The orthopedist, in evaluating spine problems, needs a great deal of information in order to make an accurate diagnosis. An accurate diagnosis is necessary in order to support the decision for or against surgery. There are a number of tests available to the orthopedist. However, not all are indicated in any one patient. We may choose to use many of them if a diagnostic problem is especially difficult. The tests may be used to "see" a lesion (such as a CT scan for herniated disc). A test may also be used to check the function of involved tissue (such as an electromyogram for a pinched nerve). Tests may also be indicated to test for associated health problems (i.e. EKG) that may have an effect on the spine. Additionally, there are so called "provocative" tests, where the tissue in question may be either anesthetized or stimulated to determine its response. The response of that tissue may be judged by the patient whether or not it is similar to their ordinary discomfort. The discussion below will attempt to define each one of these testing methods, and give a general idea about how it may be used.
The Magnetic Resonance Image (MRI Scan)
The MRI scan is now a common examination for medical use. It is an extremely sophisticated test that requires a tremendous amount of technology and skill. The MRI scan is used to see the tissues. The image created has the effect of cutting the body into thin sections. This can be done transversely or longitudinally, giving the physician a three-dimensional look at the problem. It is particularly useful for herniated discs, because it can cut into the spinal canal and show us, very often with graphic detail, whether anything is out of place. The MRI scan also has the ability to "see" chemical changes within the body. The method of the MRI scan will be described briefly below, but it may be important for the patient to understand that it does not work on the basis of simple density (such as an X-ray or CT scan) but rather actually on the chemical change. This allows the physician to see the inflammation or swelling from other reasons, such as a fracture.
The Theory Behind the MRI Scan
Basically the MRI scan is done with magnetism and radio waves. It is not done with any X-ray equipment. It has no known side effects. The MRI scan works by placing the body inside a very powerful magnetic field. In a very subtle way, this will orient the atoms (most specifically the nuclei) within the patient's body along the magnetic field. If a radio wave tuned to those nuclei is then turned on, the nuclei flip and then rapidly flip back when the radio wave is turned off. This flipping back generates another wave that can be received by an antenna or a special sensor on the patient's body. Computers then interpret these many small radio waves for distance and position to create an image. It is this image that is translated onto film for Dr. Stark's use.
The MRI Indications
Because the MRI scan is useful for anatomic, as well as chemical change, it is especially helpful for those processes, that may have caused chemical changes without much changes in the anatomy (i.e. bruising, swelling, muscle damage, etc. ).
Computerized Tomography (CT Scan)
Whereas the MRI is new, the CT scan has been available in general use for approximately 20 years. The CT scan machine, though expensive, is much less expensive than an MRI scan machine. It also requires less maintenance. Our skill of using the CT scan has advanced because of our familiarity with it over the years. It is possible to get very satisfactory diagnostic information with the use of the CT scan rather than the MRI.
Theory Behind the CT Scan
The CT scan works by x-ray density. Different structures absorb x-rays at different rates. This is the reason that on a plain x-ray, the bones appear white and tissues of less density appear black. An x-ray of the bone, is actually many, many shadows superimposed upon one another. We see the bone because it is denser and overshadows everything else around it. If we need to see the soft tissue adjacent to the bone, (or in front of or in back of the bone) the plain x-ray is unsatisfactory and a CT scan must be used.
The CT scan uses x-rays and a computer to decide what the density of the tissues is at any particular point within the extremity. This, like the MRI scan, gives a cross sectional view of the structure in question. Unlike the MRI scan however, it can only provide one plane of view, a simple cross section, or at the most two, if the more sophisticated computerized interpretation is used. Because it works by density, a CT scan is particularly helpful for those structures where bone and calcium are involved.
The CT Scan Indications
The CT scan is useful in evaluation of back problems because of its ability to create a cross sectional image of tissues. The effect would be the same as one might have of cutting across the body looking down upon the open section. It is particularly useful when one structure is too close to another, penetrating or indenting upon it. We can see it in a way that would not be evident if all the shadows were superimposed. For structures such as a disc that has ruptured in the spinal canal, or where it is surrounded by bone, no satisfactory image of the lesion itself is possible without CT scan or MRI.
