• View in gallery

    Cadaveric dissection of the plantar surface of the foot revealing the proximal attachment sites of the plantar fascia and the flexor digitorum brevis and abductor hallucis muscles.

  • View in gallery

    Cadaveric dissection of the plantar surface of the foot revealing the proximal attachment site of the medial and lateral heads of the quadratus plantae muscle after the plantar fascia and the flexor digitorum brevis and abductor hallucis muscles have been reflected.

  • 1

    Thomas J, Christensen J, Kravitz S, et al: The diagnosis and treatment of heel pain: a clinical practice guideline-revision. J Foot Ankle Surg 49: S1, 2010.

    • Crossref
    • PubMed
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 2

    Dunn JE, Link CL, Felson DT, et al: Prevalence of foot and ankle conditions in a multiethnic community sample of older adults. Am J Epidemiol 159: 491, 2004.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3

    Rome K, Howe T, Haslock I: Risk factors associated with the development of plantar heel pain in athletes. The Foot 11: 119, 2001.

  • 4

    Riddle DL, Pulisic M, Pidcoe P, et al: Risk factors for plantar fasciitis: a matched case-control study. J Bone Joint Surg Am 85: 872, 2003.

  • 5

    Moore K, Dalley A, Agur A: “Lower Limb,” in Clinically Oriented Anatomy, 7th Ed, edited by K Moore, A Dalley, A Agur, p 610, Lippincott Williams & Wilkins, Baltimore, 2014.

    • Search Google Scholar
    • Export Citation
  • 6

    Stecco C, Corradin M, Macchi V, et al: Plantar fascia anatomy and its relationship with Achilles tendon and paratenon. J Anat 223: 665, 2013.

    • Crossref
    • PubMed
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 7

    McKeon PO, Hertel J, Bramble D, et al: The foot core system: a new paradigm for understanding intrinsic foot muscle function. Br J Sports Med 49: 290, 2015.

    • Crossref
    • PubMed
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 8

    Leardini A, Benedetti MG, Berti L, et al: Rear-foot, mid-foot and fore-foot motion during the stance phase of gait. Gait Posture 25: 453, 2007.

    • Crossref
    • PubMed
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 9

    Kelly LA, Cresswell AG, Racinais S, et al: Intrinsic foot muscles have the capacity to control deformation of the longitudinal arch. J Royal Soc Interface11: 20131188; doi: .

    • Crossref
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 10

    Kelly LA, Lichtwark G, Cresswell AG: Active regulation of longitudinal arch compression and recoil during walking and running. J Royal Soc Interface12: 20141076; doi: .

    • Crossref
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 11

    Fyfe I, Stanish WD: The use of eccentric training and stretching in the treatment and prevention of tendon injuries. Clin Sports Med 11: 601, 1992.

  • 12

    Kelly LA, Kuitunen S, Racinais S, et al: Recruitment of the plantar intrinsic foot muscles with increasing postural demand. Clin Biomech 27: 46, 2012.

    • Crossref
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 13

    Selvanetti A, Cipolla M, Puddu G: Overuse tendon injuries: basic science and classification. Oper Tech Sports Med 5: 110, 1997.

  • 14

    Diehl P, Gollwitzer H, Schauwecker J, et al: Conservative treatment of chronic tendinopathies. Orthopade 43:183, 2014.

    • Crossref
    • PubMed
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 15

    Walden G, Liao X, Donell S, et al: A clinical, biological, and biomaterials perspective into tendon injuries and regeneration. Tissue Eng 23: 44, 2017.

    • Crossref
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 16

    Alfredson H, Bjur D, Thorsen K, et al: High intratendinous lactate levels in painful chronic Achilles tendinosis: an investigation using microdialysis technique. J Orthop Res 20: 934, 2002.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17

    Sharma P, Maffulli N: Biology of tendon injury: healing, modeling and remodeling. J Musculoskelet Neuronal Interact 6: 181, 2006.

Proximal Plantar Intrinsic Tendinopathy: Anatomical and Biomechanical Considerations in Plantar Heel Pain

Sean Christie PT, DPT1,2, Gary Styn Jr MD1, Gregory Ford PT, DPT, PhD, OCS1, and Karl Terryberry PhD1
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  • 1 Department of Physical Therapy, Daemen College, Buffalo, NY.
  • | 2 North Hills Orthopedic and Sports Physical Therapy, Pittsburgh, PA.

