Plantar fasciitis can be a debilitating pathology. Its onset is usually described by patients as gradual. Pain is reported as being most noticeable on initial weight-bearing in the morning,1-3 after periods of inactivity,1,2,4 after standing on hard surfaces,5 standing on tiptoes,6 or climbing stairs.6 This pain often decreases after a few minutes of weight-bearing but gradually increases again throughout the day.2,4,6
Incidence rates are difficult to determine, but several authors have suggested that plantar fasciitis is the most common cause of heel pain and may account for as much as 15% of all foot-related problems.6-8 Plantar fasciitis is an overuse injury involving inflammation of the plantar aponeurosis and perifascial structures.2,4,9 Patients with this pathology report tenderness to palpation of the medial calcaneal tubercle and the medial aspect of the proximal longitudinal arch.1,4,9,10
A variety of treatments have been described for plantar fasciitis. Conservative treatments include stretching,3,4,10-12 night splints,3,4,12 corticosteroid injections,1,3,5,12 thermal modalities,4,9 prefabricated shoe inserts,3,10,12 and custom foot orthoses.3,10,12,13 Practitioners frequently incorporate multiple interventions to treat the condition. The use of multiple interventions by previous investigators, therefore, makes it difficult to determine the effectiveness of any one specific intervention.
An understanding of the anatomy14 and function of the plantar fascia is critical for developing appropriate intervention strategies. The plantar fascia consists of a very dense connective tissue, similar in composition to tendon and ligament. Its proximal attachment is the medial calcaneal tubercle of the calcaneus (Figure 1). The tissue diverges medially and laterally as it courses anteriorly toward the forefoot, then divides into five slips in the region of the metatarsal bases and continues anteriorly toward the five toes. As the slips near the metatarsal heads, they divide into two bands. One band passes superficially to the skin. The deeper band bifurcates, with the two branches passing around and superior to the flexor tendons. The bifurcating branches then merge with the flexor sheath of the toe and deep transverse ligaments.
The anatomy of the plantar fascia explains mechanical factors that may contribute to pathology of the tissue and may guide mechanical interventions designed to decrease stress within the tissue. The fascia provides truss support for the longitudinal arch of the foot. Figure 2 depicts the manner in which truss materials support an arched structure by tying the two ends of the arch together. When a superior load is imposed on the arch, the truss materials prevent migration of the two ends away from one another, thus supporting the imposed load. Tensile stress, however, increases in the truss materials as a result. Loads that are excessive in magnitude, frequency, or duration can precipitate the development of plantar fasciitis. Patients, therefore, may report a gain in body weight15 that preceded the onset of plantar fasciitis; or beginning an exercise program16 involving ground reaction force loads that were excessive in magnitude and frequency. Prevention and rehabilitation may involve wearing shoes that provide shock absorption and exercising on ground surfaces that deform somewhat with loading.
Since the distal portions of the plantar fascia cross the plantar surface of the metatarsophalangeal (MTP) joints of all five digits, extension of the MTP joints at terminal stance tends to increase tensile stress within the plantar fascia. This mechanical factor has been described as the "windlass mechanism."6 A short triceps surae complex may also contribute to excessive and uncomfortable tensile stress within the plantar fascia during the latter portions of stance phase.9 Excessive passive tension within the Achilles tendon limits the dorsiflexion needed at the talocrural joint during middle and late stance. Inadequate dorsiflexion at the talocrural joint may cause compensatory dorsiflexion of the subtalar or midtarsal joints. Compensatory dorsiflexion of these joints, the dorsiflexion component of pronation, results in further loss of longitudinal arch height and increased tensile stress within the plantar fascia. Passive tightness within the triceps surae also may affect plantar flexion of the calcaneus, essentially moving the medial calcaneal tubercle posteriorly, away from the distal attachment site of the plantar fascia. This migration of the two attachment sites away from one another, as indicated previously, increases tension within the plantar fascia. Tightness of the triceps surae, therefore, can affect increased tensile stress within the plantar fascia in several ways. This issue can be addressed easily using stretching protocols during rehabilitation and by incorporating a temporary heel lift into any foot orthotic intervention or the sole of the shoe.
A straightforward approach to protecting the plantar fascia from excessive tensile stress is to support the medial longitudinal arch from below. This is easily accomplished through some type of arch support. Filling in the arch space with material inside the shoe supports the longitudinal arch of the foot, prevents migration of the two ends of the arch away from one another, and decreases the magnitude of tensile stress within the plantar fascia. An inexpensive off-the-shelf arch support may be sufficient for this purpose and may be the treatment of choice when finances are a concern and a custom-fabricated product may be unnecessary (e.g., when the patient does not have an extremely cavus foot or an excessive malalignment issue such as forefoot varus or tibial varum that requires custom posting).
Malalignment issues may be present, however, that indicate use of a custom-fabricated product to prevent collapse of the medial longitudinal arch. Forefoot varus is one of these malalignment issues. Forefoot varus may be the factor primarily responsible for driving compensatory pronation and the associated fall of the medial longitudinal arch. In this case, an off-the-shelf arch support will not directly address the cause of longitudinal arch collapse and the excessive tensile stress that develops within the plantar fascia. Patients in our clinic who have this profile have responded well to foot orthoses that incorporate a custom-fitted arch support and a medial forefoot wedge (post). This foot orthosis configuration transfers the ground reaction force to the medial metatarsal heads and obviates compensatory midfoot and subtalar joint pronation and the associated medial longitudinal arch collapse.
