strain estimations of the plantar fascia and other
TRANSCRIPT
Graduate Theses and Dissertations Iowa State University Capstones, Theses and Dissertations
2021
Strain estimations of the plantar fascia and other ligaments of the Strain estimations of the plantar fascia and other ligaments of the
foot: Implications for plantar fasciitis foot: Implications for plantar fasciitis
Jeff Mettler
Follow this and additional works at: https://lib.dr.iastate.edu/etd
Strain estimations of the plantar fascia and other ligaments of the foot: Implications for
plantar fasciitis
by
Jeffrey Howard Mettler
A dissertation submitted to the graduate faculty
in partial fulfillment of the requirements for the degree of
DOCTOR OF PHILOSOPHY
Major: Kinesiology
Program of Study Committee:
Timothy R. Derrick, Major Professor
Jason Gillette
Gary Mirka
Panteleimon Ekkekakis
Rick Sharp
The student author, whose presentation of the scholarship herein was approved by the program
of study committee, is solely responsible for the content of this dissertation. The Graduate
College will ensure this dissertation is globally accessible and will not permit alterations after a
degree is conferred.
Iowa State University
Ames, Iowa
2021
Copyright © Jeffrey Howard Mettler, 2021. All rights reserved.
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TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS ............................................................................................................. iv
ABSTRACT .....................................................................................................................................v
CHAPTER 1. GENERAL INTRODUCTION ................................................................................1 Purpose ...................................................................................................................................... 2 Significance of Research ........................................................................................................... 3 References ................................................................................................................................. 4
CHAPTER 2. LITERATURE REVIEW .........................................................................................6 Anatomy of the Plantar Fascia ................................................................................................... 6
Functions of the Plantar Fascia .................................................................................................. 6 Plantar Fascia Loading ......................................................................................................... 8
Anatomy and Functions of Other Ligaments of the Foot ........................................................ 10 Pathogenesis of Plantar Fasciitis ............................................................................................. 14
Etiology of Plantar Fasciitis .................................................................................................... 16 Foot Structure ..................................................................................................................... 16 1st MTP Joint Range of Motion ......................................................................................... 18
Posterior Leg Muscle Tightness and Ankle Dorsiflexion Range of Motion ...................... 19 Excessive Pronation ........................................................................................................... 20
Other Kinematic Factors .................................................................................................... 22
Multi-segment foot models ...................................................................................................... 22
Treatment of Plantar Fasciitis .................................................................................................. 24 Low-Dye Taping Technique & Variations .............................................................................. 24
Pain Reduction Following Low-Dye Taping ..................................................................... 25 Postural Effects of Low-Dye Taping.................................................................................. 26 Exercise Effects on Tape .................................................................................................... 27
Kinematic Effects of Low-Dye Taping .............................................................................. 28 References ............................................................................................................................... 28
CHAPTER 3. EFFECTS OF SPEED, INCLINE, AND SHOE STIFFNESS ON PEAK
PLANTAR FASCIA STRAIN DURING WALKING ..................................................................39 Abstract .................................................................................................................................... 39
Introduction ............................................................................................................................. 40 Methods ................................................................................................................................... 42
Participants ......................................................................................................................... 42 Data Collection Procedures ................................................................................................ 42
Data Analysis ..................................................................................................................... 43 Results ..................................................................................................................................... 44 Discussion ................................................................................................................................ 46 Conclusions ............................................................................................................................. 48 References ............................................................................................................................... 49
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Figures and Tables ................................................................................................................... 51
Appendix A: Institutional Review Board Approval ................................................................ 55 Appendix B: Modifications to the Musculoskeletal Foot Model ............................................ 56
CHAPTER 4. VALIDATION OF A SIX-SEGMENT MUSCULOSKELETAL MODEL OF
THE FOOT USED TO ESTIMATE LIGAMENT STRAINS ......................................................59 Abstract .................................................................................................................................... 59 Introduction ............................................................................................................................. 60 Methods ................................................................................................................................... 62
Data Collection Procedures ................................................................................................ 62 Data Analysis ..................................................................................................................... 63
Results ..................................................................................................................................... 65 Discussion ................................................................................................................................ 66
Conclusions ............................................................................................................................. 68 References ............................................................................................................................... 68
Figures and Tables ................................................................................................................... 70
CHAPTER 5. EFFECTS OF LOW-DYE TAPING ON PLANTAR FASCIA STRAIN AND
FOOT KINEMATICS IN INDIVIDUALS WITH PLANTAR FASCIITIS .................................78
Abstract .................................................................................................................................... 78 Introduction ............................................................................................................................. 79
Methods ................................................................................................................................... 82 Participants ......................................................................................................................... 82 Data Collection Procedures ................................................................................................ 83
Data Analysis ..................................................................................................................... 84
Results ..................................................................................................................................... 85 Discussion ................................................................................................................................ 87 Conclusions ............................................................................................................................. 91
References ............................................................................................................................... 91 Figures and Tables ................................................................................................................... 95
Appendix: Institutional Review Board Approval .................................................................. 101
CHAPTER 6. GENERAL CONCLUSIONS ...............................................................................103 Summary ................................................................................................................................ 103 Significance and Future Directions ....................................................................................... 105 References ............................................................................................................................. 105
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ACKNOWLEDGMENTS
As I think back on the path that I took to get here, I am incredibly grateful to the mentors
I had along the way. First of all, I need to thank Dr. Tim Derrick, my major advisor and primary
mentor during my dissertation. Your knowledge, your patience, and your support are all so
appreciated. You gave me help when I needed help and you gave me space when I needed to
learn on my own. You taught me how to be a skilled researcher and a caring professor by
demonstrating the qualities of a skilled researcher and a caring professor. I only hope I can
exhibit the same qualities to my own students. Next is Dr. Erin Ward, who became a second
mentor to me during my time at Iowa State University. The dedication that you showed to me
and my research has not gone unappreciated. I would have never accomplished the things I did
without your help, and for that I am so grateful. I also have to acknowledge my previous
advisors, Dr. Jae Yom and Dr. Mike Pohl, as they both played a vital role in my development as
a researcher. Dr. Yom, thank you for introducing me to the research process and filling me with
an excitement for the possibilities of research. Dr. Pohl, thank you for commitment to high-
quality research. You prepared me for this process, and for that I thank you.
Finally, I want to thank all my family and friends who have been with me
throughout this process. You all have provided me with support, encouragement, and patience,
and I am so humbled and grateful for your presence in my life.
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ABSTRACT
Plantar fasciitis is thought to occur due to excessive strain of the plantar fascia. There are
numerous anatomical, biomechanical, and environmental factors that affect plantar fascia strain.
Therefore, the first purpose of this dissertation was to investigate several biomechanical and
environmental factors thought to increase plantar fascia strain. Fifteen healthy participants
walked on a treadmill at two speeds, three inclines, and two shoe stiffness levels. A four-segment
musculoskeletal model of the foot was used to analyze the data, and a significant effect of speed
was found. Furthermore, the relationship between metatarsophalangeal (MTP) joint dorsiflexion
and arch collapse was investigated, and the amount that each contributed to total plantar fascia
strain was calculated. It was found that the increase in plantar fascia strain caused by MTP joint
dorsiflexion is counteracted by the increase in arch height that occurs with MTP joint
dorsiflexion, which is due to the function of the windlass mechanism.
The second purpose was to validate a six-segment musculoskeletal model of the foot that
estimates strains of several ligaments thought to assist the plantar fascia in arch support. Seven
fresh-frozen cadaver specimens were dissected and ligament strains were directly measured
using a manual digitizer. The directly-measured strains were compared to the model-estimated
ligament strains as a way to validate the use of the model for future studies.
The third purpose was to use the six-segment musculoskeletal model to determine the
effects of a taping procedure on plantar fascia strain. Fifteen individuals with plantar fasciitis
walked overground under two barefoot conditions: an untaped condition and a low-Dye taped
condition. The low-Dye taped condition decreased the amount of arch collapse exhibited by the
participants, and although the tape did not reduce peak plantar fascia strains during walking, it
significantly reduced plantar fascia strains during midstance. We suggest that the taping method
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is effective due to its ability to reduce cumulative strain across the entire stance phase rather than
peak strain.
The final purpose was to use the musculoskeletal model to determine the effects of the
low-Dye taped condition on several ligaments thought to assist the plantar fascia in arch support.
Significant reductions of strain in the spring ligament and long plantar ligament affirm the role of
these ligaments to provide support to the medial longitudinal arch.
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CHAPTER 1. GENERAL INTRODUCTION
The medial longitudinal arch is an evolutionary development of bipedal human gait.
There are several theories that aim to explain why the arch of the human foot evolved. First, it
increases the mechanical advantage of the ankle plantar flexors, giving them enough strength to
lift the weight of the body during stance phase [1]. Second, it gives the foot spring-like qualities,
allowing the foot to absorb and return elastic strain energy during gait [2].
The plantar fascia is an integral component of normal foot function, helping to support
the medial longitudinal arch and limit subtalar pronation. Normal function of the plantar fascia is
aided by the windlass mechanism. Because of its attachment on the proximal phalanges of the
toes, toe dorsiflexion causes the plantar fascia to wind around the metatarsal heads. In a closed-
chain environment, this increases the tension in the plantar fascia, which subsequently raises the
medial longitudinal arch and produces both rearfoot supination and tibial external rotation [3,4].
Dysfunction of the plantar fascia can be debilitating and reduce an individual’s quality of life [5].
Plantar fasciitis affects up to 10% of the population [6] and results in approximately one million
patient visits to office-based physicians and hospital outpatient departments each year [7].
However, the etiology of planter fasciitis is not well understood. While plantar fascia
dysfunction is multifactorial in nature, the development of the disorder is believed to be either
inflammatory or degenerative in nature [8–10]. Research shows that excessive strain in the
plantar fascia can produce microtears and inflammation at the insertion on the medial calcaneal
tubercle [10–13]. Consequently, research efforts have focused on ways to reduce excessive
strain.
While the plantar fascia provides a significant portion of the structural support of the
arch, it is not the only tissue that contributes to arch support [2,14]. There are numerous other
2
structures, namely the foot muscles and ligaments, that help to maintain the arch. Ligaments are
passive tissues that connect bone to bone and help to maintain the stability of a joint. They resist
joint motion either outside of that joint’s normal plane of motion or beyond that joint’s total
range of motion [15]. Ligaments are elastic and will return to their original length and shape
when relaxed as long as the tension is below the yield point. However, if tension greater than the
yield point is applied to a ligament, it displays plastic characteristics and will remain partially
elongated after tension is released [15,16]. Excessive strain applied to ligaments can increase the
resting length of the ligament, which may result in a decreased amount of support provided to the
joint [16,17]. The effects of decreased support of the medial longitudinal arch can result in the
development of a flatfoot condition [17,18], which is characterized by a reduction in the height
of the medial longitudinal arch. A flatfoot condition has been cited as a risk factor for plantar
fasciitis [19–21], so it is important to study the soft tissues that support the medial longitudinal
arch. The following dissertation describes three studies that investigate the strains applied to the
soft tissues that support the medial longitudinal arch. By using a combination of experimental
and musculoskeletal modeling techniques, the studies aim to provide insight into the
pathogenesis and etiology of plantar fasciitis, as well as the development of a flatfoot condition.