Plantar heel pain is often managed through podiatric and physical therapy interventions. Numerous differential diagnoses may be implicated in patients presenting with plantar heel pain; however, symptoms are often attributed to plantar fasciitis. Abductor hallucis, flexor digitorum brevis, and quadratus plantae share proximal anatomic attachment sites and mechanical function with the plantar fascia. Although these plantar intrinsic muscles each perform isolated digital actions based on fiber orientation and attachment sites, they function collectively to resist depression of the lateral and medial longitudinal arches of the foot. Overuse injury is the primary contributing factor in tendinopathy. The close anatomic proximity and mechanical function of these muscles relative to the plantar fascia suggests potential for proximal plantar intrinsic tendinopathy as a result of repetitive loading during gait and other weightbearing activities. To date, this diagnosis has not been proposed in the scientific literature. Future studies should seek to confirm or refute the existence of proximal plantar intrinsic tendinopathic changes in patients with acute and chronic plantar heel pain through diagnostic imaging studies, analysis of lactate concentration in pathologic versus nonpathologic tendons, and response to specific podiatric and physical therapy interventions germane to tendinopathy of these muscles.

Plantar heel pain is often managed through podiatric and physical therapy interventions. Numerous differential diagnoses may be implicated in patients presenting with plantar heel pain; however, symptoms are often attributed to plantar fasciitis. Abductor hallucis, flexor digitorum brevis, and quadratus plantae share proximal anatomic attachment sites and mechanical function with the plantar fascia. Although these plantar intrinsic muscles each perform isolated digital actions based on fiber orientation and attachment sites, they function collectively to resist depression of the lateral and medial longitudinal arches of the foot. Overuse injury is the primary contributing factor in tendinopathy. The close anatomic proximity and mechanical function of these muscles relative to the plantar fascia suggests potential for proximal plantar intrinsic tendinopathy as a result of repetitive loading during gait and other weightbearing activities. To date, this diagnosis has not been proposed in the scientific literature. Future studies should seek to confirm or refute the existence of proximal plantar intrinsic tendinopathic changes in patients with acute and chronic plantar heel pain through diagnostic imaging studies, analysis of lactate concentration in pathologic versus nonpathologic tendons, and response to specific podiatric and physical therapy interventions germane to tendinopathy of these muscles.

In addition to other sources of pathology, plantar heel pain may derive from plantar fasciitis, plantar fasciosis, or heel spur syndrome. It is the most prevalent disorder in patients seeking attention from foot/ankle specialists.1 Dunn et al2 estimate the prevalence of pain and tenderness to be 6.9% in the plantar fascia and 4.2% in the plantar heel pad in individuals older than 65 years. Rome et al3 report a 21.7% prevalence of plantar heel pain in individuals with a mean ± SD age of 24.6 ± 7.7 years. Mechanical abnormality is the most common cause of plantar heel pain; however, arthritic, neurologic, traumatic, or other systemic conditions may also play a role.1 Symptoms of plantar heel pain may resolve naturally over a few days to weeks or may persist, becoming chronic.

Annually, an estimated 2 million Americans are affected by plantar fasciitis.4 Clinical presentations characteristic of plantar fasciitis often reveal localized pain and tenderness along the central region of the midfoot where the fascia thickens, the medial tubercle of the calcaneal tuberosity, or the inferior central region of the calcaneal tuberosity.1 In addition, pain with the first few steps in the morning that eases with short-distance ambulation throughout the day, but later returns, is also characteristic of plantar fasciitis.1 It is not uncommon in clinical settings for plantar heel pain to be readily attributed to the plantar fascia. This, however, hinders unbiased consideration of alternative structures that may be involved. Assuming that radiographic imaging has ruled out heel spur syndrome and conservative management of plantar fasciitis or fasciosis has not yielded a favorable outcome, clinicians should consider alternative anatomical sources of pathology that are closely related to the structure and function of the plantar fascia.

