The Popliteal Fossa: What Sits Behind the Knee and What Swells There

Stand with your knee slightly bent and press two fingers into the soft hollow at the back. Nothing much happens. Now straighten the leg. The hollow firms up, the tendons on either side tighten like guy-ropes, and whatever was hiding in that pocket gets squeezed toward the surface. That small experiment is why a lump behind the knee often shows up on the day someone tries to kneel in the garden or stretch on a yoga mat.

Anatomists call this pocket the popliteal fossa, from the Latin poples, the ham of the leg. It is barely bigger than a folded wallet, yet it funnels the main blood supply and both major nerves to everything below the knee through a space you can cover with your palm.

That crowding is the whole story. When something in the fossa swells, it has nowhere to go, and a surprising range of problems, some trivial and a few urgent, announce themselves in exactly the same place.

Where is the popliteal area, exactly?

The popliteal region is the back of the knee, full stop. If you sit on a chair and reach behind your bent knee, the warm, slightly damp crease your fingertips find is the roof of the popliteal fossa. The word turns up in several places: the popliteal artery, the popliteal vein, the popliteal lymph nodes and the popliteus muscle all take their name from this neighborhood.

A useful way to picture the space is as a shallow diamond. The upper half of the diamond is formed by the thigh muscles descending toward the knee; the lower half by the calf muscles rising to meet them. When the knee is flexed, the diamond deepens into a real hollow. When the knee is fully straight, the surrounding tendons pull taut and the space nearly disappears, which is why lumps and fluid collections behind the knee tend to feel firmer and more obvious with the leg extended.

Skin here is thin and richly supplied with sweat glands, one reason the back of the knee is a common site for eczema flares and heat rash. Beneath the skin lies a dense sheet of connective tissue called the popliteal fascia. That sheet is tougher than it looks. It resists stretching, so anything that swells underneath it produces pressure, a sensation many people describe as tightness or fullness rather than sharp pain.

Knowing the boundaries matters because doctors reason by location. A tender spot at the upper outer corner of the diamond points toward the biceps femoris tendon or the common fibular nerve. A soft, egg-shaped swelling at the lower inner corner is classic for a Baker’s cyst. A pulsing mass dead center raises the question of the artery.

What are the borders of the popliteal fossa?

Four muscles draw the edges of the diamond, and their names are worth learning because they come up again whenever a clinician explains back of knee pain.

• Upper outer border: the biceps femoris, the outermost hamstring, whose tendon you can feel as a firm cord just above the outside of the knee.
• Upper inner border: the semimembranosus and, lying on top of it, the semitendinosus. These two inner hamstrings form the cord on the inside of the crease.
• Lower outer border: the lateral head of the gastrocnemius, the main calf muscle, with the slender plantaris tucked alongside.
• Lower inner border: the medial head of the gastrocnemius.

The floor of the fossa, from top to bottom, is the smooth back surface of the femur, the capsule of the knee joint reinforced by the oblique popliteal ligament, and the flat, fan-shaped popliteus muscle covered by its fascia. The roof is skin, a thin layer of fat and that unforgiving popliteal fascia.

Why does the arrangement matter beyond anatomy exams? Because the gap between the semimembranosus tendon and the medial head of the gastrocnemius is where a small fluid-filled cushion, or bursa, sits. Under pressure from inside the knee joint that bursa can balloon into the lump most people know as a Baker’s cyst. The medial head of the gastrocnemius is also the muscle most often implicated when the popliteal artery is squeezed during exercise in young athletes. The borders are not just lines on a diagram; they are the moving parts that cause trouble.

What sits inside the popliteal fossa, layer by layer

Imagine lifting the roof off the diamond and looking in. The first thing you meet, running up the center just under the fascia, is the small saphenous vein, the surface vein of the calf, diving through the fascia to empty into the deeper system. Beside it lie a handful of popliteal lymph nodes, usually no bigger than lentils, draining the foot and lower leg.

Next comes the tibial nerve, the larger of the two branches of the sciatic nerve. It runs straight down the middle of the fossa and continues into the calf, supplying every muscle that points the foot downward and most of the skin on the sole. Off to the outer side, hugging the inner edge of the biceps femoris tendon, runs the common fibular nerve, also called the common peroneal nerve. This one wraps around the neck of the fibula just below the knee, where it lies almost on the bone. Sit cross-legged too long or wear a tight plaster cast and this is the nerve that produces a numb outer shin and a foot that slaps the floor.

