Detailed guides to painful problems, treatments & more

Diagnosing Runner’s Knee

It usually starts with lateral knee pain during and after runs, but there are two major types

Paul Ingraham • 10m read
Photo of a male runner with knee pain, jogging away from the camera in a brightly sunlit empty garage.

Runner’s knee” refers to one of two common1 repetitive strain injuries of the knee, either iliotibial band syndrome (lateral knee pain) or patellofemoral syndrome (anterior knee pain).

Both usually affect runners, triathletes, hikers and serious walkers. They can be tough to tell apart. This quick guide and diagnostic checklist will help you figure out which type of runner’s knee you have.

There are other causes of knee pain, of course,2 but most knee pain in runners is one of these two, and most of that is PFPS, and they rarely occur together:

  1. Iliotibial Band Syndrome (ITBS) — Usually causes pain on the side of the knee. Also often called iliotibial band friction syndrome. The IT band is a huge tendon-like structure on the side of the thigh and knee. Either the tendon itself, and/or the anatomy under it, can get fatigued and irritated.
  2. Patellofemoral Pain Syndrome (PFPS) — Usually causes pain on the front of the knee, around and under the kneecap. PFPS is more common than ITBS and more common in non-runners than ITBS. Although it especially affects runners, hikers, and cyclists,3 it also affects anyone who sits for a living — the kneecap can be fatigued by a constantly flexed knee. It’s also quite common in teens.

Diagram of the knee showing IT band syndrome on the side of the knee, and patellofemoral pain syndrome on the anteriorof the knee.

Where’s the pain?

IT band syndrome dominates the side of the knee. Patellofemoral pain is more variable, but usually more in front.

Front or side? Location is the main obvious difference between IT band and patellofemoral pain

The easiest way to tell the difference between the two conditions is simply by the location of the symptoms. PFPS affects the kneecap and surrounding area, whereas ITBS definitely affects primarily the side of the knee (the side facing outwards).

The location of PFPS is less predictable,4 but it usually still has an anterior epicentre. ITBS does not spread much beyond its hot spot on the side of the knee.5

ITBS has a specific definition: it refers only to strong pain on the side of the knee, at or just above the lateral epicondyle. Pain in the hip or thigh is something else. For more detail about this common point of confusion, see IT Band Pain is Knee Pain, Not Hip Pain

“Ow! Damn! The side of my knee hurts!”

every single IT band syndrome victim ever

Some basics about both injuries to keep in mind

Beware of chronicity! Although humans are “born to run,”6 and most cases are easy to recover from,7 these injuries do have a nasty way of dragging on and on in some unlucky runners — please be aware of that risk.8 These conditions definitely do not have any guaranteed cures.

There are also many myths about both conditions that need busting, like the one about IT band stretching, the dubious importance of kneecap tracking, or the exaggerated dangers of running on pavement (full list of related articles below).

IT band pain versus patellofemoral pain: the full diagnostic checklist

Note the knee symptoms that apply to you. Whichever side has more, place your bet on that diagnosis.

Check the knee symptoms that apply to you. Whichever side gets more checks … place your bet on that diagnosis. Check all that apply. (Note: this is not a form, you do not have to “submit” it … just count checks!)

