Do I Really Need an X-ray or MRI for Lower Back Pain?

Since MRI seems to be the preferred advanced imaging study, is MRI necessary to diagnose the cause of lower back pain?

Lower back pain is one of the most common reasons why people visit their doctor or go to urgent care. Severe low back pain may lead you to think something is seriously wrong with your lumbar spine. Perhaps you ask the doctor for an x-ray (ie, plain radiographs) or MRI (ie, magnetic resonance imaging) to relieve your concerns. But, as hard as it may be to believe, the cause of most cases of lower back pain (even acute pain) is not serious and undergoing a spinal imaging test is probably not necessary.

lower back x-ray, anterior view, from the front of the bodyX-rays are often called the 'workhorses' of the radiology department and this type of spinal imaging test best detects bony structural problems. Photo Source:

Many lower back pain cases improve in days or a few weeks. A strained muscle, sprained ligament or poor posture typify causes of low back pain that can be extremely painful and possibly limit your activity level yet can be easily treated without the need for spinal imaging tests.

But what about lower back pain that lasts longer than 2 or 3 weeks—does that indicate the need for an x-ray or MRI to diagnose a spinal disorder that may be serious?

Not always. Rarely is subacute (pain lasting between 4 and 12 weeks) or chronic back pain (pain lasting 3 months or longer) an indication of an urgent lumbar spine condition. In fact, less than 1% of people with lower back pain are diagnosed by their primary care doctor with a condition that may require spine surgery—such as cauda equina syndrome, spinal infection or metastatic spinal cancer.1

What role does x-ray or MRI play in diagnosing the cause of lower back pain?

Your doctor may recommend an x-ray or MRI if your lower back pain resulted from traumatic injury, such as a fall or car accident. Of course, that doesn’t mean other potential causes of lower back pain do not warrant medical imaging immediately or at a later time.

Keep in mind, the diagnostic process starts with the doctor’s evaluation of your lower back symptoms and how they relate to findings from your physical and neurological examination and medical history. Combined, your doctor utilizes these results to determine the need for spinal imaging—as well as the type of imaging test (eg, x-ray, MRI) and timing to confirm a diagnosis (eg, cause of your lower back pain).

When may a low back x-ray or MRI be recommended?

While x-rays are sometimes called the workhorses of the radiology department, this type of spinal imaging test is best at detecting bony structural problems rather than soft tissue injury. An x-ray series (eg, anterior, posterior, lateral views) may be performed to diagnose vertebral compression fracture that may be related to the patient’s history of osteoporosis.

Unlike x-rays, MRI is a radiation-free test. MRI renders detailed three-dimensional anatomical views of spinal bone and soft tissues. Sometimes, a contrast agent or dye (eg, gadolinium) is used to highlight and  improve the quality of the MR images. The contrast is injected through an intravenous line in your hand or arm before or during a test phase. An MRI may be necessary to evaluate neurological symptoms,2 such as radiating pain or back pain that develops in a patient previously diagnosed with cancer.

Listed below are symptoms and co-existing medical diagnoses and conditions that may suggest the need for lumbar spine image tests.

Neurological symptoms

  • Lower back pain that radiates (spreads) downward into the buttocks and legs
  • Abnormal reflexes in the lower body (may indicate disruption of the nerves that enable sensation and movement)
  • Sensations of numbness, tingling and/or weakness develop
  • Foot drop (inability to lift your foot)
  • Dysfunction or loss of bowel and/or bladder control

Co-existing medical diagnoses and conditions

  • Cancer
  • Diabetes
  • Fever
  • Osteoporosis
  • Previous spinal fracture
  • Prior lumbar spine surgery
  • Recent infection (eg, urinary)
  • Use of immunosuppressant drugs
  • Use of corticosteroid medication
  • Intravenous drug use
  • Unexplained weight loss

Should I be concerned about x-ray radiation exposure?

Everyone is exposed to naturally-occurring radiation and the amount varies depending on where you live. When you undergo an x-ray, the radiation that is not absorbed by your body creates your spinal image. Your radiation dose is the amount of radiation your body absorbs every time you undergo x-ray. Radiation dose to your entire body is measured as the millisievert (mSv) also called the effective dose.

The value of effective dose helps your doctor measure your risk for potential side effects of undergoing radiographic imaging (ie, CT scans also use radiation). For example, it is known certain body tissues and organs in the lower back regions are sensitive to radiation exposure such as the reproductive organs (testicles, ovaries). Also, radiation exposure can increase the risk for cancer.3

Since MRI is advanced and radiation-free, why don’t more doctors order this test to diagnose the cause of lower back pain?

First, MRI is not appropriate in all patients because it operates using powerful magnet technology. Therefore, people who are pregnant or have metal inside their body (eg, spinal cord stimulator, heart pacemaker) cannot undergo MRI.

MRI testing is expensive, and your doctor does not want to prescribe unnecessary tests that increase your healthcare costs. According to data collected by the Kaiser Family Foundation, the cost of an MRI performed in the United States in 2014 was $1119—an amount significantly higher than other comparable countries.4

MRI results may be variable depending on who reads the images. That is one reason why spine surgeons evaluate their patients’ MRI studies themselves.

Considering the anatomical detail an MRI provides, sometimes a spinal abnormality is revealed that may appear to be serious but is not. Take this typical example: an MRI of the lower back reveals a sizable lumbar herniated disc at L4-L5 in a patient who reports no back/leg pain or other symptoms associated with that level of the lumbar spine. This is one reason why doctors combine all their findings (eg, symptoms, physical exam) to confirm a diagnosis and then recommend an appropriate treatment plan.

Key Low Back Pain Image Testing Takeaways

If you develop lower back pain, listen to your doctor’s recommendation—even if he/she doesn’t order a lumbar x-ray or MRI study right away. Keep in mind the imaging test indications mentioned earlier in this article—such as neurological symptoms and/or co-existing medical conditions that may accompany lower back pain. And, take comfort in knowing that undergoing an x-ray or MRI will not make your back pain go away faster.

Updated on: 10/29/19
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