Spine X-rays, Including Flexion and Extension (Dynamic) Views

By Mr Ahmed-Ramadan Sadek, Neurosurgeon · Last reviewed October 2026 · 6 min read

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On this page

What a spine X-ray shows
Why X-rays are not routine for back pain
Standing X-rays: alignment and balance
Flexion and extension (dynamic) views
Limitations of X-rays
How much radiation is involved?
Before your X-ray
During the X-ray
After the X-ray
Further reading

Key points

X-rays show the bones of the spine and how they line up. They do not show discs, nerves or the spinal cord.
NICE advises against routine imaging for low back pain in GP and other non-specialist settings, because it rarely changes treatment.
Standing X-rays show the spine while it carries your body weight. They are used to measure scoliosis and overall balance, and can reveal a slipped vertebra that a lying-down MRI misses.
Flexion and extension views are taken as you bend forwards and backwards, to check whether one vertebra moves more than it should.
A lumbar spine X-ray gives a dose similar to about 7 months of natural background radiation.

What a spine X-ray shows

An X-ray uses a small amount of radiation to take a picture of the inside of the body, and is mainly used to look at bone.^[1] On a spine X-ray your doctor can see the shape and height of each vertebra, how the bones line up, the gaps where the discs sit, and wear in the joints such as bony spurs. Discs, nerves and the spinal cord are soft tissues and do not show up, so if the question is whether a nerve is being pressed on, an MRI scan is needed instead.

Why X-rays are not routine for back pain

Many people expect an X-ray when they see a doctor about back pain. NICE guidance says imaging should not be offered routinely in non-specialist settings such as general practice, for low back pain with or without sciatica. Even in a specialist clinic, NICE suggests imaging only if the result is likely to change your management.^[2]

This advice has a firm basis. In a UK trial in general practices across the East Midlands, 421 people with back pain were randomly allocated to have a lumbar spine X-ray or not. Those who had the X-ray did not have better function or less pain. They were slightly more likely to still report back pain at three months and visited their doctor more often. Abnormal findings on the X-ray made no difference to how people got on. Interestingly, those who had an X-ray were more satisfied with their care at nine months, which shows how reassuring a test can feel even when it does not change the outcome.^[3]

Standing X-rays: alignment and balance

When surgeons assess the shape of the spine in adults, the most established approach is a full-length X-ray taken standing, from the front and from the side. These pictures allow a set of measurements of the spine and pelvis to be made.^[4] From the side, one thing the surgeon checks is sagittal balance: whether your head and trunk sit comfortably over your pelvis, or if you are being pitched forwards and having to work hard to stay upright. This matters a great deal when planning surgery for adult scoliosis and other deformities.

For scoliosis, X-rays are how the size of the curve is measured. The British Association of Spine Surgeons (BASS) explains that scoliosis is defined as a sideways curve of at least 10 degrees, measured as the Cobb angle, and that special standing, full-length spine X-rays are needed to measure it.^[5] Because people with scoliosis may have repeat X-rays over many years, specialists try to keep the number of pictures to what is needed.

Standing pictures also matter for degenerative spondylolisthesis, where one vertebra has slipped forward on the one below. MRI is done lying down, and in that position a slip can partly slide back into place. In one study of 416 people with lower back problems, 31 of 109 slipped levels seen on standing X-rays (28%) did not show as a slip on MRI. The authors recommended routine standing side views for this reason.^[6]

Flexion and extension (dynamic) views

Ordinary X-rays are snapshots of the spine in one position. Flexion and extension views add movement. You stand side-on to the machine and one picture is taken as you bend forward as far as is comfortable, then another as you lean back. Comparing the two shows how each vertebra moves in relation to its neighbours.

The main reason for these views is to look for instability, meaning a segment that slides or tilts more than expected, as can happen with a spondylolisthesis that moves. There is no single agreed definition. A 2026 systematic review found that more than 3 mm of forward or backward sliding between bending views has historically been a common cut-off, but recent work favours combining X-ray findings with your symptoms and examination rather than relying on one measurement.^[7] The question matters because it can influence whether a decompression alone is enough, or whether a fusion is also advised.

Bending views are sometimes used after fusion surgery too, to check that the fused level is no longer moving. If you have a lot of pain, tell the radiographer. You only need to bend as far as you comfortably can.

Limitations of X-rays

They do not show discs, nerves or the spinal cord.
Wear-and-tear changes are very common and often do not explain the pain you feel.
Small or early fractures, such as a stress fracture of the pars, can be hard to see, and CT or MRI may be needed.
Each picture shows only one moment in one position.

How much radiation is involved?

Everyone receives natural background radiation. The UK average is about 2.1 millisieverts (mSv) a year. The table uses figures from the UK Health Security Agency (UKHSA).^[8]

Test (UKHSA figures)	Typical dose	Similar to natural background over
Chest X-ray (single film)	0.02 mSv	3 days
Cervical spine (neck) X-ray	0.08 mSv	2 weeks
Thoracic spine X-ray	0.7 mSv	4 months
Lumbar spine X-ray	1.3 mSv	7 months
CT abdomen and pelvis (for comparison)	10 mSv	4.5 years

UKHSA estimates the extra lifetime risk of fatal cancer from a lumbar spine X-ray at about 1 in 15,000 for adults aged 16 to 69, and roughly five times lower for older people.^[8] Flexion and extension views add extra pictures, so the dose is a little higher than a single film. The NHS describes X-rays as usually very safe, with a very small cancer risk from repeated tests that your doctor weighs before offering one.^[1]

Before your X-ray

There is usually no special preparation for a spine X-ray. You may be asked to change into a gown and to remove anything containing metal, such as jewellery, belts or clothes with zips.^[1]

Tell the radiographer before the X-ray if you:

are, or might be, pregnant
are breastfeeding
take any medicines
have any allergies

You can also ask for a chaperone to be in the room with you.^[1]

During the X-ray

A radiographer lines the machine up with your spine and then steps behind a screen. You hold still for a few seconds while each picture is taken, and you will not feel anything. You may be asked to move into different positions between pictures, including bending for dynamic views. The X-ray itself only takes a few minutes.^[1]

After the X-ray

You can usually leave straight away. You should be told when to expect the results, which may be on the same day or at a later appointment. If you have heard nothing after a few weeks, contact the doctor who referred you or your GP.^[1]