Deeper still, in the order a surgeon would encounter them, sit the popliteal vein and finally the popliteal artery, the deepest structure of all, lying directly against the bone and joint capsule.

A memory aid taught to medical students captures the medial-to-lateral order of the big three: artery, vein, nerve. The artery is innermost and deepest, the tibial nerve outermost and most superficial. Everything is wrapped in fat that cushions the bundle as the knee bends thousands of times a day.

The popliteal artery: why the pulse behind the knee is so hard to find

Ask anyone who has done a clinical skills exam about the popliteal pulse and you will get a rueful smile. The popliteal artery is the continuation of the femoral artery, which slips from the front of the thigh to the back through a gap in the adductor muscles called the adductor hiatus. From there it runs the length of the fossa, hugging the femur and then the joint capsule, before splitting at the lower edge of the popliteus muscle into the anterior and posterior tibial arteries.

Along the way it throws off five genicular branches that form a ring of small vessels around the knee joint. This network is more than an anatomical curiosity; it is a detour system. If the main artery is compressed or narrowed, blood can sometimes route around the knee through these collaterals, which is one reason chronic narrowing here can be silent for a long time.

The pulse is elusive precisely because the artery is the deepest thing in the fossa, buried under fat, vein and nerve. Examiners feel for it with the knee bent to about 30 degrees, pressing the fingertips of both hands deep into the hollow while the patient relaxes the leg. Even then, a pulse that is easy to feel can be a warning rather than reassurance: an unusually prominent, wide popliteal pulse is one of the classic signs of a popliteal aneurysm, a localized ballooning of the vessel wall.

Mainstream vascular sources describe the popliteal artery as the most common site of aneurysm outside the abdomen, and people found to have one are frequently found to have another elsewhere, most often in the abdominal aorta. That linkage is why a surprising lump behind the knee sometimes leads to an ultrasound of the belly.

What does it mean if your popliteal area hurts?

Pain behind the knee is a location, not a diagnosis, and the honest answer is that it means many different things depending on what else is happening. Clinicians tend to sort it by three questions: Is there swelling? Is the pain worse with activity or with rest? And does it stay put or travel down the calf?

Aching that builds after a long walk or a hard training week, with no lump and no calf symptoms, most often comes from soft tissue: a hamstring tendon irritated where it anchors near the knee, a calf muscle strained at its upper attachment, or the small popliteus muscle protesting after downhill running. These typically ease over one to three weeks with relative rest.

Fullness or tightness behind the knee that is more noticeable when straightening the leg, especially in someone with existing arthritis or a past meniscus injury, points toward a Baker’s cyst. The cyst itself is rarely very painful; the underlying joint problem usually is.

Pain that arrives suddenly, concentrates in the calf as well as the back of the knee, and comes with warmth, redness or swelling of one lower leg is the pattern that should never be dismissed as a pulled muscle, because it can signal a deep vein thrombosis.

Cramping in the calf that starts reliably after a set distance of walking and disappears within minutes of stopping is the signature of restricted arterial blood flow, either from atherosclerosis in older adults or from muscular compression of the artery in younger, athletic ones.

Sharp pain when squatting or twisting, particularly with catching or locking, usually belongs to the meniscus at the back of the joint rather than to the fossa itself.

Baker's cyst: the most common lump behind the knee

The knee joint is a sealed sac lined with a membrane that produces a slippery fluid called synovial fluid. In many adults there is a small, valve-like opening between the back of that sac and the bursa lying between the semimembranosus tendon and the medial head of the gastrocnemius. When the joint is irritated and makes extra fluid, the fluid pushes through the opening, inflates the bursa and cannot easily flow back. The result is a Baker’s cyst, named after the nineteenth-century surgeon who described it, and also called a popliteal cyst.

The cyst is a symptom, not a disease in its own right. Behind almost every adult Baker’s cyst sits a knee problem generating fluid: osteoarthritis is the usual culprit, followed by meniscus tears and inflammatory arthritis. Mayo Clinic and the NHS both stress that treating the underlying joint is what actually shrinks the cyst; draining it alone tends to give temporary relief because the fluid refills.

