The Healthy Spine

Back pain is one of the most common reasons for doctor visits and absences from work. Before discussing back pain, it is important to understand the anatomy of the normal, healthy spine and how it works.

The spine consists of 33 vertebrae that stack on top of one another, separated by intervertebral discs. The spinal column supports the loads of the upper body, serves as an attachment point for muscles and ligaments, and protects the neural structures.

Intervertebral Disc

Between each vertebra is soft tissue known as the intervertebral disc, which acts as a shock absorber for the vertebrae, allowing your spine to bend and move. These discs are made up of a tough, elastic outer ring (annulus) of collagen fibers that surround a soft gel center (nucleus).

Lumbar Spine

Lumbar Spine

The lumbar spine refers to the lower back, where the spine curves inward toward the abdomen. It starts about 5-6 inches below the shoulder blades, connects with the thoracic spine at the top, and extends downward to the sacral spine.

This part of the spine bears most of the body’s weight and is the region where a majority of the motion occurs. It is associated with most of the back problems that cause back pain, as well as with pain that can radiate down to the feet.

There are 5 vertebrae in the lumbar region: L1, L2, L3, L4, and L5. Physicians commonly refer to a segment (two vertebrae and the disc between them) that is causing back and/or leg pain as a level (such as L3-L4 or L4-L5).

Each lumbar vertebra is made up of the same components:

Vertebral body: round block of bone that makes up the main section of the vertebra.

Pedicles: 2 bones that connect directly to the back of the vertebral body and are part of the bony structures that protect the spinal cord.

Lamina: 2 bones that connect to the pedicles to form the outer ring of the spinal canal.

Facet joints: each vertebra has 2 sets of facets. One pair faces up and one pair faces down. 2 adjacent vertebrae are connected in the back of the spine by 2 facet joints. These joints allow flexion (bending forward), extension (bending backward), and twisting motions.

Spinous process: along the back of your spine, furthest away from the delicate nerve roots, are the spinous processes. These are the bones you feel as run your fingers down the center of your back.

Transverse process: bony knobs that project out from the side of the spinal canal, one on the left and one on the right.

Ligaments & Muscles

The Lumbar Spinal Ligaments

The ligaments are tough bands of elastic tissue that hold the vertebrae together and help restrain excessive motion at the joints. The spinal ligaments help stabilize the spine during motion and protect the discs.

The Back Muscles

The final stabilizers of the spine are the muscles that attach to it. The paraspinal muscles that run up and down the center of the back provide support to the spine and allow movement.

In an attempt to minimize the approach-related pain associated with traditional spinal fusion procedures, minimally invasive surgical (MIS) techniques have been developed that approach the spine from the side (lateral) rather than the back (posterior).

Approaching the spine from the side may provide a less disruptive pathway, as the lateral muscles are more forgiving than the posterior back muscles. Since there is no dissection and retraction of the sensitive back muscles, patients may experience less pain and a quicker recovery.

Spinal Nerves

Spinal Nerves

The spinal cord runs from the base of the brain through the cervical and thoracic spine (spinal canal), and ends at the upper lumbar region. Where the spinal cord ends a horsetail-shaped bundle of spinal nerves, called the cauda equina, begins.

The 31 pairs of spinal nerves branch off the spinal cord (left and right) and pass through a hole on each side of the vertebrae called the intervertebral foramen. The lumbar spinal nerves communicate with your lower back, abdomen, and legs. If any of these nerves are pinched by a bulging disc, bone spur, thickened ligament, or vertebra you might experience back pain, or pain that radiates to the legs (radicular pain), or a combination of both.