Our spine is made up of individual bones called vertebrae. Each vertebra is identified by a letter and number combination. But what do they mean?

What does the Letter in the Vertebra Name Mean?

The letter indicates in which section of the spine the bone can be found. C stands for the cervical section, from the base of the skull through the neck. T stands for the thoracic section, from the neck down through the torso. L stands for the lumbar section, the lower back. S stands for the sacrum, and C for the coccyx.

What is the Number in a Vertebra Name?

Within each section, (cervical, thoracic, etc.), the vertebrae are identified by number, from top to bottom. The topmost vertebra in each section is 1, the next is 2, and so on.

So, the topmost vertebrae in the spine are C1, then C2, C3, and so on until we reach the final vertebra in the cervical section, C7.

As we travel down the spine and reach the thoracic section we transition to the “T” vertebrae. There are 12 vertebrae in the middle back, numbered 1-12. So, at the top of the thoracic region we have T1, then T2, and so on down the back until we reach T12.

Going down to the lower back we have the lumbar vertebrae. The 5 vertebrae in this section are called L1, L2, L3, L4, and L5.

In the buttocks (sacral) region there are 5 vertebrae named S1 through S5. As we grow from children to adults, these 5 vertebrae eventually fuse together to form one bone.

Below the sacral region is the coccyx. In this region, 4 vertebrae fuse together as we age. This area of the vertebrae is typically just referred to as the coccyx, or tailbone.

Why Do Doctors Refer to L4-L5? Or C5-C6?

If you are diagnosed with a spinal condition such as a herniated disc, you may hear the doctor refer to the location by a combination, like L4-L5, or C5-C6. This is how they refer to the joints of the spine. Or, with a disc, they are referring to the vertebrae above and below the disc.

So, if a doctor says you have a herniated disc at L4-L5, that means that the disc between the 4th and 5th vertebrae in the lumbar region is the one that is causing the problem.

Or, if you have a pinched nerve at C5-C6, it means that the nerve is being pinched somewhere in the joint that is formed by the 5th and 6th vertebrae in the neck.

Hopefully his introduction has helped clear up some nomenclature you may hear at the spine doctor’s office. To learn more check out our overview of spinal anatomy or our full series on spine anatomy on the blog.