What does it feel like? A smooth, soft, egg-shaped swelling on the inner side of the crease, more obvious with the knee straight, sometimes with a sense of tightness when fully bending or straightening the leg. Many are painless and are found by chance on an MRI ordered for something else. Studies of knee MRI in adults with symptoms find cysts in a wide range, roughly one in twenty to one in three, depending on the population scanned.

Two things about a Baker’s cyst genuinely deserve attention. First, a large cyst can press on the popliteal vein or the tibial nerve and cause calf swelling or tingling. Second, and more important, a cyst can rupture. Fluid then tracks down between the calf muscles, producing sudden calf pain, swelling and sometimes a bruise-like discoloration near the ankle. That picture is nearly identical to a deep vein clot, and no one can reliably tell the two apart by looking. An ultrasound settles it.

What is behind-the-knee swelling if it isn't a Baker's cyst?

Most lumps in the popliteal fossa turn out to be cysts, but the space hosts an artery, a vein, lymph nodes, nerves and fat, and each can swell. The clues that separate them are texture, pulsation, position and what the rest of the leg is doing.

What swells	How it typically feels	Telltale clue	Urgency
Baker’s cyst	Soft, smooth, inner side of crease	Firmer when knee straight, softer when bent	Routine, unless sudden calf pain
Popliteal artery aneurysm	Firm, central, often pulsating	Expands with each heartbeat; more common in older men	Prompt assessment
Deep vein thrombosis	Diffuse swelling, warmth, tenderness	Whole calf enlarged; may be red or dusky	Same-day medical care
Enlarged lymph node	Small, rubbery, mobile	Recent foot or leg infection or wound	Routine if settling; check if persistent
Lipoma or other soft-tissue growth	Soft, slow-growing, painless	Unchanged by knee position	Routine

A few points behind the table. Pulsation is the single most useful sign to check for at home: rest a fingertip gently on the lump and see whether it throbs in time with your pulse at the wrist. A cyst does not. A lump that transmits a heartbeat needs to be examined, and pressing hard on it is a poor idea.

Lymph nodes behind the knee enlarge for the same reasons nodes anywhere do, usually in response to infection downstream. A blistered heel, an infected toenail or an insect bite on the shin can all produce a tender, pea-sized node in the fossa that settles as the skin heals. Nodes that keep growing over weeks, feel hard or fixed, or appear without any obvious trigger should be looked at.

Ultrasound is the tool that resolves nearly all of these questions in a single visit. It shows fluid versus solid tissue, whether a vessel is dilated and whether blood is flowing through the vein, all without radiation.

Deep vein thrombosis: when back of knee pain is an emergency

The popliteal vein collects blood from the calf and carries it up into the thigh, and it is one of the classic sites where a deep vein thrombosis, or DVT, forms. The CDC estimates that as many as 900,000 people in the United States are affected by venous clots each year, and clots that begin in or above the popliteal vein are the ones most likely to break off and travel to the lungs.

The mechanism is not mysterious. Blood pools when the calf muscles stop pumping, whether because of a long flight, a hospital stay, a leg in a cast or a period of illness. Injury to the vessel wall, some medical conditions and some hormonal states make blood more prone to clotting. When these factors line up, a clot can form in the slow-moving blood behind the knee.

The symptoms MedlinePlus lists are deceptively ordinary: pain or tenderness in one leg, often felt in the calf or behind the knee, swelling of that leg, skin that feels warm, and redness or a change in color. Only one leg is usually involved, and that asymmetry is the most helpful clue. Roughly half of people with a DVT have few or no symptoms at all, which is why the threshold for getting checked should be low, not high.

Two situations deserve emphasis. A person with a known Baker’s cyst who develops sudden calf pain cannot assume the cyst has ruptured; a clot is just as plausible and the two are indistinguishable without imaging. And anyone with a swollen calf who develops chest pain, breathlessness or coughs up blood needs emergency care immediately, because those are signs a clot may have reached the lungs.

Massaging a swollen, tender calf is precisely the wrong instinct. It will not disperse a clot safely and could dislodge it.

What are the symptoms of a blocked popliteal artery?

Arterial blockage behind the knee comes in two speeds, and they feel completely different.