Among the other malalignment issues that may suggest the need for custom foot orthotic intervention is excessive varum of the leg, or shank (Figure 3). This curvature of the leg results in the distal third of the leg approaching the ground off the vertical (i.e., the distal leg is more medial) in the frontal plane. The ground reaction force then tends to make initial contact with the rearfoot more laterally, increasing the magnitude of the eversion moment in the frontal plane and of the triplanar pronation moment. Clinical experience suggests that patients with this alignment profile will demonstrate subtalar joint and midfoot pronation if such motion is permitted. The resulting compensatory motion, again, causes a reduction in medial longitudinal arch height and increases tensile stress within the plantar fascia. Patients in our clinic who have this particular profile have responded well to foot orthotic intervention that incorporates a custom-molded arch fill and a medial rearfoot post that is designed to transfer the ground reaction force to the medial aspect of the rearfoot and avoid unwanted compensatory motion.
We have also noted that plantar fasciitis patients who demonstrate excessive foot pronation benefit from supportive shoes. Subtalar and midfoot pronation are associated with medial displacement of the talonavicular region of the midfoot. This medial displacement occurs when the talus adducts on a calcaneus that is somewhat stabilized by the support surface. Shoes that support the foot medially may limit this motion by providing a firm, laterally directed reaction force to the medial aspect of the midfoot. Our experience has been that shoes with a straight last and a firm heel counter may provide this support. We instruct patients to wear shoes with a heel counter that is not only firm, but also provides more support for the medial aspect of the rearfoot and midfoot. This type of heel counter extends more superiorly on the medial aspect of the foot and more anteriorly toward the medial aspect of the midfoot.
Two basic scientific investigations lend some support to the previous analyses and treatment approaches. Kogler et al17 performed a cadaver study comparing the effects of five different foot orthoses and an oxford shoe on strain of the plantar fascia. Plantar fascia strain was lowest for loading conditions in which the orthoses provided a higher medial longitudinal arch. Kitaoka et al18 also reported that two foot orthotic devices were effective in maintaining medial longitudinal arch height when axial loads were imposed on cadaveric foot specimens.
Selection of the stiffness of the materials used for foot orthotic fabrication may be guided by one other consideration. Patients with plantar fasciitis often have an associated traction spur projecting anteriorly from the medial calcaneal tubercle. A traction spur, which is readily visible on a lateral radiograph, is thought to be the result of reactive bone formation secondary to the repetitive and excessive tensile stress imposed by the plantar fascia on this proximal attachment site. Even patients who do not have a traction spur may have tenderness to palpation of the medial calcaneal tubercle. In our experience these patients tolerate semirigid foot orthoses better than rigid ones. Patients with this profile experience pain not only from excessive tensile stress within the plantar fascia, but also from excessive compressive stress being imposed on the medial calcaneal tubercle. Rigid foot orthoses may be uncomfortable in such instances because the lack of deformation results in smaller contact areas for the heel and higher magnitude contact force at the heel. Smaller contact area and greater contact force result in higher magnitude contact pressures being imposed on the heel. Softer orthotic materials may result in more deformation of the orthotic materials, attenuated contact forces, and larger contact areas with the heel. Experience in our clinic is consistent with this theoretical analysis in that many of our plantar fasciitis patients come to us having tried rigid foot orthoses without successful treatment outcomes, and then respond favorably to semirigid foot orthotic intervention.
One final suggestion may be helpful regarding two aspects of daily use of semirigid foot orthoses. The classic symptom of early morning pain may be suggestive of subacute microtrauma every morning to the plantar fascia following the shortening that occurs during the sleeping hours. We advise our patients, therefore, to stretch the plantar fascia in bed prior to weight-bearing. We recommend they do so by extending the knee and dorsiflexing the ankle for a sustained 30 to 40-second stretch. We also advise that they have their supportive shoes (with orthoses in them) next to the bed so that they can protect the plantar fascia from excessive tensile stress during the first few minutes of early morning weight-bearing. They are cautioned not to take any barefoot steps during this time.
The second recommendation we make regarding the use of foot orthoses involves their use during stretching exercises for the triceps surae muscle group. We learned the hard way that patients who had tight triceps surae and plantar fasciitis would sometimes report increased pain in their plantar fascia during and following their stretching exercises when they did these exercises barefoot. These patients taught us the value of recommending that all plantar fasciitis patients wear their supportive shoes and foot orthoses when doing triceps surae stretching exercises to protect the plantar fascia from excessive tensile stress. The link between increased Achilles tendon tension during weight-bearing and excessive tensile stress within the plantar fascia was described earlier in this paper.
Finally, we recently conducted a study in which patients with chronic plantar fasciitis were treated only with semirigid foot orthoses. The manuscript for this research is currently being reviewed for publication and the specific details of the work cannot be reported here. Most of the patients in this study reported having had the condition for several months and reported they had already tried several interventions. Use of semirigid foot orthoses for two weeks resulted in a significant reduction in pain ratings during a measured walk and significant reductions in standardized measurements19 of pain and disability. Semirigid foot orthoses, therefore, may be a cost-effective intervention for plantar fasciitis considering the limited number of clinic visits required to fabricate and adjust the orthoses.
Plantar fasciitis is a debilitating patient problem that can be very recalcitrant to treatment. The previous analysis of the anatomic structure and function of the plantar fascia provides some guidance regarding how mechanical issues may contribute to the chronic inflammation of this tissue and act to sustain tissue pathology even when anti-inflammatory medication and physical therapy modalities are used as interventions. Semirigid foot orthoses and shoes may address many of these mechanical issues and result in successful resolution of the tissue pathology.
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2/1/01, Issue # 802, page 53.
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