Skip to main content

Health condition

Popliteal artery aneurysm, often silent - and why the blood clot matters more than the bulge.

A widening of the artery behind the knee. It rarely bursts, but clot within it can block the leg’s blood supply. Finding it early, and checking the aorta and other leg too, lets repair be planned rather than rushed.

Jump to treatment
A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Editorial team

    Written by our editorial team from the UK sources listed on each page.

  • 02

    Sourced from guidance

    Checked against NICE, the NHS screening programme and European vascular guidance you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK practice, including duplex surveillance, vein bypass and selective stent-grafting.

Key facts

Popliteal aneurysm at a glance.

The essentials, in plain English - what it is, who it affects, and how it is managed in the UK today.

  • What it is

    A localised bulge in the popliteal artery behind the knee - the artery that carries blood to the calf and foot.

  • Who gets it

    Mostly men over 60. It is the commonest aneurysm outside the aorta, and it is frequently found in both legs.

  • Often silent

    Many are found by chance. A lump behind the knee, calf swelling or cramping on walking may be the only clues.

  • The real danger

    Clot forming inside the aneurysm, then blocking the artery or travelling downstream. This is far commoner than rupture.

  • Check the aorta

    Popliteal aneurysms often coexist with an abdominal aortic aneurysm, so both are looked for once one is found.

  • Treatment

    Risk-factor control and surveillance for small ones; planned repair, usually vein bypass, for larger or clot-lined ones.

Why this guide matters

Found early, it is a planned operation. Found late, an emergency.

A popliteal aneurysm can sit quietly for years. The three points below shape everything else on this page.

  • Clot, not rupture, is the main risk

    The usual complication is clot forming in the aneurysm and blocking the artery or lodging downstream, which can threaten the whole leg.

  • Look at the aorta and the other leg

    These aneurysms often come in company. Scanning the abdomen and the opposite knee is part of a proper assessment.

  • Planned repair beats emergency surgery

    Outcomes are generally better when a suitable aneurysm is repaired electively than after the limb has already lost its blood supply.

How the diagnosis is made

From a lump behind the knee to a clear plan.

The steps a UK GP or vascular team will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    History and leg examination

    Your clinician asks about walking pain, swelling, cold or numb feet, smoking and family history of aneurysm, then examines both legs.

  2. 02

    Assessing

    Pulses and the popliteal fossa

    A wide, pulsatile mass behind the knee is the classic finding. Foot pulses are checked at the same time.

  3. 03

    Assessing

    Duplex ultrasound

    The first-line scan. It measures the aneurysm, shows any clot lining it and checks the blood flow in the leg.

  4. 04

    Confirming

    CT or MR angiography

    Used for planning - it maps the artery above and below the aneurysm and the vessels to the foot (the run-off).

  5. 05

    Confirming

    Screen the aorta and other leg

    An abdominal ultrasound looks for an aortic aneurysm, and the opposite popliteal artery is scanned as well.

  6. 06

    Deciding

    Vascular multidisciplinary review

    A vascular surgeon, interventional radiologist and specialist team agree whether to watch, or to repair.

  7. 07

    Deciding

    Plan and follow-up

    Either a surveillance schedule with risk-factor treatment, or a planned operation with the type of repair explained.

Typical timeline: a suspected aneurysm to a vascular plan within weeks - sooner if the leg is symptomatic.

Symptoms

What a popliteal aneurysm can feel like.

From no symptoms at all to a sudden, limb-threatening event. Knowing the difference is what matters.

  • Pulsatile lump behind the knee

    A firm, throbbing swelling in the back of the knee - sometimes noticed by the patient, more often by a clinician.

  • Calf swelling or fullness

    A large aneurysm can press on the neighbouring popliteal vein, causing swelling that can be mistaken for a clot in the leg.

  • No symptoms at all

    Many aneurysms are silent and picked up on a scan for something else, or on examination of the other leg.

  • Calf pain on walking

    Cramping that eases with rest suggests reduced blood flow, which may mean clot has already narrowed the outflow.

  • Tingling or numbness

    Pressure on the nearby nerve can cause pins and needles or altered feeling in the calf or foot.

  • Cool, pale or blotchy foot

    Small clots breaking off can block tiny vessels in the foot, causing discoloured or painful toes.

  • Sudden severe leg pain

    Abrupt pain with a cold, pale, numb leg is acute limb ischaemia and needs an emergency response.

  • Red flag - blocked or threatened leg

    A pulseless, cold or weak leg is time-critical. Call 999 rather than waiting to see your GP.

Treatment

How a popliteal aneurysm is managed in the UK.

Risk-factor control for everyone, surveillance for small aneurysms, planned repair for larger or clot-lined ones - and emergency care if the leg loses its blood supply.

  • Risk-factor control

    Stopping smoking, blood pressure treatment and cholesterol management. These slow the disease behind the aneurysm and protect the rest of your arteries.

  • Statin and antiplatelet

    Usually advised for people with arterial disease. Your vascular team decides the drugs and doses that suit you.

