EXCERPT This short article is an except of PainScience.com’s ridiculously detailed tutorial about plantar fasciitis.
When you are frustrated with a chronic condition like endless foot pain, sometimes you start to second-guess whether you really have what you think you have. Uncertainty about the diagnosis can be almost as frustrating as the pain itself. In fact, there’s excellent evidence (and it just makes sense) that feeling more confident about the nature of pain can reduce pain.1
Sometimes there’s no way out of that uncertainty … and sometimes there is.
By 2012, several studies had shown that, yes, the sole of your foot really is thicker — a lot thicker — when you have plantar fasciitis.234 A 2012 study confirmed that using ultrasound to detect this is reliable: different technicians will get the same results.5 A 2014 meta-analysis reviewing all these and more and concluded:6
Ultrasound can be considered a reliable imaging technique for assessing plantar fascia thickness, monitoring the effect of different interventions and guiding therapeutic interventions in patients with plantar fasciitis.
Such decisive conclusions are refreshing in medical science, which is usually murkier. Many such correlations are clinically meaningless, and the reliability of a lot of testing is amazingly poor.7 This is a noteworthy case of firm ground! (Interpretation is another matter. See below.)
The evidence also shows a connection between the thickening and flat feet.8 Flat feet, thick soles, and plantar fasciitis all tend to go together. Interesting.Chances are good that your plantar fascia is more than twice as thick as it should be.
So, if you have plantar fasciitis, chances are good that your plantar fascia is more than twice as thick as it should be: a nice clear physical sign that can be diagnosed with ultrasonography. (Not by feel, mind you.9) If you’d like to confirm this, all you have to do is bring it to your doctor’s attention and request ultrasound confirmation that you have “thick feet.” If your doctor is skeptical, show them the footnotes!
This evidence does not show anything about causation. The research has not confirmed that a thickened plantar fascia causes plantar fasciitis — just that they definitely tend to occur together.
It’s quite plausible that the thickened fascia is a symptom of the condition. That is, excessive loading on the arch builds up the tissue, much like a callous. Or the thickening could be, counterintuitively, a sign of weakness, thicker but not necessarily stronger— an abnormal plantar fascia that can’t handle the load.10
Examining your foot with ultrasound might turn up some other obvious cause of your pain — something interesting, other than a thickened plantar fascia. But take this with a grain of salt. Good scientific evidence has confirmed a strong correlation between thickened fascia and plantar fasciitis. But, as already discussed, other seemingly obvious issues like heel spurs do not necessarily explain anything!
For instance, we know that you can’t use X-ray and the presence of heel spurs in quite the same way to confirm your plantar fasciitis diagnosis, because heel spurs are often found in people with plantar fasciitis, but lots of people have heels spurs without plantar fasciitis. So, knowing that you have heel spurs alone doesn’t tell you all that much. If you have pain on the bottom of your foot and heel spurs and a thickened fascia confirmed by ultrasound … then, hoo boy, you’ve got a lot wrong with your foot, and a plantar fasciitis diagnosis is probably correct … but possibly not the only cause of pain.
For much (much much much) more information, see my advanced tutorial covering pretty much every imaginable thing about dealing with the condition:
I am a science writer, former massage therapist, and I was the assistant editor at ScienceBasedMedicine.org for several years. I have had my share of injuries and pain challenges as a runner and ultimate player. My wife and I live in downtown Vancouver, Canada. See my full bio and qualifications, or my blog, Writerly. You might run into me on Facebook or Twitter.
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!BACK TO TEXT
In 39 feet, both increasing and decreasing pain correlated well with changes in plantar fascia thickness, assessed with ultrasonography. The authors conclude that their study “provides evidence that changing thickness of the plantar fascia is a valid objective.”BACK TO TEXT
In this tiny study of 10 feet with plantar fasciitis, compared to 10 perfectly fine feet, “thicker fascial structures were associated with lower arched feet but only in individuals with heel pain.”BACK TO TEXT
Based on 56 feet, 20 with inferior heel pain, researchers concluded that “the reliability of sonographic examination of the thickness of the plantar fascia is high,” with no advantage to a transverse scan.BACK TO TEXT
From the abstract: “There was a higher incidence of plantar fasciitis in the flexible flatfoot group than the normal arch control group in this study.”BACK TO TEXT