Anatomy of Spinal Fractures
For spinal fractures, the most important part of the spinal anatomy for you to understand is the vertebrae. These are the bones that make up your spinal column. Spinal fractures can also affect the other parts of the spine—the nerves, spinal cord, ligaments, etc.—and this article will discuss those later.
The image below shows the different regions of the spinal column. After reading about how the vertebrae stack up, you'll learn about the different parts of the vertebrae.
The basics of spinal anatomy:
- Cervical Spine: This is your neck, which begins at the base of your skull and ends at the top of the thoracic spine (around the level of your shoulders). Where your skull joins your neck is called the occipitocervical junction, and it's possible to have a very serious fracture there.
The cervical spine contains 7 small bones (vertebrae), which doctors label C1 to C7 (the 'C' means cervical). The numbers 1 to 7 indicate the level of the vertebrae. C1 is closest to the skull, while C7 is closest to the chest.
C1 is also called the atlas—it's called that as a reference to Atlas from Greek mythology, who had to support the weight of the world on his shoulders. The atlas in the cervical spine is the first vertebra, the one that supports the weight of the head.
C2 is also called the axis. It got that name because it helps the atlas rotate, giving the neck incredible mobility. On the axis, there is a special bony projection called the odontoid process; that's the pivot point for the C1 vertebra, or the atlas.
- Thoracic Spine: Your mid-back has 12 vertebrae that are labeled T1 to T12 (the 'T' means thoracic). Most vertebrae in your thoracic spine connect to your ribs, making this part of your spine relatively stiff and stable.
It's possible to fracture a thoracic vertebra due to trauma, but it isn't as common. It is more common to have a traumatic fracture in the region where the thoracic spine and the lumbar spine come together. That's called the thoracolumbar region.
The thoracic spine is the most common area for spinal fractures caused by osteoporosis. It's also the most common area for spinal fractures caused by metastatic tumors—cancer cells that have metastasized from the original tumor location. The thoracic spine has the most blood flow of any region of the spine, so it's more likely that cancers will metastasize to that spinal region, as compared with the other spinal regions.
- Lumbar Spine: In your low back, you have 5 vertebrae that are labeled L1 to L5 (the 'L' means lumbar). Some people have 6 lumbar vertebrae. These vertebrae are your largest and strongest vertebrae, responsible for carrying a lot of your body's weight. The lumbar vertebrae are also your last "true" vertebrae; beneath this region, your vertebrae are fused by the time you stop growing. In fact, L5 may even be fused with part of your sacrum.
- Sacrum/Coccyx: The sacrum has 5 vertebrae that usually fuse by adulthood to form one bone; the coccyx—most commonly known as your tail bone—has 4 (but sometimes 5) fused vertebrae. The sacrum and coccyx are also part of your pelvis.
Now, take a look at the image below. It's a close-up of vertebrae, and it shows how the vertebrae fit together in the spinal column.
The basics of vertebra anatomy:
- Vertebral body: This is the largest part of your vertebra, and it's somewhat cylindrical in shape. The vertebral bodies are on the anterior side (front—and in this case, that means facing into your body) of your vertebrae.
You can fracture the vertebral body.
- Facet joints: Your spine also has facet joints, which are on the posterior side (back) of your vertebrae. These joints (like all joints in your body) help facilitate movement and are very important to your flexibility. The facet joints work like hinges, and they help stabilize your spine and control your movements. They're composed of the superior and inferior articular processes. Two superior articular processes are on the top of the vertebra, and two inferior articular processes are on the bottom.
The facet joints can fracture, and if they break, it's likely that your spine will be unstable. Fractured facets aren't as capable of controlling your movements.
- Pedicle: The pedicles come out from the vertebral body, and they are on the posterior side (back) of your vertebrae. You have one pedicle on each side of the bone, and they help form the ring that protects the spinal cord.
It's possible to fracture the pedicles.
In between your vertebrae, you have intervertebral discs. These discs function like cushions, absorbing shock from your movements. The discs are what allow your spine to move in multiple directions. They are made up of two parts: the center of the disc is called the nucleus pulposus, and the outer part is the annulus fibrosus. It helps to think of the disc as a jelly donut: the nucleus is composed of a gel-like substance, and surrounding it is the tougher annulus that holds in the "jelly."
The intervertebral discs and the vertebrae create the spinal canal, which protects the spinal cord and spinal nerves. You can see the spinal cord running down the center of the vertebrae in the above image, and you can see the nerves exiting the spinal canal and going to various parts of the body, where they help you feel and move.
The spinal cord tapers as it travels down the spinal canal, and it ends between the first and second lumbar vertebrae. Below that point, there's a cord-like extension and various nerves travelling to the legs.
Because the spinal cord and spinal nerves are so close to the vertebrae, if you have a spinal fracture, it is possible to damage the spinal cord or nerves. If you have a fracture below the L1-L2 (first and second vertebrae in the lumbar spine), you won't have a spinal cord injury, but it's still possible to injure the nerves.
Your back also has muscles, ligaments, tendons, and blood vessels. Muscles are strands of tissues that power your movement. Ligaments are the strong, flexible bands of fibrous tissue that link the discs and bones together, and tendons connect muscles to bones. Blood vessels provide nourishment. These parts all work together to help you move.