As is often the case, there are some terms we need to clarify before we go into the bulk of the article. Plantar fasciitis is another unfortunately named injury, as the -itis suffix implies an inflammatory cause, which we'll soon see is not the case. The plantar fascia is also sometimes referred to as the plantar aponeurosis; medically speaking, an aponeurosis is a flat band of tissue that closely resembles a tendon and connects either bone or muscle to each other, while a fascia is a band of connective tissue that encapsulates muscles. Because "plantar fascia" is the more common term, and because the injury is still most often referred to as "plantar fasciitis," those are the terms I'll be using in this article. While "heel pain" and "heel spurs" are commonly used to refer to plantar fasciitis, neither are correct: while it is indeed the most common cause of heel pain, there are other injuries, like a calcaneal stress fracture, that can cause pain at the heel. And a heel spur—a small bony growth extending from the heel bone along the plantar fascia—is neither a definitive cause nor indicator of plantar fasciitis.3
Anatomy and function
The plantar fascia as a whole is comprised of several bands of connective tissue that run along the sole of the foot, anchoring the metatarsal heads to the calcaneus (the heel bone). While there are several separate bands, the most important is the central aponeurtoic band. It runs from the medial side of the heelbone, fanning out as it attaches to each of the five metatarsal heads. At the heel, the center band of the plantar fascia is thick and has a triangular cross-section. The central band handles the bulk of the strain on the plantar fascia, and as such is the part most susceptible to injury. Some sources describe the entire collection of plantar bands as the "plantar fascia," while others refer to it as the "plantar aponeurosis" and the central band as the "plantar fascia."
On a microscopic level, the plantar fascia is much like other tendons and ligaments of the body: small, wavy proteins called collagen fibers make up the structure of the fascia, giving it strength and stiffness. The plantar fascia is stronger and stiffer than the small tendons of the body, though it is weaker and more stretchy than the patellar or Achilles tendons, which handle high loads at the knee and ankle, respectively. With a stiffness of about 200 N/mm,4 the plantar fascia isn't something you could "stretch" like a rubber band, but it's also springy enough to store and release energy elastically during the gait cycle.5
|Microscopic image of a healthy plantar fascia. From Lemont et al.|
The plantar fascia's main function seems to be supporting the arch of the foot during standing, walking, and running. It has been likened to a "tie-bar" which prevents the arch from flattening, though it is not the only contributor to arch stiffness. Even when the plantar fascia is severed, the arch retains 65% of its stiffness in static stance—the rest of the structural integrity being associated with the joint capsules and bone geometry of the foot.6, 7
|The plantar fascia acts like a tie bar, helping to support the arch of the foot when it is loaded.|
Additionally, though they are fairly inactive in "static stance" (i.e. standing still), the muscles of the foot appear to contribute to arch support during the later phase of gait. The muscles of the foot are classified as either "intrinsic" or "extrinsic." Intrinsic foot muscles, like the flexor hallucis brevis, are actually located on the bottom of the foot. Extrinsic muscles, like the flexor hallucis longus, are located along the lower leg, but have long, thin tendons that cross the ankle and attach to the foot. A highly involved cadaver study by David Thordarson and coworkers at USC in 1995 demonstrated that several of the extrinsic foot muscles contribute to arch stability, though to a lesser degree than the plantar fascia itself.8 As reported by Scott Wearing et al. in a masterful and comprehensive review on plantar fasciitis, the arch-stabilizing abilities of the intrinsic foot muscles has not been investigated, though they are "well positioned to further reduce fascial loading," and the intrinsic muscles are activated as the heel lifts off the ground during the propulsive phase of gait.6
|The windlass mechanism of the foot. From Wearing et al.|
As the foot rolls forward and the heel lifts off the ground, the toes dorsiflex, tensioning the plantar fascia through something called the windlass mechanism. As the toes "wind up" the plantar fascia (like a real windlass), it tightens, raising the arch and creating more stability through the foot. This is an important feature for the stability of the foot, but it also may hint that the greatest stress on the plantar fascia is at heel lift, not at midstance or at impact. Indeed, kinematic studies have demonstrated that the load on the plantar fascia is greatest during the early propulsive period, both in walking and running.6
Like many overuse injuries in the past, plantar fasciitis has historically been chalked up as an inflammatory overuse injury. This, in turn, informed many treatment strategies focused on reducing inflammation: icing, oral anti-inflammatories, and corticosteroid injections. However, scientific studies which actually examine tissue samples of the plantar fascia in patients with plantar fasciitis have failed to find any significant signs of inflammation. Instead, what's seen is a degeneration of the collagen fibers, much like what's seen in overuse injuries the Achilles or patellar tendons. A 2003 review article of histology studies—investigations which examine tissue samples under a microscope—discovered that inflammatory cells were hardly ever found in the tissue samples, and concluded that there is no evidence of an inflammatory role in chronic plantar fasciitis;9 instead, the pain is the result of degeneration of the fascial fibers, a condition the authors term "fasciosis." This degeneration is plainly visible in microscope images.
