I am a science writer and a former Registered Massage Therapist with a decade of experience treating tough pain cases. I was the Assistant Editor of ScienceBasedMedicine.org for several years. I’ve written hundreds of articles and several books, and I’m known for readable but heavily referenced analysis, with a touch of sass. I am a runner and ultimate player. • more about me • more about PainScience.com illustrations by Paul Ingraham,
Tried everything? Maybe not yet. Plantar fasciitis can be stubborn, but many people have never even heard of the best treatment options.
What works for plantar fasciitis? What doesn’t? And why? Soon you will be able to answer these questions as well as they can be answered. This is a detailed tutorial for both patients and professionals about stubborn cases of chronic plantar fasciitis (PF) — it is thorough and scientifically current (but still readable).
I explain all the theories, myths, and controversies and review all treatment options but the goofiest. Unlike many other conditions I write about, there are some PF treatments that are known to be at least a little effective…even with difficult cases sometimes. There’s hope.
The plantar fasciitis basics
Plantar fasciitis is a common and often persistent kind of repetitive strain injury afflicting runners, walkers and hikers, and nearly anyone who stands for a living — cashiers, for instance.
Plantar fasciitis is not the same thing as heel spurs and flat feet, but they are related and often confused.
Most people recover from plantar fasciitis with a little rest, arch support (regular shoe inserts or just comfy shoes), and stretching, but not everyone. Severe cases can stop you in your tracks, undermine your fitness and general health, and drag on for years. This tutorial is mostly for you: the patient with nasty chronic plantar fasciitis that just won’t go away. (And for the professionals trying to help.) I can’t promise a cure for your foot pain — no one ethical can. But I can guarantee a deep understanding of the subject and your options.
I am a science writer & amateur athlete in Vancouver, Canada. I started writing about it because I have my own mild but incurable chronic case, due to a weird foot bone. ~ Paul Ingraham
The plantar fasciitis misinformation explosion
In the years since I started treating and writing about plantar fasciitis treatment, there has been an explosion of free information about it on the internet. Unfortunately, no one seems to be better informed!
Unsurprisingly, a lot of the information out there is simply repetition of the same tired conventional wisdom, much of which is just wrong. Misconceptions about foot pain have been spread far and wide, thanks to the miracle of the internet!Misconceptions about foot pain have been spread far and wide, thanks to the miracle of the internet!1 (That’s the first of 156 footnotes. Click it!) While the quality of online information is gradually improving, it’s still mostly quite shallow: just the basics.
Plantar fasciitis is infamously stubborn. I suffer from an infinite, incurable case of PF myself. There’s no way I will ever fully recover, because my case is caused by a minor foot deformity — a slight twist in my foot bones. My arch is permanently challenged. This also gives me a great opportunity to perpetually test treatments: every time it flares up again, I get to try again! So I’ve tried them all personally (except surgery), and I generally do quite well controlling it. I have also helped many patients and readers with their persistent cases.
So I know from both personal and professional experience, that the prognosis isn’t always good, and patients really need to be much better informed about their options when the going gets tough.
About footnotes. There are 156 footnotes in this document. Click to make them pop up without losing your place. There are two types: more interesting extra content,1Footnotes with more interesting and/or fun extra content are bold and blue, while dry footnotes (citations and such) are lightweight and gray. Type ESC to close footnotes, or re-click the number.
and boring reference stuff.2“Boring” footnotes usually contain scientific citations from my giant bibliography of pain science. Many of them actually have pretty interesting notes.
Patients with severe plantar fasciitis face a challenge in finding good help
pro Strong enough for a pro But made for patients. The main text is user-friendly, but oodles of footnotes provide extra info and citations.
I do criticize many common practices and beliefs. If you disagree, let me know—I can take it, and I’ve made many changes over the years based on quality feedback.
Plantar fasciitis is not well understood scientifically or biomechanically, and most health care professionals are not aware of the full range of treatment options.
Most manual therapists (physiotherapists, chiropractors, massage therapists) do not know what the latest research says about plantar fasciitis, and just cannot offer patients advanced troubleshooting. I have a modern, impressive sports injuries text on my shelf which offers even less advice — a couple of paragraphs! — than many of the inadequate articles on the internet.