Purpose
Study 1
The purpose of the first study was to examine the effects of various walking conditions
on plantar fascia strain. All possible combinations of two walking speeds (preferred walking
speed and 20% greater than preferred walking speed), three inclines (0°, 5°, and 10°), and two
shoe forefoot bending stiffnesses (stiff and flexible midsole) were performed by participants on a
standard treadmill while lower extremity and foot kinematics were recorded. A four-segment
foot model (calcaneus, talus, forefoot, hallux) was created with the inclusion of the plantar
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fascia. Plantar fascia strain due to both the windlass mechanism of the 1st metatarsophalangeal
(MTP) joint and collapse of the arch was estimated and compared to previous literature to assess
the validity of the model.
Study 2
The purpose of the second study was to validate the use of a six-segment musxuloskeletal
foot model. To validate the model, several ligaments of the foot that are believed to provide
additional support to the arch were investigated, including the spring ligament, deltoid ligament,
bifurcate ligament, and cervical ligament. An axial load was applied to the tibia of cadaver
specimens, which resulted in arch collapse. Following the axial load application, ligament strains
were measured using a manual digitizer. Systematic increases in the axial load produced
corresponding increases in the amount of arch collapse, which allowed us to quantify the amount
of strain in each ligament due to arch collapse. Following the data collection, the ligament strain
results were incorporated into the six-segment musculoskeletal foot model, which was utilized in
the third and final study.
Study 3
The purpose of the final study was to investigate the effects of the low-Dye taping
method on plantar fascia and ligament strains in individuals with plantar fasciitis during walking.
Furthermore, the study examined the kinematic effects of the low-Dye taping method. The
validated six-segment musculoskeletal model of the foot was used, which included the calcaneus,
talus, navicular and cuneiforms, cuboid, metatarsals, and hallux.
Significance of Research
Walking is a very popular exercise to increase and maintain fitness, and physicians often
recommend it because it is a low-impact, low-cost exercise that can be done anywhere.
Unfortunately, plantar fasciitis can be debilitating and limit an individual’s activity level. The
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high prevalence of the disorder, as well as the lack of understanding of its etiology, makes
plantar fasciitis an important topic of research. This dissertation focuses on strains of the plantar
fascia and several other foot ligaments and their relationship to both plantar fasciitis and the
structural integrity of the medial longitudinal arch. It is hoped that the information learned in
these studies will lead to a better understanding of plantar fasciitis development and treatment, as
well as the soft tissue structures that provide support to the medial longitudinal arch during
walking.
References
[1] D.J. Morton, Evolution of the longitudinal arch of the human foot, J. Bone Jt. Surg. 6
(1924) 56–90.
[2] R.F. Ker, M.B. Bennett, S.R. Bibby, R.C. Kester, R.M. Alexander, The spring in the arch
of the human foot, Nature. 325 (1987) 147–149.
[3] J.H. Hicks, The mechanics of the foot. II. The plantar aponeurosis and the arch., J. Anat.
88 (1954) 25–30.
[4] P.A. Tansey, P.J. Briggs, Active and passive mechanisms in the control of heel supination,
Foot Ankle Surg. 7 (2001) 131–136.
[5] D.B. Irving, J.L. Cook, M.A. Young, H.B. Menz, Impact of chronic plantar heel pain on
health-related quality of life, J. Am. Podiatr. Med. Assoc. 98 (2008) 283–289.
[6] M. DeMaio, R. Paine, R.E. Mangine, D. Drez, Plantar Fasciitis, Orthopedics. 16 (1993)
1153–1163.
[7] D.L. Riddle, S.M. Schappert, Volume of Ambulatory Care Visits and Patterns of Care for
Patients Diagnosed with Plantar Fasciitis: A National Study of Medical Doctors, Foot
Ankle Int. 25 (2004) 303–310.
[8] S.C. Wearing, J.E. Smeathers, S.R. Urry, E.M. Hennig, A.P. Hills, The pathomechanics of
plantar fasciitis, Sport. Med. 36 (2006) 585–611.
[9] H. Lemont, K.M. Ammirati, N. Usen, Plantar Fasciitis: A Degenerative Process
(Fasciosis) Without Inflammation, J. Am. Podiatr. Med. Assoc. 93 (2003) 234–237.
[10] P. Kwong, D. Kay, R. Voner, M. White, Plantar fasciitis: Mechanics and pathomechanics
of treatment, Clin. Sports Med. 7 (1988) 119–126.
5
[11] D.B. Thordarson, P.J. Kumar, T.P. Hedman, E. Ebramzadeh, Effect of Partial Versus
Complete Plantar Fasciotomy on the Windlass Mechanism, Foot Ankle Int. 18 (1997) 16–
20.
[12] G.C. Hunt, T. Sneed, H. Hamann, S. Chisam, Biomechanical and histiological
considerations for development of plantar fasciitis and evaluation of arch taping as a
treatment option to control associated plantar heel pain: A single-subject design, Foot. 14
(2004) 147–153.
[13] R. Puttaswamaiah, P. Chandran, Degenerative plantar fasciitis : A review of current
concepts, 17 (2007) 3–9.
[14] C. Cifuentes-De la Portilla, R. Larrainzar-Garijo, J. Bayod, Analysis of the main passive
soft tissues associated with adult acquired flatfoot deformity development: A
computational modeling approach, J. Biomech. 84 (2019) 183–190.
[15] M.L. Root, W.P. Orien, J.H. Weed, Normal and Abnormal Function of the Foot, Clinical
Biomechanics Corporation, 1977.
[16] T.G. McPoil, G.C. Hunt, Evaluation and management of foot and ankle disorders: Present
problems and future directions, J. Orthop. Sports Phys. Ther. 21 (1995) 381–388.
[17] H.B. Kitaoka, Z.P. Luo, K.N. An, Mechanical behavior of the foot and ankle after plantar
fascia release in the unstable foot, Foot Ankle Int. 18 (1997) 8–15.
[18] G.A. Arangio, C. Chen, W. Kim, Effect of cutting the plantar fascia on mechanical
properties of the foot, Clin. Orthop. Relat. Res. (1997) 227–231.
[19] I.S. Davis, R. Ferber, J. Hamill, C. Pollard, Rearfoot mechanics in competitive runners
who had experienced plantar fasciitis, in: Proc. 29th Annu. Meet. Int. Soc. Biomech.,
2003.
[20] B.L. Warren, C.J. Jones, Predicting plantar fasciitis in runners, Med. Sci. Sports Exerc. 19
(1987) 71–73.
[21] J.E. Taunton, M.B. Ryan, D.B. Clement, D.C. McKenzie, D.R. Lloyd-Smith, Plantar
fasciitis: A retrospective analysis of 267 cases, Phys. Ther. Sport. 3 (2002) 57–65.
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CHAPTER 2. LITERATURE REVIEW
Anatomy of the Plantar Fascia
The plantar fascia is a large fibrous band that extends from the plantar aspect of the
calcaneus to the proximal phalanges of the five digits. The anatomy of the plantar fascia has been
well-defined in the literature [1–4]. It is divided into three components: the medial, lateral, and
central components. The medial component is very thin and acts as the fascial covering of the
abductor hallucis muscle. The lateral component originates on the lateral margin of the medial
calcaneal tubercle. It extends towards the cuboid bone, where it bifurcates into two portions. The
medial portion inserts into the base of the fifth metatarsal and the lateral portion blends into the
fascia of the abductor digiti minimi. The central component is the largest portion of the plantar
fascia, and it is considered to be the most structurally and functionally important of the three
components. It originates on the medial calcaneal tubercle on the plantar aspect of the foot.
Approximately 1.5 to 2 cm wide at its origin, the central component of the plantar fascia fans out
as it extends distally, forming five distinct slips. Each slip consists of a deep component, which
crosses the metatarsophalangeal (MTP) joint to attach to the proximal phalanx, and a superficial
component, which anchors into the subcutaneous tissues and skin. Furthermore, at the level of
the MTP joint, the superficial component of the most medial slip of the central component inserts
into the sesamoid bones before anchoring to the skin.
Functions of the Plantar Fascia
The plantar fascia plays a significant role in the foot by providing support to the
longitudinal arch during static weight bearing and foot flat phases of stance during gait [5].
During these periods, the medial longitudinal arch has been compared to a truss, with the
calcaneus, midtarsal joint, and metatarsals acting as the arch and the plantar fascia acting as the
7
tie-bar connecting the ends of the arch [6]. Under weight-bearing, the arch structure is
maintained due to tension placed on the plantar fascia [1,7]. The arch support function of the
plantar fascia has been documented in several cadaveric studies that investigated the effects of
plantar fascial release on arch structure [8,9]. Kitaoka, Luo, and An [9] reported an average arch
height decrease of 7.4 ± 4.1mm following plantar fascial release, while Murphy et al. [8]
reported a drop of 4.05 ± 1.73mm after release. A biomechanical model created to estimate the
effects of plantar fascia release on arch height found similar results. The model estimated a 17%
increase in total vertical displacement and a 15% increase in horizontal elongation of the arch
following plantar fascia release when the foot was placed under a constant load of 683N [10]. In
addition to the arch collapse that occurs in the sagittal plane, plantar fascia release also causes
alterations in the frontal and transverse plane. A finite element model that simulated release of
the plantar fascia found an increase in the talocalcaneal angle, which can be used as a measure of
foot pronation [11]. Pronation is a tri-planar motion consisting of a combination of dorsiflexion,
eversion, and abduction, and excessive pronation is often associated with an increased risk for
injury [12–14]. The results of the aforementioned finite element study [11] suggest that an
additional function of the plantar fascia is to prevent excessive pronation. The depiction of the
medial longitudinal arch as a truss is further supported by a study conducted by Kogler,
Solomonidis, and Paul [15], who found an increase in plantar fascia strain when an axial load
was placed on the tibia of seven cadaver feet. In addition to the longitudinal support provided by
the plantar fascia, significant transverse metatarsal head splaying in cadaver feet following
plantar fascial release suggests that the plantar fascia may also serve to provide support to the
transverse arch of the forefoot [16,17].
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The plantar fascia also plays an essential dynamic role during gait. Dorsiflexion of the
MTP joint activates the windlass mechanism of the plantar fascia [18–20]. When the toes are
dorsiflexed, the plantar fascia winds around the metatarsal heads. This increases the tension in
the plantar fascia and shortens the distance between the calcaneus and metatarsals, which causes
the arch to raise. The first digital slip produces the greatest amount of tension in the plantar
fascia due to the relatively large size of the first metatarsal head, as well as the presence of the
two sesamoid bones [21–23]. The windlass mechanism of the plantar fascia has been
demonstrated in a cadaveric study, where the arch height was raised following toe dorsiflexion
[5]. Furthermore, following plantar fascial release, the ability of toe dorsiflexion to increase arch
height is significantly attenuated [24] and the total toe dorsiflexion range of motion is increased
[25]. In a closed-chain environment, such as the propulsive phase during gait, the windlass
mechanism also produces rearfoot supination and tibial external rotation in addition to raising the
arch [18,26]. The windlass mechanism is also believed to increase the stability of the medial
longitudinal arch, as a study investigating first ray deformities found that the functional stability
of the arch was restored with correction of the deformity [27].