The degenerative model of plantar fasciitis also provides a convenient explanation for the characteristic "first-step pain" in the morning. While you sleep, your plantar fascia is not tensioned, and as the damaged areas heal, they heal in a shortened state. Once you wake up and get out of bed, your weight stretches out the plantar fascia, re-injuring the fragile, newly-healed areas.
Whether inflammation is present at any point in the injury process of plantar fasciitis (or any overuse injury of connective tissue) is still an open question. Some researchers, like J.D. Rees, A.M. Wilson, and R.L. Wolman at the Royal National Orthopaedic Hospital in the UK,10 have pondered whether there is a short "inflammatory phase" of a few days or weeks before chronic degeneration sets in. Even if there is an inflammatory phase, there's no guarantee that reducing inflammation is the right move. While icing is a tried and true treatment for virtually any running injury and is unlikely to do any harm, more aggressive anti-inflammatory measures like anti-inflammatory drugs and corticosteroids remain questionable.
|Degeneration (red arrow) in a tissue sample from a patient with plantar fasciitis. From Lemont et al.|
In another review paper, Wearing et al. detail the microanatomy of the base of the plantar fascia. As the collagen fibers that make up the plantar fascia approach the heelbone, they transition to a more fibrous material and finally a calcified, almost bone-like material as they attach to the bone. This region, called the enthesis, appears to be particularly prone to degenerative changes, including disorientation of collagen fibers, proliferation of collagen-synthesizing cells, and a buildup of calcium deposits on the fascia. Additionally, Wearing et al. show that heel spurs—spindles of bone that jut out from the base of the calcaneus deep to the plantar fascia—are likely a reaction to excessive strain on the plantar fascia, not a cause from direct traction as was hypothesized earlier. It's important to note that these bony growths are distinct from the generalized calcification seen in the fibers of the plantar fascia itself. A heel spur, Wearing et al. hypothesize, provides a "buttressing" effect by reducing bending at the insertion point of the plantar fascia. This is evidenced by the presence of heel spurs in a significant proportion of healthy people with no heel pain.
|Heel spurs, while found in conjunction with plantar fasciitis, are also common in healthy people|
Symptoms and diagnosis
While its causes and potential treatments are not obvious, on the bright side, diagnosis of plantar fasciitis is fairly straightforward. It manifests as a sharp or dull pain at the base of the heel that is at its worst after long periods of activity or time spent on your feet and, classically, hurts during your first few steps out of bed in the morning. Walking around barefoot or in unsupportive shoes will also cause a sharp pain at the base of your heel. When running, the irritation might fade away after a mile or so, only to return at the end of your run or soon after. Often, the inside (medial) base of your heel will be tender to the touch, especially when you tension the plantar fascia by dorsiflexing your big toe with your hand. These symptoms are a classic fit for plantar fasciitis, so there is not usually a need for any medical imaging (x-rays, MRIs) in routine cases.
Risk factors and possible causes
Any discussion of possible risk factors for plantar fasciitis has to distinguish between studies on sedentary or "regular" people with plantar fasciitis and studies on runners. One of the reasons plantar fasciitis can be such a frustrating injury is because, unlike IT band syndrome or other common running injuries, many of the causal factors can be related to factors outside of your running. The prevalence of plantar fasciitis among sedentary people is testament enough to this.
Perhaps because of the diverse array of people who get plantar fasciitis, there aren't any risk factors that have been consistently identified across all studies. Regardless, research on sedentary individuals has connected poor ankle dorsiflexion range of motion, obesity, working long hours on your feet, older age, and having a pronated foot type as being associated with plantar fasciitis. Again, I should point out that there has been at least one study which has found every one of these factors to not be associated with plantar fasciitis as well.11
Happily, because there are fewer studies on runners, the data available is not quite as confusing. According to current biomechanical theory, increased pronation should increase strain on the plantar fascia—as the rearfoot everts, the arch is flattened, increasing the tension across the plantar fascia.12 Additionally, arch height (either abnormally high or low) has been suggested as a risk factor as well. However, the research has been conflicting on the actual relevance of arch height and pronation.
A 1984 study by Barbara Warren found that neither arch height nor pronation reliably predicted plantar fasciitis in a group of 42 runners (21 of which had a history of plantar fasciitis).13 Additionally, a large review of injured runners at a Vancouver sports injury clinic found that, of the 158 cases of plantar fasciitis, only 30 had an abnormally high or low arch.1
On the other hand, Michael Pohl and a group of researchers at the University of Delaware examined the biomechanics of 25 healthy female runners with a history of plantar fasciitis and found no difference in any variables related to rearfoot pronation compared to a group with no history of plantar fasciitis.14 The researchers did, however, find that the previously-injured group had a greater ankle range of motion and slightly lower arches. Because this study used runners who had already recovered from plantar fasciitis, it is complicated by several factors. Citing a study that linked poor ankle dorsiflexion range of motion—a risk factor for plantar fasciitis in some studies—with increased rearfoot pronation (perhaps to compensate for the ankle), Pohl et al. hypothesize that, since rehabbing plantar fasciitis often involves stretching the calf muscles to increase ankle dorsiflexion, the lack of pronation in the study's subjects was not surprising. Another retrospective study, led by Irene Davis at the University of Delaware and including many of the same researchers, did find evidence of increased pronation in 13 women with a history of plantar fasciitis.15
However, another important risk factor was identified in the Pohl et al. study: impact force and impact loading rates. For most runners, the forces that their body absorbs during running can be separated into the "impact force," the rapid load that is experienced when your foot first strikes the ground, and the "active force," the larger and slower-loading force that occurs as you support all of your weight on your planted leg and push off from the ground. Pohl et al. found that the previously-injured runners had significantly higher impact loading rate and a trend towards higher impact forces overall, though this did not reach statistical significance.
