“Runner’s knee” refers to one of two common 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, but most knee pain in runners is one of these two, and most of that is ITBS, and they rarely occur together:
Iliotibial 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.
Patellofemoral 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, 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 teenagers.
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, but it usually still has an anterior epicentre. ITBS does not spread much beyond its hot spot on the side of the knee.
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.
IT band pain versus patellofemoral pain: the full diagnostic checklist
Symptoms that aren’t caused by either kind of runners knee
Locking, clunking, or instability is usually indicates another kind of bad news, usually trouble with the meniscal cartilage.
Swelling is never a symptom of ITBS alone, and very rarely of PFPS, it’s more likely something else is going on.
Sudden onset of symptoms, usually indicates a traumatic mechanism. Neither ITBS and PFPS start that way. They can ramp up fast — as quickly as a few minutes — but not suddenly with a surge of pain.
Throbbing pain in the back of the knee (or anywhere else) is almost certainly another issue.
Tingling or numbness are never signs of ITBS or PFPS alone.
Pain in the tendon under the kneecap — connecting the kneecap to the top of the shin — is probably just a tendinitis
Causes for ITBS versus PFPS
No one knows exactly what causes either condition. Most of the risk factors are unclear.
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.
One interesting difference is that a slower speed 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 going down-hills are quite an obvious risk factor for ITBS.