Offloading The Plantar Fascia: What You Should Know

   Heel pain is the most common musculoskeletal complaint of patients presenting to the podiatric physician. While heel pain is estimated to comprise 10 percent of athletic injuries, the incidence of heel pain in the active and sedentary population appears to be significantly underreported in the medical literature. Most experienced practitioners report that heel pain complaints have risen to epidemic proportion over the past 20 years for reasons we still do not fully understand.    Certainly, changing demographics figures into the equation. The average patient with heel pain is between the ages of 40 and 60 and this segment of the population has grown more than any other over the past two decades.    Many theories have emerged explaining the possible etiologies and anatomic structures involved with plantar heel pain syndrome.1 Today, most authorities agree that plantar fasciitis is the most common cause of heel pain in both active and sedentary patients.2-4    Lemont, et. al., have questioned the term “plantar fasciitis.”5 They examined histologic findings from specimens taken during heel spur or plantar fasciotomy surgeries, and found no evidence of inflammation. The findings of myxoid degeneration with fragmentation of the plantar fascia led Lemont to propose that the true pathology of the plantar fascia is a “fasciosis” rather than fasciitis. Other research has validated that the histologic changes in the plantar fascia associated with heel pain are consistent with structural failure and not with inflammation.6 Researchers have hypothesized that the structural failure is due to microtears in the plantar fascia in the area of its insertion on the medial tubercle of the calcaneus.7    Podiatric physicians have long believed the most appropriate treatment for the painful heel involves some method to decrease strain or offload the plantar fascia. Many of these interventions are based upon biomechanical principles. The most common principles include the use of custom functional foot orthoses, arch taping and stretching of the heel cord and calf musculature. Yet if one were to survey any group of podiatric physicians around the country, there would be a lack of agreement about how and why these interventions work. Clearly, there is little understanding of how the plantar fascia may become overloaded in stance and gait and, more importantly, how one can use certain interventions to offload the plantar fascia.

Defusing The Standard Assumptions About Custom Foot Orthoses

   It is well recognized that the plantar aponeurosis or plantar fascia is the most important static stabilizer of the arch of the human foot. In dynamic gait, the plantar fascia, through the windlass mechanism, has a threefold greater arch supporting power than the posterior tibial tendon.8    Podiatric physicians have long assumed that elongation strain on the plantar fascia occurs when external forces lower the longitudinal arch of the foot. While this is partially true, the assumption that functional foot orthoses will “raise” the arch is not correct. Furthermore, there has been a suggestion from research published in the biomechanics literature that traditional foot orthoses may actually increase strain on the plantar fascia.9    The rationale behind using custom functional foot orthoses to treat plantar fasciitis is based upon the Root theory of improving foot function. Decreasing abnormal foot movements (i.e. pronation) enhances the stability of the midtarsal joint. This minimizes the instability of the “arch” and decreases strain on the plantar fascia.    Assuming that foot orthoses will offload the plantar fascia by preventing pronation is shortsighted and erroneous in many cases. Scherer, et. al., showed in a large group of patients with plantar heel pain that the predominant foot type compensated for some type of deformity via supination of the forefoot at the midtarsal joint.10 These three foot types include a forefoot valgus, a plantarflexed first ray and any condition in which the rearfoot is everted on the forefoot in stance.    When given the choice of extrinsic posting for custom foot orthoses, most podiatric physicians in this country would opt for varus posting. Yet research has shown that applying a medial forefoot wedge under the feet of cadaver specimens actually increases strain on the central band of the plantar fascia.11 This same study showed lateral (valgus) forefoot wedges decreased strain in all of the specimens tested.    Therefore, in a small study of cadaveric feet, lateral wedging of the forefoot decreased strain in the plantar fascia while medial wedges increased strain. This validates Scherer’s previous observations that inverting or supinating the forefoot or the rearfoot would increase strain on the central band of the plantar fascia.10 These findings may appear contrary to common podiatric treatment strategies but are valid when one looks at the function of the plantar fascia from an engineering perspective.

