Diagnosing Back Pain
by Dr. C.H. Weaver M.D. updated 10/2019
Technological advances have made the diagnosis of disorders of the spine easier. However, our enthusiasm for medical technology must be tempered by recognizing that deviations from what we define as normal are not necessarily associated with a specific complaint. For example, most individuals who have bulging intervertebral discs on magnetic resonance imaging test have no symptoms associated with these alterations from normal. Therefore, any abnormality mentioned as a finding must be correlated with patient complaints to be sure that they are important.
The following is a list of common tests used by physicians to diagnose conditions affecting the spine.
- Conventional x-ray
- Magnetic resonance imaging (MRI)
- Computed axial tomography (CT)
- Bone scan
- Bone densitometry (DXA)
- Electrodiagnostic testing
- Blood tests
Conventional x ray
Radiography involves the use of radiation (x-rays) to create an image of the internal structures of the body. Previous, radiographs were created by passing small highly controlled amounts of radiation through the human body, capturing the resulting image on a special type of photographic paper. Current technology allows for the digital capture of the images without the need for film. Solid structures block the flow of x-ray beams and appear with white shadows on images. Bones are visualized well with conventional x-rays. Alterations in bone structure caused by fractures, arthritis, or cancer may be identified by conventional –ray techniques by medication from normal appearing bone in the corresponding portion of the spine. Digital x-ray allows for the use of smaller amounts of radiation with greater precision of images that would not have been recognized by older-x-ray methods.
Conventional Spine X-rays
What are conventional x-rays?
Conventional x-rays of the spine use the same technology as used for chest x-rays. Patients are positioned to allow the smallest area of exposure that allows imaging of the part of the spine under investigation. The number of pictures taken corresponds to the best alignment of the x-ray tube with the anatomic structure.
X-rays are not required for spine pain that is 8 weeks or shorter in duration. X-rays are indicated during this initial period if individuals have symptoms suggestive of a systemic illness (LOOK AT SYMPTOMS). X-rays are most useful looking at the bones and joints of the spine. Soft tissues like muscles and intervertebral discs are not visualized by this technology.
How are conventional x-rays taken?
Generally, you will be positioned on your back and on your side for an initial spine x-ray study. X-rays taken on a 45 degree angle visualize the joints of the spine. Frequently, a frontal view of the pelvis examining the sacroiliac and hip joints will be taken while lying flat on the x-ray machine. . If there is a concern regarding the stability of your spine, a standing x-ray of bending forward (flexion) and bending backwards (extension) will be added.
Magnetic resonance imaging MRI
MRI is the most recently developed diagnostic imaging technique for the evaluation of spinal conditions. Through the use of radio waves and strong magnets with some 3 times the magnetic force of the Earth, this noninvasive technique visualizes the component parts of the spine from multiple directions. Under the influence of the strong magnet, the hydrogen atoms in water in the body line up like compass needles. These hydrogen atoms are exposed to radio signals that cause them to momentarily change their spinning axis. In the process of returning to their orientation under the influence of the magnet, they release a small, brief radio signal. A radio receiver computes all these radio signals. A computer generates the image of the organs and skeletal structures based on the pattern of these hydrogen ion radio waves.
What is a MRI scan?
MRI is an imaging technique that does not use radiation for the generation of the images. Strong magnets, radio wave generator and receiver, and a powerful computer are used to generate images. MR scans are most successful using the hydrogen atoms in water to generate images. All structures of the spine can be delineated by MR including areas of inflammation. Soft tissues are most easily imaged.
How is a MRI scan taken?
The MRI is a painless procedure, but may be uncomfortable if you are experiencing spine pain. You are positioned on your back on a sliding table. The table is positioned inside the magnet that is open on both ends. The top of the tube is about 2 inches from your face. Frequently you are given earphones to listen to other sounds than the clicking of the radio wave generator. The duration of the test correlates with the number of structures to be examined.
Closed versus Open MRI scans?
In a closed MR scanner, you are on your back in a confining oval tube. The tube is open on both ends. The top of the tube is 2 to 3 inches from your face. Depending on the number of images needed, the test lasts between 20 to 60 minutes. Also during the procedure, a ticking sound is produced. For those who are scared of closed spaces (claustrophobics), an open MR scanner is an alternative. The open machine consists of a round magnet supported by 4 columns. The scanner is open on all sides. The concern about open scanners is that the images are less sharp than closed scanner images. For claustrophobic patients, oral sedation prior to a closed machine procedure is usually adequate to calm anxieties.
Lying, Sitting, Standing scanners?
You have spine pain that occurs frequently in a certain position, standing, sitting, or lying. Lying is the position least frequently associated with spine pain, but is the position most frequently used for MR scanning. Sitting and standing MRI scanners are available but in fewer numbers than standard machines. Also the quality of these sitting and standing scans are less than usual MR scans. Individuals have much greater difficulty sitting or standing in exactly the same place for periods of time when the scans are produced. Therefore, more likely than not, your scan will be done in a lying position. You will need to ask your physician if a sitting or standing study is appropriate for you and if that scanner is available in your community.