|Both the magnitude of the impact peak and the rate of loading (the slope between the arrows) while running have been linked to plantar fasciitis|
More importantly, these risk factors were confirmed in a follow-up study that was prospective—it evaluated the biomechanics of a large group of healthy runners, then waited to see who became injured. This type of study does away with many of the muddling cause/effect relationships that limit retrospective studies. Ten females running at least 20 miles a week developed plantar fasciitis, and when compared with an age- and mileage-matched group of ten women who stayed healthy, the injured runners had higher impact peaks and impact loading rates.16 Using an accelerometer strapped to the shinbone, the researchers also demonstrated higher tibial acceleration in the injured runners, proving that the higher impact forces and loading rates on the ground also translated into larger shocks being transmitted up the body.
However, a parallel study examining the rearfoot motion of the same ten women found no statistically significant differences in pronation during running (as measured by peak eversion).17 There was a statistically significant difference in standing rearfoot angle (3° in the healthy group vs. 5° in the injured group) though in practice this is so small that it's uncertain whether it's relevant in the real world.
This set of studies from the University of Delaware raises an important question: Is the plantar fascia more vulnerable to the impact forces at the beginning of contact or the active forces later in the stance phase? The Delaware studies suggest that impact is to blame, but the lines of reasoning we saw earlier suggested that the windlass mechanism, coupled with the "active" forces that occur when you push off the ground, strain the plantar fascia to a greater extent.6 It's possible that the combination of compressive forces from the ground reaction force and the tensile forces from the loading of the arch at midstance and in propulsion create unique stresses on the plantar fascia that make it more liable to be injured. This question remains unanswered as of yet. What is clear is that both retrospective and prospective studies have linked impact loading and impact force to plantar fasciitis in runners, making it one of the better risk factors identified thus far.
The pronation issue is also not entirely squared away. The weight of the evidence indicates that, in runners, pronation is not a major risk factor for plantar fasciitis by itself. However, Lee et al. appeared to show an increase in plantar fascia stress as a result of pronation, though did not link it to plantar fascia injury.12 It may be that larger factors, like variations in plantar fascia stiffness or the ability of the other structures of the foot to absorb strain, influence the actual strain on the fascia (which is quite difficult to measure in a living person!). But larger prospective studies are needed, especially ones that include men and younger, more competitive runners. The "gold standard" would be a large, prospective biomechanical evaluation of college distance runners, but until then, we'll have to tentatively conclude that pronation, whether measured statically in a navicular drop test or dynamically during gait, does not reliably predict or accompany plantar fasciitis.
The final risk factors for plantar fasciitis that have been identified in a study on running athletes are calf weakness and poor ankle range of motion. Both of these were noted in a 1991 study by Ben Kibler, Cindy Goldberg, and Jeff Chandler which examined 43 runners, basketball players, and racquet sport players with plantar fasciitis.18 Using a machine to measure joint strength and range of motion, the researchers compared the ankle on the injured side to both the uninjured ankle and the ankles of a control group without plantar fasciitis. Problematically, this control group only had five runners; the rest participated in other sports. Kibler, Goldberg, and Chandler found poor ankle dorsiflexion range of motion in the injured ankles, both when compared to the opposite side and to the healthy athletes. Plantarflexion weakness—presumably due to a lack of calf strength—was significantly different when comparing the unaffected side to the injured side, and when comparing to "standard values" from the laboratory, but not when compared to the healthy athletes.
Also notable was the presence of navicular drop (one way to approximate pronation by measuring how much the arch of the foot "collapses" when you stand on it) in only ten of the 43 athletes with plantar fasciitis, adding to our evidence that suggests pronation alone is not to blame for plantar fasciitis. Kibler, Goldberg, and Chandler, however, suggest that the calf weakness and tightness contribute to what they call "functional pronation," a theory similar to the one forwarded by Pohl et al., that is, pronation during the gait cycle that's caused by inadequate ankle dorsiflexion range of motion. But this should have been detected in Irene Davis' prospective study, so for now at least, there is no solid evidence linking "functional pronation" to plantar fasciitis in runners.
Since the root causes of plantar fasciitis are still not fully understood, treatments that are currently vetted by scientific literature are all centered around reducing the load on the plantar fascia. The established mainstream treatment strategies that are consistent with our current understanding of the causal factors of plantar fasciitis are stretching, night splinting, custom orthotics, and taping. There are also some emerging treatment strategies, like extracorporeal shockwave therapy, in addition to other treatments that are common or even accepted but are inconsistent with our understanding of the causal factors, like anti-inflammatory drugs and corticosteroid injections. Finally, we can use the factors identified in the scientific research to infer new ways to treat and prevent plantar fasciitis. Unfortunately, given the prevalence of plantar fasciitis in the general population, very few studies have investigated treatments for plantar fascia in runners, somewhat limiting our ability to gauge the efficacy of most treatments.
