Spondylolisthesis and the degenerative spine

Written by the X-Ray Atlas editorial team from the sources listed below · Medical review pending · Updated 24 October 2026 · Level: Intermediate

Degenerative change in the spine is close to universal with age, and most of it is unrelated to symptoms. For that reason plain X-rays are not routinely recommended for low back pain (NICE NG59): they rarely change management, they cannot show nerve compression, and they expose the pelvis to a relatively high radiation dose. Lumbar films are still taken, and you will meet these findings on films done for other reasons. This page teaches how to describe degenerative change, how to recognise spondylolysis and grade spondylolisthesis, and how to spot the findings that are not degenerative and need action, such as infection and tumour.

1. The role of X‑ray in back pain

NICE NG59 advises not routinely offering imaging in a non-specialist setting for people with low back pain, with or without sciatica. Imaging is considered in specialist settings when the result is likely to change management. When serious pathology is suspected, the relevant test is usually MRI (or CT), not a plain film:

• Cauda equina syndrome: emergency MRI.
• Malignancy, including metastatic spinal cord compression: MRI of the whole spine according to the local pathway.
• Infection (discitis, vertebral osteomyelitis, epidural abscess): MRI.
• Fracture: plain film may show it, but CT or MRI is often needed. See thoracolumbar spine fractures.

Plain films remain useful in some situations: assessing alignment and instability (including flexion-extension views, in specialist practice), suspected fracture in an older person, scoliosis, and follow-up after surgery.

2. Degenerative disc and facet disease

Describe degeneration using the same principles as osteoarthritis elsewhere:

Finding	What it looks like
Disc space narrowing	Reduced height of the disc space compared with adjacent levels, most often at L4/5 and L5/S1
Osteophytes	Bony spurs from the vertebral body margins, projecting horizontally or curving towards the next level
Endplate sclerosis	Increased density along the endplates either side of a narrowed disc, with smooth, intact cortical outlines
Vacuum phenomenon	Gas (dark lucency) within the disc, from nitrogen collecting in a degenerate disc. Its presence makes infection very unlikely.
Facet joint arthropathy	Narrowing, sclerosis and hypertrophy of the facet joints, best seen on obliques or CT. A common cause of degenerative spondylolisthesis.
Schmorl's nodes	Small, well-defined indentations of the endplate where disc material has herniated into the body

Report the levels involved and the severity, then make clear in the summary that these changes are common and correlate poorly with pain. Diffuse idiopathic skeletal hyperostosis (DISH), flowing ossification along the anterior aspect of at least four contiguous vertebrae with preserved disc spaces, is a separate condition that matters because the stiff spine is prone to fracture.

3. Spondylolysis

Spondylolysis is a defect in the pars interarticularis, the narrow bridge of bone between the superior and inferior articular processes. It is thought to be a stress fracture, often developing in childhood or adolescence, and it is common in sports involving repeated extension, such as gymnastics and fast bowling. It occurs most often at L5 and is frequently bilateral.

The Scottie dog

On an oblique lumbar view, the posterior elements form the outline of a Scottie dog:

• the transverse process is the nose;
• the pedicle (end-on) is the eye;
• the superior articular process is the ear;
• the pars interarticularis is the neck;
• the inferior articular process is the front leg, and the lamina is the body.

A pars defect appears as a lucent band across the neck: the dog is wearing a "collar". Oblique films are now rarely performed, especially in young people, because of the radiation dose to the pelvis; CT shows the defect clearly, and MRI can show an early stress reaction before a defect forms.

4. Spondylolisthesis and Meyerding grading

Spondylolisthesis is forward slip of one vertebra relative to the one below (anterolisthesis). A backward slip is a retrolisthesis. Spondylolisthesis is graded on the lateral view by the percentage of the upper endplate of the lower vertebra that the vertebra above has slipped across.

The main types

Type	Typical level	Cause and features
Isthmic	L5/S1	Bilateral pars defects. The posterior elements stay behind, so the canal is often widened at that level. Can progress in adolescence.
Degenerative	L4/5	Facet joint arthropathy allows the vertebra to slip forwards with its posterior elements intact, so the canal narrows (spinal stenosis). Commoner in older women. Usually grade I–II.
Traumatic, pathological, dysplastic, post-surgical	Any	Fracture, tumour or bone disease, congenital facet abnormality, or after decompression surgery

On the AP view, a severe L5 slip can produce the "inverted Napoleon's hat" sign: the L5 vertebral body, tilted forwards, is seen end-on over the sacrum, and its outline resembles an upside-down bicorne hat.

Instability (movement of the slip with posture) is assessed with flexion and extension views or upright imaging in specialist practice.

5. When it isn't degenerative

Several serious conditions can be mistaken for degeneration. The single most useful discriminator is the endplate and the disc.

Condition	Plain film clues	Next step
Discitis / vertebral osteomyelitis	Loss of disc height with erosion or indistinctness of both adjacent endplates, affecting two vertebrae and the disc between them. Early films may be normal; changes may take weeks to appear.	MRI; blood cultures; urgent clinical review. See osteomyelitis.
Metastasis or myeloma	Destruction of a pedicle on the AP ("winking owl" sign), lytic or sclerotic lesions, vertebral collapse with the disc usually preserved	MRI of the whole spine; follow the suspected cancer pathway (NICE NG12)
Fracture	Loss of vertebral height, a step in the cortex	See thoracolumbar fractures
Ankylosing spondylitis	Squaring of vertebral bodies, syndesmophytes, sacroiliitis, eventually a "bamboo spine"	See inflammatory arthritis

6. Pitfalls

• Over-calling: reporting degenerative change without context can increase anxiety and lead to unnecessary investigation. Correlate with the clinical question.
• Transitional vertebrae (sacralisation of L5 or lumbarisation of S1) cause miscounting of levels. Count from a reliable landmark and say how you have counted, especially if surgery is planned.
• Rotation can mimic a slip or hide one. Use the posterior vertebral line on a true lateral.
• Vacuum phenomenon is reassuring for infection, but it is not seen in every degenerate disc.
• Pseudo-slip: degenerative listhesis at L4/5 usually has an intact pars; isthmic listhesis at L5/S1 usually has a defect. Do not assume a pars defect without seeing it.

Red flags: act now

What to focus on, by role

Role	Priorities
Medical student	Meyerding grades, the Scottie dog, and why X-ray is not routine for low back pain.
Nurse / practitioner	Back pain red flags and the escalation route for suspected cauda equina syndrome.
Junior doctor	Request MRI, not X-ray, when red flags are present. Distinguish degenerative endplates from infective ones.
Radiographer	Justification under IR(ME)R for lumbar films given the pelvic dose; true laterals for grading.
Advanced / FRCR	Isthmic vs degenerative listhesis, transitional anatomy, discitis vs Modic change, and pathological collapse.

Practise on real spine X-rays →

References

1. NICE NG59. Low back pain and sciatica in over 16s: assessment and management. nice.org.uk
2. NICE NG12. Suspected cancer: recognition and referral. nice.org.uk
3. Radiopaedia. Spondylolisthesis. radiopaedia.org
4. Radiopaedia. Spondylolysis. radiopaedia.org
5. Meyerding HW. Spondylolisthesis. Surg Gynecol Obstet 1932;54:371–7.
6. Royal College of Radiologists. iRefer. irefer.org.uk

For education only. Not a substitute for a formal report, senior review or your local policy. Never use this page to make decisions about a real patient.