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Understanding Spine Problems

The way in which spine anatomy and the location of the back problem is typically described causes confusion for patients, and even for health care professionals who deal with back problems on a regular basis. Patients with back problems are all too often confused about what is pinching where, and how the back problem relates to their symptoms.

At, we frequently get questions such as:

  • "Is the problem at my L5 level or my L4-5 level?"

  • "What does S1 mean?"

  • "What is a 'transitional level'?"

  • "How does my sixth vertebra relate to my back problems?"

  • "How is my back causing the pain shooting down my leg?"

  • "Will my back problem leave me paralyzed?"

Even when spine specialists spend a great deal of time explaining the problem, it is still often hard to understand.

This is a common problem, and it's no one's fault. Simply put, back problems are difficult to describe and difficult to understand. The goal of this article is to explain in detail how spinal anatomy is commonly described and typical sources of confusion. Importantly, this article discusses how terminology used for spinal anatomy relates to common diagnoses and sources of back problems for patients.

Back Problems Usually do Not Involve the Spinal Cord

First, it is important to explain that the spinal cord does not usually cause back problems. Conditions that involve damage to the spinal cord (which can cause paralysis) usually involve trauma or disease in the cervical spine or thoracic spine, and this is different from the majority of back problems that cause pain.

Nerve roots exit through holes in the bone of the spine at each level. It is common for back problems to affect the nerve roots as they exit the spine and cause pain and other symptoms that radiate to the extremities (called a radiculopathy). In the low back, the way the nerve roots exit and branch off from the lumbar spine and sacral region looks like a horse's tail (cauda equina). They exit to each side between the bones in the spine, and travel down through the low back, across the back of each buttock, down into the lower extremities.

The way that back problems are described is often a source of confusion. This article provides in-depth information about two issues that are often difficult to understand:

  • Nerve root impingement - A lot of confusion occurs when a herniated disc or other back problem compresses a nerve root and the problem is described both by the intervertebral level (where the disc is) and to the nerve root that is affected. Depending on where the disc herniation or protrusion occurs, it may impinge upon either the exiting nerve root or the traversing nerve root.

  • Spinal abnormalities - Approximately one in ten adults has a structural low back abnormality that exists from birth. A typical abnormality is having an extra lumbar vertebra. Having a sixth lumbar vertebra rarely causes back problems, but it can create some confusion with how the spinal anatomy is described.

Before providing a detailed explanation of the above two anatomical issues, it is helpful to first review spinal terminology used to describe the normal spinal anatomy.

Before discussing the confusing aspects of terminology used to describe back problems, it is important to first review the overall terminology used to describe the normal anatomy of the spine.

Vertebrae Define Sections of the Spine

Spine anatomy is divided into 4 major sections, typically defined by the number of vertebrae (the round bones that make up the structure of one’s back bone) in each section. Vertebrae are also sometimes called vertebral bodies.

  1. Cervical spine (neck) - comprised of 7 cervical vertebrae (termed C1 to C7), starting with C1 at the top of the spine and ending with C7 at the bottom of the cervical portion of the spine. Neck problems can cause neck pain and/or pain that radiates down the arms to the hands and fingers.

  2. Thoracic spine (upper back) - made up of 12 thoracic vertebrae (known as T1 to T12), which are attached to the rib bones and sternum (breast bone). Because this part of the spine is firmly attached to the ribs and sternum, it is very stable and has fewer problems associated with motion.

  3. Lumbar spine (lower back) - typically including 5 vertebrae (known as L1 to L5), which have a great deal of motion and flexibility. Because this section of the spine bears most of the body’s weight and allows for the most motion (which stresses the anatomical structures), this is the area associated with most back problems. Problems in the low back can cause pain that radiates down the legs to the feet.

  4. Sacral region (bottom of the spine) - located below the lumbar spine, the sacrum is a series of 5 bony segments fused together (known as S1 to S5) that create a triangular-shaped bone that serves as the base of the spine and makes up part of the pelvis.The segment where the lumbar spine meets the sacral region, L5-S1, is an area that is prone to degenerate and create back problems. Four small bones that extend down from the sacrum make up the coccyx (the tailbone at the very bottom of the spine).

Disorders are common in the lumbar spine and at the top of the sacral region, as this area supports most of the body's weight which creates stress on the structures in this area. The combination of these two sections of the lower back is often referred to as the "lumbosacral region".

People with back problems that get better within a few weeks usually have a strained muscle (a pulled muscle) or other soft tissue damage. However, many back problems that don't get better within a few months are caused by some type of problem with a spinal disc or nerve.

Spinal Discs are in Between Each Vertebra

Spinal discs are located in between each of the vertebral bodies along the back bone and may also be referred to as an intervertebral disc, spinal disc, or disk. Each disc is named according to which two vertebral bodies it lies between. For instance:

  • The L4-L5 disc in the low back is between the L4 vertebrae and L5 vertebrae which make up the L4-L5 spinal segment.

  • The L5-S1 disc at the bottom of the spine lies between the L5 vertebra and the first bony segment at the top of the sacrum, which is sacral segment 1 (or S1).

The disc and vertebra above and below the disc comprise one segment of the spine - usually called a spinal level or spinal segment. The L4 vertebra and L5 vertebra, along with the disc in between them, make up the L4-L5 segment.

Discs are always labeled for the vertebrae that they lie between, and this is consistent throughout the length of the spine - for the cervical, thoracic and lumbar spine. For example, the C1-C2 disc in the neck lies between the first and second vertebrae in the cervical spine, and the T1-T2 disc lies between the first and second vertebrae in the thoracic spine.

However, the same is not true of how the spinal nerves are labeled, and back problems are often described by both the spinal segment and the nerve root that is affected.

Radiculopathy, Radiculitis and Radicular Pain

From top to bottom down the entire length of the spine, at each spinal level nerves exit through holes in the bone of the spine (foramen) on the right side and left side of the spinal column. These nerves are called nerve roots, or radicular nerves. They branch out at each level of the spine and innervate different parts of our body.

For example, nerves that exit the cervical spine travel down through the arms, hands, and fingers. This is why neck problems that affect a cervical nerve root can cause pain and other symptoms through the arms and hands (radiculopathy), and low back problems that affect a lumbar nerve root can radiate through the leg and into the foot (radiculopathy, or sciatica), thus prompting leg pain and/or foot pain.

As mentioned earlier, there is no spinal cord in the lumbar spine. Because of this, and because the spinal canal is usually fairly spacious in the low back, problems in the lumbosacral region (the lumbar spine and sacral region of the spine) usually cause nerve root problems, not spinal cord injury. Even serious conditions such as a large disc herniation or fracture in the low back are less likely to cause permanent loss of motor function in the legs (paraplegia, or paralysis).

The nerve roots are named for the level of the spine at which they exit. However, nerve roots are not labeled consistently throughout the length of the spine.

Radiculopathy and Sciatica

Another word for the nerve root is "radicular nerve", and when a herniated disc or prolapsed disc presses on the radicular nerve, this is often referred to as a radiculopathy. Thus, a physician might say that there is herniated disc at the L4-L5 level, creating an L5 radiculopathy or an L4 radiculopathy, depending on where the disc herniation occurs (to the side or to the back of the disc) and which nerve root is affected. The lay term for a radiculopathy in the low back is sciatica.

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