Vertebral dysfunction with acute leg and back pain

Murtagh’s syndrome A–D triage for back pain with leg symptoms — a severity ladder from surgical emergency down to very common non-specific pain. Approximately only 0.08% of back/radicular pain presentations to primary care physicians relate to true cauda equina/severe sacral radiculopathy — the ladder below exists precisely because that rare case must not be missed among the very common ones.

Syndrome	Clinical features	Frequency	Diagnosis
A — surgical emergency	Saddle anaesthesia; distal anaesthesia; UMN or LMN signs; loss of sphincter control or urinary retention; progressive leg weakness and areflexia	Very rare	Spinal cord (UMN) or cauda equina (LMN) compression
B — probably surgical emergency	Leg anaesthesia/paraesthesia; foot drop; motor weakness; absent reflexes	Uncommon	Large disc protrusion paralysing a nerve root
C	Distal pain ± paraesthesia; radicular pain (sciatica); positive dural stretch tests	Common	Posterolateral disc protrusion on a nerve root, or disc disruption
D	Non-specific lumbar pain (unilateral, central or bilateral) ± buttock and posterior thigh pain	Very common	Disc disruption, facet dysfunction, or unknown

Triage red flags for syndrome A/B (from the current AJGP cauda equina framework)

Emergency referral (same-day): bilateral pain or altered sensation extending below the knee (including saddle/genital region); bilateral leg weakness; bilaterally absent ankle jerks with radicular pain; unilateral weakness of power 3/5 or worse; any concern for urinary retention; or other red flags of serious spinal pathology (upper motor neuron signs, unexplained weight loss, night sweats, fevers, IV drug use, history of metastatic malignancy).

Urgent referral (within 24 hours/rapid assessment clinic): bilateral pain/altered sensation below the knee but without saddle/genital involvement; single-nerve-root weakness of power 4/5 or better; or severe radicular pain refractory to oral analgesia.

Does not by itself need urgent assessment: axial low back pain without radicular pain or altered sensation, or lateral thigh pain alone without extension below the knee.

Clinical pitfalls in assessing syndrome A/B: urinary retention is common with severe acute pain even without true cauda equina injury (sensitivity ~25%, specificity ~72% for retention alone), so painless retention is the more concerning pattern. Digital rectal exam/anal tone assessment is unreliable (~50% sensitivity and specificity) and current international consensus recommends against performing it in primary care — pinprick/light-touch sensation over the saddle region is the preferred, less invasive alternative. MRI, not CT, is the imaging of choice for suspected cauda equina — don’t delay referral to first obtain a community CT.

Management by category

• Syndromes A/B — urgent surgical referral (see the absolute referral criteria in lumbosacral radiculopathy).
• Syndrome C (radiculopathy) — most settle in 6–12 weeks; reassure that spontaneous recovery is expected. Back-care education, return to daily activities ASAP, NSAIDs, basic exercise (e.g. swimming), physiotherapy; epidural injection if not responding; surgical referral for severe or progressive neurological deficit. Radicular leg pain alone, without a severe or progressive neurological deficit, is not by itself considered serious pathology and does not automatically warrant imaging — image only if it will change management. Full detail: lumbosacral radiculopathy.
• Syndrome D (non-specific LBP) — managed per the low back pain (approach) hub. Core principles: actively involve the patient in managing their own pain, avoid bed rest, and encourage a quick return to usual activity including work; investigations (including imaging) are rarely indicated for non-specific LBP, and incidental degenerative findings on imaging are common even in people with no back pain at all, so unnecessary imaging risks generating concern without benefit. If stiffness dominates in an older patient, consider lumbar spondylosis.