In fact, many health professionals are not even aware of the basic evidence-based formula for plantar fasciitis rehab, never mind the options for severe and/or atypical cases. (And atypical cases are really what stubborn plantar fasciitis is all about.)
Would a rub help?
If only! A foot rub is nice, and in fact it can help a little, but massage therapy is actually one of the least effective of the common therapies for plantar fasciitis.
I’ve worked hard for many years to publish the best information about plantar fasciitis available anywhere — better researched and referenced than anything else you can find, highly readable, and even entertaining at times. Every issue is explained in a clear, friendly style that’s just like coming to my office and having a nice long conversation about it, where all your questions get answered as well as possible.
If you’ve been struggling with a tough case of plantar fasciitis, I think this tutorial will feel like a “good find”!
Nature of the Beast
What is plantar fasciitis?
Plantar fasciitis is an overuse injury, like carpal tunnel syndrome or tennis elbow in your foot, a kind of tendinitis: an inflammation and/or thickening3 and/or degeneration of the plantar fascia. It’s especially common in runners, and in menopausal women. “Many people are afraid of running because between 30 to 70 percent (depending on how you measure it) of runners get injured every year.”4 And roughly 10% of those are PF cases.5
I’ve just used the familiar terms “tendinitis” and “inflammation” to introduce plantar fasciitis in the most familiar and conventional way. However, these are misleading terms and the truth is more complicated. The plantar fascia is not really a tendon: it’s a sheet of connective tissue (“fascia”), more like a ligament than a tendon. It stretches from the heel to toes, spanning the arch of the foot, from bones at the back to bones at the front (whereas tendons connect muscles to bones).
The “itis” suffixes in tendinitis and fasciitis mean “inflammation,” Many people are afraid of running because between 30 to 70 percent of runners get injured every year. but the tissue is rarely inflamed the way we usually understand it (maybe at first, not for long). Instead, the plantar fascia shows signs of collagen degeneration and disorganization. In 2003, Lemont et al looked at 50 cases and found so little inflammation that they declared that plantar fasciitis “is a degenerative fasciosis without inflammation, not a fasciitis.”6 So it would be better to use a more generic suffix — like opathy (diseased) or osis (condition).
In fact, this is true of all so-called “tendinitis” — inflamed tendons are not so very inflamed. “Recent basic science research suggests little or no inflammation is present in these conditions.”7 And Khan et al wrote that “numerous investigators worldwide have shown that the pathology underlying these conditions is tendonosis or collagen degeneration. This applies equally in the Achilles, patellar, medial and lateral elbow, and rotator cuff tendons.”8
And in the plantar fascia, where the degeneration is “similar to the chronic necrosis of tendonosis.”9 Necrosis is bad. It’s Latin for “tissue death.” In plantar “fasciitis,” the plantar fascia is not just hurting, it’s dying — eroding like a rotten plank.10 And this isn’t just to make you squeamish: inflammation and “necrosis” are not the same medical situation, and understanding the difference is essential for effective treatment.
The arch of the foot functions like a bow (as in a bow and arrow), and the plantar fascia is like the string of the bow. The tension in the “bow string” holds the shape of the arch. But every time you step, the “bow string” stretches… and when stretched too hard and too often, it gets irritated, and then it’s like a bow shooting you in the foot!
So why does it happen? Plantar fasciitis is basically caused by chronic irritation of the arch of the foot due to excessive strain.
If the arch of your foot is like a bow, think of the plantar fascia as the bow’s string. The plantar fascia, along with several muscles both in the foot and in the leg, supports the arch and makes it springy.11 Too springy, and the foot flattens out, overstretching the plantar fascia. Not springy enough, and the plantar fascia absorbs too much weight too suddenly.
Either way, it starts to burn with the strain.
Other than the fact that it’s on the bottom of your foot and you step on it a lot, why is the plantar fascia vulnerable to strain? Why exactly? What happens?
Getting to the root of plantar fasciitis: could it be bone spurs?
Clever-sounding biomechanical explanations for plantar fasciitis are as common as plantar fasciitis itself. Many therapists and articles on the internet will insist that you must treat the “root cause” of plantar fasciitis. It would certainly be a good idea — there’s no disputing that. Now, if only it were possible to identify the root cause!
