Part of IT band syndrome
Can IT band syndrome cause knee swelling?
Warning signs, and when to get help
Can IT band syndrome cause knee swelling, or is it something else?
Both answers are true, and which one applies to you depends on what kind of swelling you have.
There are two different things people mean by a swollen knee. The first is a small, local puffiness over one tender area, the sort of thing you only notice when you compare both legs. The second is a knee that has filled up, where the dips either side of the kneecap have disappeared, the joint feels tight at the end of bending and straightening, and the whole thing looks a size bigger than its partner. IT band syndrome produces the first. It does not produce the second.
That distinction is worth more than any list of symptoms, because the two have different causes and different urgencies. A tender spot at the outside of the knee in a runner who has just doubled their mileage is a loading problem. A joint full of fluid is a question about what is happening inside the joint, and a few of the answers to that question need seeing today.
So before anything else, take thirty seconds in good light. Bare both knees, sit with them side by side and look at them rather than feeling them. Looking is safe for anyone, and the moving part that follows has two conditions on it.
If you have had an operation on this knee and were given a limit on how far it may bend, that limit holds here as much as anywhere else: look, do not bend, and ask your surgical team if you are not sure what your limit is. And if the knee is already stuck bent and will not straighten however gently you try, do not keep testing it. That is the locked knee line in the warning list at the foot of this page, and it needs assessing the same day.
Otherwise, try to straighten each leg fully and bend each one as far as it goes, moving it yourself and stopping at the first firm resistance rather than pushing through it. If one knee is puffy over a single area about the size of a coin at the outside, and both still move the same, the band is a reasonable explanation. If one has lost its shape all the way round, or stops short of the other on straightening, read the sections below before you open the IT band syndrome program.
What the swelling looks like when it is the band
Small, in one place, and tender to press.
The spot is on the outside of the knee, over the bony bump on the end of the thigh bone, just above the joint line. People find it with one finger. It is often warm to the touch after a run and not warm at all by the next morning, and it does not spread round the joint.
There is a described anatomy behind what you are feeling. Fairclough and colleagues (2006) dissected the lower part of the band in 15 donated bodies and found it anchored to the thigh bone by fibrous strands, pressing inward on a layer of fat they described as richly innervated and vascularized. Pressure on a layer like that explains tenderness and a bit of local puffiness without anything happening inside the joint at all.
Geisler (2021) frames the whole condition as an impingement rather than a friction problem, and reports, from Noble's cohort, that the most frequent complaint was sharp, focal pain at the outside of the knee after a period of running. Sharp and focal is the phrase to hold on to. A dull ache spread across the whole knee is not this picture.
One last feature: the local kind comes and goes with your training. More after a long run, less after three quiet days. Swelling that sits there unchanged whatever you do, or that keeps increasing week on week, is behaving like something else.
What a swollen knee joint feels like instead
A joint full of fluid announces itself in ways a sore spot does not.
People describe tightness more often than pain, worst at the ends of the range. Bending feels blocked by fullness. Full straightening becomes hard, and that one matters, because a knee that cannot straighten tends to stay that way if nobody addresses it. Kneeling becomes uncomfortable in a way the outside of the knee never explains. And the shape changes: the hollows beside and above the kneecap fill in, which is the easiest thing to see when you compare both legs.
The speed tells you something too. The NHS says swelling from a meniscus tear may not start for a few hours or days, and OrthoInfo describes a knee gradually becoming stiffer and more swollen over 2 to 3 days after this kind of injury. So slow swelling after a twist is not reassuring. It is characteristic. Fast swelling, inside a few hours of a twist, fall or blow, is in the emergency line in the warning list below.
Other things that fill a knee behave differently again. An arthritic knee often swells after a busy day and settles overnight, which is covered on knee osteoarthritis. A knee that swells with no clear reason at all, particularly in someone taking medicine to thin their blood, is in the warning list as a same day item. And swelling, locking and giving way separates those three symptoms for a torn meniscus, which is a common reason a knee fills up in an active adult.
Why the inflamed bursa story is the old explanation
Most of the patient pages you will find say the same thing: the band is too tight, it rubs over the bone as the knee bends, and the band and its bursa become inflamed. Two studies went looking for that bursa. Neither found one, and both were small, which is worth knowing before anyone leans on either of them.
