Low back pain without red flags

ACR AC Low Back Pain (2021); NICE NG59

Uncomplicated low back pain, with or without radicular symptoms, is self-limiting in most people, and imaging it early neither improves outcomes nor changes early management. The degenerative findings it produces are near-universal and poorly correlated with symptoms.

Back pain with or without sciatica, of less than six weeks duration or long-standing and unchanged, with no red flag for malignancy, infection, fracture, inflammatory disease or cauda equina syndrome, and no progressive neurological deficit.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Focal neurological deficit

Fever or sepsis

Immunosuppressed

Changes the differential rather than the modality.

Red flags

These accumulate rather than exclude. Back pain with one of these is a different question from back pain.

Known cancer

Back pain in a cancer patient is a different question, and staging phase changes which contrast phases are needed.

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Imaging may not be indicated

MRI Lumbar Spine — degenerative

MRI Lumbar Spine

What we'd amend, and why

Early imaging of uncomplicated back pain does not improve pain, function or satisfaction, and it does not change early management, which is conservative regardless of what the scan shows. What it does change is the conversation: degenerative findings are near-universal at every adult age, and once reported they are difficult to un-report, associating a benign self-limiting episode with a structural label and increasing the likelihood of further imaging and intervention. Imaging may not be indicated here, and the useful vetting output is to say so and to name the circumstances that would change the answer.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayadult — Adults without red flags
rulerule-mr-device-screening — MR safety screening for implants and foreign bodies; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(1)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

MR safety screening for implants and foreign bodies
Complete the MR safety questionnaire, verify implant labelling and its stated conditions of use against this scanner and this protocol, and ensure no ferromagnetic object enters Zone IV.
Radiographer at the scannerBefore the scan
Flags back if: An implant or retained foreign body that is MR Unsafe, unlabelled, or cannot be identified; or an MR Conditional device whose stated conditions this scanner or the requested protocol cannot satisfy; or a credible unexcluded intraocular metallic foreign body history.

Worth asking the referrer (1)

None of these hold the request up. They sharpen the protocol or the plan that follows.

Is there any red flag: known malignancy, unexplained weight loss, fever or infection risk, significant trauma or osteoporosis risk, progressive neurological deficit, saddle anaesthesia or sphincter disturbance, age under 20 or new onset over 50, or features of inflammatory back pain?
Any one of these moves the patient to a different card with a different and often urgent answer. Their absence is what makes this card apply.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Cauda equina features — this is an emergency MRI question

Role	Study & protocol	Why this answers the question
First line	MRI Lumbar Spine MRI Lumbar Spine — suspected cauda equina syndrome usually appropriate	Saddle anaesthesia, bilateral radicular symptoms, new sphincter disturbance or reduced anal tone take the patient off this card entirely and onto a same-day surgical pathway. The study images from the conus to the sacrum and it has to be MRI: a disc fragment, an epidural collection and a tumour can all be near-isodense to the thecal sac on CT, so a CT reported as showing no significant compression cannot fail safely here. Retention is a late sign and waiting for it is waiting for the deficit that does not recover.

Move to the cauda equina syndrome card for the coverage and out-of-hours provision detail. This arm exists so that this card cannot answer "imaging may not be indicated" to that patient.

Fever, suspected infection or immunosuppression — spinal infection until excluded

Role	Study & protocol	Why this answers the question
First line	MRI Whole Spine MRI Spine — suspected infection / discitis usually appropriate	Back pain with fever, a source of bacteraemia or immunosuppression is discitis, vertebral osteomyelitis or an epidural abscess until imaging says otherwise, and none of the reasoning about self-limiting mechanical pain applies to it. Marrow oedema either side of a disc appears on MRI weeks before anything is visible on radiographs or CT; gadolinium is what separates a phlegmon from a drainable collection and defines the epidural extension that decides whether this is an antibiotic problem or a surgical one; and the coverage is whole spine because skip lesions are characteristic. This is a same-day study in an unwell patient.

Malignancy, weight loss or night pain — a spinal metastasis question

Role	Study & protocol	Why this answers the question
First line	MRI Whole Spine MRI Whole Spine — suspected metastatic cord compression usually appropriate	These three red flags share a differential — metastasis, myeloma, and the pathological collapse that presents as ordinary back pain — and share a coverage requirement with it. Deposits are multilevel in a substantial minority, referred pain localises poorly, and a lumbar study alone misses the thoracic lesion that determines the radiotherapy field. NICE asks for whole-spine MRI within a week of suspected spinal metastases, and within 24 hours where neurological signs suggest compression. Night pain and unexplained weight loss without a known primary are weaker signals than a cancer history and still enough to take the patient off a card whose answer is "do not image".

Progressive neurological deficit — imaging is indicated now

Role	Study & protocol	Why this answers the question
First line	MRI Lumbar Spine MRI Lumbar Spine — degenerative usually appropriate	The card's own note says imaging becomes appropriate when a progressive deficit develops, and this is that patient. A worsening foot drop or a progressing radicular weakness is a surgical timing question rather than a natural-history one, and the degenerative findings that are meaningless in an intact patient become meaningful when there is a deficit to correlate them with. Extend the coverage or add the cauda equina protocol if there is any suggestion of bilateral symptoms, saddle change or a level above the conus.

Known malignancy — this card does not apply

Role	Study & protocol	Why this answers the question
First line	MRI Whole Spine MRI Whole Spine — suspected metastatic cord compression	Back pain in a patient with known cancer is a red flag by definition, and the question is no longer degenerative — it is whether there is metastatic spinal cord compression. NICE asks for whole-spine MRI within a week of suspected spinal metastases, and within 24 hours where there are neurological signs or symptoms suggesting compression. Whole spine rather than the painful level: multiple levels are involved in a substantial minority, and a lumbar study alone will miss the thoracic lesion that determines management. Move to the metastatic spinal cord compression pathway.