The slow version is peripheral artery disease, the same fatty-plaque process that narrows heart arteries. The CDC estimates it affects about 6.5 million Americans aged 40 and older, and the arteries of the thigh and knee are among its favorite targets. The hallmark symptom, described by Mayo Clinic and the American Heart Association, is intermittent claudication: a cramping, aching or heavy feeling in the calf that begins after walking a predictable distance and fades within a few minutes of standing still. The distance shrinks as the narrowing progresses. Other signs accumulate quietly: a foot that is cooler than its partner, thinning skin and sparse hair on the shin, toenails that grow slowly, a weak or absent pulse at the ankle, and wounds on the foot that take weeks to heal. Pain in the foot at night that eases when the leg hangs over the side of the bed suggests the blockage has become severe.

The fast version is acute occlusion, when a clot or a fragment from an aneurysm suddenly plugs the artery. This is a limb-threatening emergency and its features are taught with a string of P words: pain that is sudden and severe, pallor or a mottled bluish color, pulselessness at the ankle, paresthesia meaning pins-and-needles or numbness, paralysis meaning difficulty moving the foot, and a limb that is cold to the touch compared with the other side. Muscle and nerve begin to suffer irreversible damage within hours.

Popliteal aneurysms are dangerous mainly for this reason. Unlike aortic aneurysms, which threaten to burst, popliteal ones tend to fill with layered clot that can shed fragments downstream or block the vessel outright. Anyone with a pulsating lump behind the knee who develops a suddenly cold, pale or numb foot should treat it as an emergency.

Popliteal artery entrapment syndrome: the young athlete's calf cramp

Picture a 22-year-old distance runner with no risk factors for artery disease whose calves cramp and go numb after a mile, then recover completely within minutes of stopping. Blood tests are normal. Resting pulses are normal. It is easy to blame training load or shin splints, and many such athletes are told exactly that for years.

The likelier explanation is popliteal artery entrapment syndrome. In some people the medial head of the gastrocnemius attaches slightly too far outward, or the artery takes an unusual path, so that when the calf contracts hard the muscle clamps the artery against the bone. Blood flow to the lower leg drops during exertion and returns at rest. Repeated compression over years can scar the vessel wall, and in a minority of cases an aneurysm or a clot forms at the site.

A related variant, sometimes called functional entrapment, occurs in people whose anatomy is normal but whose calf muscles are large enough to compress the artery during forceful plantar flexion, the movement of pushing off the toes. This form is described mostly in highly trained athletes and military recruits.

Diagnosis rests on provocation. Ultrasound or angiography performed with the foot pointed and the calf contracted can show the artery pinched shut, whereas resting images look normal. That detail matters because a scan done at rest can miss the problem entirely.

The condition is uncommon, and the point is not to alarm every runner with sore calves. The point is that exertional calf pain in a young, otherwise healthy person that stops the moment they stop, especially if it comes with numbness or a pale foot, is a vascular pattern, not a muscular one, and deserves to be investigated with that in mind.

The popliteus muscle and the truth about massaging it

People searching for how to massage the popliteus are usually runners or hikers with a nagging ache at the back and outer side of the knee that flares on descents. The popliteus is a small, triangular muscle lying flat on the floor of the fossa. It runs from the outer edge of the femur down and inward to the back of the tibia, and its main job is to unlock the fully straightened knee by rotating the tibia slightly, letting the joint begin to bend. It also helps control the shin bone during downhill walking, which is why steep trails and long descents are its classic triggers.

Here is the honest part. There is little high-quality evidence that self-massage of this muscle changes its recovery; the modest benefits of massage for muscle soreness reported in general reviews come mostly from people feeling better in the short term, not from measurable tissue change. Gentle, comfortable work on the upper calf and the outer back of the knee is unlikely to harm you and may feel good.

What you should not do is press hard and deep into the center of the popliteal fossa. Directly under your thumb there are the tibial nerve, the popliteal vein and the artery, with almost no muscle to cushion them. Deep pressure can cause tingling in the foot from nerve irritation and is unwise over any lump, any pulsation or any calf that is swollen, warm or tender, when a clot has not been ruled out.

If you try it, work with the knee bent to about 90 degrees so the fossa is relaxed, use the pads of the fingers rather than a hard tool, keep pressure light enough that you could hold a conversation, and stop with any numbness or pins-and-needles. Pairing this with a short period of avoiding downhill running and gradually rebuilding calf and hamstring strength has more support than massage alone.

Hamstring, calf and meniscus: the muscular and joint causes of back of knee pain

For every dramatic vascular case, clinics see dozens of people whose posterior knee pain traces back to tendons, muscles or the joint itself. These are less frightening but no less real.