Plantar Fascia Loading
The load applied to the plantar fascia and corresponding strain values during both static
weight bearing and dynamic gait has been measured by several researchers. One of the first
studies to measure the peak strain on the plantar fascia measured plantar fascia load and strain in
tissue samples tested using a dynamometer. Wright and Rennels [28] found that the plantar
fascia could withstand a load between 890-1001N before failure, which was between 4-5%
strain. However, the authors conceded that the static measurements they collected in their study
could not be applied to dynamic conditions. Furthermore, failure of the tissue samples occurred
at the edges of the testing machine, so the authors did not consider their results to be true failure
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of the plantar fascia. A later study did measure higher loads of the plantar fascia before failure
[29]. The authors reported failure loads of 1189N, and it was noted that the majority of ruptures
occurred near the attachment of the plantar fascia on the medial calcaneal tubercle. Although the
plantar fascia was not loaded to failure in the study conducted by Kogler, Solomonidis, and Paul
[15], the authors reported strain values that were similar to Wright and Rennels [28] when they
measured plantar fascia strain relative to a given applied load in cadaver feet using a transducer
implanted directly into the plantar fascia. In contrast to these results, a later study by Gefen [30]
found significantly higher strain values relative to an applied load when radiographic
fluoroscopy was used to measure plantar fascia strain during walking. The author reported peak
fascial loads of approximately 1000N during walking with corresponding strain values between
9-12%. However, it is important to note that the study utilized a passive model of the foot and
ignored the intrinsic and extrinsic muscle contributions to loadbearing, which likely resulted in
an overestimation of strain values. Furthermore, the study only included the results of two
subjects. A methodologically similar study [31] reported an average peak fascial load of 488N
and an average peak strain of 4.8% when they used fluoroscopy to measure plantar fascia strains
during walking in eleven participants. The results of a gait simulation study using cadaver feet
also reported plantar fascia load values that were lower than the results from Gefen [30,32]. By
applying forces on the tendons of the extrinsic foot muscles to simulate the muscle action during
gait, the peak load applied to the plantar fascia during stance phase was significantly lower and
was approximately equal to bodyweight loads (538N) [32]. Finally, a study that utilized a rigid
body model to measure plantar fascia strain during walking found strain values that ranged
between 3.5-6% [22].
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An important factor that influences the load placed on the plantar fascia is the amount of
tension placed on the Achilles tendon. A tensile load placed on the Achilles tendon in a closed-
chain environment acts to produce calcaneal plantarflexion, which subsequently causes collapse
of the arch and an increased load placed on the plantar fascia. A cadaver study that investigated
the relationship between Achilles tendon tension, MTP dorsiflexion angle, and plantar fascia
strain found that dorsiflexion of the toes places more tension on the plantar fascia, which
increases the effect that a tensile force on the Achilles tendon has on plantar fascia strain [33]. In
other words, both an increase in MTP joint dorsiflexion and an increase in Achilles tendon
tension increases the strain on the plantar fascia. The same relationship between Achilles tendon
tension and plantar fascia strain has been reported using a gait simulator [32] and finite element
models of the foot [21,34]. Furthermore, a musculoskeletal model that considered both arch
collapse and MTP joint motion to estimate plantar fascia strain found that individuals running
barefoot demonstrated an average peak strain of 2.1% [35]. Interestingly, the authors also found
that the amount of total plantar fascia strain due to arch collapse was 2.0%, while the amount of
plantar fascia strain due to MTP joint dorsiflexion was 0.3%. The authors attributed their
relatively low strain values to their estimation of the plantar fascia resting length. While the exact
strain values may not be accurate, the results of the study helped to describe the relationship
between arch collapse, MTP joint motion, and plantar fascia strain, which exists regardless of the
specific strain values.
Anatomy and Functions of Other Ligaments of the Foot
As already mentioned, one of the functions of the plantar fascia is to provide structural
support to the medial longitudinal arch. However, the plantar fascia is not the only tissue that
helps to maintain the structural integrity of the arch [36–39]. There are many ligaments that
provide support to the arch and help to control excessive pronation. While considered passive
11
tissues, ligaments can help to resist tensile forces that develop when a joint moves beyond its
normal range of motion [40]. Ligaments that help to support the arch and control excessive
pronation include the long and short plantar ligaments, the spring ligament, the cervical ligament,
the bifurcate ligament, and the deltoid ligament, among others.
Collapse of the medial longitudinal arch is believed to include all three planes of motion
[11]. This is supported by the results of a cadaver study by Kitaoka, Luo, and An [9]. The
authors found that sectioning the plantar fascia, long and short plantar ligaments, spring
ligament, and several other ligaments to induce an unstable foot affected joint rotations of the
foot. Importantly, there were kinematic effects in all three planes of motion, suggesting that these
structures may help to prevent excessive pronation. Furthermore, the process involves both the
subtalar joint, which is the articulation of the talus and calcaneus, and the talonavicular joint.
Therefore, ligaments that cross the subtalar and talonavicular joints, such as the spring ligament,
the cervical ligament, and the bifurcate ligament, are believed to provide structural integrity to
the medial longitudinal arch. The spring ligament is composed of two components. The
superomedial component originates along the anteromedial border of the sustentaculum tali on
the calcaneus. It courses anteriorly and superiorly to attach to the middle of the navicular [41,42].
The inferior component also originates on the sustentaculum tali, but it courses anteriorly to
attach to the inferior surface of the navicular [41,42]. The cervical ligament is the strongest
ligament to connect the talus and calcaneus bones. It originates on the anteromedial segment of
the sinus tarsi and courses anteriorly and medially to attach to the inferior aspect of the talar neck
[41]. The bifurcate ligament has two components, the lateral calcaneonavicular component and
the medial calcaneocuboid component. The calcaneonavicular component originates on the
anteromedial corner of the sinus tarsi, and the calcaneocuboid component origin is slightly
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lateral. The calcaneonavicular courses anteriorly, superiorly, and medially to attach to the lateral
navicular, while the calcaneocuboid courses anteriorly and inferiorly to attach to the dorsal
cuboid [41].
The involvement of the spring ligament in arch stability is supported by the results of
Cifuentes-De la Portilla, larrainzar-Garijo, and Bayod [11], who reported that the release of the
spring ligament increased arch collapse by 14.9% and increased the talocalcaneal angle by
53.3% in a finite element model of the foot. While no research has been conducted to investigate
the role of the cervical ligament or bifurcate ligament to control excessive pronation and
maintain arch stability, anatomical descriptions of the ligaments suggest that they may be
involved. Because subtalar joint motion is directly linked to pronation, the cervical ligament,
which crosses the subtalar joint, may help to prevent excessive pronation. Furthermore, the
bifurcate ligament crosses the subtalar and talonavicular joints, which suggests it may also help
to provide stability and support to the arch.
The long and short plantar ligaments, while not strong enough to support the arch on their
own, do provide secondary support to help maintain arch height [11]. The long plantar ligament
originates on the plantar calcaneus and divides into two components as it crosses the
calcaneocuboid joint. The deep component inserts on the cuboid, while the superficial
component splits into four slips and attaches to the 2nd, 3rd, 4th, and 5th metatarsal bases [41]. The
short plantar ligament originates on the anterior tuberosity of the calcaneus and fans out until it
attaches on the cuboid [41]. The contribution of both the long and short plantar ligaments to arch
support is highlighted by the effects of plantar fascia release. Using a finite element model, Tao
et al. [37] found that release of the plantar fascia resulted in an increase in tension of the long and
short plantar ligaments by 91% and 65%, respectively.
13
The involvement of the long plantar ligament, short plantar ligament, and spring ligament
in arch stability is supported by a report from Ker et al [38], who quantified the amount of elastic
energy stored in the medial longitudinal arch as 17J. Further results in the study found that while
the stored elastic energy was reduced after sectioning of the plantar fascia, the arch continued to
store 13.3J due to the contributions of surrounding soft tissues. The authors listed the long
plantar ligament, short plantar ligament, and spring ligament as important in the maintenance of
the integrity of the arch. Another study measured the stiffness of the arch, and found that
sectioning of the plantar fascia decreased the stiffness by 25%, while sectioning the long and
short plantar ligaments and the spring ligament decreased the arch stiffness by 10% and 2%,
respectively [39]. Finally, sectioning of the plantar fascia has been demonstrated to increase
strains in the spring ligament and long plantar ligament. Under an axial load of 920N, the spring
ligament strain increased by 52% and the long plantar ligament strain increased by 94%
following plantar fascia release [43].
The anatomy of the deltoid ligament is complex and can be difficult to separate into
distinct components. It originates on the medial malleolus and fans out to attach to the navicular,
talus, and calcaneus bones. Its fan-like behavior and numerous attachments result in components
that course anteriorly, inferiorly, and posteriorly [41,44]. Consequently, the deltoid ligament
helps to stabilize the talus on the medial side of the foot [41]. The results of a study examining
the effects of dorsiflexion, plantarflexion, eversion, and inversion on ligament elongation support
the deltoid ligament’s role to provide stability to the foot and ankle [44]. The authors found that
the tibiotalar and tibiocalcaneal components of the deltoid demonstrated elongation under both
dorsiflexion and eversion, while the tibionavicular component of the deltoid demonstrated
elongation following ankle eversion [44]. A large portion of the eversion and dorsiflexion motion
14
in the study came from the ankle joint, but both the subtalar and talonavicular joints provided
additional motion as well. The elongation of the deltoid ligament due to dorsiflexion and
eversion suggests its involvement in preventing excessive pronation of the foot.
Research related to adult acquired flatfoot disorder can provide insight into the role of
ligaments in arch stability. Adult acquired flatfoot disorder is a disorder that results in functional
loss of the posterior tibial tendon. Because the disorder reduces the action of the posterior tibial
tendon as an invertor, the action of the peroneus brevis, its antagonist, is unopposed, which
increases rearfoot eversion and forefoot abduction [45]. Consequently, excessive stress is placed
on secondary ligaments and other soft tissues of the medial foot to oppose the rearfoot eversion
action of the peroneus brevis [46]. By comparing ligament degeneration using MRI between
individuals with adult acquired flatfoot disorder and controls, researchers found that the
superomedial component of the spring ligament demonstrated the most damage, suggesting it
plays a significant role in arch stability [46]. Furthermore, the inferior component of the spring
ligament and the tibionavicular component of the deltoid both showed degeneration as well,
suggesting that they also help control excessive pronation and provide stability to the arch.
Another study using MRI for diagnosis of adult acquired flatfoot disorder found a greater amount
of spring ligament injuries in the adult acquired flatfoot disorder group when compared to the
control group [47].
Pathogenesis of Plantar Fasciitis
Plantar fasciitis is estimated to affect two million people in the United States each year
[48], and up to 10% of the population will deal with the disorder at some point in their lives [49].
Planter fasciitis is defined by pain in the heel that is often localized at the insertion of the plantar
fascia on the medial calcaneal tubercle on the plantar aspect of the foot. It is frequently
associated with first step pain that lessens or resolves as the individual warms up. In more severe
15
cases, the pain may increase following prolonged standing or high levels of activity throughout
the day [50]. Several changes in the properties of the plantar fascia have been reported in
individuals with plantar fasciitis. An examination of 13 feet with plantar fasciitis and 40 healthy
feet using sonoelastography showed that individuals with plantar fasciitis exhibited plantar fascia
that were softer and less stiff than the age-matched individuals in the healthy group [51]. This is
notable as reduced elasticity in the plantar fascia makes it less resistant to strain, which may
increase the risk for injury [52]. Another effect of plantar fasciitis is a significant increase in
plantar fascia thickness near its insertion into the calcaneus [53–56]. For example, Gibbon and
Long [54] used high-resolution ultrasound to measure plantar fascia thickness in 48 healthy
volunteers and 190 patients with plantar fasciitis, and they found that the individuals with plantar
fasciitis displayed significant thickening of the plantar fascia. The authors noted the similarity in
the response at the plantar fascia to tendon injury, which results in thickening of the tendon due
to an inflammatory response. Plantar fasciitis is traditionally believed to be an inflammatory
disease, which is implied by the “-itis” suffix. The inflammation of the plantar fascia is believed
to occur due to excessive or repetitive tensile force applied to the tissue that produces
microscopic tears within the fascia, which subsequently leads to an inflammatory response
[24,49,57–59].
