Heart and circulation

Vein Pain Behind the Knee: What It Can Mean and What to Ask

Vein pain behind the knee? See what sources link with it, the urgent signs to act on first, and questions to save for your appointment.

By Cardio Guardian Editorial TeamPublished October 14, 202610 min read

Pain behind the knee that seems to come from a vein is a description, not a diagnosis: the sources used here link pain in that area with a blood clot in a deep vein, a clot or inflammation in a vein near the skin, varicose veins, a Baker cyst and knee joint problems, and some of these look alike. The popliteal vein, a deep vein, runs through the hollow at the back of the knee and is one of the most common places for deep vein thrombosis to develop. [1] MedlinePlus says a Baker cyst that breaks open can cause pain, swelling and bruising on the back of the knee and calf, and that a blood clot can cause the same signs and needs medical attention right away. [2] Noting when the pain started, where any swelling is and what happened beforehand gives a clinician something to work with; only their assessment, which may include an ultrasound, can find the cause. [3]

Urgent symptoms come first. Call 911 for severe chest pain or pressure, severe shortness of breath, suddenly not being able to speak, see, walk or move, or suddenly being weak or drooping on one side of the body. [4] If leg swelling comes with shortness of breath, or with chest pain that feels like pressure or tightness, MedlinePlus says to call 911. [5] Difficulty breathing, or chest pain or discomfort that gets worse with a deep breath or coughing, can be signs of a blood clot in the lungs (pulmonary embolism), which CDC says needs immediate medical attention. [6] Do not wait for a routine callback from your provider: go to an emergency department or call 911 or your local emergency number for help. [4] NHLBI says to call 911 if you see any bleeding from varicose veins. [7] Call your healthcare provider right away for swelling, pain or tenderness, warmth, or red or discolored skin in a leg, which can be signs of a blood clot in a deep vein (deep vein thrombosis); CDC says this needs prompt medical attention. [3] [6] Do not wait to see whether the pain behind your knee settles before getting help for these signs.

Save questions for my appointment

This page is general education for adults. It cannot tell you what is causing the pain, and it gives no medicine, massage, exercise or home-testing advice.

What sits behind the knee

The hollow at the back of the knee is called the popliteal fossa. The popliteal vein, the popliteal artery and the tibial nerve all run through it. The popliteal vein is a deep vein of the leg, and the small saphenous vein, a surface vein that drains the back of the lower leg, empties into it. [1] A Baker cyst also forms here, as a buildup of joint fluid that makes a swelling behind the knee. [2] For a fuller tour of this area, see our guide to the blood vessels in the knee.

What the sources connect with pain behind the knee

Pain in this area does not reliably point to one cause. The list below is a guide to the conversation with a clinician, not a way to decide the cause yourself.

A blood clot in a deep vein (deep vein thrombosis). MedlinePlus says deep vein thrombosis mainly affects the large veins in the lower leg and thigh, most often on one side of the body. [8] NHLBI lists swelling, pain or tenderness, cramping, aching or increased warmth, and red or discolored skin around the clot. [3] CDC says about half of people with deep vein thrombosis have no symptoms at all. [6]
A clot or inflammation in a vein near the skin (superficial thrombophlebitis). MedlinePlus describes swelling and pain in the affected area, skin redness that is not always present, and warmth and tenderness over the vein. [9] A 2025 review in JAMA says people typically notice a tender, red cord under the skin, and that a surface vein clot can extend into deep veins. [10] Such a clot can form in the small saphenous vein at the back of the calf. [1]
Varicose veins. NHLBI describes swollen, twisted veins just under the skin, usually in the legs, with bulging, bluish veins, aching pain and swelling. Symptoms may get worse after long periods of sitting or standing and ease when lying down or with the feet up. [7]
A Baker cyst. MedlinePlus says most people with a Baker cyst have no symptoms; a large cyst may cause discomfort or stiffness, and the swelling behind the knee may be painless or painful and feel like a water-filled balloon. It commonly occurs with a meniscus tear, knee arthritis or gout. [2] StatPearls describes tightness, discomfort or pain behind the knee, and lists deep vein thrombosis, other cysts and masses, and a bulge in the artery behind the knee (popliteal artery aneurysm) among conditions that can look similar. [11]
Knee joint problems and injuries. MedlinePlus lists arthritis, a torn meniscus, bursitis, ligament injuries and infection in the knee joint among causes of knee pain, which may start suddenly after an injury or exercise or begin as mild discomfort and slowly get worse. [12]