The Plain X-Ray
Plain x-rays are a series of shadows collected on a film. The shadows are not black and white as a shadow in the sun would be, but various stage of gray based on how much x-ray a given tissue will allow to pass. Calcium absorbs most x-ray, and fat absorbs very little. For this reason, and x-ray shows a bone to be quite white and the fat to be black. The x-ray, because it is based on density, is very helpful for evaluating bone. It is particularly helpful where there is very little surrounding or overlapping tissues (such as in the arm or leg).
The x-ray is a foundation for the work-up of back problems. In addition to providing information on the bony anatomy, x-rays also provide information on the alignment, the character of the bone, and surrounding tissues. Unlike a CT scan or MRI scan that shows the structures in cross section, the x-ray gives a more complete picture of the overall anatomy. One might understand the difference between the two types of information if one considers a common household object, such as a baseball. Where a CT scan would show the internal structure, the cork, the wrappings, etc., it would not give the person who had ever seen a baseball a very good indication of what a baseball looks like. An x-ray, being more of a photographic image would do that.
Myelogram / Discogram
Sometimes when the anatomy is overlapping or difficult to demonstrate, the physician will choose to put a contrast agent (an x-ray dye) into the tissue to notice how this contrast agent is distributed. This leaves a shadow. We may choose to put dye into the spinal canal (a myelogram), or the disc (a discogram).
Sometimes it is difficult to tell where the pain is coming from. By stimulating tissues that are known to cause similar types of pain, we may be able to determine whether or not the patient's pain is provoked or aggravated. A discogram is ordinarily done this way. The placement of the dye provides a great deal of information about the structure and integrity of the disc internally, but the patient's response to the placement of the dye, whether it is painless or painful is very important. We may choose to place contrast material, salt solution, or local anesthetic into tissue such as the disc, the nerve root, the small facet joints, or the muscle. The pattern of the patient's response is very helpful, often establishing a likelihood of involvement of one tissue over another.
The Electromyogram (EMG)
An electromyogram is a test of nerve function. It works by creating electrical impulses within the nerve and then monitoring the nerves response. It measures the speed at which those impulses travel, and the response of the target tissue (the muscle). These two measurements of nerve function help determine if the nerve has been functioning properly. Often times it is hard to know whether the nerve is impaired by a problem high in the nerve (such as in the back), or lower in the extremity. Additionally, the neurologist, (the nerve specialist who performs the EMG), can often make statements about which nerve is likely to be involved, based on which muscles are reacting abnormally. This is particularly useful when a nerve problem is strongly suspected, but the symptoms are not specific enough to make an accurate diagnosis.
The EMG Method and Theory
The EMG works by passing a small electrical impulses through the nerve. If the nerve is healthy, the impulses pass rapidly from one point to another, and their effect on the muscle is normal. If the nerve is unhealthy, because of pressure on the nerve, it will conduct the nerve impulses less well. Additionally, the muscle will not react normally, because its nerve supply has been impaired. Damage to the nerve that serves a muscle, results in a series of changes to the muscle, as well as to the nerve, and the response of these tissues to stimulation will often demonstrate these changes.
Dr. Stark will choose to use the EMG if the diagnosis is in question. The EMG may help either to establish the location or severity of the nerve problem. For example, the muscle that raises the big toe off the floor is almost always supplied by the fifth lumbar nerve root. If the patient has a generalized leg pain, and weakness cannot be demonstrated, testing by EMG will often show whether or not the nerve function is healthy. If the symptoms are vague and difficult to define, an abnormal test of the toe extensor muscle would suggest strongly that the fifth lumbar root is the problem. If that muscle is functioning normally, other muscles can be tested to evaluate the next nerve (the first sacral) or the nerve above (the fourth lumbar). Often our ability to see abnormalities (such as reflex abnormality or muscle wasting) is limited, but with the EMG our diagnostic ability can measure it.
In summary, a variety of diagnostic aids are available to the patient and the physician for the evaluation of low back problems. Just as a low back problem may cause local pain, referred pain, (pain away from the site), or interference in tissue distant from the site of injury (the atrophy following a disc herniation), a variety of tests are available to evaluate local effects as well as distant ones. Because a change may be structural (such as a fracture or herniated disc) or chemical (such as edema or atrophy), tests should also be able to distinguish between structural and chemical/metabolic ones.