However, several authors have questioned the role of inflammation in the pathogenesis of
plantar fasciitis [4,60]. According to Lemont, Ammirati, and Usen [60], in addition to the
classical signs of inflammation of pain, heat, swelling, redness, and loss of function, histological
signs of inflammation, such as the presence of leukocytes, macrophages, lymphocytes and
plasma cells, should also be present. While the authors found several signs of fiber fragmentation
and degeneration in the plantar fascia of 50 individuals with chronic plantar fasciitis, they found
16
no histological signs of inflammation. Similar findings were reported by Tountas and Fornasier
[61] who analyzed 20 patients with subcalcaneal pain. Varying degrees of fascial degeneration
was found in the patients, but no signs of active inflammation were present. Consequently, this
has led some to theorize that plantar fasciitis does not result in an inflammatory response, but is
instead caused by degeneration of the fascia due to repetitive microtears that cannot be overcome
by the body’s ability to repair itself [4,50].
Etiology of Plantar Fasciitis
Despite uncertainty regarding the pathogenesis of plantar fasciitis, it is largely agreed that
the cause of plantar fasciitis is multifactorial in nature and includes anatomical, biomechanical,
and environmental factors. Several of the potential anatomical and biomechanical factors are
described below. However, environmental factors are beyond the scope of this literature review
and therefore will not be discussed.
Foot Structure
Foot structure has been theorized to contribute to plantar fasciitis risk [57,62,63]. A pes
planus foot structure is defined as a flat foot position. Consequently, a pes planus foot structure is
typically associated with excessive pronation generally defined by a collapsed arch and an
everted rearfoot position during static stance. Due to the pronated position associated with pes
planus, it is often cited as a risk factor for plantar fasciitis [57,63,64]. In 1987, Sarrafian [1]
discovered an increase in plantar fascial tension when the hindfoot and midfoot were in pronated
positions and the forefoot was in a supinated position. In this flat foot position, the medial
longitudinal arch of the foot is lower and the foot is longer. Therefore, it was concluded that a
foot in this position could place an increased tensile load on the plantar fascia, thereby increasing
the risk for microdamage and subsequent development of plantar fasciitis [57,65,66]. A study
conducted by Prichasuk and Subhadrabandhu [67] supported this conclusion, as they reported
17
that 82 patients with plantar heel pain had a lower calcaneal pitch than 400 healthy subjects in
the control group. Huang et al. [66] also discovered a higher risk for plantar fasciitis in
individuals with flat feet. They found that ten out of the 23 individuals with flat feet in their
study had plantar fasciitis, while only two out of the 23 individuals with normal arched feet had
plantar fasciitis.
Alternatively, a pes cavus foot has also been theorized to place an individual at a greater
risk for the development of plantar fasciitis [57,63]. According to Krivickas [68], a cavus foot is
rigid and lacks the ability to absorb forces, which increases the amount of stress placed on the
plantar fascia. In fact, a study conducted by Di Caprio et al. [69] found that 57.1% of the patients
with plantar fasciitis had pes cavus feet, compared to 16.7% with pes planus feet and 23.2% with
normal arches. Similar results were reported by Warren and Jones [14], who found that the
participant group with current symptoms of plantar fasciitis had higher arches than both the
participant group with resolved plantar fasciitis and the healthy control group. However, the
authors did not provide any quantitative results in their study.
Despite the studies described above, results regarding the relationship between foot
structure and plantar fasciitis have overall been inconclusive. Several studies have reported no
significant differences in arch height between individuals with plantar fasciitis and healthy
individuals [65,70,71]. The complicated relationship between foot structure and plantar fasciitis
is further elucidated by the results of Taunton et al. [13]. The authors found that of the 267
individuals with plantar fasciitis who participated in the study, only 20 had pes planus and 27
had pes cavus, which only accounts for 7.5% and 10.1% of the study population, respectively.
The results of the preceding studies highlight the multifactorial nature of plantar fasciitis. Foot
18
structure appears to play a role in the development of plantar fasciitis in some, but not all,
individuals.
In addition to the studies above that measured arch height, rearfoot eversion during static
stance can also be used as a measure of foot structure as it is an indirect measure of foot
pronation. A greater rearfoot eversion position during stance has been reported in individuals
with plantar fasciitis [14,72], which suggests a more pronated position and therefore a pes planus
foot. The results reported by Davis, Milner, and Hamill [72] support this relationship, as
individuals with plantar fasciitis in their study displayed a lower arch height in addition to
greater rearfoot eversion during static stance when compared to the healthy control group.
Rearfoot eversion also appears to have an indirect effect on plantar fascia tension. In a recent
study, Lee, Hertel, and Lee [73] reported that rearfoot eversion influences the amount of arch
collapse that occurs during gait, which consequently increases tension in the plantar fascia.
However, individuals with plantar fasciitis in the study conducted by Warren and Jones [14] had
higher arches than the control group even though they displayed a more everted rearfoot during
static stance, which suggests the relationship between arch height and rearfoot eversion is
complicated. Furthermore, studies by Allen and Gross [74] and Ribeiro et al. [75] reported no
differences in rearfoot eversion position during static stance between individuals with plantar
fasciitis and healthy individuals.
1st MTP Joint Range of Motion
Because the plantar fascia crosses the MTP joint to attach to the proximal phalanges, the
relationship between first MTP joint range of motion and plantar fasciitis has been investigated.
Creighton and Olson [76] discovered a decrease in passive extension range of motion of the first
MTP joint in runners with plantar fasciitis compared to runners without plantar fasciitis. Aranda
and Munuera [77] reported similar results in 50 individuals with plantar fasciitis when compared
19
to 50 matched control individuals. These results suggest that the plantar fascia exhibits reduced
extensibility when an individual has plantar fasciitis. Alternatively, the reduced extensibility may
precede the pathology and contribute to the development of plantar fasciitis. In contrast to the
results of Creighton and Olson [76], Allen and Gross [74] reported no differences in passive
extension range of motion of the first MTP joint between individuals with plantar fasciitis and
healthy controls.
Posterior Leg Muscle Tightness and Ankle Dorsiflexion Range of Motion
Tightness of the gastro-soleus complex increases the tension on the plantar fascia
[33,34,78]. This tightness causes a reduction in ankle dorsiflexion range of motion, which has
been cited as a risk factor for plantar fasciitis [71,72,79,80]. Clinical assessment of 254 patients
with plantar fasciitis revealed that 83% demonstrated limited ankle dorsiflexion range of motion,
26% of which were due to tightness of the gastro-soleus complex and 57% of which were due to
isolated tightness of the gastrocnemius [81]. Slightly lower but similar statistics have been
reported in other studies as well [13,82]. Furthermore, it has been found that individuals with less
than 0° of ankle dorsiflexion range of motion had an odds ratio of 23.3 when compared to
individuals with greater than 10° of dorsiflexion range of motion. Furthermore, a dorsiflexion
range of motion between 1-5° and a dorsiflexion range of motion between 6-10° resulted in odds
ratios of 8.2 and 2.9, respectively, when compared to a dorsiflexion range of motion greater than
10° [80]. These results suggest that the risk for plantar fasciitis is greatly increased as the ankle
dorsiflexion range of motion is decreased due to tightness of the gastrocnemius or gastro-soleus
complex. This is supported by the results of several studies that found a reduction of passive
ankle dorsiflexion range of motion in individuals with plantar fasciitis when compared to
individuals without plantar fasciitis [14,71,72,79]. Cornwall and McPoil [83] suggest that a
limitation in ankle dorsiflexion range of motion leads to equinus of the foot. Foot equinus results
20
in premature heel rise during gait, which can lead to abnormal pronation and subsequent
increased stress placed on the plantar fascia.
Hamstring tightness has been proposed to increase tension on the plantar fascia and
therefore increase the risk for plantar fasciitis [84,85]. It is thought that increased hamstring
tightness causes early contraction of the posterior leg muscles during the gait cycle, which
decreases ankle dorsiflexion during gait [84,86]. Harty et al [84] investigated the relationship
between hamstring tightness and plantar fasciitis risk when they compared static knee extension
flexibility between individuals with plantar fasciitis and healthy individuals. They reported a
decreased knee extension angle in the plantar fasciitis group and suggested that the increased
knee flexion may produce a forward shift in plantar foot pressures during walking, which places
increased tension on the plantar fascia. Their conclusion was further supported when they placed
healthy individuals into knee braces to limit knee extension range of motion and found that the
healthy individuals demonstrated a forward shift in plantar foot pressures as their knee extension
range of motion decreased during walking. The possible role of hamstring tightness on plantar
fasciitis was reinforced by Labovitz, Yu, and Kim [85], who revealed that 62.0% of feet with
plantar fasciitis displayed hamstring tightness on the pathological side, while only 20.6% of feet
without plantar fasciitis displayed the same muscle tightness.
Excessive Pronation
Much of the research on foot kinematics and plantar fasciitis has focused on the role of
pronation, which has often been attributed as a risk factor for plantar fasciitis [12–14]. In support
of this, 54.7% of patients with plantar fasciitis exhibited excessive pronation according to a study
conducted on 267 individuals [13]. However, it is important to note that this assessment was
performed visually. Davis et al. [12] used rearfoot eversion as a measure of pronation and found
21
that runners with plantar fasciitis exhibited significantly greater maximum rearfoot eversion
during running when compared to healthy controls.
A relationship between excessive pronation and plantar fasciitis has not always been
found, leading some to question the role of pronation in the development of plantar fasciitis
[4,70,87,88]. Again using rearfoot eversion as a measure of pronation, Davis et al. [72]
conducted a prospective study in female runners and found that females who developed plantar
fasciitis displayed no difference in peak rearfoot eversion from females who stayed healthy over
the course of the study. A study conducted by Wearing et al. [55] that used arch height as a
measure of pronation also reported no differences in maximum arch angle or range of arch
motion between a group of individuals with plantar fasciitis and a healthy control group. While
the two-dimensional nature of the study by Wearing et al. [55] is a limitation, a more
comprehensive study utilizing a multi-segment foot model to compare the foot kinematics
between individuals with plantar fasciitis and healthy individuals also found no differences in
maximum arch angle or maximum rearfoot eversion between the groups [89]. The authors did
report significantly greater total rearfoot motion in the plantar fasciitis group than the control
group, as well as greater rearfoot eversion maximum velocity in the plantar fasciitis group that
trended towards significance [89], which suggests that a relationship between pronation and
plantar fasciitis may exist, albeit a more complicated relationship. Furthermore,
Bovonsunthonchai et al. [90] reported reduced peak forefoot-rearfoot dorsiflexion angles in
individuals with plantar fasciitis compared to healthy individuals, which means that the
individuals with plantar fasciitis displayed higher arch heights. Although the study by Chang et
al. [89] reported peak forefoot-rearfoot dorsiflexion angles to be the same between individuals
with plantar fasciitis and individuals without, they did note a greater forefoot-rearfoot
22
plantarflexion angle at initial contact in individuals with plantar fasciitis. The alterations in
forefoot-rearfoot angle may serve as a protective measure to reduce the stress placed on the
plantar fascia, as a flatter arch increases the tensile load on the plantar fascia [1].
Other Kinematic Factors
While not studied as extensively as pronation, several other lower extremity kinematic
differences have been noted between healthy individuals and individuals with plantar fasciitis.