Age and background change how likely each cause is, but they do not decide it. MedlinePlus says deep vein thrombosis is most common in adults over age 60 but can occur at any age. [8] NHLBI says the chance of venous thromboembolism nearly doubles every 10 years after age 40, and that women are more likely than men to get it before menopause and men more likely after. [13] StatPearls says Baker cysts occur most often in adults aged 35 to 70, and in children most often between ages 4 and 7. [11]

What two studies add

A Baker cyst and a deep vein clot can be hard to tell apart without imaging. One hospital in Zagreb, Croatia, looked back at the records of outpatients who had an ultrasound of the leg veins in 2008 and 2009 to check for deep vein thrombosis and found ten with a complicated Baker cyst. The authors wrote that when a Baker cyst causes a swollen, painful calf, it cannot be told apart from deep vein thrombosis by a simple clinical examination. [14] This was a small review at one hospital, and the abstract does not say how many people were scanned. StatPearls also stresses getting an ultrasound to make sure nothing else is going on. [11]

A clot in a surface vein can come with a deeper one. A 2016 analysis pooled 21 studies of people diagnosed with a surface vein clot in the legs. At the time of diagnosis, about 18 in 100 also had deep vein thrombosis; in the 11 studies that looked for it, about 7 in 100 had a clot in the lungs. Results varied widely between studies, and younger age, female sex, recent injury and pregnancy were linked with lower rates. [15] These figures describe people already diagnosed with a surface vein clot, not everyone with pain behind the knee.

Onset, swelling and context checklist

The checklist sets out what to note before you see a clinician, what the sources say about each item and what a clinician may ask or check. It is not a way to decide the cause yourself. NHLBI says your provider will identify your risk factors and look for other causes of your symptoms. [16]

What to note about pain behind the knee, what the sources say about it, and what a clinician may ask or check
What to note	What the sources say	What a clinician may ask or check
Onset	Knee pain may start suddenly, often after an injury or exercise, or begin as mild discomfort and slowly get worse. [12] A Baker cyst can break open, causing pain, swelling and bruising on the back of the knee and calf. [2]	Your recent medical history, especially any long periods without movement. [16] A physical exam of your knees, hips, legs and other joints. [12]
Swelling	Deep vein thrombosis most often affects one side of the body. [8] MedlinePlus says to contact your provider right away for new or worsened swelling in only one leg. [5]	Which parts swell, whether the swelling is above or below the knee, and whether it is worse in the morning or evening. [5]
Skin and veins	Swelling, pain or tenderness, warmth, and redness or discoloration are the most common signs of deep vein thrombosis. [6] A tender, red cord under the skin is typical of a surface vein clot. [10] Bulging, bluish veins are a varicose vein symptom. [7]	An exam for a red, swollen or tender leg. [8] A D-dimer blood test, or a compression ultrasound that looks for clots in the deep veins of the legs. [3]
A lump behind the knee	A Baker cyst may feel like a water-filled balloon and can be painless or painful. [2] Other cysts, solid masses and a popliteal artery aneurysm can look similar. [11]	A look for a soft lump, comparing both knees; X-rays do not show the cyst, but an MRI can. [2] An ultrasound to make sure nothing else is going on. [11]
The knee itself	Catching, locking or other signs of a meniscus tear can come with a Baker cyst. [2] A knee that buckles, clicks or locks, or that you cannot put weight on, is a reason to contact your provider. [12]	Sometimes an X-ray, MRI or CT scan of the knee. [12]
Recent events	Recent surgery, most commonly hip, knee or female pelvic surgery; fractures in the pelvis or legs; bed rest or sitting in one position too long, such as on a plane or car trip. [8] NHLBI says clot risk is highest in the first 3 months after surgery. [13]	Whether you have been in the hospital recently, especially for surgery, an injury or an infection. [16]
Health background	A family history of blood clots, pregnancy or giving birth within the last 6 months, estrogen or birth control pills, cancer, obesity and smoking. [8] Knee arthritis, a meniscus tear or gout, which often come with a Baker cyst. [2]	The medicines you take and whether you have had cancer care. [16]
Breathing or chest symptoms	Difficulty breathing, or chest pain that gets worse with a deep breath or coughing, can be signs of a clot in the lungs; CDC says this needs immediate medical attention. [6]	Not something to note for later: get emergency help as described in the urgent box above. [4]