Muhle and colleagues (1999) imaged six donated knees with MR arthrography at full extension, at 30 degrees and at 60 degrees of bend, then checked the imaging against macroscopic and microscopic sections of the same specimens. In none of the six was there a primary bursa between the bony bump at the outside of the thigh bone and the band. The lateral synovial recess of the joint did not interfere with that bump at any of the three angles either.
Fairclough and colleagues (2006) came at it from a different direction, with 15 donated bodies, 6 healthy volunteers scanned with MRI and 2 athletes who had the condition at the time. Their sentence is short: in no cadaver, volunteer or patient was a bursa seen.
Six specimens and fifteen bodies are small numbers, and it is worth saying what they do and do not support. They do not prove that nobody anywhere has a bursa in that corner; a sac of that kind can form in response to pressure, and nothing here rules that out in an individual. What they do support is that a bursa is not a normal structure at that spot, so an explanation that depends on one being inflamed is resting on a structure neither study could find: not in Muhle's six knees, and not in any cadaver, volunteer or patient in Fairclough's series. The better-supported account is the one Fairclough's group proposed and Geisler (2021) built on: a richly supplied fat layer being compressed, with fluid collecting in the space around it.
Why does this matter to you rather than to an anatomist? Because the bursa story leads somewhere, and where it leads is friction massage aimed at a structure that was not found, and stretching aimed at a band that does not lengthen. Geisler's own recommendation is that stretching and deep friction massage of the lower band be left out of the plan.
One further consequence, if you have been offered an injection or an operation for this, or have already had one. The missing bursa changes the explanation and not the examination. An injection at that spot goes into the tissue and the fluid filled space Muhle's imaging describes, whether or not a bursa is there, and whether to inject, or to release the band, is a decision for the clinician who has examined your knee rather than something to settle from an anatomy paper. Do not cancel either on the strength of this page.
What the finding does not change at all is what you watch for afterwards. Any needle or cut into or around a joint gives germs a way in, and the NHS lists joint surgery among the ways septic arthritis starts, with recent joint surgery and an artificial joint among the things that raise the risk. So a knee that turns hot, red, more swollen or more painful over the days after an injection or an operation, or a temperature alongside it, is the same day line in the warning list below rather than a flare of the old problem.
When swelling means something else is going on
Five patterns in a swollen knee change what you do today, whatever anyone calls the condition. Each has its own line in the warning list at the foot of this page, with the timing on it.
- Swelling that came up fast, within a few hours of a twist, fall or blow, or with a pop or a snap. That is the emergency line.
- A hot, red, swollen knee, or knee pain with a high temperature or feeling hot, cold or shivery. The NHS lists severe pain in one joint that started suddenly, swelling, a change in the skin color around it and difficulty moving it among the reasons to get urgent advice for septic arthritis, and that is the one pattern never managed at home.
- A knee that is locked, meaning stuck bent and unable to straighten fully even after gently trying. Same day.
- A knee that swells with no clear reason at all, which carries more weight again if you take medicine to thin your blood. Same day.
- A knee that keeps giving way, or that gave way after a recent injury, or that gives way and is also very painful or swollen. Same day, and the line tells you what to leave out in the meantime.
One addition that is not about the knee. A calf or thigh that is newly swollen or getting more swollen, warm, tender, red or darker than usual is a different problem from a swollen knee joint, and it is in the warning list as a possible clot. Readers with a sore leg who have been less active than usual, or who have had surgery or a long trip, are exactly the people who meet it.
One more addition is about age rather than about the knee. In someone who is still growing, a lump or swelling around the knee or thigh that keeps getting bigger is not read as a training problem, and nor is pain that wakes them at night or rest pain that keeps getting worse. That has its own line in the warning list, at a day or two rather than a few weeks, because a swelling in a growing bone is checked early.
Swelling behind the knee, and swelling that comes and goes
Swelling at the back of the knee is not where this condition lives, and it has its own short list.
