Reasoning GP · Algorithm · 1-page summary
Leg pain
For: adults, children and young people with calf, shin or thigh pain, face to face, in hours or OOH. Not for: major trauma or an obvious fracture (trauma pathway), leg ulcers or a child with a limp (their own algorithms).
Core rule: one discriminator separates each emergency from benign leg pain — unilateral swelling with VTE risk, the 6 Ps, pain out of proportion, systemic toxicity, bladder or saddle symptoms — and each is acted on before, not after, imaging.
0Stop — call 999 now
- Acute limb ischaemia: sudden painful, pale, pulseless, cold, paraesthetic or paralysed leg (6 Ps) → 999 even if not yet frankly pale or pulseless.
- Compartment syndrome (pain out of proportion, worse on passive stretch, tense calf; after trauma, crush or an anticoagulant bleed) or necrotising fasciitis (spreading erythema, toxicity, crepitus) → 999
- Suspected PE: breathlessness, pleuritic pain, haemoptysis, syncope, tachycardia, hypoxia or shock → 999 (two-level PE Wells).
- While waiting: no compression. Do not delay transfer for an ABPI, imaging, absent pulses or compartment pressures.
1Triage by history — which system?
| Pattern | Points to → next step |
|---|---|
| Swollen tender calf | One leg + VTE risk → DVT: Wells, Same-day |
| Fixed walking distance | Calf cramp eased by stopping → PAD → ABPI |
| Rest / night foot pain | Eased by hanging the leg down → CLTI (block 2) |
| Standing / walking | Eased by sitting or bending → spinal stenosis |
| Dermatomal | Back-to-leg pain + tingling → sciatica (L5/S1) |
2Screen — one row is enough
- DVT: Wells ≥2 → USS within 4 h (D-dimer if negative); ≤1 → D-dimer. Scan delayed → interim anticoagulation, scan within 24 h. Same-day
- Spine: bladder or bowel change, saddle anaesthesia, bilateral sciatica, severe or progressive motor deficit; fever with back pain; cancer with back pain and neurology → Emergency spinal, same day — not a GP MRI.
- CLTI: rest pain, tissue loss, gangrene → Same-day vascular call; sepsis or rapid deterioration → 999
- Hot, febrile, swollen leg or a rapidly enlarging soft-tissue mass → Same-day
- Bone (NG12): under-18s, unexplained bone pain or swelling → consider X-ray within 48 h; suggests sarcoma → consider referral within 48 h. Adults: X-ray suggests sarcoma → consider suspected cancer pathway. 60+ with persistent bone pain → offer myeloma bloods.
- Lump increasing in size: consider USS within 2 weeks (48 h if under 18); suggests sarcoma, or uncertain with concern → consider referral.
3Assess — both legs
☐ Calf: swelling, tenderness, circumference ☐ All four pulses, capillary refill ☐ L5/S1 power, reflexes, sensation, SLR ☐ Spine, hip; saddle sensation if concern ☐ Calf-squeeze (Achilles)
Bloods as indicated: FBC, CRP/ESR, U&E, HbA1c, bone profile + ALP; CK if diffuse muscle pain; ferritin (restless legs). Do not: D-dimer first when Wells ≥2; image early uncomplicated sciatica or a calf strain; delay vascular referral for an ABPI.
4Classify — only if the screen is negative
- Calf strain / tennis leg — sudden in activity. Gap, positive calf-squeeze → Achilles rupture: Urgent orthopaedics
- Ruptured Baker's cyst — mimics DVT; DVT pathway first.
- Sciatica / spinal stenosis — dermatomal pain + tingling; neurogenic claudication eased by flexion.
- PAD — ABPI below 0.9; diabetes, CKD or over ~1.3–1.4 → toe pressures.
- Cramps / restless legs — night spasms; urge to move at rest.
- Uncertain — say so; recheck neurology and pulses; think stress fracture, sarcoma.
5Treat today — doses: NICE/SPC, BNF, local formulary
- Calf strain: relative rest, early movement, progressive loading; paracetamol ± topical or short NSAID.
- Sciatica (NG59): stay active; consider physio/exercise; NSAID lowest dose, shortest time. Do not offer gabapentinoids, oral steroids, benzodiazepines, or opioids for chronic sciatica.
- Claudication: supervised exercise, statin, antiplatelet where indicated, stop smoking, BP and diabetes control.
- Cramps / restless legs: stretching, drug review; ferritin → iron if deficient; quinine not routine. Venous: compression only after ABPI or equivalent.
6Refer routinely
- Lifestyle-limiting claudication → vascular surgery.
- Sciatica still limiting despite conservative care (no fixed week cut-off) or spinal stenosis → spinal/MSK; stable significant deficit → Urgent
- Vein service (CG168): symptomatic varicose veins, venous skin changes, venous ulcer unhealed at 2 weeks or recurrent, thrombophlebitis with venous incompetence.
7Never reassure by
- Palpable pulses — they may persist in partial occlusion.
- Waiting for absent pulses in compartment syndrome — a late sign.
- A normal ABPI in diabetes or CKD.
- A normal X-ray when bone pain persists.
- A "Baker's cyst" before DVT is excluded.
- More analgesia for sciatica without re-examining for deficit or cauda equina.
8Safety-net — say it, then document it
999 / A&E “Leg suddenly cold, pale, numb or weak; calf more swollen or tense with severe pain; fast-spreading redness with fever; breathless, chest pain, coughing blood, fainting or racing heart; numbness between the legs, new bladder or bowel problems, or symptoms in both legs.”
Within 1 week “Worse or night-time bone pain, a new or growing lump, or weight loss — contact us within a week (within 48 hours for a child).” Most strains and sciatica improve over several weeks; if recovery stalls, re-examine rather than re-prescribe.
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies
Pulses, calf and L5/S1 neurology recorded, both legs
Wells recorded if the calf is swollen
Working diagnosis or uncertainty stated; review interval set
Safety-net given and documented
Summary of the full Reasoning GP leg pain algorithm, which holds the detail, examination, investigations and evidence. Sources: NICE NG158, CG147, NG59, NG12 (updated April 2026), CG168. Clinical reference — follow local DVT, vascular and spinal pathways and check doses: NICE/SPC, BNF.