Acute lower back pain

At a glance

• Sort every patient into one of three groups: non-specific low back pain (over 90%), radicular pain or radiculopathy (about 5 to 10%), or serious pathology (under 1% in primary care, more in ED).
• Don't image without suspected serious pathology. The Australian Low Back Pain Clinical Care Standard (2022) makes this a quality statement.
• First-line treatment is reassurance, advice to stay active and self-management. Paracetamol and opioids work no better than placebo in Australian trials.
• Most acute episodes improve substantially within 6 weeks, but recurrence within a year is common.

Cord, conus, cauda equina and root lesions are covered in depth in Spinal cord and nerve root compression.

Causes

Group	Causes	Clues
Non-specific	No identifiable structural cause	Mechanical pain, well person, normal neurology
Radicular	Disc prolapse (under 50), foraminal stenosis (over 50), canal stenosis	Leg pain worse than back pain, dermatomal, positive straight leg raise
Fracture	Osteoporotic vertebral fracture, trauma, pathological fracture	Older age, prolonged corticosteroids, minor trauma, sudden onset
Malignancy	Metastases (breast, prostate, lung, kidney, thyroid), myeloma, lymphoma	Previous cancer, weight loss, thoracic or night pain, age over 50
Infection	Vertebral osteomyelitis, discitis, epidural abscess, TB	Fever, injecting drug use, diabetes, dialysis, recent bacteraemia or spinal procedure
Inflammatory	Axial spondyloarthritis	Under 40, morning stiffness over 30 minutes, better with exercise, uveitis, psoriasis, IBD
Cauda equina syndrome	Large central disc, tumour, haematoma, abscess	Saddle anaesthesia, bladder or bowel change, bilateral leg symptoms
Referred (non-spinal)	AAA or dissection, pyelonephritis, renal colic, pancreatitis, retroperitoneal haematoma, hip OA, pelvic disease	Pain not changed by movement, abdominal signs, haemodynamic change

• In the Sydney primary care cohort (Henschke 2009), 11 of 1,172 patients had serious pathology, 8 of them fractures.
• Pitfall: an older smoker with "back pain and a bit of hypotension" has a leaking AAA until proven otherwise. See Aortopathy, aortic aneurysm and dissection.

Focused history

• Onset and mechanism: sudden pain after minor trauma in an older person suggests fracture. Gradual pain with fever suggests infection.
• Character: mechanical pain worsens with activity and eases with rest. Inflammatory pain is worse after rest and at night, with prolonged morning stiffness.
• Leg pain: below the knee in a dermatomal pattern means radicular pain. Pain in both legs on walking, relieved by sitting or bending forward, is neurogenic claudication from canal stenosis.
• Neurological and sphincter symptoms: weakness, numbness, saddle numbness, urinary hesitancy, retention or altered sensation, faecal incontinence, sexual dysfunction.
• Systemic: fever, sweats, weight loss, past cancer, immunosuppression, injecting drug use, recent infection or procedure.
• Medications: corticosteroids (fracture), anticoagulants (epidural haematoma, retroperitoneal bleed).
• Psychosocial risk factors ("yellow flags"): fear-avoidance, catastrophising, low mood, belief that pain means harm, work dissatisfaction, a compensation claim. These predict chronicity better than imaging findings do.

Focused examination

• General: temperature, pulse and BP, weight, lymph nodes, breast and prostate where malignancy is possible, and abdominal palpation for an aneurysm.
• Spine: inspection, focal bony tenderness (fracture, infection, metastasis), range of movement, Schober test if spondyloarthritis is possible.
• Neurological examination of the legs: power by myotome, knee and ankle reflexes, dermatomal sensation, plantar responses and gait. L5 weakens big toe extension and hip abduction; S1 weakens plantarflexion and loses the ankle jerk.
• Straight leg raise (sensitive for L5 or S1 root irritation) and the crossed straight leg raise (more specific). Femoral stretch test for L2 to L4.
• Perianal sensation and anal tone when cauda equina syndrome is a concern, plus a post-void bladder scan.
• Hips: reduced internal rotation points to hip OA presenting as buttock or thigh pain.

Red flags

Suspect	Flags
Cauda equina syndrome	Saddle anaesthesia, new bladder or bowel dysfunction, bilateral sciatica, progressive leg weakness
Malignancy	Past history of cancer (the most useful single flag), unexplained weight loss, age over 50, failure to improve after a month
Infection	Fever, injecting drug use, immunosuppression, haemodialysis, recent bacteraemia or spinal procedure
Fracture	Older age, prolonged corticosteroid use, significant trauma, osteoporosis
Vascular	Pulsatile abdominal mass, hypotension, tearing pain, known aneurysm

• Red flags individually have poor accuracy (Downie 2013 meta-analysis). Most people with one flag have non-specific pain. Use them in combination with the overall picture.
• Pitfall: missing epidural abscess in an afebrile person on dialysis or who injects drugs. A raised CRP and escalating pain are often the only clues.

