Low Back Pain and Red Flags
Pain from the spine's muscles, discs and facet joints is usually a benign, self-limiting mechanical process, but the same anatomy can be compromised by fracture, infection, malignancy or nerve root/cauda equina compression, so every assessment is really a search for the minority who need urgent action.
In a nutshell
Most low back pain is benign mechanical strain of the discs, facet joints and paraspinal muscles that resolves with activity and simple analgesia. The essential task at every presentation is screening for red flags (cauda equina compression, fracture, infection and malignancy), each of which has its own mechanism and its own urgent pathway.
Classic presentation
A patient with axial low back pain related to lifting or posture, no neurological deficit, and improvement over one to two weeks with activity and analgesia, versus a patient with saddle anaesthesia and new urinary retention who needs emergency MRI.
Key points
- Non-specific mechanical back pain is the commonest presentation and is managed with activity, not bed rest, and simple analgesia.
- Cauda equina syndrome is a surgical emergency: saddle anaesthesia, bladder/bowel dysfunction, bilateral leg weakness and reduced anal tone need same-day MRI and urgent decompression.
- Spinal infection, vertebral fracture and malignancy each have a distinct red flag signature: fever/risk factors, trauma/osteoporosis, and night pain/weight loss respectively.
- Imaging is reserved for red flag features; imaging everyone with simple back pain over-detects incidental degenerative change without improving outcomes.
- Delay in recognising and treating cauda equina syndrome causes irreversible neurological, bladder and bowel damage: timing is the discriminator between good and poor outcome.
First-line investigation
A structured red flag history and neurological examination at every presentation; urgent MRI only if cauda equina or significant cord/root compression is suspected.
First-line management
Encourage staying active with simple analgesia for non-specific pain; emergency MRI and same-day spinal surgical referral if cauda equina syndrome is suspected.
Exam traps
- Bilateral leg symptoms, saddle anaesthesia or new urinary/bowel dysfunction mean cauda equina syndrome until excluded. Do not wait for outpatient MRI.
- Routine imaging for uncomplicated low back pain without red flags is not recommended and can lead to unnecessary intervention.
- Unremitting pain that is worse at night or unrelieved by rest points away from mechanical pain and towards malignancy or infection.
- A normal peripheral neurological exam does not exclude early cauda equina syndrome. Ask specifically about bladder, bowel and saddle sensation.
Educational content pending clinical review. Not medical advice.