Mainstream treatments well-supported by research
Stretching is the "go-to" prescription for most podiatrists, physical therapists, and orthopedists when they have a patient with plantar fasciitis. Stretching the calf muscles with straight-knee and bent-knee calf stretches is thought to reduce stress on the plantar fascia by decreasing the tension through the calf and Achilles tendon. While calf stretching is widely accepted as a treatment method for plantar fasciitis, there is no set protocol for how often and how long to stretch. A typical program might consist of 10x10sec stretches of both the gastrocnemius (straight knee) and soleus (bent knee) muscles, three times a day. A 2006 clinical trial by DiGiovanni et al. found that a "tissue specific" stretch that targeted the plantar fascia directly led to better outcomes than a calf stretching program.19 The stretch, which is done while sitting and involves gripping your toes with your hand and dorsiflexing them, was shown in a study on cadaver feet to produce a better stretch through the plantar fascia than a calf stretch.20 By engaging the windlass mechanism, the plantar fascia stretch more directly targets the injured area. While the studies to date have compared calf stretching against plantar fascia stretching, it is probably better to do both. In addition to the 3*10x10sec stretches daily, DiGiovanni et al. recommend doing the plantar fascia stretch before getting out of bed in the morning and before rising after being seated for a long time.
|DiGiovanni et al.'s plantar fascia stretch|
Interestingly, some studies have linked hamstring tightness to plantar fasciitis as well.21 A 2011 study, for example, found both calf tightness and hamstring tightness when a group of patients with plantar fasciitis was compared to a group of healthy controls.22 Another study investigated the effects on gait by artificially simulated hamstring tightness by using an adjustable knee brace; they demonstrated that a tight hamstring could lead to increased loading on the forefoot during the push-off phase of walking, which the authors hypothesized would increase strain on the arch via the windlass mechanism.23 Thus, it makes sense to include hamstring stretching in a treatment program for plantar fasciitis too! Given the small number of papers citing these articles, it is likely that hamstring tightness is being overlooked as a possible contributing factor to heel pain.
Night splinting is another strategy which attempts to reduce strain on the plantar fascia by stretching the calf and, depending on the splint type, the plantar fascia itself. As the name suggests, a night splint is a brace you wear while you're asleep which keeps your ankle in a dorsiflexed position, reducing calf tightness and hopefully avoiding or limiting the "first step pain" that occurs with plantar fasciitis.24 Some types of night splints, including two found to be very successful treatments in scientific studies, also dorsiflex the toes to engage the windlass mechanism.25, 26 Given the success of the tissue-specific plantar fascia stretch, night splints should stretch the toes as well. The most accessible, comfortable, and least awkward splint that does this is the Strassburg sock (tested by Barry et al.), which is available online and, perhaps as a testament to its usefulness, at many locally-owned running stores. Other splints are bulky, hot, and uncomfortable—though the Strassburg sock isn't the most comfortable thing in the world either.
Taping is a more direct way to reinforce the arch and take stress off the plantar fascia. Using a technique called a low Dye strapping (named after its inventor, Ralph W. Dye),27 regular athletic tape is used to create a support system along the sole of the foot. Its efficacy is good for short-term relief,28, 29 and the best theory for its function is that it acts as an "external plantar fascia" by forming a taut bridge between the metatarsal heads (the first in particular) and the heelbone, just like the plantar fascia does! When you stand, walk, and run with a low Dye taping applied, you can feel the tension in the tape—this, presumably, is tension that would have otherwise been applied to the internal structures of your foot, including the plantar fascia. While I usually find traditional athletic tapings useless for running injuries, plantar fasciitis is an exception, perhaps because the strong and rigid tape functions well when it is mimicking another strong, rigid structure that runs from bone to bone.
|Instructions for applying a basic low Dye taping. It will take some practice to get the tensions right, so get yourself a few rolls of athletic tape and set aside some time to experiment with it until the taping is supportive but not too tight.|
Another strategy to unload the plantar fascia is through a prefabricated or custom orthotic. Unlike the soft, gel-based shoe inserts you see at drug stores, the type of insole that's used to treat plantar fasciitis is fairly rigid. While there is ample evidence that orthotics work,25 especially for plantar fasciitis, it's not entirely clear how.
A number of mechanisms might be responsible for the ability of a custom orthotic to offload the plantar fascia. The raised material under the arch can directly support the bones of the midfoot, reducing the weight that's transferred to tension on the plantar fascia. The direct support under the arch may also reduce the amount the arch flattens when weight-bearing, also offloading the fascia. Various ways of angling the forefoot and rearfoot of the orthotic could also reposition the foot, effectively shortening the length of the arch to further reduce tension on the plantar fascia. The cupped heel of most orthotics could also redistribute some of the compressive forces from the ground. Finally, simply elevating the heel (as virtually all custom orthotics do) can transfer more weight to the forefoot, unloading the base of the arch, and reducing tension in the Achilles. However, an elevated heel may lead to more compressive forces at heelstrike. All of these mechanisms are largely hypothetical, as no study that I'm aware of has investigated the specific mechanics of how orthotics reduce strain on the plantar fascia.
