Lumbar X-ray for low back pain is a commonly ordered test that offers a quick, relatively inexpensive look at the lumbar or lower spine vertebra. Lumbar X-rays only show bones and not the soft tissues like disks, ligaments, nerves, and cord. Therefore, the evaluation will mostly be limited to the bones. Some abnormalities in the bones will not even show up on lumbar X-ray.
Getting a lumbar X-ray for back pain may be an appropriate start to the evaluation. But it is important to remember that it’s not very high yield for identifying the cause of the pain. In my experience, the most significant finding is a compression fracture. The vertebra is compressed because the bone is weak or because you have had some trauma. A compression fracture on X-ray looks like a wedged vertebra or one that has lost height. Sometimes a piece of the vertebra goes back into the canal.
Other common findings include what we call degenerative changes. Most people have this with advancing age. The disks degenerate and lose height. This looks like a decreased disk space, or space between vertebra on X-ray because we don’t actually see the disk. Other degenerative findings include arthritis of the facets or the joints between the vertebra. Spurs can form in the vertebra and cause bony outgrowths. Bony outgrowths sometimes bridge the disk spaces.
More rarely, I see spread of cancer show up on these X-rays. This can be seen as lucent or dense white sclerotic lesions. Other times, you can see multiple compression fractures which can be because of weakened bone or because the bone is weakened from cancer. Rarely the X-ray can raise suspicion of infection but this is better seen with MRI of the lumbar spine.
Many other causes of lower back pain are not seen on X-ray of the lumbar spine. Causes such as disk herniations, infections, soft tissue injuries, cord abnormalities and even some bone abnormalities. Sometimes the cause of back pain is not revealed on any imaging. An abnormality seen on imaging may not necessarily be the cause of pain and needs to be correlated with your symptoms.
Lumbar X-rays for lower back pain are therefore commonly done but are fairly low yield for identifying the cause of the pain. They are a good starting point for major bone abnormalities like compression fractures, cancer, or infection. They will not identify many other important causes. They are quick and easy to do and provide an overview of the bony structure.
Further workup will be needed for low back pain if it persists or there are other concerning features. Findings like fever, weakness in the legs, incontinence or cancer. Your doctors will determine the need for further workup based on your presentation.