Contrast or No Contrast?
Gadolinium is a chemical that has magnetic properties. In areas where the integrity of the blood vessels has been damaged (cancer, infection, inflammation) gadolinium injected into a vein will escape from blood vessels into damaged tissues. These tissues look the same in regular MR scans, but stand out on contrast MR. Contrast MR scans are ordered after spine operations to identify scar tissue and when tumors or inflammation are suspected. Gadolinium should not be used in individuals with compromised kidney function. The contrast can cause unusual scarring in a variety of tissues when used in people with kidney failure.
People who have pacemakers, or have ferrous-based metal clips should not come close to the MR magnet. Pacemakers may misfire and metal clips may move around. Severely claustrophobic patients may be unable to tolerate the scanner in any form.
Computed axial tomography CT
CT or CAT scans create cross-sectional images of the bony structures of the spine. The CT scanner is a motorized table that moves the patient through a circular opening and an X-ray machine that rotates around the patient. Computers attached to x-ray detectors produce a “slice” of the patients. Multiple slices are generated to see the spine over a distance. With a computer, the slices can form a three-dimensional model of the spine and the neural foramena.
What is a CT scan?
CT scans uses x-rays generated from multiple directions to form an image.. A computer is able to generate images that recreate a virtual slice through the body. CT scanners use many x-rays to generate images. The radiation exposure is much greater with this procedure.
Radiation exposure form CT scans for studies of the abdomen and pelvis are associated with an increased risk of developing cancer. The amount of x-ray for a spine study is substantial. Younger individuals are at greater risk that those who have CT scans later in life. The bottom line is that CT scan should be used if it is the only test that can diagnose your problem.
How is a CT scan taken?
CT scans are taken while you lie flat on your back in the center of an open circular overhead structure that supports the scanning machine (gantry). The machine revolves around you taking images from multiple directions. The test is not uncomfortable other than the discomfort associated with lying still for 20 to 40 minutes.
Before the availability of MRI, myelography was the “gold standard” of imaging structures for imaging structures including the spinal cord and roots. The procedure requires a spinal puncture. A spinal puncture is done by advancing a needle between the spinous processes past the dura, the outer covering of the spinal canal. Once the needle is positioned, contrast dye is injected into the space. The dye outlines the bones and disc placement. The procedure can cause a headache, and rarely, a seizure if the contrast reaches the brain. One advantage of a myelogram is that it can be taken in a standing or sitting position. The ability to test in a “functional” position that reproduces pain is particularly helpful for diagnosing spinal stenosis.
What is a myelogram?
A myelogram is a technique where contrast dye is injected into the spinal canal through a spinal needle. The flow of the dye and its eventual location in the spinal canal identify anatomical abnormalities. In the past, oil-based contrast dye was used but was associated with inflammation of the interior of the spinal canal. Currently, water-based dyes are used with a smaller risk of inflammation but a shorter time to generate the images and an increased risk of seizures.
How is a myelogram taken?
Myelograms are used for evaluation of neck and low back disorders. The injection of the dye into the spinal canal is instilled near the base of the skull or in the lumbar area. The neck injection is more painful than the lumbar injections since a greater amount of tissue needs to be entered in order to gain access to the cervical canal. However, the amount of dye needed for a cervical image is less. The images need to be completed within 20 to 30 minutes after the injection to avoid dilution.
Certain precautions are necessary before and after myelography. Any drugs that lower seizure thresholds should be discontinued for 2 days before the procedure. Food should be avoided for 4 hours before the procedure. After the procedure, patients sit in a semi erect position in bed for several hours. After, lying down with the head slightly raised is allowed. The most common complaints after a myelogram is headache followed by nausea and vomiting.
Bone scan or radionuclide scan involves an injection of a small amount of a radioactive material intravenously. The radioactive fluid is attracted to bone cells. More active bone cells involved with inflammation or fracture take up a greater amount of radioactivity than normal cells. These spots are darker on the scan. A few hours after the injection, the scanning begins with you lying flat on your stomach for about 60 minutes while a scanner measures the radioactivity in the lumbar spine. The presence of “dark” spots does not indicate a specific diagnosis because a number of different health problems result in increased activity. Additional evaluation is usually required to establish a specific diagnosis.
What is a bone scan?
A bone scan (radionuclide imaging) is a technique to visualize organ activity by measuring the uptake of a small amount of radioisotope material. The radioactivity level is in proportion to the uptake by the targeted organ. Different isotopes are taken up by specific organs. Bone can is not invasive or associated with significant risk. Bone scans are an excellent technique to identify abnormalities in bone. Decreased activity in bone results in a decrease in activity on the scan. Increased activity, as associated with a fracture or cancer, results in a hot spot on the scan.
