X-rays provide detail of the bone structures in the spine, and are used to rule out back pain resulting from:
- Instability (such as spondylolisthesis)
They image bones by shooting an x-ray beam through the body. The calcium in bone blocks penetration of the x-ray beam and the image of the bones is picked up as a shadow on a film positioned on the other side of the patient.
X-rays provide for excellent bony detail because bone consists mainly of calcium. However, discs and nerve roots do not have any calcium, so an x-ray does not capture an image of these structures. An x-ray, therefore, cannot be used to diagnose lumbar disc herniation or other causes of nerve pinching.
X-rays should not be performed on women who may be pregnant.
An MRI scan is a completely different technology from an x-ray and CT scan and represents the single most useful imaging study available for spine surgery.
An MRI scan is particularly useful as an aid in the assessment of certain back conditions by providing detail of the spinal disc (such as for degenerative disc disease, isthmic spondylolisthesis) and nerve roots (such as for lumbar disc herniation, lumbar spinal stenosis). MRI scans are also useful to rule out tumors or spinal infections.
A CT scan is essentially a fancy x-ray that can take cross section images of the body.
They provide excellent bony detail, yet through multiple views are also capable of imaging for back pain caused by specific conditions, such as:
- lumbar disc herniation
- lumbar spinal stenosis
Like an x-ray, a CT scan works by shooting an x-ray beam through the body. Next, a computer is used to reformat the image into cross sections of the spine. This process is repeated at multiple different intervals.
When combined with a myelogram, a CT scan provides for excellent nerve detail during an examination of back pain. The myelogram adds some additional risk and expense to the CT scan but provides substantial information about the nerve roots.
A myelogram consists of injecting a radiographically opaque dye (dye that is picked up by x-ray) into the sac around the nerve roots, which in turn lights up the nerve roots.
An EMG assess the electrical activity of a nerve root and is sometimes recommended for patients with back pain. After three weeks of pressure on a nerve root, the muscle the nerve goes to will begin to spontaneously contract. Compression of a nerve will also slow electrical conduction along that nerve. EMG's are also sometimes useful to distinguish nerve degeneration (neuropathy) from nerve root compression (radiculopathy).
The test involves placing small needles into the muscles, so there is some discomfort for the patient. There are no major risks, although the tests are not highly reliable in determining which nerve is compressed.
A bone scan is sometimes performed to rule out an inflammatory process (such as a tumor or infection) or an occult fracture (small fracture not seen on an x-ray) as the cause of back pain.
A bone scan is performed by injecting a small amount of radioactive marker into an intravenous line (IV). Three hours later the patient is placed through a scanner and the radioactive marker will be concentrated in any region where there is high bone turnover.
Discography (also called a discogram) is a diagnostic procedure used to determine if one or more discs are the cause of back pain. The procedure involves pressurizing discs by injecting them with a sterile liquid to induce pain in the affected discs.
Discography Video: Non-Surgical Back Pain Diagnostic Procedure
Dual Energy X-ray Absorptiometry (Dexa scan)
A dexa scan is used specifically to assess a patient's risk of fracture by detecting osteoporosis of the vertebral bodies, which is a thinning of the bones as we age and a possible source of back pain.
A dexa scan takes about ten minutes and is associated with minimal radiation exposure.