The NHS describes a Baker's cyst as a soft lump at the back of the knee, which can come with knee or leg pain, tightness, stiffness or aching, difficulty bending the knee and clicking, often worse after walking. A cyst like that is usually a sign of something else irritating the joint, not a problem in its own right, which is why finding one leads to a question about the knee in front of it. Our Baker's cyst page covers the management, and pain behind the knee covers what else sits back there.
Two things about a cyst deserve naming. The NHS advises urgent advice if leg pain or swelling suddenly gets worse, if the leg becomes swollen, bruised or warm, if the skin turns red or darkened, or if the swelling becomes harder or softer, because a cyst can burst and because a clot in the leg produces a similar picture. And it says to call emergency services or go to an emergency department if leg pain and swelling come with breathlessness or chest pain.
Swelling that comes and goes is a different pattern again, and the useful question is what it follows. Swelling that tracks your training, up after the long run and down after a rest day, is behaving like a loading problem. Swelling that arrives out of nowhere, or after a small twist, or with catching or locking, is behaving like something inside the joint.
Does IT band syndrome show up on a scan?
Yes, although a scan is not usually how it is diagnosed, and the thing it shows is more interesting than a yes or no.
Muhle and colleagues (1999) reviewed 17 MRI studies in 16 patients with the condition. The abnormality they found was either poorly defined signal change or a well-circumscribed collection of fluid, and in both cases it sat in a compartment-like space bounded on the outer side by the band and on the inner side by the meniscocapsular junction, the lateral collateral ligament and the bony bump at the end of the thigh bone. Their conclusion was that MRI accurately depicts that compartment-like distribution.
Read that geographically and it answers the question you came with. The fluid is outside the joint, in a space the band forms one wall of. That is why a scan of this condition does not look like a knee effusion, and why a genuine effusion on a scan points the clinician somewhere else.
X-rays show none of it, since they show bone. In practice imaging is ordered to exclude the look-alikes rather than to confirm the diagnosis, and Geisler (2021) lists those look-alikes for pain on the outside of the knee: patellofemoral pain and instability, a lateral collateral ligament sprain, osteoarthritis in the outer compartment and lateral meniscal problems. Outer knee pain walks through the same ground from the symptom end.
What helps the sore spot settle
Less of what brings it on, and more work for the hip, in that order.
Cutting back is the part people skip. The pain in this condition is tied to repetition through a bent knee, so the single most reliable change is fewer of those repetitions for a few weeks, which usually means shorter runs, flat ground and no downhill. The IT band syndrome program sets out how much to cut and what tells you it is working, and the marker it uses is not how much it hurts but when in a run the pain arrives.
For the sore spot itself, the NHS self care for knee pain is an ice pack or a bag of frozen peas wrapped in a towel for up to 20 minutes every 2 to 3 hours, limiting the weight you put through the knee, and paracetamol or ibuprofen as tablets or gel. Never put ice on skin that cannot feel properly, and take it off before you fall asleep. If you have had an operation on the knee, ask your surgical team before you put ice over the wound or the dressing, because teams differ on that. Ice settles symptoms; it does not treat the cause, and six weeks of icing the same knee is a sign the training needs changing rather than the ice pack.
Then the hip work, which is what the evidence actually supports. In a 2024 systematic review of conservative treatment in runners with this condition, 13 studies and 201 participants, hip abductor strengthening was the ingredient that recurred, and pain and function improved over 2 to 8 weeks (Sanchez-Alvarado and colleagues, 2024). The authors could not pool the results, and 6 of the 13 were case reports or case series, so this is a direction rather than a prescription. Judge your own progress by the next morning, and the pain monitoring model guide explains how.
Swelling in a knee that has been operated on
If you have had an operation on this knee, follow the program your surgeon and physio gave you instead of this one. Swelling after surgery is a different subject from swelling with IT band syndrome, and the questions worth asking about it are not the questions above.
Some swelling is expected after a knee operation, and it often lasts longer than people expect. What matters is not the amount but the direction. Swelling and pain that settle unevenly, worse after a busy day and better after a quiet one, are the ordinary pattern. Swelling and pain that climb steadily from the first few days onward, instead of easing, are the pattern that gets a phone call.
A knee that fills quickly and feels tight and full in the first days, rather than swelling slowly, gets the same call the same day, because that is how bleeding into the joint behaves, and it carries more weight again if you take medicine to thin your blood. Compare today with yesterday and last week rather than with your other knee, because the other knee is not a fair comparison after an operation.
