INTRODUCTION

Few conditions affecting human foot have stimulated more interest and controversy among health care professionals than plantar heel pain syndrome.  Over the past decade, new surgical  approaches have been popularized which have fuelled considerable debate and critical analysis about the validity and success of all interventions for treatment of plantar heel pain—both operative and non-operative.   

Among all disciplines is near universal agreement that the vast majority of patients with plantar heel pain will be successfully treated with non-operative strategies.  However, there is  no uniform agreement both within or between these disciplines as to which conservative interventions are most appropriate in achieving a successful outcome in treating plantar heel pain. 

As managed care economics affected the medical profession during the 1990’s,  health care providers were pressured to develop evidence based outcomes research to justify the costs and benefits of prevailing clinical treatment strategies.  Standards for quality outcomes research have evolved for most health care disciplines, including podiatric medicine.  However, scrutiny of published research reporting outcomes of treatment of plantar heel pain in the podiatric and orthopaedic literature reveals numerous shortcomings in terms of valid design, methodology, and interpretation of results.  

The purpose of this article is to 1)  Evaluate prevailing theories about the pathomechanics of plantar heel pain, 2)  Present controversies that currently exist regarding etiology  and  treatment and, 3) Review outcomes reports of non-operative interventions used to treat large groups of patients with plantar heel pain syndrome.

MYTHS ABOUT  HEEL SPURS 

In a series of elegant anatomic studies using micro cryomicrotomy, McCarthy clearly showed that the common plantar calcaneal spur is not  invested by the plantar fascia.  Rather, the spur is invested by the abductor hallucis and flexor digitorum brevis muscle origins and is clearly found superior to the origin of the plantar aponeurosis.  In light of these  findings, the direct link between plantar fascial overload and the formation of calcaneal spurs must be questioned. 

In 1963,  Rubin showed that only 10% of patients with radiographic evidence of heel spurs were actually symptomatic. Since then, many authors have demonstrated that the majority of plantar heel spurs found on foot x-rays are asymptomatic. 

Thus the role of a heel spur in the pathomechanics of plantar heel pain syndrome is still poorly understood.  Yet, clinicians commonly use the term heel –spur syndrome and many treatment strategies employ methods to theoretically off-load a plantar calcaneal spur.

Plantar fascia strain has been speculated to result from every imaginable foot type and biomechanical etiology.  Both the podiatric and orthopaedic literature are replete with unsubstantiated explanations of plantar fascial strain resulting from cavus foot types, flat foot types, pronated feet and supinated feet. In almost every case, these pathologies have  been speculated to cause a lowering of the medial arch of the foot, resulting in fascial strain.

A valid, and well substantiated arch lowering force on the human foot is a tight heel cord (Ref).  Tightening of the heel cord in cadaver models not only lowers the arch, it causes significant rotational movements of the forefoot upon the rearfoot including midtarsal joint pronation and dorsiflexion and inversion of the first ray segment. (Ref)

Interestingly, the presence of a tight  heel cord has  not been consistently found in groups of patients with plantar heel pain syndrome.  In her study  of 91 patients with heel pain, Barbara Warren found that the heel cord was actually tighter in a control group than in a  group of patients with plantar heel pain. Conversely, Kibler found that the heel cord was tighter on the symptomatic side of patients with heel pain, but could not rule out a cause vs. effect relationship.  Amis found that 75% of his patients with heel pain had a tight heel cord. However, there is no universal agreement as to the "normal" range of ankle joint dorsiflexion necessary for humans, so studies of tight heel cords are open to considerable subjective interpretations.  The essential factor in evaluating this possible link between a tight heel cord and plantar heel pain is the role of calf and Achilles stretching in non-operative treatment programs.  Indeed, although stretching is integral in most recommended treatments, the success of such and intervention is questionable.  This will be discussed later in this article.

The plantar fascia is the most important arch-supporting mechanism of the human foot.  In his study of cadaver models subjected to axial load, Thornardsen found that the plantar fascia had a two fold greater contribution to arch stability than the posterior tibial tendon.  In his  series on the role of the plantar fascia and arch support, Sharkey found a significant elongation and deformation of the arch with complete fasciotomy.

The arch of the  human foot has been described as both a beam and a truss.  Recent experimental evidence has validated the truss mechanism as the primary explanation of stability.  A beam relies on the interlocking relationship of the building blocks (bones) and the soft tissue connections on the concave surface (ligaments).  The truss is  described as two struts connected by a tie rod (plantar fascia).  Cadaveric studies have shown that, without intact ligaments, the bone architecture of the human foot is incapable  of maintaining an arch configuration when axial load is applied.  When the entire central band of the plantar fascia is severed, the human arch integrity is severely compromised, with documented shift of alignment of the tarsal bones in all three cardinal body planes.  In addition, Sharkey showed, in cadaver models void  of  an intact central plantar fascia, that greater loads were transmitted to the central metatarsals, due  to loss of stability of  the proximal phanlanx.  Bending and strain of the metatarsals can possibly lead to stress fractures in patients who have undergone complete plantar fasciotomy.
 