Anatomy of the Plantar Fascia

The plantar fascia is a mediolateral continuation and thickening of the crural fascia on the plantar surface of the foot comprised of longitudinal, transverse, and vertical dense regular connective tissue fibers.5 In addition, Stecco et al6 identified the presence of oblique fibers in the microscopic portion of their study. The plantar fascia is an inert structure functioning to preserve the integrity of the lateral longitudinal arch and the more prominent medial longitudinal arch (MLA) of the foot during weightbearing activities. The plantar fascia attaches proximally to the medial tubercle of the calcaneal tuberosity, thickens centrally in the region of the midfoot, and extends distally as five longitudinal bands to blend with the tendinous sheaths enveloping the flexor digitorum longus, flexor digitorum brevis (FDB), flexor hallucis longus, and flexor hallucis brevis muscles.5 Although there is a clear and accepted proximal attachment of the plantar fascia to the calcaneus, Stecco et al6 revealed a 1- to 2-mm band of tissue corresponding to the calcaneal periosteum joining the plantar fascia with the paratenon of the Achilles tendon. Superficial to the plantar surface of the metatarsal heads, the superficial transverse metatarsal ligament attaches to these longitudinal bands to maintain the adjacent interlongitudinal fiber distances. The vertical fibers of the plantar fascia are multitudinous and function to limit shear forces between the plantar subcutaneous tissue and plantar fascia by way of insertion in the superficial fascia.5 Whereas the plantar fascia is inert, superficial, and most commonly attributed to plantar heel pain, numerous dynamic structures immediately deep and adjacent to the plantar fascia serve a similar function and attach to the same region of the calcaneus.

Dynamic MLA Integrity

The plantar intrinsic foot muscles abductor hallucis (AH) and FDB share attachment to the medial calcaneal tubercle with the plantar fascia, as shown in Figure 1. In isolation, the AH muscle will abduct and flex the great toe at the metatarsophalangeal joint. The FDB muscle will flex the lateral four digits at the proximal interphalangeal and metatarsophalangeal joints. The medial head of the quadratus plantae (QP) muscle does not attach specifically to the medial calcaneal tubercle; however, it does attach to the medial plantar surface of the calcaneus just anterior to the medial calcaneal tubercle. Although the QP muscle does not perform an isolated digital action, the two heads converge on the posterolateral margin of the tendon of the flexor digitorum longus muscle to posteriorly redirect the posteromedial line of action of the flexor digitorum longus muscle. The proximal and distal attachments relative to the action of the QP muscle are visualized in Figure 2.

Figure 1. . Cadaveric dissection of the plantar surface of the foot revealing the proximal attachment sites of the plantar fascia and the flexor digitorum brevis and abductor hallucis muscles.
Figure 1

Cadaveric dissection of the plantar surface of the foot revealing the proximal attachment sites of the plantar fascia and the flexor digitorum brevis and abductor hallucis muscles.

Citation: Journal of the American Podiatric Medical Association 109, 5; 10.7547/17-198

Figure 2. . Cadaveric dissection of the plantar surface of the foot revealing the proximal attachment site of the medial and lateral heads of the quadratus plantae muscle after the plantar fascia and the flexor digitorum brevis and abductor hallucis muscles have been reflected.
Figure 2

Cadaveric dissection of the plantar surface of the foot revealing the proximal attachment site of the medial and lateral heads of the quadratus plantae muscle after the plantar fascia and the flexor digitorum brevis and abductor hallucis muscles have been reflected.

Citation: Journal of the American Podiatric Medical Association 109, 5; 10.7547/17-198