Iliotibial Band Syndrome
Patellofemoral Pain Syndrome
The epicentre of the pain is on the side of the knee. Symptoms may occur nearly anywhere around the entire knee, particularly in severe cases, but the worst spot has to be on the side of the knee. The epicentre of the pain is somewhere under or around the kneecap. As with ITBS, symptoms may occur nearly anywhere, but it will usually be mainly on the front of the knee.
There is a spot on the side of your knee, right around the most sticky-outy bump, that is sensitive to poking pressure, but your kneecap is not particularly sensitive when pushed firmly straight into the knee. It’s not very comfortable pushing your kneecap straight into your knee, but there is no particularly sensitive spot on the side of your knee.
Pain tends to be worse when descending stairs or hills, and is either not painful at all or noticeably less painful when ascending. Pain tends to be worse when ascending stairs or hills, but may be painful both ascending and descending.
Pain first started while going downhill. Pain first started while going uphill.
Both PFPS and ITBS can start over the course of a few hours or a day, but ITBS almost always does. If the pain started relatively quickly, check this box. If your pain grew relatively slowly, over months or years, check this box.
Doing a deep knee bend does not especially hurt. Doing a deep knee bend definitely hurts.
Pain is not particularly affected by sitting, although it might get worse after sitting for quite a while (longer than an hour). Pain is clearly aggravated by sitting with knees bent. When you get up, it hurts more than it did when you sat down.
You do not have any obvious structural problems in the legs. You are a little knock-kneed, have flat feet, or kneecaps that seem to be kind of at a funny angle.
Symptoms tend to be quite consistent and predictable, with only minimal changes in the intensity of the epicentre over time, and almost no change in the exact location of the hottest spot. PFPS may also have consistent symptoms, in which case you can’t really check either side for this point. However, if you experience seemingly mysterious fluctuations in intensity or location — if you find that the problem is just not very predictable — this is a strong indicator that you have PFPS, not ITBS, so you should check this side. has very detailed tutorials about each of these knee pain conditions. Now that you have a better idea what kind of knee pain you have, read more about it. Much more! (Fun fact: after publishing this document for seventeen years now, I have quite good statistics on it, so I know that 60% of visitors will choose to read more about ITBS, and 40% will choose PFPS.)
Continue reading about
iliotibial band syndrome
Continue reading about
patellofemoral pain syndrome

Symptoms that aren’t caused by either kind of runners knee

It’s possible to have more than one significant knee condition at once, of course — including both ITBS and PFPS. However, it’s unusual. Here is a short list of symptoms that you should not see with either ITBS or PFPS:

Medicine is messy and diagnosis is hard, and important things can get missed. There are many knee conditions, and even many non-knee conditions that can masquerade as a knee problem, at least for a while. This is a rather exotic “for instance,” but consider the case of a hockey referee who spent months investigating what everyone thought was knee injury — physical therapists, surgeons — when in fact he was in the early stages of Parkinson’s disease, and physical therapists and surgeons all missed it.10

Causes for ITBS versus PFPS

No one knows exactly what causes either condition. Most of the risk factors are unclear. Nearly every popular idea — such as hip weakness or “imbalances” — is someone’s unproven pet theory, often to “explain” a treatment they are selling. The only thing that we know for sure is that the risk of both injuries goes up with training volume, and both are more likely to affect inexperienced runners. Almost everything else is speculation or wishful thinking. But there are a couple of safer bets …

One interesting difference is that a slower pace is actually a risk factor for ITBS, while this is likely not a factor for patellofemoral pain.

Just as climbing hills is more likely to aggravate an existing case of patellofemoral pain, it’s also more likely to cause it, whereas substantial descents are quite an obvious risk factor for ITBS.

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About Paul Ingraham

Headshot of Paul Ingraham, short hair, neat beard, suit jacket.

I am a science writer in Vancouver, Canada. I was a Registered Massage Therapist for a decade and the assistant editor of for several years. I’ve had many injuries as a runner and ultimate player, and I’ve been a chronic pain patient myself since 2015. Full bio. See you on Facebook or Twitter., or subscribe:

Much more reading about IT band pain, patellofemoral pain, and running

PainScience has extremely detailed guides to iliotibial band syndrome (ITBS), patellofemoral syndrome (PFPS) and many other book excerpts and related articles:

What’s new in this article?

Six updates have been logged for this article since publication (2007). All updates are logged to show a long term commitment to quality, accuracy, and currency. more Like good footnotes, update logging sets apart from most other health websites and blogs. It’s fine print, but important fine print, in the same spirit of transparency as the editing history available for Wikipedia pages.

I log any change to articles that might be of interest to a keen reader. Complete update logging started in 2016. Prior to that, I only logged major updates for the most popular and controversial articles.

See the What’s New? page for updates to all recent site updates.

2023 — Cited a case study about mistaking Parkinsonian dystonia for a knee injury.

2019 — Added a footnote listing several other conditions that can mimic ITBS and/or PFPS.

2018 — Added a short section about causes, continuing to work on making the page more of a useful on-stop resource.

2018 — Added more basic information about ITBS and PFPS to the introduction, hopefully boosting the usefulness of the page.