One such measure that has been reported is peak 1st MTP dorsiflexion angle, which has been
found to be greater in individuals with plantar fasciitis compared to healthy controls during
walking [55,89]. In contrast to these results, Bauer [65] reported no differences in 1st MTP joint
range of motion between plantar fasciitis patients and healthy controls during running. It has
been established that increasing toe dorsiflexion produces a direct rise in plantar fascia tension
[21,33,91]. Therefore, an increase in peak 1st MTP dorsiflexion angle during walking may
contribute to an increased risk for plantar fasciitis. Other kinematic differences reported in the
literature include increased calcaneocuboid eversion range of motion in individuals with plantar
fasciitis [65], reduced peak forefoot inversion in individuals with plantar fasciitis [90], and
reduced total rearfoot frontal plane motion in individuals with plantar fasciitis [90].
Multi-segment foot models
Conventional gait analysis utilizes models that represent the human body as a system of
rigid segments. The simplest way to represent the foot is as a single rigid segment, in which
motion of the rearfoot is measured relative to the tibia. However, research has demonstrated both
kinematic and kinetic errors associated with single-segment models [92,93]. For example,
significant differences in sagittal and frontal plane angles were reported at the ankle joint when
comparing a single-segment model to a multi-segment model in children with flat feet [93].
23
The discovery of these errors has motivated researchers to create more sophisticated
models to better represent motion of the foot. One common model used is the Milwaukee Foot
Model, a three-segment model that divides the foot into rearfoot, forefoot, and hallux segments
[94–96]. The three-segment model allows for measurement of midtarsal joint motion, as well as
first MTP joint motion. A four-segment foot model proposed by Leardini et al. [97] further
divides the medial column of the foot by separating the foot into rearfoot, midfoot, forefoot, and
hallux segments. Such a configuration allows further quantitative assessment of structural
deformities in the medial column of the foot as well as kinematics during dynamic activities,
which is particularly important when analyzing populations with midfoot deformation or
dysfunction.
Previous research has reported considerable relative motion to occur between the
metatarsals during walking [98], which suggests that modelling the forefoot as a single rigid
segment may not be appropriate. To address this issue, the Jenkyn model is a four-segment foot
model that divides the foot into hindfoot, midfoot, medial forefoot, and lateral forefoot segments
[99]. The Ghent foot model is similar to the Jenkyn model, but it is a five-segment model that
also includes the hallux segment to allow for first MTP joint measurement. The KU-Leuven foot
model is an alternative five-segment model that includes the calcaneus, talus, midfoot, forefoot,
and toes [100]. Significant motion in the lateral column of the foot has been reported in the
literature [98,101]. Consequently, a six-segment model has been utilized by some researchers,
which includes the rearfoot, medial midfoot, lateral midfoot, medial forefoot, lateral forefoot,
and hallux [65,102]. The number of segments and the desired complexity of the foot model is
dependent upon the research question. Ultimately, the researcher should choose a model that is
24
sophisticated enough to answer the research question while still producing quality data based on
the technical capabilities of the research equipment.
Treatment of Plantar Fasciitis
There are several conservative treatment options for plantar fasciitis, including rest,
physical therapy, night splints, anti-inflammatory methods, pain reduction methods, and
mechanical methods [50,103]. Treatment using anti-inflammatory methods may consist of
NSAIDs or steroid injections [104,105], while pain reduction methods may consist of analgesics
or accommodative foot pads [106]. Mechanical treatment methods may consist of custom
orthotics, over the counter shoe inserts, or night splints [107]. Orthotics are proposed to reduce
the symptoms of plantar fasciitis. This is possibly due to the orthotic helping to maintain medial
longitudinal arch height [108], as plantar fascia strain has been found to be the lowest when
wearing orthotics that maintain medial longitudinal arch height [15].
Low-Dye Taping Technique & Variations
An alternative mechanical treatment option is taping. While it is often used as a way to
determine the potential success of custom orthotics [109,110], taping has also been used as a
treatment method [59,111]. The low-Dye taping method was designed to control excessive foot
pronation by preventing medial longitudinal arch collapse [112]. It consists of an anchor strip of
tape that originates on the lateral aspect of the fifth metatarsal head, wraps behind the calcaneus,
and attaches on the medial aspect of the first metatarsal head. Then, a series of stirrups are
applied on the plantar aspect of the foot, originating on the lateral side of the foot and attaching
to the medial side. Some tension is applied to the tape during the application of the stirrups to
oppose pronation. The stirrups begin below the medial longitudinal arch and are applied on the
plantar aspect of the foot in a proximal direction until the plantar calcaneus is covered.
25
Several authors have modified the low-Dye taping method. For example, Schulthies and
Draper [113] included figure-eight strips along with the low-Dye method described above, which
they did to allow the subtalar joint to remain in a neutral position. Following the application of
the anchor strip, a strip of tape is applied which originates at the first metatarsal head, crosses the
plantar foot, wraps behind the calcaneus, and attaches back on the first metatarsal head. Saxelby,
Betts, and Bygrave [111] utilized a similar method, but the figure-eight strips originated at the
first metatarsal head, crossed the plantar foot, wrapped behind the calcaneus, and then crossed
the plantar foot again to attach on the fifth metatarsal head. Finally, the augmented low-Dye
taping method was described by Vicenzino et al. [114]. In addition to the low-Dye technique, the
authors also include two calcaneal slings and three reverse sixes. The calcaneal slings originate
on the anterior tibia, run distally towards the medial malleolus and under the midfoot, then wraps
around the calcaneus until it attaches back on its origin. The reverse sixes originate at the medial
malleolus, run around the dorsum and under the midfoot, and then run vertically to cross the
origin and then attach on the medial tibia.
Pain Reduction Following Low-Dye Taping
Many studies have demonstrated the ability of low-Dye taping to reduce pain and
improve function in plantar fasciitis patients [103,115–117]. For example, Landorf et al. [116]
found that individuals with plantar fasciitis who received low-Dye taping for three to five days
saw a significant reduction in pain when compared to a control group who did not receive taping.
There are several proposed reasons for this, including altered plantar pressures [111,118–121],
altered surrounding muscular activity [121–123], altered posture, or altered kinematics. In
general, research has found an increase of plantar pressure under the lateral midfoot and a
decrease in plantar pressure under the medial midfoot [118,119,121]. The changes in plantar
pressure under the midfoot may be accompanied by changes under the rearfoot and forefoot as
26
well [111,118,120], but these findings have been inconsistent. Few studies have investigated the
effect of low-Dye taping on muscle activation during walking, although decreases in posterior
tibialis [122–124], anterior tibialis [122–124], peroneus longus [122], and medial gastrocnemius
[124] muscle activations have been reported in healthy individuals following low-dye taping.
Postural Effects of Low-Dye Taping
The postural effects of low-Dye taping have been investigated in greater detail. More
specifically, the effects of taping on navicular height [114,123,125–132] and rearfoot eversion
[125,129,133] during static stance have been measured. Holmes, Wilcox, and Fletcher [128]
investigated the effects of the low-Dye taping method described by Schulthies and Draper [113]
on navicular height in 40 healthy subjects with flat feet. They found that after taping, the
navicular height during neutral loaded standing was not significantly different from the navicular
height when the foot was placed in the unloaded subtalar neutral position. In contrast, Vicenzino
et al. [132] reported a significant increase in medial longitudinal arch height in 18 healthy
individuals following application of augmented low-Dye tape. Harradine, Herrington, and
Wright [133] utilized the Saxelby et al. [111] low-Dye taping method when they analyzed the
effects of taping on rearfoot eversion in 22 healthy participants. They reported a static rearfoot
angle that was significantly less everted following low-Dye taping.
The majority of the studies related to the postural effects of low-Dye taping have been
conducted on healthy individuals. However, Jamali et al. [125] investigated the effects of
windlass taping on 20 individuals with plantar fasciitis. The windlass taping method utilizes the
figure-eight strips that Schulthies and Draper [113] described, but it does not include the stirrups
along the plantar foot that is characteristic of low-Dye taping. Regardless, they found a small but
significant increase in navicular height, as well as a reduction of rearfoot eversion, in the taping
condition when compared to the barefoot condition. One study investigated the effects of the
27
augmented low-Dye taping method on tibial rotation and found a significant reduction in tibial
internal rotation following taping [134].
Exercise Effects on Tape
The effects of low-Dye taping methods on foot posture following exercise have been
detailed as well. Despite an immediate increase in navicular height and reduction of rearfoot
eversion following taping, exercise results in a reduction of these effects, which has been
attributed to a loss of tensile strength of the tape due to exercise [127]. For example, after 30
minutes of walking, Harradine et al. [133] found that that there was no significant difference of
the rearfoot eversion angle between the taped condition and the barefoot condition, which
indicates a loss of tensile strength of the tape. Holmes et al. [128] also reported a significant
reduction of navicular height after 10 minutes of walking with a taped foot. However, they found
that the navicular height after 10 minutes of walking during the taped condition was still
significantly higher than the navicular height during the barefoot condition, which suggests that
taping can still provide support, even after it has lost some of its tensile strength due to exercise.
Ator et al. [127] suggested that low-Dye taping may remain effective following exercise due to
its ability to prevent pronation at the extreme ranges of motion. Vicenzino et al. [130] provided
further support to the benefits of taping even after exercise when they included a control group in
their study. When analyzing the effects of the augmented low-Dye tape method, the authors
reported a significant decrease in navicular height following 10 minutes of exercise. Importantly,
they also reported a significant decrease in navicular height following 10 minutes of exercise in
the control group. Consequently, the navicular height between the taped group and the control
group was significantly different following exercise, which suggests the tape was able to
successfully maintain the navicular height despite losing some of its strength.
28
Kinematic Effects of Low-Dye Taping
Dynamic kinematics are also affected by low-Dye taping methods. O’Sullivan et al. [135]
found a significant reduction of subtalar joint pronation during walking as a result of low-Dye
taping. Vicenzino et al. [131] and Yoho et al. [136] also both reported significant increases in
arch height during walking following low dye taping methods when compared to a barefoot
condition. However, several studies have reported no kinematic effects of low-Dye taping on
rearfoot motion during walking [133,137] and running [138]. Keenan and Tanner [137] noted
that the low-Dye taping method increased the maximum inversion angle of the rearfoot but had
no effect on the maximum eversion angle. It is clear that more research needs to be conducted on
the effects of low-Dye taping on foot kinematics using a multi-segment foot model.
References
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[3] M.R. Hedrick, The Plantar Aponeurosis, Foot Ankle Int. 17 (1996) 646–649.
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39
CHAPTER 3. EFFECTS OF SPEED, INCLINE, AND SHOE STIFFNESS ON PEAK
PLANTAR FASCIA STRAIN DURING WALKING
Jeff H. Mettlera, Erin Wardb, Timothy R. Derricka
a Department of Kinesiology, Iowa State University, 534 Wallace Rd, Ames, Iowa, 50011,
United States b Central Iowa Foot Clinic, 1302 Warford St, Perry, Iowa, 50220, United States
Modified from a manuscript under review in Gait & Posture
Abstract
Plantar fascia strain is influenced by both metatarsophalangeal (MTP) motion and arch
collapse. However, the effects of walking speed, incline, and shoe stiffness on plantar fascia
strain are unknown. Therefore, the purpose of the study was to compare the effects of speed,
incline, and shoe stiffness on peak plantar fascia strain using a musculoskeletal model of the
foot. Fifteen healthy adults participated in a repeated measures study, in which they walked on a
treadmill at two speeds, three inclines, and two shoe stiffness levels. Foot kinematics were
collected and a musculoskeletal model of the foot was used to estimate plantar fascia strain due
to MTP and midtarsal joint motion. A 2x3x2 repeated-measures ANOVA was performed to
determine the effects of speed, incline, and shoe stiffness on plantar fascia strain. Further post-
hoc tests were conducted to investigate the individual contributions of MTP and midtarsal joint
motions to total plantar fascia strain. There was a significant main effect of speed, with increased
peak plantar fascia strain during fast walking. The MTP angle at peak plantar fascia strain was
more dorsiflexed during fast walking, which resulted in significantly increased peak plantar
fascia strain due to MTP dorsiflexion and significantly increased total peak plantar fascia strain.