Although each of these plantar intrinsic muscles performs individualized actions, their primary role is collective in maintaining the MLA of the foot during weightbearing activities.5 McKeon et al7 further elaborate on this in likening the core of the foot to the core of the lumbopelvic spine in that dynamic stability is achieved through the interactions among passive, active, and neural subsystems. In relation to the core of the foot, the dynamic role of the plantar intrinsic muscles in weightbearing activities is included in the active subsystem7 in addition to the various extrinsic muscles of the anterior, lateral, superficial-posterior, and deep-posterior compartments of the anatomical leg. With closed-kinematic-chain pronation during the early stance phases of the gait cycle and other dynamic weightbearing activities, the calcaneus everts with coupled talar plantarflexion and adduction. The talar head subsequently depresses the MLA, placing a tensile load on the plantar fascia and resulting in an increased posteroanterior dimension of the foot.8,9 The plantar intrinsic muscles allow this depression via eccentric contraction,10 which transmits the greatest amount of stress to tendons.11 The intrinsic muscles are then active in maintaining the end physiologic range of MLA depression via isometric contraction in midstance. In their electromyographic study, Kelly et al12 identified a strong correlation between AH, FDB, and QP muscle activation during center-of-pressure translation t the medial border of the foot during single-limb stance. This correlation relates to the proposed mechanisms of proximal plantar intrinsic tendinopathy in that these muscles are recruited during the unilateral stance phase of the gait cycle as the center of pressure courses from lateral in heel strike, lateral in flatfoot, medial in midstance, and medial to the first metatarsal head during push-off. Although the passive tensile checkrein function of the plantar fascia limits depression of the MLA, the plantar intrinsic muscles attaching to the medial calcaneal tubercle actively generate tension to draw the forefoot posteriorly toward the calcaneus as the foot/ankle complex begins to supinate in later stance phases of the gait cycle. The notion of proximal stability for distal mobility applies to all mobile segments of the body. Germane to foot and ankle biomechanics, the forefoot translates anteriorly with weightbearing as tension of the plantar fascia is directed to the stable medial calcaneal tubercle, where point tenderness is often present. The same mechanical model applies throughout weightbearing and the gait cycle to the plantar intrinsic muscles immediately deep to the plantar fascia with respect to their collective action and shared proximal attachment site with the plantar fascia.

Tendinopathy

Although small compared with other tendons subjected to tendinopathic changes, these plantar intrinsic muscles each attach to the plantar calcaneus by way of their proximal tendons. With repetitive use and submaximal load, tendinous microtrauma and corresponding lesions may develop should tenocytes and their corresponding extracellular matrix fail to adapt to these pathologic stimuli.13 These overuse injuries are the primary etiology of tendinopathies.14,15 With repetitive cyclic loading during gait and weightbearing activities, the plantar intrinsic muscles are predisposed to overuse and tendinopathic changes based on their collective function to actively maintain the MLA of the foot in conjunction with the plantar fascia. With tendon injury, repair is often prolonged secondary to low cellularity and poor vascular supply.14 In addition to the slow healing characteristics of tendon, the daily contractile repetition in gait and other weightbearing activities affords minimal time for recovery and healing of the potentially microtraumatized proximal tendon(s). The physical principle of cross-sectional area in relation to load tolerance before tissue failure should be considered regarding the functional responsibilities of the plantar intrinsic musculature. As is visible in Figure 2, the tissue substances of the AH, FDB, and the medial head of the QP muscles are appreciably small given their mechanical responsibilities in weightbearing. In Figures 1 and 2, viewers can appreciate the morphological similarities between these intrinsic muscles and the plantar fascia. With these similar morphological characteristics, proximal anatomical attachment site, and functional responsibilities in static and dynamic weightbearing activities, a diagnosis of plantar fasciitis likely involves more structures than the plantar fascia alone.

Conclusions

To our knowledge, proximal plantar intrinsic tendinopathy has yet to be proposed and subsequently investigated in the physical therapy and medical literature. Based on the similar proximal anatomical attachment site and collective function of the AH, FDB, and medial head of the QP muscles relative to the plantar fascia, there is potential for these structures to be involved, pathologically, in patients with plantar heel pain. In patients with plantar heel pain attributed to the plantar fascia alone, proximal intrinsic tendinopathic changes are not deservingly considered in relation to their dynamic responsibilities similar to the inert checkrein function of the plantar fascia. Future studies should seek to investigate the existence of proximal plantar intrinsic tendinopathy through histologic analysis of the proximal osteotendinous and musculotendinous junctions as well as the proximal tendon midsubstances of the aforementioned plantar intrinsic muscles. If degenerative tendinopathic changes are revealed, research should investigate how these patients respond to conservative treatment techniques specific to tendinopathy of AH, FDB, and the medial head of the QP muscles based on their individual and collective muscle actions. Microdialysis of lactate levels in these proximal tendons may also yield compelling insights as Alfredson et al16 demonstrated a twofold increase in pathologic tendons relative to nonpathologic tendons. With tendon injury and subsequent remodeling, cross-sectional area and mass increase.17 Therefore, individuals with a history of unilateral plantar heel pain would be suitable for study in comparing structural changes with the contralateral foot. Finally, magnetic resonance imaging and ultrasonography should be performed in vivo to assess the integrity and structural features of these proximal tendons, differentiating between these muscles and the plantar fascia and corresponding junction regions in symptomatic individuals.

