allow nerve rootlets to exit the spinal canal and leave the vertebral column.
- Lumbar disc herniation is a common cause of lower back pain that can radiate into one or both legs, called lumbar radiculopathy. This condition can develop when lumbar nerves are compressed.
Low Back Supported by Lumbar Ligaments, Tendons, and Muscles
Systems of strong fibrous bands of ligaments hold the vertebrae and discs together and stabilise the spine by helping to prevent excessive movements. The 3 major spinal ligaments are the (1) anterior longitudinal ligament, (2) posterior longitudinal ligament and (3) ligamentum flavum. Spinal tendons attach muscles to the vertebrae and work together to limit excessive movement.
Fig. 2. Lumbar spinal ligaments support the low back and help limit excessive movement.
Photo source: Shutterstock.com
Lumbar Spine Nerves
The spinal cord ends between the first and second lumbar vertebrae (L1-L2). Below this level, the remaining nerves form the cauda equina, a bundle of nerves resembling a horse’s tail. These small nerves transmit messages between the brain and structures in the lower body, including the large intestine, bladder, abdominal muscles, perineum, legs, and feet.
4 Ways to Protect Your Low Back
Considering upwards of 80% of adults will visit a doctor for lower back pain at some point in their life, it pays to take care of your lumbar spine to help avoid painful, unnecessary wear-and-tear to this vulnerable segment of your spinal column. You can minimise your risk of a lower back problem by:
- Lose Weight. Even a five-kilogram loss can help reduce lower back pain.
- Strengthen and maintain core (abdominal) muscles. The abdominal and lower back muscles work together to form a supportive “girdle” around your waist and lower back. Stronger muscles can help stabilise the lower back and can help reduce injury risk.
- Stop smoking. Nicotine reduces blood flow to the spinal structures, including the lumbar discs, and can accelerate age-related degenerative changes.
- Proper posture and body mechanics. Keep your spine erect and lift objects with your legs. Always ask for help to carry heavy objects. Although your lumbar spine is capable of bending and twisting simultaneously, you should avoid doing so.
Witten by Stewart G Eidelson, MD.
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