Collectively, the vertebral bodies comprise the boney building blocks of the spine. They are stacked on top of each other with a disc in between each one. All of the vertebral bodies act as a support column to hold up the spine. This column supports about half of the weight of the body, with the other half supported by the muscles.
Each area of the spine has some differences in the form and function of vertebral bodies and how they are attached to adjacent structures.
The cervical spine has seven vertebral bodies (segments). The top two segments are unique:
- The first cervical segment (called the atlas) is a ring that does not have a vertebral body. It is attached to the second vertebral body (the axis), which acts as a post that the first vertebral ring rotates around. Most of the rotation in the neck is located in these top two segments.
- Like the rest of the spine, the next five vertebral segments have three joints at each segment, including one disc in the front and paired facet joints in the back.
Unlike the rest of the spine, the segments in the cervical spine contain openings in each vertebral body for arteries to carry blood to the brain (vertebral artery running through the transverse foramen).
The thoracic spine has twelve vertebral bodies. These structures have very little motion because they are firmly attached to the ribs and sternum (breastbone). Because there is little motion, this region of the spine is not usually a source of back pain, although the junction between the spine and the ribs (costovertebral junction) can be a source of pain.
The lumbar spine has five vertebral bodies that extend from the lower thoracic spine (upper back) to the sacrum (bottom of the spine). The vertebral bodies of the lower back are the largest of the spine because they bear the majority of the body's weight.
The paired facet joints on the back of the vertebral segments are aligned so that they allow flexion/extension but not a lot of rotation. Most causes of back pain originate in the lumbar spine.
In This Article:
Vertebral Components of the Lumbar Spine
The thick oval segment of bone forming the front of the vertebral segment is the vertebral body. Each segment of the lumbar spine is comprised of the following structures:
- The vertebral bodies are attached to a bony arch through which all the nerve roots run. The vertebral arch is comprised of two pedicles, the short stout processes that extend from the sides of the vertebral body and two laminae, the broad flat plates that project from the pedicles and join in a triangle to form a hollow archway (the foramen).
- The vertebral arches are interconnected by paired facet joints, which in combination with the disc, create a three joint complex at each vertebral motion segment. This three-joint complex at each vertebral segment (the facet joint) allows for motion in flexion, extension, rotation, and lateral bending.
- The facet joints have cartilage on each surface and a capsule around them. The cartilage can degenerate as one ages, and lead to degenerative arthritis.
- The spinous process protrudes from the junction of the two laminae and these are the ridges that can be felt through the skin along the back of the spine.
- Transverse processes project from the junction of the pedicles and lamina. The structures of the vertebral arch protect the spinal nerves that run through the spinal canal. A back surgery known as a lumbar laminectomy involves the removal of the laminae to gain access to the vertebral canal.
Lower Back Motion and Back Pain
Fifty percent of flexion (bending forward) occurs at the hips, and fifty percent occurs at the lumbar spine (lower back). The motion is divided between the five motion segments in the lower back, although a disproportionate amount of the motion is at L4-L5 (lumbar segment 4 and 5) and L3-L4 (lumbar segment 3 and 4).
Consequently, these two segments of the lower back are the most likely to break down with degeneration. As these segments break down they can become unstable with an excess of motion creating lower back pain. There are a number of non-surgical treatments available to help manage the low back pain, and a surgical fusion can help alleviate the back pain by stopping the motion.
Vertebral Compression Fractures and Back Pain
Since they are major load bearing structures, vertebral bodies are also prone to developing compression fractures, particularly in patients with osteoporosis (which weakens the bone). These fractures can lead to chronic back pain and progressive misalignment or deformity of the spine.
Over time, a misalignment or deformity in the spine places stress on muscles, tendons, ligaments, and bones throughout the back and can result in impaired balance or walking ability.