Back Pain

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Diagnosis

Physicians often use a patient history, a physical examination, and x-rays or other imaging tests to help diagnose back pain.

Lumbosacral spine (LS) x-rays usually include 3 images—one frontal image and two from the sides. One view includes the entire lumbosacral spine, and the other film is a lateral "spot film" which is directed to the joint between the lowest lumbar vertebra and the sacrum. In certain circumstances, oblique views may be added on.

LS x-rays provide information about degenerative changes and also provide a good look at disc spaces. This test is used to determine if all of the vertebrae line up properly. The lumbar vertebrae are located between the lowest thoracic vertebra and the sacrum. Although the entire LS spine, from L1 at its highest to L5 at its lowest, may be affected, the lowest part is affected far more often.

In some cases, LS spine films detect the 5th lumbar vertebra appearing to "slide off" the sacrum below it. In a sense, the vertebral column is a long tunnel, with the spinal cord running through it. If you remove one vertebra, it would look a bit like a ring. The column works fine as long as all the rings line up properly, but sometimes, one of the vertebra is incomplete. If that incomplete ring is L5, which must support the other vertebrae, problems occur.

A vertebra with an incomplete ring is known as spondylolysis; one vertebra slipping over another results in a condition called spondylolithesis. Either of these conditions, especially when they affect the lower lumbar vertebrae, can cause back pain. The x-ray is a good diagnostic test for these conditions, but, in some cases, additional imaging tests are needed. Although the vertebrae are clearly visible on x-ray, the critical soft tissues (e.g., discs, nerves) are not.

Before the advent of CT scan (computed tomography), most lower back pain was diagnosed using myelography. In this test, dye is injected into the spinal canal in the lower back (lumbar puncture) and a number of x-rays were taken in many different positions. Images of the spinal sac can detect a disc pushing into it. Myelograms still may be used in difficult cases, but instead of a series of x-rays, the imaging is generally done using CT.

CT scan also may be used to diagnose lower back pain. This test enables the radiologist to identify the discs and determine what effects they have on adjacent structures (e.g., nerves). CT also can detect spondylolysis, spondylolithesis, and spinal stenosis (narrowing).

For patients who have had lower back surgery, the situation is more complicated. In addition to other soft tissue (e.g. discs, nerves, muscles), there is also scar tissue. It may be difficult to determine if density is scar tissue or a recurrent ruptured disc. To differentiate between the two, the radiologist administers intravenous contrast, which lightens the scar, but not the disc.

In more complicated cases, MRI scan (magnetic resonance imaging) may be used. MRI scan can obtain information about an entire section, in any plane. The radiologist can rotate the images and look at them from the side, obliquely, or as cross-sections. MRI is also a better modality to study soft tissues.

Different magnetic sequences demonstrate fairly subtle differences in soft tissue structures in the back. In patients who have had back surgery, an MRI contrast agent (gadolinium) may be administered to help differentiate between disc material and scar tissue. This contrast agent is inert, is unlikely to cause any problems, and is injected through a very small needle, which is nearly painless.

Prevention

Not all back pain can be prevented. It is important to take care of the back by keeping fit and exercising. Swimming and walking are particularly good forms of exercise for patients with chronic lower back pain. Firm options are preferable in mattresses, box springs, couches, and chairs.

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