When to contact a healthcare provider

These are reasons the sources give to contact a provider. The urgent signs above come first.

MedlinePlus says to contact your provider if you have symptoms of deep vein thrombosis [8], and right away if your swollen foot or leg is red or warm, you have a fever, or you have new or worsened swelling in only one leg. [5]
Swelling behind the knee that becomes large or painful. MedlinePlus says a lump that grows quickly, night pain, severe pain or fever needs more tests. [2]
You cannot bear weight on your knee; you have severe pain even when not bearing weight; your knee buckles, clicks or locks; you have a fever, redness or warmth around the knee or a lot of swelling; or you have pain, swelling, numbness, tingling or bluish discoloration in the calf below the sore knee. [12]
Thrombophlebitis symptoms that get worse, or new symptoms such as a whole limb becoming pale, cold or swollen. MedlinePlus says to contact your provider right away. [9]
Varicose veins that suddenly get worse, or a sore near them. NHLBI says to call your provider right away. Bleeding from a varicose vein is a reason to call 911, as above. [7]
If you think a medicine may be involved, do not start, stop or change a medicine on your own; ask your clinician. [5]

Questions to save for your appointment

Write your answers before your visit and take them with you. The questions follow what the sources say clinicians ask about leg swelling, knee pain and blood clot risk. [5] [12] [16] This page does not collect anything you write.

Download the appointment question sheet (PDF, 2 pages, 46 KB)

When and how the pain started

When did the pain behind my knee start, and did it come on suddenly or slowly?
Did it start after an injury, a fall, exercise or a twist of the knee?
Where exactly is the pain: behind the knee only, in the calf below it, or along a vein I can see or feel?
Which words describe it most closely: aching, cramping, throbbing, tight, burning or sharp?
Is it getting worse, staying the same, or coming and going?

Swelling and other changes

Is there swelling behind my knee, in my calf or in my whole leg, and is it in one leg or both?
Is the skin red, warm, bruised or a different color, or can I feel a tender cord under the skin?
Do I have bulging, twisted veins near the sore area?
Is there a lump behind my knee, and has it changed in size?
Does my knee catch, lock or buckle, or is it hard to bend, straighten or put weight on?
Have I noticed numbness, tingling, or a pale, cold or bluish calf or foot?

Recent events and my health background

Have I recently had surgery, a broken bone, a hospital stay, bed rest or a long trip?
Have I had a blood clot, or has anyone in my family had one?
Do I have arthritis, gout or an earlier knee injury?
Am I pregnant, or have I given birth in the last 6 months?
Do I take estrogen or birth control pills, and do I smoke?
Have I had cancer or cancer treatment?
Which medicines do I take, and have any changed recently?

Questions to ask my clinician

What do you think is causing the pain, and what else could it be?
Do I need an ultrasound or any other test, and what will each one show?
If it is not a clot, what is the next step?
Should I see a specialist, and which kind?
Is there anything I should avoid doing with this leg until we know the cause?
Which changes mean I should call you right away or get emergency care?