There are three particularly common biomechanical “explanations” for plantar fasciitis, which I will cover over the next three sections. None of them is completely useless, but none even remotely qualifies for “root cause” status:
flat feet and/or pronation
Unfortunately, there are so many possible causes of plantar fasciitis — probably several of them happening at the same time — that it is effectively impossible (or just extremely impractical) for therapists to make any confident biomechanical diagnosis. It’s simply too complicated an equation, and the scientific literature is riddled with contradictions. Let’s start breaking this down with bone spurs…
Surely hard bony growths in the arch are painful?!
Bone spurs on the heel (aka heel spurs and calcaneal spurs) seem like they must be a smoking gun — a simple and obvious cause of plantar fasciitis. They are common — about 10–20% of the population12 has an extra bit of bone growing on the front of the heel. They often get the blame for plantar fasciitis because it seems so obvious that having a bony outcropping on your heel would indeed cause heel pain, for much the same reason that you wouldn’t want a rock in your shoe. Even more damning: they are indeed found more in people with plantar fasciitis than without.
Not as bad as it looks. Having a bone spur is more like stepping on a cracker than a nail. A very thin cracker.
Seems straightforward, right? Wrong.
Unfortunately for common sense, bone spurs aren’t very bone-y: they’re merely a modest calcification of the plantar fascia. The spur is brittle and thin. It’s not much more like bone than tinfoil is like a sheet of steel. It makes the plantar fascia a bit crispy and crunchy.13 So bone spurs aren’t as much of a painful mechanical problem as they sound: more like stepping on a cracker than a nail. A very thin cracker.
So perhaps it isn’t too surprising that lots of people have painless spurs. And there is good evidence that, when there is pain, it’s not the spur that hurts but the plantar fascia itself or other soft-tissue structures.1415 And surgically removing a bone spur does not necessarily relieve pain, which makes it a lot less likely that it was causing it in the first place.1617 Spurs also tend to just grow back. No wonder a 2007 study concluded, “Overall, the presence of a calcaneal spur [was] not correlated with patient satisfaction and recurrences.”18 And it’s why there is a broad consensus that they are not the culprit. In a 2014 review in the journal Foot & Ankle Specialist, Moroney et al wrote:
Though once synonymous with plantar fasciitis, calcaneal spurs have, for several decades, largely been regarded in the orthopaedic literature as incidental findings.
But they probably aren’t completely irrelevant. They also wrote:
However, it may be premature to completely dismiss the significance of plantar calcaneal spurs.
It’s clear that spurs are probably more painful and problematic when other tissue X factors are present, but those factors can and do also cause plantar fasciitis symptoms whether you have a heel spur or not — and heel spurs may be completely painless without those factors!
Of all the possible “root causes” of plantar fasciitis, bone spurs superficially seem like the simplest and most obvious — and yet it’s neither. As tempting as it is, it turns out that you just can’t count on a nice straightforward connection between heel spurs and plantar fasciitis.
Other alleged root causes are even less satisfying.
Maybe it’s my pronation? Or flat feet?
“My therapist said I’m a pronator.” I hear this a lot. It’s not clear that it matters.
Pronating is rolling the foot inward. It is almost synonymous with having flat feet, because the arch tends to collapse as you roll the foot inward. They don’t necessarily go together, but they often do, and they are both routinely claimed as root causes of plantar fasciitis. Personally, I think therapists just like to accuse their patients of “pronating” because it makes us sound like we know what we’re talking about. Sound a little harsh? Some experts believe the idea of pronation is so useless — and yet so common! — that they have called for it to be abolished:19
[Overpronation] contributes nothing to our understanding — it is not definable, not reliable or valid, not diagnostic, its relationship to injury is not fully understood, and it does not dictate what the most appropriate management plan may be. It should not be replaced, it should be removed.
It’s just as likely that under-pronation and high arches are a problem. While flat feet are a more popular cause, one professional will blame high arches, but the next will say it’s flat feet … about the same patient. Surprisingly, professionals often seem to have trouble deciding whether a given foot has a flat arch or a high arch!2021
So why are experts contradicting each other? Probably because both flat and high arches are factors in plantar fasciitis.222324
For years, I incorrectly told plantar fasciitis clients with high arches that they were exceptional, because I knew only the conventional wisdom: plantar fasciitis afflicts the flat-footed. But obviously the plantar fascia can also be irritated by a too-tall arch.25 This is a Goldilocks case: the arches need to flex and give just the right amount — not too little, and not too much.