Four post-operative routes are in the warning list below and none of them waits.
- Infection in the wound or the joint. A wound that is oozing, leaking or coming apart at the edges, or a knee that is getting more tender, swollen, red or painful instead of less, with or without a temperature. That means contacting your surgical team the same day, or urgent medical advice if you cannot reach them, and the line carries the signs of sepsis that mean emergency services instead.
- A clot in the leg. A calf or thigh that is newly swollen or getting more swollen, warm or tender, especially in the weeks after an operation when you are moving less than usual.
- A repair that has given way. After an operation on the meniscus, a knee that locks, catches or gives way again, that pops or shifts inside, or that swells up or becomes much more painful after a twist, a kneel or a deep bend. Keep your weight off it and take the same day route on that line. One route sits above that one: if the knee swelled very quickly after a pop or a snap, the emergency department line in the warning signs below applies whichever operation you had, and a call to your surgical team is not a substitute for it.
- A break in the bone around a knee replacement. If you have a replaced knee, a fall or a knock that leaves it newly painful, swollen or bruised counts even when you can still walk on it and the leg looks normal, and the line tells you to stop the exercises, go back to your crutches or sticks, keep your full weight off that leg and have it checked by your surgical team the same day. If you cannot put weight on the leg, the knee or thigh is very painful, or the leg looks out of shape or shorter than the other, that line sends you to an emergency department instead. So does a knee that ballooned within a few hours of the fall or the knock, under the fast swelling line above.
A fifth belongs here even though it is not urgent. If the knee will not straighten as far as the other one, or will not bend as far as your physio expects, and it is not improving from week to week, that is worth contacting your physio or surgeon within the next few days rather than stretching harder at it. A swollen knee tends to settle into a slightly bent position, and the last few degrees of straightening are the ones that get lost.
A word on the operations that most often bring someone to a page about outer knee pain. After a meniscus repair or a trim, swelling that follows a twist or a deep bend is the signal, and the caps on bending and weight bearing are your team's rather than this page's. Which of those two you had changes the caps a great deal, so it is worth knowing which it was.
A trim takes the torn piece away, and OrthoInfo says that operation typically allows immediate weight bearing and full movement soon afterwards, with healing of roughly 3 to 6 weeks. A repair stitches the torn edges back together and has to heal as a join, which is why the same source puts rehabilitation after a repair at about 3 to 6 months, and why surgeons commonly restrict deep bending, twisting and weight bearing through the early part of that, in ways that differ from surgeon to surgeon. Both of those are the usual course rather than your permission: a cap your own team has given you stands until they lift it. If nobody has told you which of the two operations was done, ask, and if a repair and a reconstruction were done in the same sitting, ask which timetable you are on, because it is usually the repair that sets the longer limits.
After a ligament reconstruction, the limits cover twisting and single leg loading and change month by month to a timetable you were given.
After a release at the outside of the knee, ask which release it was, because two different operations share that name. A release or lengthening of the band itself, cut across or rejoined as a Z, is what is occasionally done for this condition when months of load management have not settled it (Villanueva and colleagues, 2021). A lateral retinacular release is an operation on the tissue that holds the kneecap in its groove, done for a kneecap tracking too far to the outside, and the two complications it is best known for are bleeding into the joint and a kneecap that then slips the other way (Minghao and colleagues, 2023). For both, the expected course and the restrictions vary enough between surgeons that there is no general rule worth printing here, so outer knee swelling after one is a question for the team who did it. A knee that fills up tight and fast after either, rather than staying sore in one spot, is a call to them the same day and not something to wait out.
If you no longer have your instructions, ring the team who operated rather than working from a program written for a knee that has not been operated on, including this one.
For a replaced knee specifically, how long swelling lasts after a knee replacement answers the timeline question properly. It is written for a replacement and not for an arthroscopy, so take the timings there as replacement timings.
When should you get a swollen knee checked?
Today, if the swelling fits any of the patterns above. Otherwise, within a couple of weeks if it is not going anywhere.
