What is a Flexion-Extension X-ray?

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Cervical or Lumbar Instability

Back and neck pain patients and doctors are often confused by the idea of instability in the spine. From the patient’s standpoint, since they’ve mostly heard about herniated discs and compressed nerves, this idea is a bit foreign. Doctors are primarily looking for things that show up on MRIs, so they frequently miss the concept of spine instability altogether. Despite this, finding out if your back or neck is unstable is often critical for finding relief. The test that can discover instability is called a flexion-extension x-ray and despite this being common, it’s usually performed so badly that the results are worthless. Here’s how you can make sure that your test is done right.

What is Spine Instability?

Your spine is made up of the neck (cervical), upper back (thoracic), and low back (lumbar) areas. One of the biggest challenges of walking upright on two legs, rather than on four, is keeping the spine stable. Think of it this way–your spine is made up of 24 vertebrae that are stacked like kid’s blocks. When was the last time you stacked more than 20 blocks on top of each other without the whole rickety tower collapsing?

To keep the spine from collapsing, you have two main systems. One is strong ligaments that limit motion in certain areas, sort of like flexible duct tape between the blocks. The other is made up of stability muscles (called multifidus) which help adjust one vertebrae on the other as you move. If the ligaments get injured or the muscles go off line, the vertebrae can move too much, leading to too much motion between them, or an unstable spine. This is a big deal, as unstable vertebrae can cause pain by placing excessive wear and tear on the spine joints (facets) or disc, and can irritate or pinch the spinal nerves leading to nerve pain or sciatica. In fact, sometimes the spine looks fine on MRI when the real culprit is instability.

Can Instability be Seen on an X-ray or MRI?

Since regular x-rays and MRIs are static images without any movement, these tests can’t identify instability, which happens only with movement. Hence, many patients who have normal or unimpressive x-rays or MRIs are later diagnosed with instability as the cause of their back or neck pain.

What is a Flexion-Extension X-ray?

In order to replicate the conditions under which there is too much movement in the spine vertebrae, an x-ray can be taken when the patient moves. This is called a flexion-extension x-ray. For the low back, the patient is asked to bend forward and then backwards while x-ray images are taken in both positions. For the neck, the patient looks down and then up.

The Problem with Flexion-Extension X-rays

In a perfect world, the technologists taking these images would perform each one with enough movement to show if any instability is present. All too frequently, this doesn’t happen. In fact, most of the time they do it wrong. Why?

Radiology techs get in trouble if a patient reports that this test flared up their pain. Hence, they learn over time that pushing patients to their limit on this test is not advisable. In addition, having the patient get the needed motion may be more technically difficult for the tech. However, if there’s not enough motion, the test can be a “false negative”. This means that instability may be present, but the test will miss it.

How to Make Sure Your Test is Worthwhile

flex ext thumbThe trick to this test is to softly ignore the instructions of the radiology tech and get as much flexion (bending forward) and extension (bending backwards) as possible. This may require you to stick to your guns and insist you drive the amount of movement needed. So for a low back test, for the firstc flex ext thumb image bend forward to touch your toes. Then for the second, bend backwards as far as you can. For the neck, look down as far as you can and then look up as far as possible. 

The upshot? A simple test may be able to help your doctors figure out if you have instability causing your neck or back pain. However, knowing how to make the test work to get real results is critical to figuring out what’s wrong!

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16 thoughts on “What is a Flexion-Extension X-ray?

  1. chris

    You frequently blog about facet joints regarding cervical instability. Considering this is about flexion/extension, wouldn’t the anterior/posterior ligament be a main focus? Have you treated damage in theses ligaments before?

  2. Ted Martin

    So if a flexion-extension x-ray shows instability in the lumbar spine, what can be done about it?

    1. Regenexx Team Post author

      Ted,
      This will explain more about how the back works for context: https://youtu.be/o9jzzCINbHM What we do is treat the lax or injured ligaments. This explains more about how we do that: https://regenexx.com/blog/avoid-back-surgery-by-learning-more-about-the-acl-of-the-low-back-the-iliolumbar-ligament/

    2. Regenexx Team Post author

      Ted,
      We treat the cause of the instability, most commonly the ligaments. In the low back the iliolumbar ligament (ILL) stabilizes the most mobile vertebra (the one at the bottom of the spine-L5). While all of the low back bones have ligaments to hold them together (think duct tape), usually only L5 (and sometimes L4) has an extra set of ligaments. This extra reinforcement reaches out from the transverse processes at the side of the vertebra and grabs onto the pelvis (see below). The ligament literally prevents the L5 vertebra from slipping forward, something it tends to do when you bend forward or if your low back has extra curve. In addition, if your muscular stability is trashed due to nerve problems at L5 or S1 causing your multifidus to atrophy, the ILL is extra important because it’s literally most of what keeps the L5 vertebra from slipping into your abdomen! Also note below that the ligament, when over stretched and painful, can refer pain into the front of the groin and low back. This instability also contributes to degenerative disc disease and can take nerves offline, so it is very important to get treatment.

  3. chris

    Clarification; anterior/posterior longitudinal ligament

    1. Regenexx Team Post author

      Yes, from an anatomic perspective both could be beneficial in the treatment of cervical instability. However, the anterior longitudinal ligament is not a target of our treatments due to the anatomic difficulty of approach. The posterior longitudinal ligament, is and we do treat on occasion, however it is a higher risk injection. Generally we use the facets as well as the posterior elements including the supraspinous /interspinous / ligamentum nuchae (for upper cervical instability) ligaments as well as multifudus muscles to work with cervical instability, when simple facet work seems inadequate.

  4. Ted Martin

    Having watched the first YouTube video that you mentioned, it’s my understanding that herniated discs, bulging discs, torn discs, degenerated discs, facet joint injury or arthritis, and stenosis can be diagnosed by an MRI. But what about Multifidus Atrophy?

    1. Regenexx Team Post author

      Ted,
      Yes, certain areas with the right view and resolution can be visualized on MRI. See: https://regenexx.com/blog/should-i-get-back-surgery/

  5. Candie Shannon

    I had this test done and was found to have 20mm of movement at the C1C2… is this bad?

    1. Chris Centeno Post author

      You mean you had 2 cm C1-C2 overhang on a DMX study?

  6. Allison

    Since you now do alar and transverse ligament injections could you perhaps also inject certain areas of the ALL with the same method?

    1. Regenexx Team Post author

      Allison,
      The procedure includes the Alar, Tranverse and Accessory ligaments. Please see: https://regenexx.com/blog/candidacy-for-ccj-instability-procedure/

      1. Allison

        Yes but I’m referring to the anterior longitudinal ligament.

        1. Regenexx Team Post author

          Allison,
          The answer is Yes.

  7. Robert venezia

    I’m in severe pain , I live in a smaller Southern California town I’m afraid the Kaiser office isn’t capable of getting the test performed properly . I emailed my Kaiser Dr and his response was they will bring to our office to see if test can be performed .. very concerning because I’m positive it’s my L5 S1 and MRI didn’t show much but my numbness tingeling and solid leg pain tells me otherwise .

    1. Regenexx Team Post author

      Robert,
      They are bringing the X-Ray unit to your office? If you can’t get a flexion-extension X-ray, the proper type of exam should suffice. There are Regenexx Doctors at 3 different locations in Southern California who can do that type of exam. Put in your zip code, or city and state to see what’s closest. Make sure the word Spine is to the right of the Clinic name. We are very familiar with L5 S1 instability! Here is the link:https://regenexx.com/find-a-physician/

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