An increase in MTP dorsiflexion angle was found with increasing incline, but the main effect for
incline was not significant. The main effect of shoe stiffness was also not significant, meaning
peak total plantar fascia strain was not affected by incline or shoe stiffness. Our findings
40
highlight the relationship between MTP dorsiflexion and arch collapse due to the windlass
mechanism. Although increased MTP dorsiflexion angle causes increased plantar fascia strain,
the action of the windlass mechanism raises the arch height, which subsequently reduces plantar
fascia strain.
Introduction
The plantar fascia is a large fibrous band extending from the plantar aspect of the
calcaneus to the proximal phalanges of the five digits. Dorsiflexing the metatarsophalangeal
(MTP) joints causes increased plantar fascia tension in what has been termed the windlass
mechanism [1]. The plantar fascia is an integral component of normal foot function, helping to
support the medial longitudinal arch and limit subtalar pronation. Excessive strain in the plantar
fascia can produce microtears and inflammation at the insertion on the medial calcaneal tubercle
[2–5], which is believed to lead to plantar fasciitis. This condition is most commonly
characterized by pain in the plantar heel and is estimated to affect two million people in the
United States each year [6]. There are several biomechanical factors attributed to its
development, such as a tight Achilles tendon, subtalar pronation and the windlass mechanism
[7].
Research conducted in both cadavers [8] and a finite element model of the foot [9] found
that plantar fascia tensile strain (PFS) increased with MTP dorsiflexion due to the windlass
mechanism of the plantar fascia. Similar results were reported by McDonald et al. [10] when
they created a musculoskeletal model of the foot to estimate PFS. The authors [10] also
described an increase in PFS due to arch collapse, which is caused by both ground reaction
forces and Achilles tendon forces [8].
The sesamoid bones are located below the head of the first metatarsal. They serve a
pulley function for the muscles that stabilize the hallux and consequently increase their
41
mechanical advantage during MTP dorsiflexion [11]. Studies have reported up to a 30% decrease
in the effective tendon moment arm of both the flexor hallucis brevis [12] and flexor hallucis
longus [13] with the excision of both sesamoids during MTP dorsiflexion, which demonstrates
the function of the sesamoid bones. The first digital slip of the plantar fascia also attaches to the
sesamoid bones [14], which suggests that the sesamoids may influence the moment arm of the
plantar fascia, thereby affecting PFS during MTP dorsiflexion. While research has shown the
contributions of PFS due to both MTP dorsiflexion and arch collapse in vivo, it is currently
unknown how the inclusion of dynamic sesamoid bones in the musculoskeletal model will affect
strain values.
Walking is a very popular exercise to increase and maintain fitness, and it is often
recommended to individuals by physicians because it is a low impact exercise and can be done
anywhere. Unfortunately, up to 10% of the population will experience plantar fasciitis [15],
which can limit exercise and prevent further fitness improvements. Consequently, it is important
to discover what walking conditions produce the lowest values of PFS, thereby reducing the risk
for developing plantar fasciitis. It has been shown that walking and running at various treadmill
inclines results in increased Achilles tendon strain [16]. Because an increase in PFS has been
reported due to increased tension at the Achilles tendon [8,9,17], it is possible that gait speed and
incline may affect PFS. In addition, research suggests that shoe flexion stiffness may contribute
to overall magnitude of PFS by decreasing MTP dorsiflexion and thereby reducing the windlass
effect [18]. Therefore, the purpose of the study was to create a musculoskeletal model with
realistic sesamoid movement to determine the contributions of MTP and midtarsal joint motion
to plantar fascia strain. A further purpose was to use the model to determine the effects of speed,
grade, and shoe stiffness on PFS. It was hypothesized that increased speed, incline, and shoe
42
flexibility would all increase peak plantar fascia strain during treadmill walking in healthy
individuals without plantar fasciitis.
Methods
Participants
A total of fifteen healthy participants (13 males, 2 females; age: 25.8±8.2yrs;
height: 1.8±0.1m; mass: 72.2±16.2kg) completed the study. Participants were between the ages
of 18-65 and fit into a men’s size 9-10 (women’s 10.5-11.5) shoe. Individuals were excluded
from participating if they had any current pain that might affect their walking or if they
previously had foot surgery.
Data Collection Procedures
After providing written informed consent using a form approved by the university
Institutional Review Board, anthropometric measurements were collected. Three marker triads
were attached to the participants’ right foot on the hallux, over the navicular tuberosity, and on
the calcaneus using cyanoacrylate [19]. Participants were provided with shoes that had portions
of the footwear upper cut out, which allowed marker triads to be attached directly to the skin in
order to more accurately define the locations of the anatomical landmarks.
The gait analysis was completed using an eight-camera motion analysis system (Vicon
MX, Vicon, Centennial, CO) and a standard treadmill. A standing calibration trial was captured,
and then participants performed a five-minute warmup at a self-selected walking speed on the
treadmill. Self-selected walking speed was operationally defined as a comfortable pace utilized
under normal circumstances. After the warmup, participants walked on the treadmill during
twelve conditions for one minute each. 30 seconds of marker trajectory data were collected and
tracked using Nexus software (Nexus 1.8.5, Vicon, Centennial, CO). The conditions included all
possible combinations of two speeds (preferred walking speed and 20% greater than preferred
43
walking speed), three inclines (0°, 5°, and 10°), and two shoe forefoot bending stiffnesses (stiff
and flexible midsole). Conditions were presented in a counterbalanced order within each shoe
condition, and shoe order was alternated between subjects. Two pairs of the same model of shoe
were utilized (New Balance, Boston, MA), with the only difference being a stiff thermoplastic
polyurethane layered between the midsole and outsole of one pair (stiff: 0.45 Nm/degree;
flexible: 0.075 Nm/degree).
Data Analysis
Raw 3D coordinate data were low-pass filtered at 6 Hz and input into Matlab software
(MathWorks, Inc., Natick, MA). A four-segment musculoskeletal model of the foot was created
by modifying a five-segment model [20]. Further modifications were done to include the plantar
fascia, sesamoid bones, and MTP motion that more closely followed the head of the first
metatarsal during flexion and extension (Figure 3.1). Translation and rotation of the sesamoids
were visually matched to follow the contour of the first metatarsal head, and movement was
calculated as a function of the first MTP joint angle. The insertion of the plantar fascia was
placed at the base of the first phalange to model the digital slip where the greatest strains occur
[9]. These modifications are detailed in Appendix B.
Movement of the model was driven by rotation about the mediolateral axis of the MTP
joint and 3D rotations at the midtarsal joint. Peak total PFS was calculated as the maximum
percent change in length of the plantar fascia from normal standing and was due to both the
windlass mechanism of the MTP joint and collapse of the arch (midtarsal joint movement). Peak
total PFS was found during each gait cycle, which occurred in the stance phase just prior to toe-
off (about 58% of the gait cycle). In addition, contributions to peak PFS from rotation about the
mediolateral axis of the MTP joint and all three axes of the midtarsal joint were estimated by
freezing all degrees of freedom in the model except the one of interest.
44
A 2x3x2 repeated-measures ANOVA (speed x incline x shoe stiffness) was performed to
analyze peak total PFS. Significance was set to α=0.05. Greenhouse-Geisser corrections were
applied whenever the assumption of sphericity was violated. A linear trend was used to identify
significance for incline. To further investigate contributions of movement of the MTP and
midtarsal joints on plantar fascia strain, post hoc analyses were conducted. 2x3x2 repeated-
measures ANOVAs were performed on peak PFS due to MTP joint motion, peak PFS due to
motion about the midtarsal mediolateral axis, peak PFS due to motion about the midtarsal
vertical axis, peak PFS due to motion about the midtarsal anteroposterior axis, MTP dorsiflexion
angle at peak total PFS, and midtarsal angle at peak total PFS. The same procedures mentioned
above were utilized. Generalized eta squared (ηG2) was calculated as a measure of effect size
[21,22]. All results are reported as means and 95% confidence intervals. All statistical analyses
were performed in SPSS (SPSS Inc., version 25; Chicago, IL).
Results
Plantar fascia strain throughout the gait cycle is negative at initial contact, indicating a
reduced strain magnitude relative to standing (Figure 3.2). Strain rapidly increases during foot
flat and then remains approximately zero or slightly negative during midstance. There is a rapid
increase in strain magnitude during late stance which decreases to a negative value during swing.
Therefore, peak PFS occurs immediately before toe-off at 56-60% of the gait cycle. At this point
nearly all of the strain in the plantar fascia is due to MTP joint dorsiflexion (2.8 to 3.7% strain
across all conditions). The midtarsal angle at peak PFS is generally negative, indicating the arch
was higher than normal standing (Figure 3.3). Therefore, the contribution of midtarsal joint
movement to peak planar fascia strain is very small to slightly negative (0.2% to -0.9% across all
conditions). Overall, the peak plantar fascia strain decreased from 2.8-3.7% to 2.0-2.4% when
both the MTP and midtarsal joints were included in the model (Table 3.1).
45
There were no statistically significant interactions between speed, incline, and shoe
stiffness. Mean values for peak total PFS are presented in Table 3.1. This table also contains
information concerning the contributions of the MTP and midtarsal joints to the resulting peak
PFS. There was a significant effect of speed, with greater total strain during fast walking
(preferred = 2.1±0.09%, fast = 2.4±0.08%; p = 0.02; ηG2 = 0.29) (Figure 3.2A). The main effect
of incline was not significant for peak total PFS (0° = 2.0±0.3%, 5° = 2.3±0.3%, 10° =
2.4±0.4%; p = 0.14; ηG2 = 0.10) (Figure 3.2B), nor was the main effect of stiffness (stiff =
2.1±0.4%, flexible = 2.4±0.4%; p = 0.4; ηG2 = 0.049) (Figure 3.2C).
Further analyses revealed a significant main effect of speed for MTP angle at peak PFS,
with a more dorsiflexed MTP angle at peak PFS for the fast walking condition compared to the
preferred walking condition (preferred = 13.2±0.9°, fast = 15.7±0.8°; p = 0.006; ηG2 = 0.34). This
resulted in increased PFS due to the MTP dorsiflexion (preferred = 3.0±0.2%, fast = 3.5±0.2%; p
= 0.004; ηG2 = 0.37). A significant linear trend was found for incline for both the MTP angle at
peak PFS (0° = 12.3±1.9°, 5° = 14.9±2.2°, 10° = 16.4±1.3°; p = 0.003; ηG2 = 0.21) and for PFS
due to MTP joint motion (0° = 2.8±0.4%, 5° = 3.3±0.5%, 10° = 3.7±0.3%; p=0.003; ηG2 = 0.23).
As the incline increased, the MTP angle at peak PFS increased, which caused the PFS due to
MTP joint motion to also increase. Finally, the main effect of stiffness for MTP angle at peak
PFS and for PFS due to MTP joint motion were trending towards significance, with a more
dorsiflexed MTP angle at peak PFS (stiff = 13.2±1.7°, flexible = 15.9±1.7°; p = 0.09; ηG2 = 0.18)
and greater PFS due to MTP joint motion (stiff = 2.9±0.4%, flexible = 3.6±0.4%; p = 0.08; ηG2 =
0.19) in the flexible shoe condition compared to the stiff shoe condition.