Pronation is one side of a Goldilocks equation too. The truth is that excessive supinating — rolling outwards — is probably just as much of a problem26 — but that gets almost completely ignored. You never hear about supinating.
If you walk in a shoe store and their sole basis for choosing a shoe for you is how much your pronate and what your arch looks like, turn around and walk out the door. The science simply does not support this protocol.
As much as the body likes things to be just right, it’s also super adaptable. Many flat-footed pronators and high-arched supinators in fact do not have plantar fasciitis. And many people who do have plantar fasciitis have completely normal arches, and neither pronate nor supinate excessively. Arch height and pronation are almost certainly risk factors … but not root causes.
Probably my calves are too tight!
Could be. Tight calves are another classic plantar fasciitis scapegoat, and the gastrocnemius and soleus muscles (the big calf muscles) certainly can put a strain on the plantar fascia.27 This situation is typical for people with a leaning-forward “ski jumper” postural pattern. And of course it is the predictable side effect of wearing high-heeled shoes for many years.28
For interesting contrast, the Twa people of Africa grow up climbing trees, which earns them amazingly limber calves that allow their ankles to bend halfway (45˚) to the shin29 — two to four times greater than the average urban person! Look at them go:
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This document and all of PainScience.com was, for many years, created in my so-called “spare time” and with a lot of assistance from family and friends. Undying thanks to my wife, Kimberly, for countless indulgences large and small, and for being my “editor girlfriend”; to my parents for (possibly blind) faith in me, and much copyediting; and to Mike Gobbi, buddy and digital mentor, for many of the nifty features of this document (hidden and obvious). And thanks to all of the above, and many others, for many (many) answers to “what do you think of this?” emails.
Thanks finally to every reader, client, customer, and big tipper for your curiosity, your faith, and your feedback and suggestions and stories. Without you, all of this would be pointless.
Regular updates are a key feature of PainScience.com tutorials. As new science and information becomes available, I upgrade them, and the most recent version is always automatically available to customers. Unlike regular books, and even e-books (which can be obsolete by the time they are published, and can go years between editions) this document is updated at least once every three months and often much more. I also log updates, making it easy for readers to see what’s changed. This tutorial has gotten 64 major and minor updates since I started logging carefully in late 2009 (plus countless minor tweaks and touch-ups).
Most links to sections shown here work for customers only. For access to all sections, buy the tutorial for $19.95. You’ll get the full version right away.
— Minor update: Added an analogy, an example, a useful link, and generally modernized the section.
— New section: An important tip I should have written about long ago, finally added.
— Science update: More recent test and reviews of steroid injection now cited. No significant change in recommendations, but the evidence is more settled now.
— Science update: Significant revision in light of (finally!) good new evidence about natural running and injury prevention.
— Good news update: Another good news update: ESWT is starting to look more promising. The section has been revised to be much more positive.
— New advice: Not only a new section but new good news! First version added Feb 2, substantial edit and expansion Feb 26.
— Update: Careful and thorough editing/update of NSAID recommendations, especially with regards to safety.
— Science update: Some good news changed to bad news: a discouraging follow-up study on arch-specific stretching.
— Upgraded: Many editorial and referencing improvements.
— New section: A short new section, finally, on PRP injections. It’s brief, but links to a main, free article covering the topic in some detail.
— Major edit: Modernized. I continue to hone my understanding of pain weirdness science and its implications.
— Minor addition: Brief review of calf-stretching gadgets
— Upgraded: Much more information about the (minor) significance of bone spurs. They may not matter a lot, but it’s good, useful, evidence-based context.
— Major update: The first complete professional editing of this book has now been completed. Although the difference will not be obvious to most readers, several hundred improvements and corrections were made, and it is definitely a smoother read.
— Minor update: Added a fun science item about the amazing ankle mobility of the Twa people of Africa.
— New recommendation: Now recommending a specific type of MRI to scan for bone swelling. Thanks to reader R Russell for the suggestion.
— Minor update: Added a terrific quote from a famous podiatrist about inconsistency in orthotics prescriptions.
— Minor update: Upgraded risk and safety information about Voltaren Gel.
— Product upgrade: Audiobook version now available.
— Improved: Expanded and edited. Reflexology and acupuncture added.
— improved: A little more and better advice.
— Minor update: More detail in my personal story of truly structural foot problem.