How is a bone scan taken?
Small amount of a radioactive isotope that attaches to bone is injected intravenously. The patient is placed in front of a scanner that detects the areas of radioactivity. The scans are taken up at variable times after the injection. Some scans are taking very soon after injection while others are taken 2 to 4 hours after injection. Occasionally, scans are taken 1 to 3 days after injection particularly in older patients to allow for a measurable effect shown by growing bone after an osteoporotic fracture.
What is a SPECT scan?
Single-photon emission computed tomography (SPECT) bone scan offers more accurate localization of lesions than associated with bone scans. Radioactivity can be localized to specific portions of a structure such as a vertebral body versus a spinous process, or a facet joint. Facet joint arthritis can be identified by SPECT scan. SPECT scan can also be used to evaluate the status of spinal fusions after operative procedures.
What is a PET scan?
Positron emission tomography (PET) is a radioactive technique that identifies an increased metabolic rate in the studied organ. Increased metabolism is seen in tumor cells before there are anatomic changes. This technique is used more frequently to identify early stages of lung and breast cancer. The technique is used infrequently for the evaluation of the spine.
Discography is a radiographic technique to identify painful intervertebral discs. With the use of an x-ray machine, a thin needle is advanced into an intervertebral disc. First, dye is injected into the disc to visualize the integrity of the center and outer portions of the disc. If pain is generated, an anesthetic is injected to resolve pain. This is considered a positive test. The test is used to determine the source of back pain when other radiographic techniques have been inconclusive in finding a source of pain. The procedure is often damaging to spine structures and may not be predictive of the benefit of spinal surgery for abnormal disc levels.
Bone densitometry DXA
Dual energy x ray absorptiometry (DXA) is the technique most commonly used to determine the amount of calcium in the lower spine and hips. Low energy x rays are used to determine the difference between beam absorption by bone versus surrounding soft tissues, like muscle. Bone tissues absorb the beam of x rays while the x rays pass through the soft tissues. The difference in absorption corresponds to the amount of calcium in the spine and thigh bones. The test is done while lying flat on your back on a table. The arm of the machine passes over you for about fifteen minutes. Other bone density measuring techniques use the heel as the measuring location. The machine is portable so it is more accessible. Unfortunately it is less accurate than the DXA of the hips and spine.
What is a DEXA?
DEXA scan uses two sources of x-ray energy to separate soft and bone tissue components of bone and surrounding tissues. DEXA is used to measure the bone mineral density of the lumbar spine and long bones. A phantom of a constant density is used to calibrate the machine. The precision of DEXA for bone mineral density of the vertebral spine is 1%, with accuracy variability of 4% to 8%.
How is a DEXA taken?
The test is done while lying flat on your back on a table. The arm of the machine passes over you for about fifteen minutes. Other bone density measuring techniques use the heel as the measuring location. The machine is portable so it is more accessible. Unfortunately it is less accurate than the DXA of the hips and spine.
Electrodiagnostic tests, nerve conduction velocity (NCV) and electromyography (EMG) evaluate the function of peripheral nerves that supply sensation and motor signals to the arms and legs. They demonstrate abnormalities in nerve and muscle function but do not identify the specific cause. EMG evaluate the electrical activity generated by muscles at rest and when contracting. NCV measures the speed of transmission of the electrical signals in a nerve. Both of these tests are useful in differentiating among neurologic disorders that cause arm and leg pain.
EMG involves inserting small needles into normal and muscles thought to be damaged. The amount of irritation and the amount of electricity generated by the muscle help determine the degree of injury to the muscle and the nerve that supplies it.
NCV determines the speed of signals as they travel down nerve in the arms or legs. Pads are placed of the far end of an arm or leg. Another pad is placed over the same nerve in a location further up the leg. An electrical signal is generated in the pad closer to the center of the body. The signal is detected in the distal pad and the speed of the signal is matched against normal speeds. Slower speeds suggest the nerve is being compressed in a location away from the spine.
Although the tests do not define a specific cause of dysfunction, the tests do identify the level of nerve damage. This helps direct therapy to the specific level that is damaged. This can help direct locations for injections or surgical decompression.
Laboratory blood tests are rarely needed for evaluation of individuals with spinal pain. Blood tests are reserved for those individuals that have symptoms suggestive of a systemic illness. Only a few blood tests are useful for identifying abnormalities associated with systemic spinal illness. These include a complete blood count (CBC), complete metabolic count (CMC), erythrocyte sedimentation rate (ESR) and C reactive protein (CRP).
CBC includes determination of red and white blood cells and platelets. These counts can be abnormal in the setting of inflammatory diseases (ankylosing spondylitis) and cancer (multiple myeloma). CMC tests the status of calcium metabolism, liver function, and kidney function. These counts can be abnormal with hormonal diseases causing osteoporosis. CBC and CMC are more often obtained to monitor for toxicity of drugs.