The main effects of speed, incline, and stiffness were not significant for the midtarsal
angle at peak PFS or for the peak PFS due to midtarsal joint motion.
46
Discussion
The results of the study supported the hypothesis that greater peak total PFS would be
observed in individuals walking at increased speeds. However, the hypotheses that greater
incline and increased shoe flexibility would produce greater peak plantar fascia strain were not
supported.
The trend of increased strain with increased MTP dorsiflexion angle from the current
study is consistent with results from previous studies [8,9,23]. In addition, the peak overall
strains estimated in the current study are similar to the strains reported by McDonald et al. [10],
who estimated peak strain values from their model ranging between 0.6-2.1% during a running
protocol. Therefore, it can be concluded that our model can be used to estimate plantar fascia
strains based on MTP and midtarsal joint movements.
The results of the current study demonstrate the function of the windlass mechanism. The
increased walking speed produces a greater MTP dorsiflexion angle at peak PFS, which tightens
the plantar fascia and acts to increase the total PFS [1,8,9,23]. However, the increased MTP
dorsiflexion angle also causes the arch to raise, as seen by the midtarsal angle about the
mediolateral axis (Figure 3.3) [1]. In contrast to the effect of increasing the MTP dorsiflexion
angle, the increase in arch height acts to reduce the total PFS, as indicated by the negative values
of PFS due to movement about the midtarsal mediolateral axis. While peak total PFS was only
significantly different between the preferred walking speed and the fast walking speed, the
relationship between the MTP angle and the midtarsal angle about the mediolateral axis and their
respective contributions to total PFS can be observed in all the walking conditions (Table 3.1).
In addition to raising the arch, the windlass mechanism also produces supination about
the midtarsal joint [1,14,24]. This supination motion, which is a combination of plantarflexion
about the mediolateral axis, adduction about the vertical axis, and inversion about the
47
anteroposterior axis, can be inferred by analyzing the PFS due to movements about the three
midtarsal axes. PFS due to movement about the midtarsal vertical axis is due to the adducted or
abducted position of the forefoot at the time of peak PFS. The negative values indicate that the
forefoot is in an adducted position about the midtarsal vertical axis at the time of peak PFS.
According to the results of our study, the contribution of the PFS due to movement about the
midtarsal vertical axis is -0.6 to -0.7% across all conditions. While this position acts to reduce
the total PFS, it does not appear to be affected by the various walking conditions, as seen by the
consistency of the values (Table 3.1).
PFS due to movement about the midtarsal anteroposterior axis is due to the inverted or
everted position of the forefoot at the time of peak PFS. The negative values indicate that the
forefoot was in an inverted position about the midtarsal anteroposterior axis at the time of peak
PFS. However, the contribution of the PFS due to movement about the midtarsal anteroposterior
axis was minimal (-0.002 to 0.2%) and not substantially affected by the various walking
conditions (Table 3.1).
Excessive and repeated strain on the plantar fascia is thought to contribute to the
development of plantar fasciitis [2–5]. Treatment strategies such as stiff midsole plates or rocker
soles are frequently used to limit MTP dorsiflexion, thereby reducing the windlass effect
[18,25,26]. The results of our model revealed that despite a reduction of MTP dorsiflexion due to
a stiff thermoplastic polyurethane in the midsole, there was no significant change in peak PFS.
Any reduction of MTP dorsiflexion that occurs with the stiffer midsole is mitigated by greater
arch collapse. Our findings are supported by the results of Greve et al. [27], who reported no
significant differences between peak PFS between stiff and flexible shoe conditions.
48
The results of our study suggest that both MTP dorsiflexion and arch collapse should be
considered when the reduction of peak PFS is the goal, as limiting MTP dorsiflexion may not be
enough to reduce excessive strain of the plantar fascia. It is possible that the efficacy of treatment
strategies such as stiff midsole plates or rocker soles may be due to reasons other than a
reduction in peak PFS. Therefore, these treatment strategies for plantar fasciitis should be
investigated further to determine their efficacy.
There are several limitations to the study. First, the current study used a static standing
position as the neutral reference system. Consequently, the estimated PFS is likely lower than the
true physiological strain that actually occurs during gait. Next, the arch was modelled by
securing a triad over the navicular, which was used to represent the entire forefoot segment.
Because the rigid body assumption was likely being violated in the forefoot segment [28–30], the
accuracy of the model may have been improved by including more segments into the foot model.
However, the current model was chosen to preserve the integrity of the shoe structure as much as
possible. Finally, participants were recruited for the study if they were healthy and fit into the
custom made men’s size 9-10 shoes. Convenience sampling resulted in many of the participants
being healthy, college-aged males. Caution must be taken when applying the results of the study
to other populations, such as females, other age groups, or pathological groups. These effects
should be investigated in a population with plantar fasciitis to further understand the interaction
between MTP dorsiflexion, arch collapse, and peak PFS while walking during different
conditions.
Conclusions
The results of this study show that greater speed produces an increase in peak plantar
fascia strain during walking. However, walking on varying inclines or wearing a stiff shoe does
not alter peak plantar fascia strain during walking. This can be attributed to the action of the
49
windlass mechanism, as reduced MTP dorsiflexion allowed for greater arch collapse. The
interaction between MTP dorsiflexion and arch collapse needs to be investigated further to
understand how they affect plantar fascia strain. In addition, investigating these effects on a
population with plantar fasciitis would provide further insight regarding the interaction between
these factors and how they may play a role in the development of plantar fasciitis.
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Figures and Tables
Figure 3.1: Marker triads were placed on the calcaneus, navicular, and hallux. The four-
segment model of the foot allowed rotation about the mediolateral axis of the
metatarsophalangeal (MTP) joint and about all three axes of the midtarsal joint. In addition,
translation and rotation of the sesamoids followed the contour of the 1st metatarsal head and
were calculated as a function of the MTP joint angle.
X
Z
Z
Y
52
Figure 3.2: Mean ensemble curves of total plantar fascia strain for A) speed; B) incline; and C)
shoe stiffness, throughout the entire gait cycle. Toe-off is indicated by the vertical dashed line.
C)
-4
-2
0
2
0 20 40 60 80 100
PF
Str
ain
(%
)
0°5°10°
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100
PF
Str
ain (
%)
Gait Cycle (%)
Stiff
Compliant
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100P
F S
trai
n (
%)
Preferred
FastA)
B)
C)
53
Figure 3.3: The interaction between the metatarsophalangeal (MTP) and midtarsal joints about
the mediolateral axis demonstrates the function of the windlass mechanism. An increase in MTP
dorsiflexion tightens the plantar fascia, which raises the arch. Toe-off is indicated by the vertical
dashed line.
-15
-10
-5
0
5
10
15
20
25
0 20 40 60 80 100
An
gle
(°)
Gait Cycle (%)
MTP Angle
Midtarsal Angle
54
Table 3.1: Peak total plantar fascia strain (PFS) and the contributions to peak plantar fascia strain from rotation about the
mediolateral axis of the MTP joint and all three axes of the midtarsal joint (Mean ± 95% CI) are presented below. In addition, MTP
and midtarsal angles at peak total plantar fascia strain are also given.
* Denotes significance at the p < 0.05 level. # Denotes a significant linear trend at the p < 0.05 level.
Values at Peak Total PFS
Walking
Condition
Peak Total
PFS
MTP
Angle
Midtarsal
Angle (ML-
axis)
PF Strain
due to
MTP
PF strain due
to midtarsal
AP-axis
PF strain due to
midtarsal VERT-
axis
PF strain due to
midtarsal ML-
axis
Speed
Preferred 2.1 ±
0.09%*
13.2 ±
0.9°* -0.3 ± 1.0°
3.0 ±
0.2%* 0.004 ± 0.1% -0.6 ± 0.05% -0.2 ± 0.5%
Fast 2.4 ±
0.08%*
15.7 ±
0.8°* -1.7 ± 0.9°
3.5 ±
0.2%* 0.1 ± 0.1% -0.7 ± 0.04% -0.8 ± 0.4%
Incline
0° 2.0 ± 0.3% 12.3 ±
1.9°# 0.004 ± 1.8° 2.8 ±
0.4%# 0.02 ± 0.09% -0.6 ± 0.1% -0.1 ± 0.8%
5° 2.3 ± 0.3% 14.9 ±
2.2°# -1.7 ± 2.0° 3.3 ±
0.5%# 0.2 ± 0.3% -0.6 ± 0.07% -0.9 ± 1.0%
10° 2.4 ± 0.4% 16.4 ±
1.3°# -1.4 ± 0.7° 3.7 ±
0.3%# -0.002 ± 0.2% -0.7 ± 0.1% -0.6 ± 0.4%
Shoe Stiffness
Stiff 2.1 ± 0.4% 13.2 ±
1.7° -0.3 ± 1.0° 2.9 ± 0.4% -0.02 ± 0.2% -0.6 ± 0.1% -0.2 ± 0.5%
Flexible 2.4 ± 0.4% 15.9 ±
1.7° -1.7 ± 1.0° 3.6 ± 0.4% 0.1 ± 0.2% -0.6 ± 0.1% -0.9 ± 0.5%
55
Appendix A: Institutional Review Board Approval
56
Appendix B: Modifications to the Musculoskeletal Foot Model
Model Creation
The musculoskeletal model utilized in this study was based on the joint and muscle data of
Arnold et al. (2010) with foot and ankle modifications detailed in the KU Leuven foot model
(Malaquias et al., 2017). The addition of the KU Leuven model allowed midfoot and
metatarsophalangeal joint (MTP) to be defined. Four additions/changes were made to this
previously published model.
1. The first slip of the plantar fascia was added with an origin on the calcaneal tuberosity,
moving over the sesamoid bones and inserting onto the proximal first phalanx (Table 1).
2. Sesamoid bones were added at the head of the first metatarsal by creating translations and
sagittal plane rotation based on sagittal plane MTP movement (Table 2). Rotation and
translation of the sesamoids were visually matched to follow the contour of the 1st
metatarsal head (Figure 1).
3. The first slip of the plantar fascia was included to model the region where the greatest
plantar fascia strains occur. Therefore, motion of the first phalanx was optimized to
visually follow the non-spherical shape of the metatarsal head. The first phalanx was
translated in the anterior and medial directions as the MTP joint was dorsiflexed (Table
3).
4. Direct measurement of the talus was not possible due to external marker limitations.
Instead, inversion/eversion and abduction/adduction motions that occurred at the ankle
joint were attributed to the subtalar joint. Plantar/dorsiflexion was attributed to the
talocrural joint.
57
Table 3.2: Locations of the origin, via points, and insertion of the first slip of the plantar fascia.
Segment Anteroposterior
(m)
Vertical (m) Mediolateral (m)
Origin Calcaneus -0.0235 -0.0265 -0.0100
Via Point Sesamoids -0.0040 -0.0060 0.0000
Via Point Sesamoids 0.0040 -0.0070 -0.0010
Insertion Hallux 0.0159 -0.0100 -0.0311
Table 3.3: Sagittal plane rotation and translation of the sesamoids as a function of measured
MTP joint angle.
MTP
Angle (°)
Sagittal
Angle (°)
Anteroposterior
Translation (m)
Vertical
Translation (m)
Mediolateral
Translation (m)
-10 0.0 0.0562 -0.0200 -0.0250
0 0.0 0.0593 -0.0199 -0.0253
10 6.7 0.0620 -0.0198 -0.0256
20 13.3 0.0641 -0.0197 -0.0259
30 20.0 0.0656 -0.0196 -0.0262
40 23.3 0.0665 -0.0193 -0.0265
50 26.7 0.0668 -0.0189 -0.0268
60 30.0 0.0670 -0.0185 -0.0271
Table 3.4: Translation of the hallux as a function of the measured MTP joint angle.