Perhaps because of the poor understanding of exactly how orthotics affect the plantar fascia, research to date has not found any advantages to a custom orthotic over a prefabricated orthotic when treating plantar fasciitis. One study, for example, found that prefabricated shoe inserts led to slightly better results than a custom orthotic;30 another found custom and over-the-counter orthotics to have similar results after 3 months of use. in a 2004 review on the use of orthotics in treating plantar fasciitis, Karl Landorf and Ann-Maree Keenan conclude:31
From the evidence to date, it seems that foot orthoses do have a role in the management of plantar fasciitis and that prefabricated orthoses are a worthwhile initial management strategy. At this time, however, it is not possible to recommend either prefabricated or customized orthoses as being better, and it cannot be inferred that customized orthoses are more effective over time and therefore have a cost advantage. Additional good-quality randomized controlled trials are needed to answer these questions.
For the time being, a well-made prefabricated orthotic like Superfeet or Powerstep has a few advantages over a custom orthotic. First, and perhaps most important to an injured runner, it's available immediately; there is no waiting period to make an appointment, get your foot casted, and wait for the orthotics laboratory to receive the cast, fabricate the orthotic, and ship it back to the podiatrist's office, which usually takes a few weeks. Second, they are cheaper by about an order of magnitude (~$40 vs. $400). Third, it is not broadly understood why an orthotic helps with plantar fasciitis, so when getting a custom orthotic, you are relying on the opinion of the podiatrist who orders it (and the laboratory he or she uses).
|Studies to date have shown that over-the-counter orthotics like Superfeet (right) show similar success rates in treating plantar fasciitis when compared to custom orthotics (left, from Roos et al.)|
The ability to customize an orthotic can, in theory, be a huge boon if done properly. Regular readers of this blog will know that I tend to ascribe to Benno Nigg's theory on orthotics: If an orthotic encourages the foot's "preferred path of motion," it can reduce tissue stress. The problem is that there is no universal preferred path of motion for every foot, and nobody can agree on the right way to go about making a custom orthotic for plantar fasciitis! If an over-the-counter orthotic is not working for you, a custom orthotic might be worth a try. And even if you decide to get an orthotic right away, a prefabricated insert can hold you over until your custom orthotic arrives.
Other mainstream treatments
Tissue manipulation is one category of treatment that is popular among runners and even recommended by orthopedists, physical therapists, and podiatrist from time to time. "Tissue manipulation" can be as simple as rolling a golf ball or a tin can along the bottom of your foot or as complicated as a series of treatments with Graston technique or Active Release Technique. Unfortunately, I found no controlled studies which examined any type of soft-tissue treatment for plantar fasciitis. More research is needed in this area. In the meantime, you can experiment with rolling your foot with various kinds of tools (golf balls, lacrosse balls, and tennis balls all work, but my favorite is a specially-made rubber ball with nodules) and possibly Graston or ART if you have a stubborn case, but realize that you are treading on untested ground; evidence thus far is purely anecdotal. Soft tissue manipulation is purported to work by removing or breaking down tightness, scar tissue, or adhesions in the plantar fascia—an explanation that could possibly fit in with the degenerative model of plantar fasciitis. Regardless, the entire paradigm of "adhesions and scar tissue" is unproven, controversial, and ultimately a topic for another day!
Plantar fasciitis is also commonly treated by nonsteroidal anti-inflammatory drugs (NSAIDS) like Aleve (naproxen) and Advil (ibuprofen) and often injections of corticosteroids, but given our current understanding of the injury, there are issues with these treatments. Most prominent among these is Lemont, Ammirati, and Usen's review of histology studies, which found no evidence of inflammation.9 Additionally, a 2007 study which examined the efficacy of NSAIDs on 29 patients with plantar fasciitis found no statistically significant difference at one, two, or six months between the group treated with celicoxib, a prescription-strength NSAID, and a placebo.32 The authors noted a nonsignificant trend towards better outcomes in the NSAID group, though the magnitude of the differences appeared relatively small. As this was the only high-quality study on the efficacy of NSAIDS, it is certainly nothing to base a treatment plan on. Given the concerns about side effects33 and their influence on tissue healing,34 using NSAIDs to treat plantar fasciitis is very questionable.