Investigations

• Non-specific low back pain: no imaging and no blood tests.
• Suspected serious pathology: MRI is the preferred test, because it's more sensitive and avoids radiation. The urgency depends on the suspicion:
  • Cauda equina syndrome or progressive neurological deficit: emergency MRI, any time of day, and same-day surgical referral.
  • Suspected infection: FBC, CRP, ESR, blood cultures before antibiotics, and MRI with gadolinium of the whole spine.
  • Suspected malignancy: FBC, ESR or CRP, calcium, ALP, serum protein electrophoresis and free light chains, PSA in men, then MRI. Neurological signs mean MRI within 24 hours (see the cord compression note).
  • Suspected osteoporotic fracture: plain X-ray first, then bone density and a secondary-cause screen (see Osteoporosis).
  • Suspected axial spondyloarthritis: CRP, HLA-B27, and MRI of the sacroiliac joints rather than the lumbar spine. Refer to a rheumatologist.
• Radicular pain without red flags: imaging only if surgery or an injection is being considered after failure of conservative care, usually beyond 6 weeks.
• Disc bulges, degeneration and facet arthropathy are common in pain-free people and rise with age. Reporting them increases anxiety and surgery without improving outcomes.

Management

Non-specific low back pain

The 2022 Clinical Care Standard sets out 8 quality statements: initial clinical assessment, psychosocial assessment, reserving imaging for suspected serious pathology, patient education and advice, self-management, physical activity, judicious use of pain medicines, and review and referral.

• Explain and reassure: the risk of serious disease is low, the back is strong, and pain doesn't mean damage.
• Stay active and return to normal activities and work as early as possible. Avoid bed rest.
• Heat and simple self-management. Physiotherapy referral for those at higher risk of a poor outcome or slow to improve.
• Screen for risk of chronicity with STarT Back or the Örebro questionnaire. In the STarT Back trial (Hill 2011), matching treatment to risk improved disability and cut costs. NICE amended NG59 in July 2026 so that risk stratification informs shared decisions but no longer points high-risk patients to a psychological therapy package.

Pain medicines

The goal is to let the person move, not to remove all pain. Prescribe the lowest dose for the shortest time and document a stopping plan.

Drug	Evidence and advice
NSAIDs	Small short-term benefit. First choice if a medicine is needed and there's no contraindication (renal impairment, peptic ulcer, heart failure, older age)
Paracetamol	PACE (2014, Sydney): no better than placebo for acute low back pain
Opioids	OPAL (2023, Sydney): no better than placebo at 6 weeks, more harm. Only in carefully selected patients, a few days at most
Gabapentinoids	Avoid. PRECISE (2017) found pregabalin didn't help sciatica
Benzodiazepines, antidepressants	Avoid (2022 Care Standard)
Muscle relaxants	Low-certainty, small effect at best; sedation and dependence
Oral corticosteroids	Not recommended for non-specific pain or sciatica

• Codeine has been prescription-only in Australia since 2018, and the TGA's 2020 opioid reforms cut pack sizes for immediate-release opioids. Short courses and small supplies match this.
• Pitfall: sending a patient home from ED on a week of oxycodone "just in case". That's how persistent opioid use starts.

Radicular pain

• Same principles: activity, reassurance, NSAIDs if safe. Most improve within 6 to 12 weeks.
• Epidural corticosteroid injection gives short-term relief only.
• Surgical referral for progressive or severe motor deficit, cauda equina features, or disabling leg pain beyond 6 to 12 weeks. Early discectomy relieves pain faster, but outcomes at 1 year are similar to conservative care.

Review and referral

• Review within about 2 to 4 weeks if not improving, re-examining for red flags.
• Refer when red flags appear, neurology progresses, symptoms persist beyond 6 to 12 weeks with high disability, or inflammatory back pain is suspected.

Special populations

• Older people: fractures, malignancy, AAA and canal stenosis are all commoner. NSAIDs carry more renal and GI risk, and opioids cause falls and delirium.
• Pregnancy: pelvic girdle pain and lumbar pain are common. Paracetamol is preferred if a drug is needed. NSAIDs are avoided from 20 weeks. MRI without gadolinium is safe.
• Aboriginal and Torres Strait Islander people and rural patients: higher rates of diabetes and renal disease (infection risk and NSAID harm) and less access to MRI and physiotherapy. Arrange transfer early when red flags are present rather than waiting.
• Compensable injuries: workers' compensation and legal claims predict slower recovery. Encourage graded return to work.

Pitfalls

• Ordering a lumbar X-ray or CT "for reassurance" in non-specific back pain.
• Prescribing paracetamol, opioids or pregabalin as if they work for acute back pain.
• Advising bed rest.
• Waiting for urinary retention before imaging suspected cauda equina syndrome.
• Missing AAA, epidural abscess or myeloma because back pain is so common.
• Imaging the lumbar spine instead of the sacroiliac joints when axial spondyloarthritis is the question.