— Expanded: Added much more detailed self-help information for trigger points.
— Major upgrade: Rewritten, modernized, expanded.
— Minor update: Some customizing of “brain wrangling” for plantar fasciitis.
— Science update: Weak but interesting new evidence on natural running and injury prevention.
— Rewritten: Bigger, better, more positive discussion of this option.
— Major update: A “minor” science item really changed the tone of this section. The point is still the same — avoid heels — but now it’s a more interesting point.
— Science update: Unimportant but interesting science update about the forces required for arch muscles to activate for support.
— New section: New standard section I’m introducing to most of the tutorials to “manage expectations.” Too many readers assume there’s going to be a specific miracle treatment plan.
— Rewritten: Completely revised to reflect new science and new understanding of the interaction of ice with “inflammation.”
— New science: Same content, more science support.
— New section: No notes. Just a new section.
— Science update: References pretty much completely renovated and upgraded — and generally good news for once.
— New section: No notes. Just a new section.
— Like new: Major upgrade, with a much more detailed introduction to this part of the book, and long and useful list of summarized treatment options.
— Minor update: Slightly expanded and clarified. Added a note about feeling a thickened plantar fasciitis with your fingers.
— Minor update: Several minor clarifications and improvements.
— New section: No notes. Just a new section.
— New section: No notes. Just a new section.
— New section: No notes. Just a new section.
— Edited: Revision in preparation for audiobook production, with a focus on modernizing information about trigger points.
— Edited: Revision in preparation for audiobook production, with a focus on modernizing information about trigger points.
— Rewritten: Merged information on arches and pronation, rewrote for clarity, and added a couple nice new supporting quotes.
— Edited: Longer and clearer than before. In particular, I came up with a much better way of explaining the fragility of “bony” spurs.
— Science update: Added good new evidence that customization of orthotics isn’t very accurate.
— New section: Inspired by something surprising that I learned writing the new surgery section, this is a brief description of another major possible explanation for persistent symptoms.
— New section: Substantive new section of about 1400 words, with several footnotes and new references.
— More expert opinion: Added a particularly strong anti-steroids opinion to the section.
— Minor update: Added some more detail to exercise description, and a whimsical ankle coordination challenge.
— Minor update: Addressed some common fears about the threat of getting out of shape while resting.
— Minor update: Added reference to Kong et al, about the effect of shoe wear.
— New section.: Now cautiously endorsing Oesh shoes for reducing impact.
— Minor update: Added a reference about high heels and knee pain.
— Minor update: Added a reference about the poor overall quality of online information about common injuries. See Starman et al.
— Major update: Major improvements to the table of contents, and the display of information about updates like this one. Sections now have numbers for easier reference and bookmarking. The structure of the document has really been cleaned up in general, making it significantly easier for me to update the tutorial — which will translate into more good content for readers.
— New section: Finally, long overdue, a new section on this topic (for all the running injury tutorials, in fact).
— Minor update: Added a reference to a large, interesting study that showed that custom orthotics failed to reduce injury rates in marines.
— Improved: Beefed up with better explanations and science about how plantar fasciitis involves more “degeneration” of your foot than inflammation.
— New cover: At last! E-book finally has a “cover.”
— Expanded: Added a substantial chunk of content about a promising experimental treatment protocol. Unproven but interesting.
— Minor Update: Some new comments on Graston Technique in response to a reader’s questions.
— Minor update: Added an answer to a reader question, “Are soft night splints good enough?”
In 2010, the Journal of Bone & Joint Surgery reported that “the quality and content of health information on the internet is highly variable for common sports medicine topics,” such as knee pain and low back pain — a bit of an understatement, really. Expert reviewers examined about 75 top-ranked commercial websites and another 30 academic sites. They gave each a quality score on a scale of 100. The average score? Barely over 50! For more detail, see Starman et al. BACK TO TEXT
These researchers used ultrasonography to show that people with plantar fasciitis have thickened connective tissue on the bottom of their feet. The results were clear and unambiguous — a rare bit of clarity in a murky subject!
