Lumbar Spine Anatomy and Pain

The lumbar spine refers to the lower back, where the spine curves inward toward the abdomen. It starts about five or six inches below the shoulder blades, and connects with the thoracic spine at the top and extends downward to the sacral spine.

“Lumbar” is derived from the Latin word “lumbus,” meaning lion, and the lumbar spine earns its name. It is built for both power and flexibility (i.e. lifting and bending). The lumbar spine has several distinguishing characteristics:

• The lower a vertebra in the spinal column, the more weight it must bear. The five vertebrae of the lumbar spine (L1-5) are the biggest unfused vertebrae in the spinal column, enabling them to support the weight of the entire torso.
• The lumbar spine meets the sacrum at the lumbrosacral joint (L5-S1). This joint allows for considerable rotation, so that the pelvis and hips may swing when walking and running.
• The lumbar spine’s lowest two spinal segments, L4- L5 and L5-S1, which include the vertebrae and discs, bear the most weight and are therefore the most prone to degradation and injury.
• The spinal cord travels from the base of the skull through the spinal column and ends at about T12-L1. At that point numerous nerve roots from the spinal cord continue down and branch out, forming the “cauda equina,” named for its resemblance to a horse’s tail. These nerves extend to the lower extremities (buttocks, legs and feet). Because the spinal cord does not run through the lumbar spine, it is quite rare that a lower back problem would result in spinal cord damage or paralysis.

Common Causes of Pain in the Lumbar Spine

Lower Back Pain Causes Video

There are many structures in the lumbar spine that can cause pain – any irritation to the nerve roots that exit the spine, joint problems, the discs themselves, the bones and the muscles can all be a source of pain. Many lumbar spine conditions are interrelated. For example, joint instability can lead to disc degeneration, which in turn can put pressure on the nerve roots, etc.

The following outlines the more common causes of lower back pain.

• Muscular problems. The most common cause of lower back pain is muscle strain or other muscle problems. Strain due to heavy lifting, bending, or other arduous or repetitive use can be quite painful but usually heal within a few days to a few weeks.
• Degenerative discs. Intervertebral discs are spongy pads that act as shock absorbers between each of the lumbar spine’s vertebrae. As the disc degenerates, they can create pain in the disc space. This condition can be referred to with many different terms – on this site it is consistently termed “degenerative disc disease”.
• Herniated disc. Herniated discs are most common in the lumbar spine. A herniated disc may happen suddenly due to injury or heavy lifting or happen slowly as a part of general wear and tear on the spine. Leg pain (sciatica) is the most common symptom of a herniated disc.
• Sacroiliac joint dysfunction. The sacroiliac joint, which connects with the bottom of the lumbar spine and the top of the tailbone, can cause lower back pain and/or sciatica pain if there is any type of dysfunction in the joint that allows too much movement or restricts normal movement.
• Spondylolisthesis. Spondylolisthesis occurs when one vertebra slips forward over the one below it. The slip most commonly occurs in the lower lumbar vertebrae (e.g. L4 –L5 or L5 – S1). If the slipped vertebra compresses the nerve root at that level, it can result in leg pain and possibly foot pain.
• Osteoarthritis. Osteoarthritis in the lower back is sometimes called facet joint arthritis. Aging and wear and tear can cause the normally smooth cartilage covering the facet joints in the back of the spine to become worn and frayed. Excess friction can produce bone spurs and joint swelling that cause tenderness, pressure to the nerve, and limited range of motion.
• Lumbar stenosis. The narrowing of the spinal canal or nerve root canals (gaps where the nerve endings exit the spinal column) can cause the nerve endings to be squeezed, resulting in leg pain, tingling, numbness and even difficulty walking. This narrowing is often the result of bone spurs and joint swelling from osteoarthritis.

The sciatic nerve, which extends from the lower back down each leg to the foot, can become pinched or irritated from any of the above conditions, often resulting in a burning pain and/or tingling sensation down the back of the leg and possibly into the foot. The common term to describe this type of leg pain is sciatica.

For more in-depth information, see the Lower Back Pain Center

• Article written by:
• Eben Davis, DC

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