The hamstring tendons anchor around the fossa, and the biceps femoris tendon on the outer side is a frequent source of pain in cyclists and sprinters. It hurts to touch, aches after activity and is aggravated by hard acceleration. Semimembranosus tendinopathy on the inner side produces a similar picture and is easily confused with a small Baker’s cyst, since both sit in the same corner.

The gastrocnemius attaches to the back of the femur just above the joint, and a strain of its upper fibers, more common in people over 40 who lunge for a tennis ball or push off suddenly, causes a sharp pain and tenderness right at the lower border of the fossa. Bruising may appear a day or two later.

The meniscus, the cartilage cushion inside the knee, has a back portion, the posterior horn, that tears with twisting or, in older adults, with everyday degeneration. Pain is felt deep behind the knee, squatting is uncomfortable and the knee may click, catch or feel as if it will give way. A meniscus tear is also one of the common engines behind a Baker’s cyst, so the two often travel together.

Nerve irritation rounds out the list. The common fibular nerve, running along the outer edge of the fossa, is vulnerable to pressure from crossed legs, tight boots, prolonged squatting or a direct blow. The result is numbness on the outer shin and top of the foot and, if severe, weakness lifting the foot. Most cases recover over weeks once the pressure is removed.

Sorting these out relies less on scans than on a careful history and a hands-on examination that reproduces the pain with specific movements.

When to see a doctor about back of knee pain or swelling

Most aches behind the knee settle with a couple of weeks of easing off, and it would be wrong to send every reader to a clinic. The following patterns are the exceptions, drawn from what the NHS, Mayo Clinic and MedlinePlus advise.

Get emergency care now if you have a swollen or painful calf together with chest pain, sudden breathlessness or coughing up blood, since these can indicate a clot that has traveled to the lungs. Seek emergency care as well if one foot suddenly becomes cold, pale or mottled, numb or difficult to move, particularly if you know you have a lump behind the knee or a history of aneurysm.

Arrange to be seen the same day if one calf becomes swollen, warm, red or tender, whether or not you recall an injury, and even if you have already been told you have a Baker’s cyst. A ruptured cyst and a deep vein thrombosis look alike; only an ultrasound distinguishes them. Same-day care is also appropriate if a lump behind the knee pulsates.

Book a routine appointment if a painless lump persists longer than two to three weeks or is growing, if you cannot fully bend or straighten the knee, if the knee locks or gives way, if the pain wakes you at night, if calf cramping reliably starts after walking a set distance, or if you notice numbness or weakness in the foot that is not improving.

Whatever the situation, bring specifics. How long the swelling has been there, whether it changes with knee position, what makes the pain better or worse, any recent long journeys, surgeries, casts or illnesses, and whether anyone in your family has had clots or aneurysms all shorten the path to an answer.

How doctors examine the popliteal fossa and what the tests actually show

The examination usually begins with the patient lying face down, knee straight, then bent. The clinician looks for asymmetry between the two hollows, feels for a lump and notes whether it softens when the knee bends, a classic sign of a Baker’s cyst known as Foucher’s sign. Fingers rest lightly on any mass to detect pulsation. Pulses at the ankle and the top of the foot are compared side to side, and skin temperature and color are checked. Measuring calf circumference at a fixed point below the kneecap on both legs gives a number to track.

Ultrasound is the workhorse test and often the only one needed. It distinguishes fluid from solid tissue in seconds, shows whether a cyst connects to the joint, measures the diameter of the popliteal artery, and, with the Doppler function switched on, reveals whether blood is moving through the vein or whether a clot is blocking it. It is painless, involves no radiation and can be repeated freely.

MRI comes into play when the question is what is happening inside the knee itself: a meniscus tear, cartilage wear or ligament damage that might be driving fluid production. It also maps the full extent of a large or ruptured cyst.

For suspected arterial problems, the first step is often an ankle-brachial index, a simple comparison of blood pressure at the ankle with blood pressure at the arm. A ratio well below one suggests narrowing somewhere in the leg. Where entrapment is suspected, imaging is repeated with the calf contracted, because a resting scan can look entirely normal. CT or MR angiography then provides a detailed roadmap of the vessels if an intervention is being considered.

None of these tests is exotic, and most are available in an outpatient setting. The bigger barrier is usually delay, the weeks spent assuming a swelling behind the knee is just one of those things.