The NHS asks for advice from 111 for a knee that is very painful, a knee you cannot move or put weight on, a knee that is badly swollen or has changed shape, a knee that locks, gives way or clicks painfully, with painless clicking noted as normal, and a high temperature or feeling hot, cold or shivery with redness or heat around the knee. For knee pain that has not improved within a few weeks, it says to see a GP. Those are the floor rather than the ceiling, and nothing here replaces being examined.
Two more reasons to book an appointment, both of them about getting the label right. A tender spot at the outside of the knee is shared by several conditions, and telling them apart is a job for someone who can put their hands on the joint. And a swollen knee needs a cause: a joint that keeps filling with fluid is a finding, not a diagnosis, and it deserves an explanation rather than a label borrowed from a page you read at eleven at night.
If what you have is the small, local, training-related kind, the IT band syndrome program is the place to go next. If it is the knee that has filled up, swelling, locking and giving way and the meniscus tear program cover the commonest reason, and the warning list below covers everything that should not wait.
Related exercise programs
Warning signs
Get emergency help now
- Emergency: pain, tingling, numbness or weakness in both legs, numbness or altered feeling around your genitals or bottom, or new trouble peeing or controlling your bladder or bowels. The same applies if you lose feeling in one leg. Call emergency services or go to an emergency department straight away. These can be signs of pressure on the nerves at the base of the spine (cauda equina syndrome).
- Emergency: the knee has moved out of place, looks misshapen or is pointing at an odd angle, or you have tingling or no feeling in the knee, leg or toes, or your foot turns cold, pale or blue. Go to an emergency department straight away. Do not drive yourself: ask someone to drive you or call an ambulance.
- Emergency: the knee became very swollen very quickly, within a few hours of a twist, fall or blow, or you felt a pop or snap. Go to an emergency department straight away. Do not drive yourself: ask someone to drive you or call an ambulance.
- Emergency: you have had a knee replacement and, after a fall or a knock, you cannot put weight on the leg, your knee or thigh is very painful, or the leg looks out of shape or shorter than the other. Go to an emergency department straight away, and do not drive yourself. If you cannot get up, call emergency services. A broken bone around a knee replacement is rare, but it needs treatment in hospital. If a smaller fall or knock leaves the knee newly painful, swollen or bruised, even if you can still walk on it and the leg looks normal, stop the exercises, go back to your crutches or sticks and keep your full weight off that leg, and get it checked by your surgical team the same day. A break in the bone around a new knee is not always obvious at first, and walking normally on one can move the broken ends apart.
- Emergency: you are still growing and have pain that wakes you at night, pain at rest that keeps getting worse, or a lump or swelling around the knee or thigh that keeps growing. If you also have a rash that does not fade when you press it, call emergency services or go to an emergency department.
Get help today
- Same day: the pain started with a fall, a twist or a blow to the knee, and now the knee is very painful or swollen, or you cannot put weight on the leg or move the knee. Get medical advice the same day, and go to an emergency department if the pain is severe. This points to an injury, not IT band syndrome.
- Same day: the knee swells up, locks so you cannot straighten it, gives way under you, or clicks painfully. These can be signs of a problem inside the joint, such as a torn meniscus (the cartilage cushion in the knee) or a ligament injury. Get medical advice the same day and stop running and riding until it has been checked.
- Same day: the knee is locked, which means it is stuck bent and you cannot fully straighten it, even after gently trying to move it, or you cannot bend or straighten the leg at all. Get assessed the same day by a doctor, at urgent care or at an emergency department. A torn piece of meniscus can get caught in the joint and block it, and when a tear like this can be repaired, it should be done as early as possible. A knee that catches for a moment and then frees itself can happen with a meniscus tear. That is not the same as a locked knee, but tell your physio or doctor about it.
- Same day: the knee swells up with no clear reason, especially if you take medicine to thin your blood. Get medical advice the same day.
- Same day: you cannot walk or put weight on the leg, whether or not there was a fall or injury, or you have very bad knee pain after a fall or injury, or very bad knee pain that came on suddenly with no injury at all. Get medical advice the same day.
- Same day: the knee keeps giving way under you, or it gave way after a recent injury, or it gives way and is also very painful or swollen. Get medical advice the same day. If it only happens now and then, with no recent injury and no swelling, it is not an emergency, but book an assessment with a physio or doctor in the next few days. Until it has been checked, leave out the exercises you do standing on one leg, hold the rail on stairs and take care on uneven ground, because a knee that gives way without warning is how people fall.