Bring to your appointment

This sheet with your answers
A list of every medicine and supplement you take, including any recent changes
Dates of any recent surgery, injury, hospital stay or long trip
Reports from any earlier leg ultrasound, knee imaging or blood tests, if you have them

Bring this sheet to any appointment where the pain behind your knee comes up, whether with your primary care provider or a specialist.

What this page cannot tell you

It cannot tell you whether a clot, a surface vein, varicose veins, a Baker cyst or your knee joint is behind the pain. CDC says the diagnosis of deep vein thrombosis requires special tests that only a doctor can perform. [6]
It does not suggest massage, stretching, exercise, any test you can do at home, or any medicine.
The two studies described above covered one Croatian hospital and people already diagnosed with a surface vein clot, and the other sources are general US patient education and reference chapters for clinicians. Your age, health and history may change what applies to you. [14] [15]
Symptom lists are typical examples, not complete lists, and a deep vein clot can cause no symptoms. [4] [6]

For more on how blood moves through the body, browse Heart and circulation or test what you know with our circulatory system worksheets. Related reading covers the purpose of valves in veins, whether varicose veins cause foot pain and what heavy legs can mean. For practice reading what a label does and does not say, try the food label reading worksheet.

Common questions

What vein is behind the knee?

The popliteal vein, a deep vein that runs through the hollow at the back of the knee alongside the popliteal artery and the tibial nerve. The small saphenous vein, a surface vein from the back of the calf, drains into it. [1]

Can a Baker cyst feel like a blood clot?

Yes. MedlinePlus says both can cause pain, swelling and bruising on the back of the knee and calf, and a small hospital study found the two could not be told apart by a simple examination. StatPearls stresses an ultrasound to tell them apart. [2] [14] [11]

Is pain behind the knee a sign of a blood clot?

It can be one possibility, but it is not specific: the sources also link pain there with surface vein problems, varicose veins, a Baker cyst and knee joint problems. Swelling, warmth, redness and tenderness in the leg are reasons to call your provider right away, and about half of people with a deep vein clot have no symptoms. [9] [7] [2] [12] [3] [6]

Can varicose veins cause pain behind the knee?

NHLBI lists aching pain and swelling in the legs among varicose vein symptoms. It says to call your provider right away if varicose veins suddenly get worse or you notice a sore, and to call 911 for any bleeding from them. [7]

What tests might a clinician use?

For a possible clot, NHLBI describes a D-dimer blood test and a compression ultrasound of the leg veins. For a Baker cyst, MedlinePlus says X-rays do not show the cyst but an MRI can. Which tests you need depends on your history and exam. [3] [2] [16]

Should I massage or stretch a sore vein behind my knee?

Not before a clinician has checked it. The sources used here give no massage or stretching advice for pain that could come from a clot, and MedlinePlus says a blood clot may be dangerous and needs medical attention right away. [2]

Urgent symptoms come first. Call 911 for severe chest pain or pressure, severe shortness of breath, suddenly not being able to speak, see, walk or move, or suddenly being weak or drooping on one side of the body. [4] If leg swelling comes with shortness of breath, or with chest pain that feels like pressure or tightness, MedlinePlus says to call 911. [5] Difficulty breathing, or chest pain or discomfort that gets worse with a deep breath or coughing, can be signs of a blood clot in the lungs (pulmonary embolism), which CDC says needs immediate medical attention. [6] Do not wait for a routine callback from your provider: go to an emergency department or call 911 or your local emergency number for help. [4] NHLBI says to call 911 if you see any bleeding from varicose veins. [7] Call your healthcare provider right away for swelling, pain or tenderness, warmth, or red or discolored skin in a leg, which can be signs of a blood clot in a deep vein (deep vein thrombosis); CDC says this needs prompt medical attention. [3] [6] Do not let a list of questions delay getting help.