2016 — Significant revision. The article now gets to the point quicker, and is less wordy overall. Several side points were been moved into footnotes. Added some links and a couple citations.

2016 — Improved some formatting, especially on mobile.

2007 — Publication.


  1. Taunton JE, Ryan MB, Clement DB, et al. A retrospective case-control analysis of 2002 running injuries. Br J Sports Med. 2002;36(2):95–101.

    This report on two year’s worth of injuries among Vancouver runners — many of whom I probably run with every day on Vancouver’s sea wall — found that “patellofemoral pain syndrome was the most common injury, followed by iliotibial band friction syndrome, plantar fasciitis, meniscal injuries of the knee, and tibial stress syndrome.”

  2. Here are some of the other candidates which can get confused with ITBS and PFPS. Most of them shouldn’t get mistaken for runner’s knee, but they do sometimes anyway.

    • arthritis, of course (usually not limited to one part of the joint)
    • meniscal tears (usually “crunchier”)
    • patellar tendinitis, Jumper’s knee (usually obviously localized to the tendon)
    • prepatellar bursitis (usually obviously just under the skin of the kneecap)
    • plica syndrome (which can be its own thing, or the actual mechanism of PFPS)
    • popliteal artery entrapment syndrome (pain is very severe and makes the calf pale/cold)
    • popliteal tendinitis (usually obviously localized to the back of the knee)
    • infrapatellar fat pad impingement
    • biceps femoris tendinitis (again, usually obviously in the tendon)
    • lateral collateral ligament sprain (usually obviously caused by trauma)
  3. Clarsen B, Krosshaug T, Bahr R. Overuse Injuries in Professional Road Cyclists. Am J Sports Med. 2010 Sep. PubMed 20847225 ❐ Almost 40% of pro cyclists will get anterior knee pain in any given year.
  4. “Patellofemoral pain” is a symptom with several possible causes. In many cases, a more specific diagnosis is possible, but it’s just called PFPS if a more specific diagnosis can’t be made.
  5. Some small amount of variation is possible thanks to the variety of human anatomy and the weirdness of chronic pain.
  6. Bramble DM, Lieberman DE. Endurance running and the evolution of Homo. Nature. 2004 Nov;432(7015):345–52. PubMed 15549097 ❐ This historically significant paper injected a huge dose of scientific credibility into the idea of “natural running,” concluding “The fossil evidence of these features suggests that endurance running is a derived capability of the genus Homo, originating about 2 million years ago, and may have been instrumental in the evolution of the human body form.”
  7. Most people just need a little rest, some stretching that’s probably just a placebo, and maybe a change in running style. But mostly rest and then baby steps back to normal training loads.
  8. When the pain is new, it’s impossible to know which way it’s going to go. Maybe it will go away quickly … and maybe it won’t. So it’s a great idea to be well prepared and well informed just in case, because stubborn cases of both conditions are shockingly hard to get good help for. Both are misunderstood and mistreated by most doctors and therapists. They know the conventional wisdom … but much of that is wrong. Many runners with knee pain don’t prepare for the worst by educating themselves about the condition. They get help slowly — if at all — and then weeks later realize they aren’t getting good help. By that time, their training schedule is blown to hell.
  9. “Tendinitis” versus “tendonitis”: Both spellings are acceptable these days, but the first is the more legitimate, while the second is just an old misspelling that has become acceptable only through popular use, which is a thing that happens in English. The word is based on the Latin “tendo” which has a genitive singular form of tendinis, and a combining form that is therefore tendin. (Source: Stedmans Electronic Medical Dictionary.)

    “Tendinitis” vs “tendinopathy: Both are acceptable labels for ticked off tendons. Tendinopathy (and tendinosis) are often used to avoid the implication of inflammation that is baked into the term tendinitis, because the condition involves no signs of gross, acute inflammation. However, recent research has shown that inflammation is actually there, it’s just not obvious. So tendinitis remains a fair label, and much more familiar to patients to boot.

  10. Ferreira D, Araújo R. A professional sportsperson with subtle motor symptoms and signs: early-onset Parkinson's disease. Lancet. 2023 Feb;401(10377):e18. PubMed 36841616 ❐ PainSci Bibliography 51317 ❐


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