Corticosteroids, another mainstay of traditional plantar fasciitis treatment, do have some studies supporting their efficacy in short-term pain relief, but there are concerns about their effects on the integrity of the plantar fascia. A 2003 review study by the Cochrane Collaboration, a foundation for evidence-based medicine, supported corticosteroids for short-term (~1 month) relief of plantar heel pain, but the review was later withdrawn, as it was out of date. A 1999 study similarly found benefits one month after a corticosteroid injection, but no benefit thereafter.35 Corticosteroids may be useful for short-term pain relief, but it is important to note that two studies have also connected steroid injections into the plantar fascia with ruptures—actual tears in the plantar fascia itself, a much more serious injury. The first, published by JR Sellman in 1994, presented a series of 37 patients with plantar fascia ruptures, all of which had received corticosteroid injections for plantar fasciitis.36 A more comprehensive report by JI Acevedo and JL Beskin at Georgia Baptist Medical Center described 765 patients diagnosed initially with plantar fasciitis.37 Some 51 ended up with a plantar fascia rupture, 44 of which were associated with a corticosteroid injection. In the course of treating the 765 patients, the authors injected 122 with corticosteroids, of which 12 ended up with a fascia rupture. Given the relatively high incidence of ruptures associated with corticosteroids, this should give any runner pause when considering an injection. Interestingly, these reports parallel other studies concerning tendon ruptures following corticosteroid injections,38 drawing another parallel between plantar fasciitis and injuries to the large tendons of the body.
One possible alternative to direct injections is iontophoresis, a process by which medication is delivered through the skin using an electric current. It is thought that iontophoresis might offer a safer way to deliver drugs, as one study found that rabbit tendons were not degenerated by iontophoretic delivery of a corticosteroid, but were when the drug was delivered via injection.39 Two reports have found iontophoresis, either of a corticosteroid or 5% acetic acid (the same concentration as household vinegar!), results in benefits at four weeks after treatment in patients with plantar fasciitis when combined with other traditional treatments (stretching, icing, etc.).40, 41 The presumptive action of the corticosteroid—reduction of inflammation—is clear, but the action of iontophoretically delivered acetic acid is less so. Hypothetically, the acid molecules could help dissolve the bony, calcified areas on the plantar fascia enthesis, restoring flexibility or allowing tissue remodeling to occur. Do recall, though, that Wearing et al. proposed that the calcification of the fibers at the base of the heel (the enthesis) and the concomitant formation of heel spurs deep to the plantar fascia were a reaction to excessive strain on the plantar fascia, not a cause.6 Since one of these trials demonstrated that iontophoresis of acetic acid delivered superior results to iontophoresis of corticosteroids, it represents an encouraging direction for future research, but little is known about long-term effects; as we saw with corticosteroid injections, this can be an important consideration when choosing treatments. One study which presented a series of 34 patients treated with acetic acid iontophoresis found excellent results after only a few weeks of treatment and reported no long-term risks after a ~2 year follow-up, but more work is needed.42
Extracorporeal shockwave therapy, or ESWT, is another emerging treatment with a backing theory more in line with our current understanding of the causes of plantar fasciitis. Shockwave therapy delivered by a souped-up ultrasound machine which delivers high-intensity shockwaves to an injured area. The intent is to cause a controlled amount of microtrauma, which will hopefully stimulate the body to restart the healing process. Some studies43, 44 have found shockwave therapy to be beneficial in regular patients with chronic plantar fasciitis and one even had success treating runners with plantar fasciitis.45 However, a 2005 review by Charles Cole, Craig Seto, and John Gazewood at the University of Virginia cited better-designed studies of sedentary patients that found no benefit to ESWT; they did, however, endorse shockwave therapy for treating runners.2 As ESWT has shown promising results in the treatment of other common running injuries,46, 47 it should be investigated further as an option for recalcitrant cases of plantar fasciitis.
Making alterations to running form
Returning to running-specific treatments, the work of Pohl et al. and Davis et al. allow us to derive some recommendations for changing your running form if you have suffered or are suffering from plantar fasciitis. Given the demonstrated link between impact forces, impact loading rates, and plantar fasciitis in runners, it makes a lot of sense to work to reduce these. By far the easiest and safest way to go about doing so is by increasing your stride frequency. A 10-20% increase in the number of steps per minute that you take while running will lead to a substantial reduction in impact shock. But what of the studies that linked maximum strain in the plantar fascia with the active or propulsive phase of gait? Fortunately, a higher stride frequency reduces active forces too! This was demonstrated in a 1995 study by Hamill, Derrick, and Holt.48 Another important thing to note about changing your stride frequency is that your running economy will decrease, probably because you're accustomed to your usual running form.
|Dathan Ritzenhein knows a few things |
about the risks of changing your form
While a midfoot or forefoot striking style also attenuates the impact shock while running, it's less certain to help with plantar fasciitis. For one, transitioning to a forefoot strike transfers loads from the heel, shin, and knee to the foot, ankle, and calves. More loading on the Achilles will increase tension in the plantar fascia as well. Additionally, changing your footstrike style is a major alteration to your form that is unlikely to come without consequences. For some injuries, like chronic shin splints or recurrent knee problems, a forefoot or midfoot strike offers enough theoretical benefits to be considered as a potential treatment, but with plantar fasciitis, there's no evidence as of yet that footstrike style affects loading in the arch. I would very much like to see some research in this area.