Financial Disclosure: None reported.

Conflict of Interest: None reported.

References

  • 1

    Thomas J, Christensen J, Kravitz S, et al: The diagnosis and treatment of heel pain: a clinical practice guideline-revision. J Foot Ankle Surg 49: S1, 2010.

    • Crossref
    • PubMed
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 2

    Dunn JE, Link CL, Felson DT, et al: Prevalence of foot and ankle conditions in a multiethnic community sample of older adults. Am J Epidemiol 159: 491, 2004.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3

    Rome K, Howe T, Haslock I: Risk factors associated with the development of plantar heel pain in athletes. The Foot 11: 119, 2001.

  • 4

    Riddle DL, Pulisic M, Pidcoe P, et al: Risk factors for plantar fasciitis: a matched case-control study. J Bone Joint Surg Am 85: 872, 2003.

  • 5

    Moore K, Dalley A, Agur A: “Lower Limb,” in Clinically Oriented Anatomy, 7th Ed, edited by K Moore, A Dalley, A Agur, p 610, Lippincott Williams & Wilkins, Baltimore, 2014.

    • Search Google Scholar
    • Export Citation
  • 6

    Stecco C, Corradin M, Macchi V, et al: Plantar fascia anatomy and its relationship with Achilles tendon and paratenon. J Anat 223: 665, 2013.

    • Crossref
    • PubMed
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 7

    McKeon PO, Hertel J, Bramble D, et al: The foot core system: a new paradigm for understanding intrinsic foot muscle function. Br J Sports Med 49: 290, 2015.

    • Crossref
    • PubMed
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 8

    Leardini A, Benedetti MG, Berti L, et al: Rear-foot, mid-foot and fore-foot motion during the stance phase of gait. Gait Posture 25: 453, 2007.

    • Crossref
    • PubMed
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 9

    Kelly LA, Cresswell AG, Racinais S, et al: Intrinsic foot muscles have the capacity to control deformation of the longitudinal arch. J Royal Soc Interface11: 20131188; doi: .

    • Crossref
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 10

    Kelly LA, Lichtwark G, Cresswell AG: Active regulation of longitudinal arch compression and recoil during walking and running. J Royal Soc Interface12: 20141076; doi: .

    • Crossref
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 11

    Fyfe I, Stanish WD: The use of eccentric training and stretching in the treatment and prevention of tendon injuries. Clin Sports Med 11: 601, 1992.

  • 12

    Kelly LA, Kuitunen S, Racinais S, et al: Recruitment of the plantar intrinsic foot muscles with increasing postural demand. Clin Biomech 27: 46, 2012.

    • Crossref
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 13

    Selvanetti A, Cipolla M, Puddu G: Overuse tendon injuries: basic science and classification. Oper Tech Sports Med 5: 110, 1997.

  • 14

    Diehl P, Gollwitzer H, Schauwecker J, et al: Conservative treatment of chronic tendinopathies. Orthopade 43:183, 2014.

    • Crossref
    • PubMed
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 15

    Walden G, Liao X, Donell S, et al: A clinical, biological, and biomaterials perspective into tendon injuries and regeneration. Tissue Eng 23: 44, 2017.

    • Crossref
    • Web of Science
    • Search Google Scholar
    • Export Citation
  • 16

    Alfredson H, Bjur D, Thorsen K, et al: High intratendinous lactate levels in painful chronic Achilles tendinosis: an investigation using microdialysis technique. J Orthop Res 20: 934, 2002.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17

    Sharma P, Maffulli N: Biology of tendon injury: healing, modeling and remodeling. J Musculoskelet Neuronal Interact 6: 181, 2006.

Corresponding author: Sean Christie, PT, DPT, 5551 Copper Dr, Apt 205, Erie, PA 16509. (E-mail: sean.christie@daemen.edu)