  • Surveillance

    Small, symptom-free aneurysms without clot may be scanned at intervals by duplex ultrasound, with repair if they grow or change.

  • Screening the aorta and other leg

    A scan of the abdomen and the opposite knee is part of the plan, as further aneurysms are common.

  • Open exclusion and bypass

    The standard repair. The aneurysm is bypassed with a length of your own vein, restoring flow to the calf and foot.

  • Endovascular stent-graft

    A covered stent placed through a needle puncture. It suits carefully selected patients with the right anatomy and healthy run-off.

  • Thrombolysis

    A clot-dissolving drug delivered through a catheter into the blocked artery, sometimes used to clear the run-off before repair.

  • Thrombectomy or emergency bypass

    For a blocked artery and threatened limb: the clot is removed or the blockage bypassed as an emergency operation.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or vascular surgeon knows your history and can tell you which parts apply to you. If in doubt, get seen - and if your leg turns cold, pale or numb, call 999.

  • NICE. Peripheral arterial disease: diagnosis and management (CG147).

  • NICE. Abdominal aortic aneurysm: diagnosis and management (NG156).

  • European Society for Vascular Surgery. Clinical Practice Guidelines on the management of acute limb ischaemia (2020).

  • NHS Abdominal Aortic Aneurysm Screening Programme. Information for men aged 65 and over.

Red flags

When a leg is in danger.

Acute limb ischaemia is an emergency: pain, pallor, pulselessness, paraesthesia, paralysis and perishing cold. If you have these, call 999.

  • Sudden severe leg pain

    Abrupt pain in the calf or foot, especially with no injury, may be a blocked artery. Call 999.

  • Pale, cold or mottled foot

    A foot that is markedly whiter, colder or blotchier than the other side suggests loss of blood supply.

  • Loss of pulse

    A previously palpable foot pulse that has disappeared is a warning that the artery may have clotted.

  • New numbness or pins and needles

    Altered feeling in the foot with any of the above means nerves are short of blood - an emergency.

  • Weakness or inability to move

    Difficulty moving the toes or ankle is a late and serious sign that the limb is in danger.

  • A growing lump behind the knee

    A known lump that has become larger, tender or more painful should be reviewed promptly, not left for the next appointment.

  • Sudden calf swelling

    A swollen, tight calf may reflect vein compression or a blood clot. It needs same-day assessment.

  • Blue or dark toes

    Discoloured toes after a cool, painful foot suggest small clots have travelled from the aneurysm.

  • New pain in the abdomen or back

    Because aortic aneurysms often coexist, sudden severe abdominal or back pain is also an emergency.

Living with it

A manageable condition, with vigilant follow-up.

Four things that make the biggest difference - stopping smoking, taking preventive medicines, keeping scans and knowing the emergency signs.

A quiet reminder

Speed matters more than certainty.

If the leg suddenly changes, do not wait to see whether it settles. An unnecessary call costs little; a delayed one can cost the limb.

  1. 01 Smoking

    Stop, and stay stopped

    Smoking drives arterial disease. NHS stop smoking services and medicines can more than double your chance of quitting for good.

  2. 02 Medicines

    Take them every day

    Statin and antiplatelet treatment work by long-term prevention. Do not stop them without speaking to your team.

  3. 03 Follow-up

    Keep every scan

    Surveillance only protects you if it is kept up.

  4. 04 Know signs

    Know the emergency signs

    Learn the six Ps - pain, pallor, pulselessness, paraesthesia, paralysis and perishing cold - and act on them straight away.

Frequently asked

Everything we get asked about popliteal aneurysm.

Quick answers on risk, screening, repair and what to do in an emergency.

  • What is a popliteal artery aneurysm?

    A localised widening of the popliteal artery behind the knee. It is the commonest peripheral arterial aneurysm, most often seen in men over 60, and it is frequently present in both legs.

  • Is a popliteal aneurysm likely to burst?

    Rupture is uncommon. The main danger is clot forming in the aneurysm, which can block the artery or travel down to the foot. This can cause acute limb ischaemia, a limb-threatening emergency.

  • Why am I being scanned for an aortic aneurysm as well?

    Popliteal aneurysms often occur alongside an abdominal aortic aneurysm, and the other knee may be affected too. Finding all of them at once means the right plan can be made in one go.

  • When does a popliteal aneurysm need repair?

    Most vascular teams consider repair when the aneurysm is large - commonly around 2 cm - or when it contains clot, causes symptoms or has poor blood flow beyond it. Smaller, symptom-free aneurysms may simply be watched.

  • Is repair done through the leg or with a stent?

    The standard operation is open exclusion with a vein bypass. A stent-graft placed through a small puncture is an option for selected patients whose anatomy and blood vessels below the knee suit it. Your vascular team explains which is safer for you.

  • What should I do if my leg suddenly goes cold and painful?

    Call 999. Sudden pain with a pale, cold, numb or weak leg may be a blocked artery. The sooner blood flow is restored, the better the chance of saving the limb.

Related content

Keep reading.