The absence of red flags is what makes the low back pain card apply. Known malignancy is one, so the answer here is deliberately not the one this card otherwise gives.

Significant trauma — this is a fracture question, not a mechanical one

Role	Study & protocol	Why this answers the question
First line	CT Lumbar Spine CT Lumbar Spine — Unenhanced, Thin Section usually appropriate	Everything this card says about self-limiting mechanical pain assumes there was no injury, and once there was, the question becomes bony and the answer inverts. Radiographs miss a clinically significant proportion of thoracolumbar fractures, particularly the posterior element and endplate injuries that decide whether a fracture is stable and particularly at the thoracolumbar junction where bowel gas, the diaphragm and endplate obliquity defeat plain films — so radiographs are not the cheap first look here, they are the study that clears nothing. Thin-section CT with sagittal and coronal reformats is the reference test. The threshold falls to almost nothing in osteoporosis, in a patient on corticosteroids, and in ankylosing spondylitis or diffuse idiopathic skeletal hyperostosis, where a trivial mechanism produces a highly unstable transverse fracture through fused bone and the whole spine rather than the painful segment is at risk. Check first for a trauma or body CT already acquired in this episode: reformats from it answer the question with no further exposure. This is the thoracolumbar spine trauma pathway, and the patient belongs on it.
Second line	MRI Lumbar Spine MRI Lumbar Spine — degenerative	What the CT cannot answer, and in an older patient it is frequently the real question. CT dates a vertebral collapse poorly; the fluid-sensitive fat-suppressed sagittal sequence is what says whether the fracture is acute, and it is also what identifies the marrow replacement, soft-tissue component or posterior element involvement that mark a collapse as pathological rather than osteoporotic. MRI additionally shows the cord and conus, an epidural haematoma, and the posterior ligamentous complex whose integrity moves a fracture across the operative threshold — none of which CT sees. Where there is a neurological deficit it is added the same day rather than electively.

Move to the thoracolumbar spine trauma card for the paediatric fork, the coverage and the classification detail. This arm exists so that this card cannot answer "imaging may not be indicated" to a patient who has broken their back.

Adults without red flags

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	MRI Lumbar Spine MRI Lumbar Spine — degenerative usually not appropriate	Early imaging of uncomplicated back pain does not improve pain, function or satisfaction, and it does not change early management, which is conservative regardless of what the scan shows. What it does change is the conversation: degenerative findings are near-universal at every adult age, and once reported they are difficult to un-report, associating a benign self-limiting episode with a structural label and increasing the likelihood of further imaging and intervention. Imaging may not be indicated here, and the useful vetting output is to say so and to name the circumstances that would change the answer.
Reasonable alternative	Spinal radiograph Spinal radiograph — AP and lateral usually not appropriate	Radiographs are not a lower-risk compromise. They deliver gonadal and marrow dose for findings that are almost entirely degenerative and non-actionable, and they cannot address the neural structures that a symptomatic patient is actually worried about. Substituting them for a declined MRI trades one unhelpful study for a more irradiating one.

Imaging becomes appropriate when a red flag appears, when a progressive deficit develops, or when a specialist is making a surgical or injection decision that the scan would inform.

Pitfalls

Missing a red flag hidden in a brief referral. A short history of "back pain" can conceal weight loss, night pain, fever or a cancer history, and the safest response to a thin request is to ask rather than to decline.
Reading "usually not appropriate" as a permanent no. The same patient at six weeks with a progressive foot drop, or at any point with a new red flag, has a different and often urgent indication.
Reporting incidental degenerative findings without context, which converts a self-limiting episode into a structural diagnosis the patient carries for years.
Substituting radiographs for a declined MRI, which adds radiation without adding an answer.
Overlooking inflammatory back pain in a younger patient, where morning stiffness and alternating buttock pain point to sacroiliitis and a different pathway entirely.
Answering "imaging may not be indicated" to back pain that followed an injury. A vertebral fracture is a bony question with a different first study, radiographs miss the posterior element and endplate injuries that decide stability, and in osteoporosis, on corticosteroids or in an ankylosing spine a trivial mechanism is enough.

What makes a good request

NICE is explicit that imaging should not routinely be offered in a non-specialist setting, and that in a specialist setting it should be offered only if the result is likely to change management.
The ACR describes uncomplicated acute low back pain and radiculopathy as a benign self-limited condition that does not warrant imaging, with imaging considered after roughly six weeks of unsuccessful conservative management, or where a red flag is present.
Disc degeneration, bulges, annular fissures and facet arthrosis are present in a large majority of asymptomatic adults of the same age. Reporting them in a patient with back pain risks attributing symptoms to findings that would be there anyway.
The trigger for imaging is a change in the clinical situation — a new deficit, a new red flag, or a decision point about surgery or injection — rather than duration of pain alone.

Scoring this once it is done

The classification and risk tools this question ends in.

Meyerding Grading (Spondylolisthesis)Kellgren-Lawrence Grade

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

MRI Lumbar Spine — suspected cauda equina syndrome MRI Spine — suspected infection / discitis MRI Whole Spine — suspected metastatic cord compression MRI Lumbar Spine — degenerative CT Lumbar Spine — Unenhanced, Thin Section Spinal radiograph — AP and lateral

Confirm locally

MRI Lumbar Spine — degenerative: timings are typical — confirm against local protocol.
Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.