Young CS, Rutherford DS, Niedfeldt MW. Treatment of Plantar Fasciitis. Am Fam Physician. 2001 Feb 1;63:467–74. PainSci #56910. Such degeneration is “similar to the chronic necrosis of tendonosis, which features loss of collagen continuity, increases in ground substance (matrix of connective tissue) and vascularity, and the presence of fibroblasts rather than the inflamatory cells usually seen with the acute inflammation of tendinitis.” BACK TO TEXT
The necrosis “features loss of collagen continuity, increases in ground substance (matrix of connective tissue) and vascularity, and the presence of fibroblasts rather than the inflammatory cells usually seen with the acute inflammation of tendinitis.” BACK TO TEXT
The arch muscles do less than you might think: Basmajian et al showed in 1963 that muscles in the arch of the foot only kick in to under heavy loads: about 180 kilograms. Although that sounds like a lot, loading may spike that high in an average person with every step, so the strength and responsiveness of the arch muscles may still be routinely important. We don’t have muscles there for nothing, of course. Nevertheless, this study pretty clearly shows that “the first line of defense” against arch collapse is the shape of the bones, the elasticity of ligaments, and probably the “stirrup” tendons from leg muscles — but not so much the strength of the arch muscles. BACK TO TEXT
In 1995, Barrett et al found that 21% of 200 randomly selected American corpses had heel bone spurs, and in 2014 Moroney et al found 12% in about 1100 foot x-rays (though they qualify that: “This is a lower rate than that cited in many published series.”) BACK TO TEXT
Some bones spurs are undoubtedly thicker and harder than others, just like some people have much larger calluses than other people. (I have a callus on one foot that is always far thicker and sturdier than I seem to need.) But regardless, the spur tends to disintegrate the further it gets from the heel. BACK TO TEXT
This paper reports on a study of twenty patients in the years after surgical removal of bone spurs. Although most of the patients had “excellent” or “good” results three years later, their spurs had reformed in many casees, and analysis of the soft tissues showed that “changes within the fascia, rather than the spur, are primarily responsible for the pathogenesis of the syndrome.”
This is a bit of a cheat: I don’t have a proper reliability study to back this up, just a professional story: when I worked as massage therapist, it was common for people to come into my office with so-called “flat” feet, convinced by a previous massage therapist (or chiropractor) that they “have no arch left” (or some other motivating hyperbole) … when in fact I could still easily get my finger under their arch up to the first knuckle. That’s something that you simply can’t do on someone who really has flat feet. Similarly, though not so common, I have often seen people accused by another professional of having high arches, when in fact they look nothing like it to me. So take such diagnoses with a grain of salt. BACK TO TEXT
This is an expert opinion paper — not original research — which simply states that excessive pronation in the foot (part and parcel of having flat feet) is “the most common mechanical cause of structural strain resulting in plantar fasciitis.” This is debatable. The relevance of the reference is simply to demonstrate the diversity of opinion on the subject. It may well be that pronation and/or flat feet is the most common cause of plantar fasciitis, but it is certainly not the only mechanical factor that does so.
From the article: “A review of the literature reveals that a person displaying either a lower- or higher-arched foot can experience plantar fasciitis. Patients with lower arches have conditions resulting from too much motion, whereas patients with higher arches have conditions resulting from too little motion.”
If the arch is high, it means the arch-support system may be too rigid and not springy enough, so it absorbs too much force too quickly. BACK TO TEXT
Hertling D, Kessler R. Management of common musculoskeletal disorders. 3rd ed. Lippincott; 1996. p434. “Functionally abnormal supination is a failure of the foot to pronate, resulting in a foot unable to compensate normally. There is prolonged supination during the stance phase and a delayed pronation during the gait cycle. Stress fractures, metatarsalgia, plantar fasciitis, and Achilles tendinitis are common in this type of foot.” BACK TO TEXT
High heels are often vilified, but this carefully done 2010 study showed that the body adapts effectively and minimally, producing quite similar functional results. The most interesting implication of their results is simply that “muscle structure may adapt to a chronic change in functional demand” — which might seem obvious, but that little bit of science has been hard to nail down over the years, and this is a good piece of the puzzle.
Chronic heel wearers do have shortened calf muscles, stiffer Achilles tendons, and a smaller ankle range of motion, but these changes “seem to counteract each other since no significant differences in static or dynamic torques were observed.” In other words, high heel wearers are not progressively disabled: their ankles work fine, just differently. This doesn’t mean there’s no conceivable harm (for instance, Kerrigan found evidence of harm to the knees), but it does tend to downgrade concern on the topic.