The role of shoes and foot strength
Something that goes hand-in-hand with discussions on footstrike style is footwear and barefoot running. While barefoot training or minimalist shoes are often recommended for foot problems by a range of sources online, it almost goes without saying that there's no evidence supporting it in the scientific literature. Considering what we already know about the mechanics of the arch, we can easily explain why barefoot or minimal footwear is more painful than supportive footwear when you've got plantar fasciitis: a low heel, a lack of cushioning, and a lack of arch support all increase demands on the plantar fascia, exacerbating the pain. However, I do believe there is something to be gleaned from the runners who found that minimalism and/or barefoot running was the answer to their arch problems, and this is the role of the intrinsic and extrinsic foot muscles.
As we saw earlier, the extrinsic foot muscles have been demonstrated to support the arch during both walking and standing, and the intrinsic foot muscles are suspected to play a role as well.6 As evidence for this, it has been demonstrated that fatiguing the intrinsic foot muscles leads to a temporary increase in pronation and a lowering of the arch.49 Exercises for the intrinsic and extrinsic foot muscles may present a new direction for research, as strengthening these may be another way to take strain off the plantar fascia. The only study that's investigated anything along the lines of minimalist or barefoot training is a 2005 conference proceeding that demonstrated that a 5-month period of wearing a highly flexible shoe (the Nike Free) for warm-up periods before workouts in a group of athletes increased the strength of several extrinsic foot muscles when compared to another group who wore traditional shoes for their warm-ups. This study had its problems (not the least of which was being funded by Nike!), but it opens the door to the possibility of training with highly flexible shoes, or none at all, to increase the strength of the muscles of the foot. Another possibility is that minimalist or barefoot training could be used to put a controlled stress on the plantar fascia, much like targeted exercises for the Achilles or patellar tendons. Obviously, more research is required here. It's important to reiterate that any minimalist or barefoot training cannot be recommended right now, as all evidence indicates that it will increase stress on the fascia, causing further injury. If barefoot or minimalist training has a role in all of this, it is either as a preventative measure or as a late addition to a rehabilitation program.
Several things need to be demonstrated with scientific research before barefoot or minimalist training can be mentioned as a possible treatment option. These are:
1) Barefoot and/or minimalist training strengthens the intrinsic and extrinsic muscles of the foot—highly likely, in my opinion, but not certain.
2) Strengthening the intrinsic and extrinsic muscles of the foot takes strain off the arch—again, a mostly reasonable assumption but far from a definite one
3) Barefoot and/or minimalist training can safely strengthen the intrinsic and extrinsic foot muscles without causing excessive strain on the plantar fascia in injured patients—very much up in the air.
Targeted exercises for the plantar fascia—a missing link
Given the emerging evidence that shows the similarities between plantar fasciitis and chronic injuries to tendons like the Achilles and patellar tendons, I am surprised that nobody has explored targeted exercises to induce tissue remodeling. The use of eccentric exercises as a treatment for chronic tendinopathy is a fairly mature treatment, and it has been linked to direct, positive changes in the structure of injured tendons.50
The only study I came across that used any type of exercise (not counting stretches) was an interesting but poorly-executed study on using a minimalist shoe (the Nike Free again) and an exercise program to treat plantar fasciitis.51 The study in question, published in 2009, split 24 subjects into an experimental and control group. Both groups performed a set of strength, balance, and stretching exercises; the control group wearing their regular running shoes, while the experimental group was issued a pair of Nike Frees to be worn only while doing their rehab exercises. The experiment ran for 12 weeks and, while the analysis found the group wearing the flexible shoe did significantly better than the control group, three participants in the Nike Free group dropped out during the course of the study. Two of these left because their pain increased. Instead of considering these subjects in the final analysis, as is standard practice with clinical studies, the authors excluded them, marring their data and calling the statistical significance between the groups into question, as pointed out by Craig Payne, a podiatrist and lecturer at La Trobe University. Additionally, the study had a design flaw you may have already picked up on: The control group kept using their regular running shoes—presumably, the ones they got injured in! Additionally, the study was, of course, funded by Nike. On the bright side, if we disregard the analysis flaws and conflicts of interest, this study did demonstrate the successful use of a true exercise program which incorporated strength, balance, and coordination exercises in addition to stretching. The exercises used in the study were carioca side-steps, balance-walking along a straight line, a modified calf raise, one-legged balance, and ankle inversion/eversion strengthening, in addition to calf and plantar fascia stretching. I'd like to see more studies test out various strength exercises, especially considering Kibler, Goldberg, and Chandler's 1991 study demonstrating calf weakness in athletes with plantar fasciitis.18
This massive, sprawling article is a testament to the complexity and frustrations associated with plantar fasciitis. Things aren't nearly as clear as with some other injuries, and this problem is only made worse because of the relatively high incidence of plantar fasciitis in the general population. It's not clear what, if any, risk factors are unique to runners. Additionally, given a particular runner with plantar fasciitis, it's hard to tell what's the cause of the injury: something related to his or her lifestyle, or something related to his or her running!