- Same day: the knee is hot, red and swollen, or you have knee pain with a high temperature or feel hot, cold or shivery. Get medical advice the same day, and go to an emergency department if you feel very unwell. This can be a sign of infection in the joint, which needs treatment quickly.
- Same day: since your operation, your wound is oozing, leaking or has pus coming out of it, or its edges start to come apart, or your knee is tender, swollen, painful or red and it is not getting better or is getting worse, or you have a high temperature or feel hot and cold or shivery. Redness can be harder to see on brown or black skin. Contact your surgical team the same day, or get urgent medical advice if you cannot reach them. These can be signs of an infection in the wound or the knee joint. If you feel very unwell, go to an emergency department. If you have a very high or very low temperature, shivering you cannot control, you are breathing very fast or finding it hard to breathe, you are confused or your speech is slurred, your skin, lips or tongue look blue, gray, pale or blotchy (on brown or black skin this can be easier to see on the palms of the hands or soles of the feet), or you have a rash that does not fade when you press it, call emergency services, as this can be sepsis.
- Same day: since an operation on your meniscus, the knee locks, catches or gives way again, or you feel a pop or a shift inside it, or it swells up or becomes much more painful after a twist, a kneel or a deep bend. Keep your weight off it and contact your surgical team, or get assessed the same day at urgent care or an emergency department. A repair can come apart before the tear has healed, and a trimmed meniscus can tear again. If the knee is only a little achy after a busy day, with no swelling and no catching, it is not an emergency, but tell your physio or surgeon in the next few days.
- Same day: a calf or thigh that is newly swollen or getting more swollen, warm, tender, red or darker than usual, has swollen veins that are sore to touch, or has a throbbing or cramping pain that does not fit your injury or condition, or that feels different from normal muscle soreness after exercise. This can be a sign of a blood clot (deep vein thrombosis), especially after surgery, an injury, time in a cast or boot, a long trip or a spell of being much less mobile than usual. Get medical advice the same day. If you are also short of breath or have chest pain, call emergency services.
- Same day: pain at night or at rest that keeps getting worse. If you are being treated for cancer now, contact your cancer team the same day.
Book an appointment
- Within a day or two: you are still growing and have pain that wakes you at night, pain at rest that keeps getting worse, or a lump or swelling around the knee or thigh that keeps growing. See a doctor within a day or two. Ask for an urgent appointment rather than the next routine one, and say what the pain does at night and whether a lump is getting bigger. Do the same if the pain comes with looking pale, unusual tiredness, fevers with no clear cause, bruising or bleeding easily, or weight loss. Bone pain that is worse at night, or a new lump, needs checking to rule out rarer causes such as a bone tumor or a blood cancer (leukemia).
- Within a day or two: pain at night or at rest that keeps getting worse. If you have had cancer, now or in the past, see your doctor sooner, within a day or two, and mention it, even if the pain is not getting worse. Do the same if you have knee pain and are losing weight without trying, even if it does not hurt at night.
- Within a few days: your knee will not straighten as far as the other one, or will not bend as far as your physio expects, and it is not improving from week to week, or it is slowly losing movement it had. This is not an emergency, but contact your physio or surgeon within the next few days, and tell them if the knee feels blocked at the very end of straightening, or clunks or hurts there, rather than simply feeling tight. Getting the knee fully straight is one of the first aims of rehab, and stretching harder is not the answer. A knee that is stuck bent and will not straighten however gently you try is a different problem, and it has its own warning above.
- Within a few days: pain at night or at rest that keeps getting worse. See your doctor within a few days.
- Within 2 weeks: pain that spreads from your lower back or buttock down the outside of the thigh or below the knee, especially with numbness, tingling or pins and needles in the leg or foot. The pain may be coming from your back rather than the knee. Book an appointment with a doctor or physio. If your leg or foot is getting weaker, for example your foot drags, catches on the ground or slaps down when you walk (foot drop), get medical advice the same day, and if the weakness is getting worse by the hour, go to an emergency department.
Common questions
Can a tight IT band cause knee swelling?
