Anatomy of the Spine

This information relates to normal spinal alignment. The spine is a series of building blocks called vertebra stacked one on top of another, separated in the front by the discs and in the back by the facets. From the front view, the spine should be straight with the center of the head sitting on a plumb line directly over the pelvis. The side view of the spine has multiple curves that when added together should also have the head sitting directly over the pelvis.

On the side view, there are 2 forward curves (the thoracic spine and sacrum) called a kyphosis and two backward curves (the cervical spines and lumbar spines) called a lordosis. These side curves are like springs and balance each other out.

What Causes a Curve in the Spine?

The curves of the spine originate in the shapes of the discs and the shapes of the vertebral bodies. In the cervical and lumbar spine, the vertebra are square and the discs are trapezoidal. If you could stack these vertebra on top of each other without the discs, you would have a straight column. It is the angular shape of the discs that cause the lordotic or backwards curves that occur in the neck and lower back.

The thoracic spine has a forward or kyphotic curve. This curve is mainly caused by the shape of the vertebral bodies. If you took the discs out and stacked up these vertebra, there would still remain a forward curve. The discs however do contribute as much as 50% of the curve in the thoracic spine.

These facts are important as you can see some of the problems that can secondarily occur with alignment and degeneration of the discs. Losing disc height in the lumbar spine can cause a flat back syndrome where the individual feels pitched forward. Losing disc height in the thoracic spine can increase the forward curve (the kyphosis) and again, the individual feels pitched forward. Losing disc height in the cervical spine makes the patients head feel front heavy and has difficulty “holding it up”.

What is Normal Spinal Alignment?

Normal spinal alignment and balance are very important to energy consumption with standing and walking. If the head is directly over the pelvis which is the center of gravity point for the body, there will be little need for muscle contraction to keep the head and torso over this balance point. The energy expenditure necessary for walking with good balance is very minimal. Conversely, if there is an abnormal curve and the head is off the midline, the amount of muscle contraction necessary to walk makes this amount of energy expenditure very fatiguing.

The front to back view of the spine should be straight. Any curve greater than ten degrees is called a scoliosis. Small scoliosis curves for many patients are just a finding on an X-ray that has no bearing on the patient’s well being. Only if the curve is large or advances does a scoliosis need attention.

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(Click to Enlarge Image) This is a picture of the normal alignment of the spine when viewed from the side (sagittal alignment). The curves of the neck and lower back are in the same direction (lordosis) and the mid-back curve (kyphosis) is reversed. All curves add up to make the spine align with the head directly over the pelvis.

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