Frequently asked questions

Where is the popliteal area?

The popliteal area is the back of the knee, the soft hollow you can feel when the leg is bent. It is bordered by the hamstring tendons above and the calf muscle heads below, and it contains the popliteal artery, popliteal vein, tibial nerve and a few lymph nodes. When the knee straightens, the surrounding tendons tighten and the hollow nearly flattens out.

What does it mean if your popliteal area hurts?

It depends on what accompanies the pain. Aching after activity without swelling usually reflects a strained hamstring tendon, upper calf or popliteus muscle. Fullness that is worse with the leg straight suggests a Baker’s cyst. Sudden pain with a warm, swollen calf can signal a deep vein clot and needs same-day assessment, while cramping that comes on after walking a set distance points to reduced arterial blood flow.

What is a Baker's cyst and does it go away on its own?

A Baker’s cyst is a fluid-filled swelling behind the knee formed when synovial fluid from an irritated joint escapes into a bursa beneath the inner hamstring tendon. Small cysts sometimes settle without treatment, especially in children. In adults, the cyst usually persists or recurs until the underlying knee problem, most often osteoarthritis or a meniscus tear, is addressed, because that is what keeps producing the fluid.

What are the symptoms of a blocked popliteal artery?

A gradual blockage from peripheral artery disease causes calf cramping after a predictable walking distance that eases with rest, along with a cooler foot, weak ankle pulses, thin skin and slow-healing wounds. A sudden blockage is an emergency: severe pain, a pale or mottled foot, no pulse at the ankle, numbness, weakness moving the foot and a limb that feels cold compared with the other side.

How can I massage the popliteus muscle to relieve pain?

Gently, and with realistic expectations. Evidence that massage speeds recovery of this small muscle is limited, though light work may feel soothing. Sit with the knee bent to about 90 degrees so the hollow relaxes, use fingertips rather than a hard tool on the upper calf and outer back of the knee, and keep pressure mild. Avoid deep pressure in the center of the fossa, where nerves and blood vessels sit, and skip massage entirely if the calf is swollen, warm or tender.

How do I know if a lump behind my knee is a Baker's cyst or something serious?

You often cannot tell by feel alone, which is why a persistent lump deserves an ultrasound. A Baker’s cyst is typically soft, sits on the inner side and firms up when the leg is straight. Warning features that should prompt earlier assessment include a lump that pulses with your heartbeat, one that grows quickly or feels hard, sudden calf swelling and pain, or numbness and coldness in the foot.

Can a Baker's cyst cause a blood clot?

Not directly, but the two are linked in two ways. A large cyst can press on the popliteal vein, slowing blood flow and contributing to calf swelling, and a cyst that ruptures produces calf pain and swelling that mimics a deep vein thrombosis almost exactly. Because the symptoms overlap so closely, anyone with a known cyst who develops sudden calf pain should be checked for a clot rather than assuming the cyst has burst.

What is popliteal artery entrapment syndrome?

It is a condition, mostly seen in young athletes, in which the medial head of the calf muscle compresses the popliteal artery during exertion, cutting blood flow to the lower leg. Typical symptoms are calf cramping, numbness or a pale foot that begins after a set amount of running and resolves within minutes of stopping. Resting scans can look normal; imaging performed while the calf is contracted is needed to show the pinched artery.

Why is the pulse behind the knee so hard to feel?

Because the popliteal artery is the deepest structure in the fossa, lying against the femur and joint capsule beneath fat, the popliteal vein and the tibial nerve. Clinicians locate it by bending the knee to about 30 degrees, relaxing the leg and pressing both sets of fingertips deep into the hollow. An unusually easy, wide pulse is not necessarily reassuring, since it can indicate an aneurysm of the artery.

When should I see a doctor for back of knee pain?

Seek emergency care for a swollen calf with chest pain or breathlessness, or for a suddenly cold, pale or numb foot. Arrange same-day assessment for one calf that becomes swollen, warm or tender, or for a lump that pulses. Book a routine visit for a lump lasting more than two to three weeks, a knee that locks or will not fully straighten, pain that wakes you at night, or calf cramping that reliably starts after walking a fixed distance.

References

• NHS — Baker's cyst
• Cleveland Clinic — Baker's Cyst (Popliteal Cyst)
• MedlinePlus — Deep Vein Thrombosis

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.