Regardless of these difficulties, there's a lot that we've been able to establish. Plantar fasciitis is an injury that manifests as damage and degeneration to the fibers that make up the plantar fascia, and is similar in this way to Achilles tendonitis or patellar tendonitis. There is little evidence for any role of inflammation in the injury process, especially in chronic cases. It presents as an aching or stabbing pain at the base of the heel and is especially painful immediately after you get out of bed in the morning and after you finish a workout or a long day on your feet. Potential risk factors that have been associated with plantar fasciitis include:
- Calf tightness (causing poor ankle range of motion)
- Hamstring tightness
- High impact forces while running
- High impact loading rates while running
Additionally, calf weakness was linked to plantar fasciitis, but only in one study. Pronation, either while standing or while running, has not consistently been associated with plantar fasciitis, and the strongest studies we have thus far—the prospective investigations by the University of Delaware lab—have not found an association between pronation and plantar fascia injury in runners. Arch height also appears to be a poor predictor of plantar fasciitis in runners. While these two factors are unsuccessful at predicting plantar fasciitis by themselves, it does not necessarily mean they are unrelated in all cases.
Treatment is generally centered on reducing strain on the plantar fascia. Options that have been proven to be successful and are consistent with our understanding of the basis of the injury include:
- Calf stretching, 3-5x daily for 10x10sec, both with a bent knee and a straight knee
- Plantar fascia stretching 3x daily plus before getting out of bed or standing after being seated for a long time, 10x10sec
- Prefabricated or custom orthotics
- Low Dye taping of the arch
- Night splinting, preferably with a device like the Strassburg Sock which dorsiflexes the toes as well as the ankle
Additionally, hamstring tightness has been linked to plantar fasciitis in a few recent studies, so incorporating hamstring stretches into your rehab routine is a logical choice.
Icing is a safe and nearly universal treatment for any running injury, and veteran road racers often recommend either using ice cups or a frozen water bottle to ice the plantar fascia. It should be noted that no studies investigated the efficacy of icing on plantar fascia pain. Changing your footwear to something comfortable and supportive can go a long ways towards reducing pain in your arch, especially if you have a habit of wearing hard-soled or unsupportive shoes. Additionally, try to avoid walking around barefoot, especially on hard surfaces. Many runners like to get a pair of supportive sandals, slippers, or running shoes to wear around the house, and in severe cases, even in the shower!
While nonsteroidal anti-inflammatory drugs and corticosteroid injections have been mainstays of treatment for quite some time, there is no good evidence for the efficacy of NSAIDs, and the risk of a plantar fascia rupture is probably not worth getting a month's worth of relief from a corticosteroid injection for most runners. Iontophoresis, particularly of acetic acid, may offer a safer and more effective alternative to corticosteroid injections, but there is only one study examining the long-term effects of iontophoresis. Extracorporeal shockwave therapy is another emerging treatment for chronic cases with promising initial results but no information on long-term results or risks.
Soft tissue manipulation, either through simple methods like rolling your arch with a golf ball or through treatments like Graston Technique and Active Release Technique, have anecdotal support among runners and even medical professionals but have not been vetted by any scientific research.
Increasing your stride frequency is a very good way to lower your impact forces and impact loading rates while you run. While there's nothing "magical" about a cadence of 180 steps per minute, it's a good target for most people. Barring that, just try to increase your stride frequency by about 10%.
While plantar fasciitis shows many similarities to chronic tendon injuries, there are no scientifically-supported strengthening exercises to prevent or treat plantar fascia injuries. Foot exercises like towel-grips are occasionally recommended by physical therapists or websites, but seem woefully inadequate given the magnitude of the forces the plantar fascia handles during walking and running. The strength exercises that successfully treat degenerative injuries to tendons are targeted, eccentric, and involve progressive and heavy loads. Future research should investigate the influence of intrinsic and extrinsic foot muscle strengthening on strain in the plantar fascia and explore ways to capitalize on the link between chronic tendon injuries and plantar fasciitis; these studies may open the door to targeted exercises for the foot or for barefoot or minimally-shod activities as a strategy to put a controlled stress on the arch. Until that research is done, however, there is reason to believe that barefoot or minimalist-shoe activities will make plantar fasciitis worse, not better. Calf strengthening might be useful, as one study connected calf weakness to plantar fasciitis in athletes.18 While transitioning to a forefoot or midfoot strike could lower your impact forces and loading rates, it will also increase strain on the Achilles and calf, which would in turn increase strain on the plantar fascia, making the end result unclear. Modulating your stride frequency likely carries a lower risk of complications.
Paradoxically, despite the length of this article and the array of references that follow, plantar fasciitis is still an elusive injury. Right now, since there is no rigorously-tested protocol, the best method for treatment is probably an aggressive combination of all of the successful treatments. If you are proactive about treating plantar fasciitis early with icing, wearing supportive shoes, using a low Dye arch taping, doing calf, hamstring, and plantar fascia stretching, wearing a Strassburg sock at night, rolling with a golf ball, using over-the-counter orthotics, and increasing your stride frequency when you return to running, you may not need to resort to more intensive, advanced, and expensive treatments like iontophoresis, Graston or Active Release Technique, custom orthotics, or extracorporeal shockwave therapy. Until better and more comprehensive treatment protocols are developed, the best strategy is to hit it early and hit it hard with everything we've got.
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