Spinal anatomy is a remarkable combination of strong bones, flexible ligaments and tendons, large muscles and highly sensitive nerves. It is designed to be incredibly strong, protecting the highly sensitive nerve roots, yet highly flexible, providing for mobility on many different planes. Most of us take this juxtaposition of strength, structure and flexibility for granted in our everyday lives—until something goes wrong. Once we have back pain, we’re driven to know what’s wrong and what it will take to relieve the pain and prevent a recurrence.

How the Spine May Produce Back Pain
Many different structures in the spine can cause back pain, potentially when:

• The large nerve roots that go to the legs and arms are irritated
• The smaller nerves that innervate the spine are irritated
• The large paired back muscles (erector spinae) are strained
• The bones, ligaments or joints themselves are injured
• The disc space itself is a source of pain.

Therefore, a review of spinal anatomy is important to understand the causes of back pain, neck pain and sciatica (leg pain), and evaluate treatment options.
Cervical, Thoracic, Lumbar and Sacral Spinal Anatomy

There are four major regions of the spine:

The cervical spine (neck)
The neck supports the weight of the head and protects the nerves that come from the brain to the rest of the body. This section of the spine has seven vertebral bodies (bones) that get smaller as they get closer to the base of the skull. Most of the rotation of the cervical spine comes from the top two segments whereas most of the flexion/extension movement comes from C5-C6 and C6-C7 (each motion segment is named by the two vertebral bodies that are connected).

Acute neck pain is most often caused by a muscle, ligament or tendon strain (such as from a sudden force or straining the neck), and will usually heal with time and non-surgical treatments to alleviate the neck pain (such as ice and/or heat, medications, chiropractic or osteopathic manipulation, etc).

For patients with neck pain that lasts longer than two weeks to three months, or with mainly arm pain, numbness or tingling, there is often a specific anatomic problem. For example, pain that radiates down the arm, and possibly into the hands and fingers, is usually caused by a cervical herniated disc or foraminal stenosis pinching a nerve in the neck. Treatment options for neck pain will differ depending on the specific diagnosis.

The thoracic spine (upper back)
The 12 vertebral bodies in the upper back make up the thoracic spine. The firm attachment of the rib cage at each level of the thoracic spine provides stability and structural support to the upper back and allows very little motion. The thoracic spine is basically a strong cage and it is designed to protect the vital organs of the heart and lungs.

The upper back is not designed for motion, and subsequently, injuries to the thoracic spine are rare. However, irritation of the large back and shoulder muscles or joint dysfunction in the upper back can produce very noticeable back pain.

The lumbar spine (lower back)
The lower back has a lot more motion than the thoracic spine and also carries all the weight of the torso, making it the most frequently injured area of the spine.

The motion in the lumbar spine is divided between five motion segments, although a disproportionate amount of the motion is in the lower segments (L3-L4 and L4-L5). Consequently, these two segments are the most likely to breakdown from wear and tear (e.g. osteoarthritis). The two lowest discs (L4-L5 and L5-S1) take the most strain and are the most likely to herniate. This can cause lower back pain and possibly numbness that radiates through the leg and down to the foot (sciatica).

The vast majority of episodes of lower back pain are caused by muscle strain. Even though a muscle strain doesn’t sound like a serious injury, trauma to the muscles and other soft tissues (ligaments, tendons) in the lower back can cause severe back pain. The good news is that soft tissues have a good blood supply, which brings nutrients to the injured area, facilitates the healing process and often provides effective relief of the back pain.

The sacral region (bottom of the spine)
Below the lumbar spine is a bone called the sacrum, which makes up the back part of the pelvis. This bone is shaped like a triangle that fits between the two halves of the pelvis, connecting the spine to the lower half of the body.

The sacrum is connected to part of the pelvis (the iliac bones) by the sacroiliac joints. Pain in the sacrum is often called sacroiliac joint dysfunction, and is more common in women than men. The coccyx—or the tailbone—is in the sacral region at the very bottom of the spine. Tailbone pain is called coccydynia, which is more common in women than men.

Source: www.spine-health.com, Peter F. Ullrich, Jr., MD