In static, resting stance, the muscles of  the leg and foot are inactive.  Maintanance  of arch integrity is entirely dependent on the osseous locking of the tarsus and the truss mechanism of the plantar fascia.  Without the aid of the extrinsics to  maintain the arch, static stance may be the most stressful situation for the plantar fascia.

Anecdotally, clinicians have reported the most difficult challenges in managing plantar fasciitis in patients engaged in prolonged standing activities. Comparisons between the dynamic foot condition and the resting, static foot position offer interesting challenges for treatment options for off-loading the plantar fascia.

Recent insight into the effects of off-loading the plantar fascia in a static foot model were offered in a series of  studies conducted by Kogler et al.  In nine cadaver specimens, axially loaded, six degree medial wedges placed under the forefoot caused an increased strain in the plantar fascia while six degree lateral wedges caused a significant decreased strain.  Rearfoot wedges, both medial and lateral, had no significant effect on plantar fascial strain.

In another study published by  Kogler, the effect of heel elevation on plantar fascia strain was determined.  Simple blocks of  2,4 and 6 cm thickness were placed under the heel of 12 cadaver specimens and plantar fascia strain was measured and compared to the heel flat condition.  Surprisingly, there was no evidence of any reduced fascial strain with heel elevation.  However, when the heel was elevated with shank contour platforms (simulating the effect of footwear with elevated heels) there was a significant decrease in strain of the plantar fascia with increased elevation of the platform.

The results of  Kogler’s research validates the experience of many patients who obtain relief of plantar heel pain syndrome by wearing shoes with elevated heels.  The mechanical off-loading of the plantar fascia cannot, however, be explained by heel elevation alone.  In fact, with a true truss mechanism, elevating the proximal strut (calcaneus) can be expected to actually increase strain in the tie rod (plantar fascia).  The reduction in plantar fascia strain occurring with contoured shank platforms, according to Kogler, may be the result of lateral arch elevation which secondarily raises the medial arch and thus decreases strain on the medial fascial structures.

The problem with most of the cadaver studies on plantar fascia biomechanics is the fact that the investigators did not evaluate or report on the foot-type of the specimens.  The presence of  a forefoot varus or valgus  could have significant effect on the response to medial and lateral wedging of the forefoot, as well as the lateral arch raising effect of a shank contoured elevation platform.

Another issue to consider is the phase in the gait cycle that is  simulated in cadaver studies of lower extremity function.  Kogler, Thornardsen and Kitaoka all evaluated their cadaver specimens in a foot-flat, static stance position.  Sharkey evaluated plantar fascia mechanics in terminal stance (propulsive phase) when maximal strain on the plantar fascia is thought to occur.  This assumption is somewhat debatable.  Although ground reaction forces peak at heel rise and extrinsic muscle activity also reaches maximal tension, the windlass mechanism allows transmission of tension into kinetic movement of pedal and leg skeletal segments.  Therefore, energy or  strain in the plantar fascia is transferred to other parts  of the foot during terminal stance.  Without a functioning windlass, occurring with hallux limitus or  during static stance, strain develops in the plantar fascia and cannot be dissipated or transferred into joint movement.

Podiatric  physicians have long employed biomechanical principles in the treatment of patients with plantar heel pain.  However, there is no  consensus in the podiatric literature in terms of a uniform treatment approach utilizing functional foot orthoses and proper footwear prescription.

Many practitioners seek to control pronation of the subtalar joint  thru the use of medially posted foot orthoses both in the rearfoot and forefoot.  As Kogler’s work has shown, and from a simple understanding of the truss mechanism of the  plantar fascia, the application of a medial post under the forefoot will actually increase strain in the plantar fascia for most foot types.  One possible  exception is the true forefoot varus, which is  un-common, and in the author’s experience, is rarely associated with plantar heel pain syndrome.

EVALUATING TREATMENT OUTCOME REPORTS

A total of 10 published papers reporting outcomes of various  treatments of plantar heel pain will be reviewed.  These papers have all been published within the past decade and combine similar modalities commonly employed in this country for treatment of plantar heel pain.  Although the treatment strategies are similar the results and conclusions vary significantly amongst the investigators.

Wolgin surveyed 100 patients who were treated with a variety  of common non-operative interventions for plantar heel pain syndrome.  Average time for follow up survey was 47 months.  Good results were obtained in 82 out of 100 patients, 14 achieved fair results and 3 had poor results.  The patients rated Achilles stretching as the most effective treatment followed by  rest and NSAIDS, both of which were higher rated than “custom inserts.”  Patients who did poorly were overweight, had bilateral symptoms and had symptoms for  a prolonged period of time (more than 10 months) before seeking medical attention.

Tisdel and Harper utilized a short leg walking  cast on 32 patients who had failed 12 months  of non-operative treatment for plantar heel pain.  After six weeks of  cast immobilization,  the patients were then followed and interviewed at an average of 15 months post treatment.  Despite the fact that good results were obtained in only 25% of the patients and over 40% of the patients were dissatisfied, the authors concluded that “Casting appears to be a reasonable  option for patients with recalcitrant heel pain and should be offered before surgical intervention.”