Understanding The Biomechanics Of Plantar Fascia Overload

   The plantar aponeurosis of the human foot has three segments: a medial, central and lateral band. The medial and lateral portions are thin fascial coverings of the abductor hallucis and abductor digiti minimus muscle bellies respectively. The strong central band originates primarily from the medial calcaneal tubercule and is the structure most commonly implicated as the source of subcalcaneal pain. The medial portion of the central band appears to be the point of maximal tenderness in most patients with subcalcaneal pain. This portion is directly connected to the sesamoid apparatus and the base of the proximal phalanx of the first metatarsophalangeal joint (MTPJ).    The medial central band of the plantar fascia is an integral structure of the truss mechanism of the medial arch of the foot. From an engineering standpoint, a truss is a triangular structure that contains three elements: two beams or struts and a single connecting tie rod. By placing this triangle upright and applying a load to the apex, the tie rod connecting the beams at the base minimizes compressive stress on the two beams. Lapidus initially described the truss mechanism. He delineated the two beam segments as the first metatarsal-medial cuneiform and navicular (first ray); and the calcaneus and talus. The tie rod was the central band of the plantar fascia.    In his research on plantar fascia strain, Kogler points out that the talonavicular joint is the apex of the medial arch and is also the junction of the two beams of the truss mechanism of the foot.11 Kogler found that foot orthoses which raised the talonavicular joint and prevented dorsiflexion of the distal strut (first ray) were most effective in reducing strain in the central band of the plantar fascia.    Sarrafian has proposed a “twisted plate” model of the human foot which can also explain how wedging of the forefoot can raise the arch and decrease strain of the plantar fascia.12 Sarrafian believes the evolution of the foot started with a flat plate of bones which gradually assumed a “twisted” configuration whereby the talus ended up on top of the calcaneus while the forefoot remained plantargrade. The twisting movement was an inversion of the rearfoot on the forefoot. This allowed formation of the medial longitudinal arch spanned by the central band of the plantar aponeurosis.    According to that model, one can further raise the arch by further “twisting” of the plate (i.e., inverting the rearfoot on the forefoot or everting the forefoot on the rearfoot). Sarrafian also showed the plate becomes “untwisted” and the arch lowers when the forefoot is inverted by applying a medial (varus) forefoot wedge.    Understanding the truss mechanism and accepting the research of Scherer, Kogler and Sarrafian, one can try to develop strategies to offload the medial central band of the plantar fascia. The first strategies are related to using custom functional foot orthoses while some other treatment methods outside of orthotic use will also be suggested. No controlled clinical studies have been conducted to prove the efficacy of any of these interventions. In fact, few have undertaken randomized controlled clinical trials to validate the treatment success of most treatment protocols for plantar heel pain syndrome.

Essential Keys To Preventing Dorsiflexion Overload Of The First Ray

   The distal strut of the truss mechanism of the human foot is the first ray and may be the most important structure in terms of reducing strain in the plantar fascia. Our strategy here is quite simple. The less the first metatarsal dorsiflexes, the less elongation strain occurs in the medial portion of the central band of the plantar fascia.    Many well-meaning podiatric physicians will actually dispense devices that will dorsiflex or overload the first ray. This can occur when one takes the neutral suspension cast in a supinated position or when the clinician uses foam boxes in the casting process.    Also keep in mind that many orthotic fabrication laboratories have abandoned the original Root protocol in establishing the proper width of the functional foot orthosis in the forefoot. According to Root principles, one should trim the orthosis medially to a line that bisects the first metatarsal. This will allow the first ray to plantarflex medially off the orthosis during terminal stance. If the orthotic footplate is wider than the bisection of the first metatarsal, this will inhibit the first ray from plantarflexing after heel rise and blockage of the windlass mechanism will occur. To improve plantarflexion of the first ray during stance and gait, I recommend the following orthotic strategies:    • Push down on the first metatarsal during the negative casting process. This will optimize the position of the first ray and enable one to capture a valgus forefoot to rearfoot relationship. Accordingly, this helps ensure a lateral forefoot wedging effect of the balanced foot orthoses.    • Make sure the lab trims the footplate according to Root Functional Theory. Trim the plate at the bisection of the first metatarsal.    • Consider using a first ray cutout to ensure freedom of the first ray to plantarflex below the plane of the lesser metatarsals. This is especially important when the patient demonstrates a forefoot varus deformity.    • Consider adding a reverse Morton’s extension. This elevates the lesser metatarsals and allows the first ray to drop into plantarflexion. This may be especially important when the patient demonstrates a forefoot valgus deformity. The patented Kinetic Wedge® (invented by Howard Dananberg, DPM) is another technique to enhance first ray plantarflexion during the propulsive phase of gait.    • When the negative cast shows a varus of metatarsals two through five, and a valgus of metatarsals one through five in the forefoot, ask the lab to use “no filler” between the forefoot platforms. This will again ensure that the first metatarsal lies below the plane of the lesser metatarsals and the orthotic footplate will not cause dorsiflexion.

Why It Is Vital To Support The Talonavicular Joint

   The talonavicular joint is the apex of the truss of the foot. If one can apply elevation specifically to this joint, this will reduce vertical load on the two beams and elongation strain in the tie rod (plantar fascia).    Unfortunately, this is easier said than done. As Kogler pointed out in his paper, the traditional Root foot orthosis does not contact or directly support the talonavicular joint.9 Essentially, the trim lines of this device fall slightly lateral to the axis of rotation of this joint. Furthermore, it is common practice for custom foot orthotic labs to add plaster “expansion” to the positive cast in this area to reduce the chance of arch irritation by the orthotic.    If one employs a proper neutral suspension cast technique, it is not necessary for the lab to add plantar arch fill to the cast under the talonavicular joint. If using foam boxes or relying on pressure mapping to produce a model of the patient’s foot, then one will not obtain an orthotic that contours tightly to the talonavicular joint. Follow proper Root suspension casting technique and ask the lab to use no plaster arch fill on the positive cast. Also ask the lab to modify the trim lines to ensure the orthotic supports the talonavicular joint. At the same time, one must attend to the trim lines under the first ray to ensure they fall no further medially than the bisection of the first metatarsal.

