However, they are important to verify the diagnosis if surgery is contemplated and are sometimes necessary to clarify the differential diagnosis. If the history is suggestive of lumbar spinal stenosis, MRI or CT scans should be performed. If the patient has undergone a fusion and instability might be causing the pain, flexion-extension X rays of the lumbosacral spine are indicated. Lumbar myelogram with CT scan is usually indicated only when surgery is being contemplated, especially in cases of spinal stenosis, lateral-recess stenosis, multiple abnormal discs, or possible neoplasm. In most cases of low back pain, plain X rays of the lumbosacral spine are unnecessary.
Oblique views are of little value.
Flexion-extension views may be helpful in patients who have had a surgical fusion in the past or who are known to have spondylolisthesis. With regard to radiation exposure, a full lumbosacral spine series gives peak gonadal doses of 200 to 400 mrads to women and 50 to 125 mrads to men. It does not allow multiplanar views of the spine, and the conus and levels above L3 are usually not imaged. CT is probably better than MRI for demonstrating abnormal facet joints, severe degenerative changes in elderly patients, and unstable fusions. In most cases, it is inadvisable to proceed to disc surgery on the basis of CT findings alone.