Mizel utilized a shoe modification with steel shank and anterior rocker for  patients who had failed a 10 month course of  previous  treatment for plantar heel pain syndrome.  After 16 months of this treatment, 59% of the patients reported symptoms resolved, 18% were improved, 15% reported no change, and 7% were  worse.  After two years of treatment, with 59% of the patients resolved, the authors concluded that “The method is effective for treatment of plantar fasciitis.”

Davis, Severud and Baxter reported on the results of non operative treatment of 105 patients with heel pain syndrome.  A self-administered patient questionnaire was completed an average of 29 months after initiating treatment.  Treatment included Rest, NSAID, viscoelastic heel pad, Achilles stretch, occasional steroid injection, and custom foot orthosis “when warranted.”    In rating their level of pain resolution, 58% of the patients reported good results, 31% fair, and 10% poor with  an average time to resolution of 5.1 months.  Somehow, the authors concluded that “The treatment protocol used in this study was successful for 89.5% of the patients.”

This same significant favorable outcome with a mechanical approach to off-loading the plantar fascia was obtained by Scherer and co-workers.  In their prospective study of 73 patients, a subgroup receiving low-dye strapping and custom functional foot orthoses only obtained  Good results in 81% of the patients, fair results in 15%, and poor results in 4%.

There are numerous  difficulties  in evaluating all of these  outcome studies and drawing meaningful conclusions.  Clearly, there were differences in assessment of success depending on whether the results were determined by  confidential patient interview or obtained by interview from the treating practitioner.   It is well known that patients will report a more favorable outcome to the  treating doctor versus a more realistic assessment in a confidential survey, conducted by a neutral party.

Of interest is the disparity between a patient assessment of successful treatment outcome (Good, Fair, Poor)  versus  overall pain relief.  In many studies, a majority of patients reported a good outcome, yet still had  significant pain.  As Martin states, in evaluating patients who  have been treated for long term heel pain, “Because of the chronic nature of the patient’s symptoms, their expectations for complete relief may have been low.”  Thus, many patients who present for treatment of plantar heel pain have already had their pain for an extended period and have formed opinions that their pain will never be totally cured.

Among almost  all of these studies, was near universal agreement that the longer the patient had experienced pain prior  to treatment, the less likely would a successful treatment outcome occur.  In general, those patients having pain for more than 12 months prior to treatment were most resistant to non-operative interventions. 

In this regard, there  appears a  disparity among clinicians as to the amount  of time necessary to expect significant pain relief with non-operative care.  Several authors concluded that certain treatments were effective, even though the time of treatment needed to achieve measurable success exceeded two years.  One  has to question the  overall efficacy of such  interventions if, during the  two years of treatment, the patient lost significant time from work or discontinued a potentially  beneficial cardiovascular exercise program. 

In the final analysis, the treatment strategy that yielded the best results in the shortest period of time was the combination of low-dye strapping and prompt institution of custom functional foot orthotic therapy.  Both Scherer and Lynch, utilizing these strategies, achieved better results that the other groups in less than one-fourth the period of  time.

CONCLUSIONS

Plantar heel pain syndrome continues to stimulate controversy regarding pathomechanics and treatment.  Patients developing heel pain can expect to be offered a divergent approach, depending on the specialty they seek treatment from.  Even within certain specialties, there is considerable variation of opinion regarding the pathomechanics and treatment of  plantar heel pain syndrome.

Recent cadaveric studies have shed light on the role of the plantar fascia in supporting the arch as well as the effects of certain strategies to decrease strain in this structure.  Some widely accepted notions about forefoot wedging and heel elevation have now been disputed.  Relating the results of laboratory research to a practical clinical setting and to a variety of foot types remains a challenge to today’s podiatric physician.

Non-operative treatment strategies for plantar heel pain have been evaluated in outcomes studies by a number of investigators. The results of these studies are contradictory, and conclusions must be made cautiously.  The reasons for such skepticism are the following:

1.       True outcomes research has yet to be conducted in this area, following accepted methodology and utilizing appropriate measurement techniques.

2.       Assessment of a successful outcome of treatment will vary significantly depending on whether the patient versus the clinician provides the final analysis.

3.       Patients with plantar heel pain have poor expectations for total, permanent pain relief when they  present for treatment.

4.       Clinicians can use treatments that require up to 24 months to  achieve success, yet conclude such treatments are effective.

5.       The longer a patient has symptoms prior to treatment, the  less likely  any non-operative treatment is going to be successful.

Although comparisons between studies are difficult to make, some findings appear worth noting. Specifically, those groups of patients with plantar heel pain, treated promptly with low-dye taping and custom functional foot orthosis therapy, had the most favorable outcome of treatment.

Until further insight into the pathomechanics of plantar heel pain is attained, there will continue to be controversy----and significant numbers of patients suffering from this disorder.