Not in the way the phrase implies, because the tight feeling and the swelling are separate things. The band is a thick sheet of fibrous tissue, and it does not swell like a muscle after a hard session. What can look puffy is the small area at the outside of the knee where the band presses on the tissue underneath. Fairclough and colleagues (2006) described that tissue as a layer of richly innervated and vascularized fat, and a nerve-rich, blood-rich layer under pressure is a far better explanation for a tender, slightly swollen spot than a band that has tightened. Nothing you do to the band changes its length anyway, which is covered on the IT band syndrome program.
Can IT band syndrome cause swelling behind the knee?
It is not where this condition sits, so swelling at the back of the knee is worth a different look. IT band syndrome hurts over the bony bump on the outside of the knee, roughly where the seam of your trousers runs. A soft lump at the back of the knee with tightness, stiffness, difficulty bending and clicking, often worse after walking, is the NHS description of a Baker's cyst, and our Baker's cyst page covers it. The NHS advises urgent advice if leg pain or swelling suddenly gets worse, the leg becomes swollen, bruised or warm, the skin turns red or darkened, or the swelling becomes harder or softer, because a cyst can burst and because a clot in the leg can look similar. Pain behind the knee sets out the other causes.
Can IT band syndrome cause knee pain and swelling together?
Yes, as long as the swelling is the local kind. A tender, faintly puffy spot at the outside of the knee that hurts on running and on stairs, and settles with rest, is an ordinary presentation. Pain plus a knee that is swollen all round is a different combination and is worth getting assessed, because the conditions that fill a joint with fluid are not treated the way this one is. The pain monitoring model guide explains how to judge whether the sore spot is settling week by week.
Will an MRI show whether my knee swelling is the IT band?
It can show where the fluid is sitting, which is the part that answers this question. In Muhle and colleagues (1999), the fluid in patients with this condition sat in a compartment outside the joint, with the band forming its outer wall. Fluid inside the joint is a different finding and points the clinician elsewhere. That said, a scan is normally ordered to exclude other causes rather than to confirm this one, and the decision to scan at all belongs to whoever examines the knee.
References
- Muhle C, Ahn JM, Yeh L, Bergman GA, Boutin RD, Schweitzer M, Jacobson JA, Haghighi P, Trudell DJ, Resnick D. Iliotibial band friction syndrome: MR imaging findings in 16 patients and MR arthrographic study of six cadaveric knees. Radiology. 1999;212(1):103-110. https://doi.org/10.1148/radiology.212.1.r99jl29103
- Fairclough J, Hayashi K, Toumi H, Lyons K, Bydder G, Phillips N, Best TM, Benjamin M. The functional anatomy of the iliotibial band during flexion and extension of the knee: implications for understanding iliotibial band syndrome. Journal of Anatomy. 2006;208(3):309-316. https://doi.org/10.1111/j.1469-7580.2006.00531.x
- Geisler PR. Current Clinical Concepts: Synthesizing the Available Evidence for Improved Clinical Outcomes in Iliotibial Band Impingement Syndrome. Journal of Athletic Training. 2021;56(8):805-815. https://doi.org/10.4085/1062-6050-548-19
- NHS. Knee pain. Page last reviewed 21 December 2023. https://www.nhs.uk/symptoms/knee-pain/
- NHS. Meniscus tear (knee cartilage damage). Page last reviewed 2 September 2026. https://www.nhs.uk/conditions/meniscus-tear/
- NHS. Septic arthritis. Page last reviewed 3 September 2026. https://www.nhs.uk/conditions/septic-arthritis/
- NHS. Baker's cyst. Page last reviewed 26 June 2025. https://www.nhs.uk/conditions/bakers-cyst/
- Sanchez-Alvarado A, Bokil C, Cassel M, Engel T. Effects of conservative treatment strategies for iliotibial band syndrome on pain and function in runners: a systematic review. Frontiers in Sports and Active Living. 2024;6:1386456. https://doi.org/10.3389/fspor.2024.1386456
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Written and checked by the PocketPhysio editorial team. Last updated 2026-10-21.
This page is general education, not a diagnosis or a personal treatment plan. See a physiotherapist or doctor for advice about your own situation.