What You Should Know About The Proximal Strut

   The proximal strut is the talus and the calcaneus. One can raise this strut by increasing calcaneal pitch. To some, this means supinating the foot whereas others believe it means decreasing pronation of the foot. A more realistic view is the fact that the most important area of contour of a custom functional foot orthosis to the bottom of the foot is the plantar portion of the heel cup and the junction of the heel cup to the mid-portion of the orthotic foot plate. The distal portion of the heel cup contours to the body of the calcaneus and prevents plantarflexion of the calcaneus.    The lab must fill this part of the positive cast and this part of the orthotic must tightly contour to the patient’s foot. Keep the lab on notice by periodically checking positive casts to ensure that the plantar surface of the calcaneus has not been filled with plaster.

How To Reduce Tension In The Heel Cord

   The tendo-Achilles is the most powerful arch-lowering influence on the foot. Not only does the calf musculature exert the strongest plantarflexion moment on the ankle joint, this force occurs through the midfoot to the metatarsophalangeal joints. When the osseous-ligamentous locking mechanism of the midtarsal joint stabilizes the midfoot, the plantarflexion moment of the tendo-Achilles exerts to the metatarsal heads. The metatarsal heads plantarflex on the fixed toes during the propulsive phase of gait. If the midfoot is unlocked and unstable, the tendo-Achilles exerts a plantarflexion moment of the rearfoot upon the forefoot, which results in lowering the proximal strut of the truss mechanism.    Podiatric physicians have long recognized that a tight heel cord will cause compensatory pronation of the foot at the subtalar and midtarsal joints. Pronation at these joints also causes lowering of the medial longitudinal arch and increased strain in the plantar fascia.    Functional foot orthoses can “shield” the plantar fascia to some extent from the damaging influence of the tendo-Achilles. By locking the midtarsal joint and preserving a rigid beam effect of the midfoot, one can expect a functional foot orthosis to minimize sagittal plane deforming forces on the medial arch. At the same time, when there is significant equinus deformity, a functional foot orthosis is not adequate to dissipate the powerful deforming force of the heel cord. Therefore, patients will not tolerate orthotic interventions designed to minimize midtarsal joint collapse. Therefore, one must employ other measures to decrease the force of the tendo-Achilles on the plantar fascia.

What The Literature Reveals About Static Stretching, Night Splints And Footwear

   • Static stretching. Perhaps no other treatment for plantar heel pain is so universally agreed upon by practitioners from multiple disciplines than having a patient perform a regular program of calf and Achilles stretching. Numerous studies have shown that heel cord stretching by itself is one of the most effective treatments for relieving plantar heel pain.13-15    Not only will stretching theoretically decrease plantarflexion moment on the proximal strut of the truss mechanism of the arch, there may be a decreased strain directly on the insertional area of the central band of the plantar fascia on the calcaneus. Surgeons and anatomists have agreed that the insertion of the tendo-Achilles blends almost imperceptibly with the origin of the central band of the plantar fascia. The failure of the plantar fascia at the calcaneal attachment may be the result of a two-way deforming force in both a proximal and distal direction.    • Night splints. Several studies have documented the efficacy of night splints to treat plantar heel pain syndrome.16,17 While some studies have shown less promising results, one has to recognize the advantage of night splints in preventing contracture of both the heel cord and plantar fascia during the prolonged positioning of sleep. If these splints prevent morning pain when patients get up, it is theorized that less trauma is occurring to the injured fascia and healing is occurring. While this treatment does not offload the plantar fascia, one should consider it as an adjunct to other treatment interventions.    • Footwear. Proper footwear can not only decrease strain in the heel cord but also stabilizes the midtarsal joint and indirectly offloads the plantar fascia. Kogler’s research indicated that in static stance, the simple elevation of the heel was not enough to offload the plantar fascia adequately.18 The contoured shank profile of a shoe coupled with a heel lift was more effective in offloading the plantar fascia. Therefore, a shoe with a stiff, contoured shank may stabilize the midtarsal joint and when one combines this with heel elevation of at least 2 cm, it should significantly offload the plantar fascia.    There is also a theory that many feet have a disproportionate amount of pressure on their heels, as opposed to the forefoot, in static stance. This is not always predictable by assessing foot type but clinicians can easily detect this via pressure mapping with a Matscan® or similar instrumentation. By emphasizing heel elevation for these patients, either through footwear or heel lifts, a shift of pressure can occur from the heel to the forefoot. Less pressure on the heel may decrease direct trauma on the injured fascia.

In Summary

   Plantar heel pain syndrome is most commonly associated with elongation strain and subsequent degeneration of the plantar fascia near its origin on the medial calcaneal tubercule. Podiatric physicians commonly apply biomechanical principles in treatment protocols for plantar fasciitis. The Root theory of foot orthotic therapy has potential for significant positive effects in offloading the plantar fascia if practitioners as well as orthotic fabrication laboratories follow the principles of the theory.    In addition, several modifications of traditional orthotic therapy may further offload the plantar fascia and enhance clinical outcomes in the treatment of this common podiatric malady. Dr. Richie is an Adjunct Associate Professor in the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt College. He is the Immediate Past President of the American Academy of Podiatric Sports Medicine.
 

References:

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