What Is Plantar Fasciitis?
Plantar fasciitis is degenerative irritation of the plantar fascia where its central band anchors to the inner heel, at a point called the medial calcaneal tuberosity. The fascia runs under the sole in three bands and divides toward the toes into five slips, one to each. Pain is sharpest on the first steps out of bed.
This is a middle-age condition more than an athlete’s one, peaking between 40 and 60. Prevalence estimates across adult populations range from under 1% to about 10%.
Where the Heel Pain Comes From
Pressing the origin of that central band at the inner heel reproduces the pain almost exactly. The location is specific enough to serve as the diagnosis on its own. In everyday use the fascia supports the arch and absorbs load with every step.
Described in 1954, the mechanism has not been revised since. The heel bone and the metatarsals, the long bones behind the toes, form a triangular truss with the fascia as the tie-rod along its base. When the toes bend upward in late stance, as the heel lifts at toe-off, the fascia winds around the metatarsal heads and shortens. The arch rises and the foot stiffens into a lever. Clinicians call that the windlass mechanism, and the tissue performing it is the tissue that hurts.
First contact in the morning is sharp, several minutes of walking dull it down, and by late afternoon the pain has returned. Runners meet that curve compressed into a single session, a few minutes of pain and then an ache they can run through. The easing is a mechanical effect of loading warm tissue and says nothing about repair.
How the injury arrives is a question of weekly distance. Runners covering more than 25 miles a week have around six times the odds of those covering 4 to 12 miles, with no other variable in that data reaching significance.
A clinician confirms it with the windlass test, in which the big toe is bent upward by hand until the fascia winds tight and the heel pain reproduces. Diagnostic ultrasound looks for a fascia thicker than 4 mm. Imaging is not required to reach the diagnosis. About a third of cases are bilateral, meaning both feet at once.
Is Plantar Fasciitis Inflammation or Degeneration?
The suffix -itis means inflammation. In 2003, tissue taken during 50 heel-spur surgeries for chronic plantar fasciitis was examined under a microscope. It showed myxoid degeneration, a breakdown of the fascia’s internal structure, along with fragmentation of the band itself. Not one of the 50 samples showed inflammatory cells.
The collagen-building fibroblasts multiply and thicken in a degenerating fascia. The collagen they lay down loses its alignment, while new vessels grow in chaotically beside zones with almost no blood supply.
Those 50 feet had failed everything else for months or years before anyone operated, so the histology describes the tissue late and says nothing about week three. Newer work has moved to a smaller scale, looking for pro-inflammatory cytokines, the molecules that transmit an inflammatory signal. The signaling itself was never measured in those samples, so the strong version of the claim, that inflammation has been disproved, overstates what was found.
The same 2003 paper also questioned serial corticosteroid injection into the fascia.
Fasciosis, Fasciopathy and Plantar Heel Pain
Fasciosis, proposed alongside the 2003 histology, asserts degeneration specifically. The neutral construction used for tendon problems gives fasciopathy, which says the tissue is diseased without naming a mechanism. Plantar heel pain, the broadest of the three, is used more widely now because pain under the heel can come from the fat pad, from local nerves, or from the heel bone as well as from the fascia. None of them replaced it, because clinicians and patients already had a word that communicated.
The clinical practice guideline that sets current best practice was revised in 2023 and still carries plantar fasciitis in its title. The standard reference entries open on the absence of inflammatory cells and then use the -itis name throughout. Even the billing code is out of step, since plantar fasciitis is indexed to M72.2, a code filed under fibroblastic disorders.
Do Heel Spurs Cause Plantar Fasciitis?
About half of people with plantar fasciitis also have a calcaneal spur, a bony outgrowth under the heel bone. A spur is a common finding in feet that hurt and explains nothing about why a particular heel is painful. Spurs turn up in 10% to 63% of heels that have never hurt.
Treatments and How Long Their Effects Last
No trial has examined anti-inflammatory medication on its own for this condition. That gap has stayed open since 2005. Ice was never trialed alone either. Corticosteroid injection, orthoses (shoe inserts), and progressive loading (strength work under increasing weight) all produce one trial pattern, with the treated group ahead at 3 months and the gap gone by 12. What differs is the size of the early effect.
Corticosteroid injection produces the largest short-term gain in function of the injectable options, with pain falling over roughly 4 to 12 weeks before the effect fades. Guidelines discourage repeating it, because the fascia can rupture.
Runners describe the pain dropping away within 10 seconds of an insert going in. A three-arm trial set two real devices, one prefabricated and one custom semirigid, against a sham foam insert with no arch support built in. The real devices beat the sham on function at 3 months and were indistinguishable from it at 12. They were never distinguishable from each other.
One intervention was designed around the degenerative reading. A 2015 trial randomized 48 people to stretching or to high-load strength work, which in the trial was a single-leg heel raise performed with a towel bunched under the toes so that the windlass pre-tensions the fascia before the calf lifts. At 3 months the strength group scored 29 points better on the Foot Function Index, a 0-to-100 questionnaire covering pain and disability. Both groups improved and were indistinguishable at every later measurement. Roughly 75% of cases resolve inside 12 months whatever is done, most of that in the first 3. Every arm of every trial is measured against that curve.
Conditions Mistaken for Plantar Fasciitis
A calcaneal stress fracture presents at the heel and behaves differently under examination. The pain spreads across the heel rather than concentrating at one point, and squeezing the heel from both sides reproduces it sharply. It does not ease over the first minutes of activity. Heel pain that wakes a runner at night, or that begins after a sudden jump in weekly distance, has stopped behaving like the injury on this page. Imaging of the heel bone tells the two apart.
Heel fat pad atrophy is the other condition confused with this one. The pad under the heel bone thins and loses the chambered structure that absorbs impact, so people report a deep, bruise-like ache in the middle of the heel that is worse barefoot on hard floors and builds through the day. It lacks the first-step signature entirely. Repeated corticosteroid injection is one recognized cause of that thinning, so the treatment built on the inflammation model can produce the condition it gets mistaken for.
The cost of the wrong suffix is paid by the runner who reads it literally. Icing a degenerating band of collagen, resting it, and expecting the whole thing over in two weeks is taking the name at its word, when recovery is measured in months and a substantial share of cases are still symptomatic a year on. What is worth knowing alongside the word is that the tissue underneath has never matched it.