MTP
Angle
(°)
Anteroposterior
Translation (m)
Mediolateral
Translation (m)
-10 0.0605 -0.0141
0 0.0612 -0.0141
10 0.0619 -0.0134
20 0.0626 -0.0127
30 0.0634 -0.0121
40 0.0641 -0.0114
50 0.0648 -0.0107
60 0.0655 -0.0100
58
Figure 3.4: A) rotation and translation of the sesamoids were visually matched to follow the
contour of the 1st metatarsal head. The effect of sesamoid rotation and translation on plantar
fascia strain and plantar fascia moment arm are depicted in B) and C).
A) B)
C)
59
CHAPTER 4. VALIDATION OF A SIX-SEGMENT MUSCULOSKELETAL MODEL
OF THE FOOT USED TO ESTIMATE LIGAMENT STRAINS
Jeff H. Mettlera, Erin Wardb, Timothy R. Derricka
a Department of Kinesiology, Iowa State University, 534 Wallace Rd, Ames, Iowa, 50011,
United States b Central Iowa Foot Clinic, 1302 Warford St, Perry, Iowa, 50220, United States
Modified from a manuscript to be submitted to Computer Methods in Biomechanics and
Biomedical Engineering
Abstract
In addition to the plantar fascia, there are several secondary ligaments that help to
provide support to the medial longitudinal arch. Because of their contribution to arch support,
these ligaments may influence the magnitude of the load placed on the plantar fascia, thereby
playing a factor in the development of plantar fasciitis. However, the nature of ligaments poses
limitations to the types of analyses that can be performed. To address this limitation,
musculoskeletal models can be used to provide information about in vivo kinematics and tissues
mechanics that would otherwise be impossible to measure directly. Therefore, the purpose of the
study was to validate a musculoskeletal model of the foot by comparing model-estimated
ligament strain values to directly-measured ligament strain values from seven fresh-frozen
cadaver specimens. The estimated ligament strains from the model were compared to the
directly-measured strains and evaluated using Pearson correlation coefficients and coefficients of
repeatability (CR). Results showed CR values between the ranges of 0.8-8.3% and statistically
significant Pearson’s R values in the inferior slip of the spring ligament (p = 0.0008) and the
tibionavicular slip of the deltoid ligament (p = 0.002), as well as nearly significant correlations in
the tibiocalcaneal slip of the deltoid ligament (p = 0.06) and the calcaneonavicular slip of the
bifurcate ligament (p = 0.05). The results indicate that the model can be used to estimate strains
60
of the ligaments that help to support the arch on the medial side of the foot. A secondary purpose
was to validate the use of skin-mounted markers in the musculoskeletal model, so bone pin
estimated ligament strains and skin marker estimated ligament strains were compared. Results
showed statistically significant Pearson’s R values in nearly all the ligaments and CR values that
were all between the ranges of 0.03-1.6%, indicating that skin markers can be used in the model.
Introduction
Ligaments are passive tissues that connect bone to bone and act to provide stability to a
joint. They can either resist excessive motion beyond a joint’s total range of motion or motion
outside of a joint’s normal plane of motion (Root, Orien, and Weed 1977). Along with the
plantar fascia, ligaments crossing the midfoot provide secondary support to the medial
longitudinal arch and help to control motions such as excessive pronation (Huang et al. 1993;
Ker et al. 1987; Kitaoka et al. 1997; Tao et al. 2010). Both arch collapse and excessive pronation
have been cited as risk factors for plantar fasciitis (Irving et al. 2007; Kwong et al. 1988;
Taunton et al. 2002; Warren and Jones 1987), potentially due to increased tensile load placed on
the plantar fascia (Bauer 2012; Kwong et al. 1988; Sarrafian 1987). Because the ligaments
crossing the midfoot provide structural support to the medial longitudinal arch, they may
influence the magnitude of load placed on the plantar fascia, thereby playing a role in the
development of plantar fasciitis. These ligaments include the long and short plantar ligaments,
the spring ligament, and the deltoid ligament. While no research has been conducted on them, the
orientation of the bifurcate and cervical ligaments suggest they may also help to support the
midfoot. However, despite the role that ligaments play in arch support and providing stability to
the foot, there is very little published information on the behavior of the ligaments in the foot. It
is currently unknown how many of the ligaments behave. Therefore, the primary purpose of this
study was to validate a six-segment modified musculoskeletal model of the foot by comparing
61
estimated ligament strain values from the model to directly measured strain values from loaded
cadaver specimens.
Musculoskeletal models provide information about kinematics and tissue mechanics
using a simplified representation of the system. They are made up of body segments connected
by joints with a defined number of degrees of freedom at each joint. Furthermore, the model may
include muscles and ligaments with specified origins and insertions that cross the joints.
Simplified musculoskeletal models of the foot have been created and validated in the past
(Kidder et al. 1996; Leardini et al. 1999; Myers et al. 2004). While they can provide useful
information, those models are not sophisticated enough to realistically replicate the complex
motions that occur in the foot during gait (Neptune, Wright, and van den Bogert 2000).
To address this limitation, Malaquias et al. (Malaquias et al. 2017) developed the KU
Leuven model, a five-segment model of the foot (talus, calcaneus, midfoot, forefoot, toes) with
five anatomical joints (ankle, subtalar, midtarsal, tarsometatarsal, and metatarsophalangeal)
based on CT scans used in OpenSim (Delp et al. 2007). The model included both intrinsic and
extrinsic muscles of the foot, as well as the major ligaments. While the kinematics were
validated by comparing to joint kinematics published in literature (Lundgren et al. 2008),
validation of the ligament strains estimated using the model was limited. The authors reported
physiologically acceptable values, as the average maximum elongation of the ligaments was
below the rupture threshold of 8% (Nordin and Frankel 2001). However, the authors
acknowledged that further refinement of their model in regards to the foot ligaments was needed.
Furthermore, the KU Leuven model treats the tarsals and metatarsals as single segments (midfoot
and forefoot, respectively), which may limit our understanding of the medial column of the foot
during walking. In addition, there are physiological differences in motion between the medial
62
and lateral columns of the foot (Lundgren et al. 2008), so it is important to model the medial and
lateral columns of the foot separately.
Skin-mounted markers are frequently used to estimate the position, velocity, and
acceleration of the underlying bones. However, previous research on the foot has reported
significant kinematic differences between bone pins and skin markers (Nester et al. 2007).
Furthermore, bone pins are invasive and impractical to use in many situations. Therefore, an
additional purpose of the study is to compare the estimated ligament strains between bone pins
and skin markers in order to validate the use of skin markers for our musculoskeletal model.
Methods
Data Collection Procedures
Seven fresh-frozen cadaver feet were analyzed for the study. An experienced podiatrist
dissected the foot to expose the two slips of the spring ligament (superior and inferior), three
slips of the deltoid ligament (tibionavicular, tibiocalcaneal, and tibiotalar), two slips of the
bifurcate ligament (calcaneocuboid and calcaneonavicular), and cervical ligament. Following
dissection, K-wire pins were placed at the origin and insertion of each ligament. Each cadaver
was placed on a portable force platform (Advanced Mechanical Technology, Inc., Watertown,
MA, USA) underneath a pneumatic actuator mounted on a frame (Figure 4.1). The actuator was
used in conjunction with the force platform to apply an axial load of 10N to the tibia of each
cadaver specimen. A manual digitizer (Microscribe G2, Revware Inc., Raleigh, NC, USA) was
used to define the origin and insertion of each ligament using the K-wire pins at the 10N load,
and this was considered the baseline length of each ligament.
Simultaneously, kinematic data were collected at 225 Hz using a 12-camera motion
analysis system (Qualisys Oqus 600+, Qualisys NA, Inc., Buffalo Grove, IL, USA). Intracortical
bone pins with reflective marker triads attached to the end were inserted into the calcaneus, talus,
63
navicular, 1st metatarsal, hallux, and cuboid (Figure 4.2). Marker trajectory data were collected
and tracked using QTM software (Qualisys Track Manager 2020.2, Qualisys NA, Inc., Buffalo
Grove, IL, USA). Following digitization of the ligaments and the kinematic collection during the
baseline condition, the axial load was increased to 250N, 500N, 750N, and 1000N, and the
digitization process was repeated at each load. The load condition was collected in the same
order for all specimens, and one of the researchers monitored the load to ensure the magnitude
stayed constant throughout the entire condition. The axial load resulted in arch collapse, and the
strain response of each ligament due to the collapse in the arch was measured.
Data Analysis
Raw 3D coordinate data were input into a custom Matlab script (MathWorks, Inc.,
Natick, MA, USA) and filtered at 8 Hz using a 2nd order low-pass Butterworth filter. An 11
degree of freedom (11DOF) musculoskeletal model of the foot was modified (Malaquias et al.
2017) to include six segments of the foot (calcaneus, talus, navicular and cuneiforms, cuboid,
metatarsals, and hallux) (Figure 4.3).
Furthermore, the sesamoids were separated from the metatarsal segment, and translation
and rotation of the sesamoids was achieved by moving them around the curvature of the first
metatarsal head as a function of the first MTP joint angle. The center of rotation of the
talonavicular joint was moved to the center of the talar head and visually adjusted so that the
navicular bone rotated about the articular surface of the talus. The calcaneocuboid joint center of
rotation was similarly adjusted so that it rotated about the proximal surface of the joint. Three-
dimensional helical segment and joint angles were calculated. Cadaver dissections were used to
define two slips of the spring ligament, three slips of the deltoid ligament, two slips of the
bifurcate ligament, and the cervical ligament. Strains of the spring, deltoid, bifurcate, and
cervical ligaments were estimated as the percentage change in length relative to the baseline 10N
64
load condition. Pearson’s correlation coefficients (r) were calculated to investigate the
relationship between ligament strains estimated from the model and the strains measured with
the digitizer, and were evaluated for significance at α = 0.05. Additionally, Bland-Altman plots
were utilized to compare the model-estimated ligament strains to the directly-measured ligament
strains, and the coefficient of repeatability (CR) for each ligament was assessed to test the
agreement (Giavarina 2015). CR represents the value in which 95% of the measurement
differences lie.
In addition to the bone pins that were inserted into the bones to directly measure
kinematics, reflective marker triads were also placed on the skin overlaying the calcaneus,
navicular, and hallux bones to measure foot kinematics captured by the skin markers (Figure
4.2). To accommodate the reduced number of skin markers on the foot, the model was further
modified by freezing all motions of the TMT and calcaneocuboid joints and estimating talus
motion, thereby creating a four-segment, 7DOF model (Figure 4.4). Talus motion was
considered to be the same as leg motion in the frontal and transverse planes and considered to be
the same as calcaneus motion in the sagittal plane. This allowed for a representation of both
subtalar and talonavicular joint motions, even when using skin markers which cannot be placed
over the talus. Movement of the model ankle joint using calcaneal and tibial markers was limited
to the sagittal plane, with frontal and transverse plane motions between these bones attributed to
the subtalar joint. Previous research regarding this assumption has shown that it is appropriate
for some individuals, although substantial variation was noted (Arndt et al. 2004; Engsberg,
Grimston, and Wackwitz 1988). The same four-segment model with the frozen TMT and
calcaneocuboid joint motion was used to measure foot kinematics captured by the bone pins, and
65
the data from the two methods were compared using Pearson’s correlation coefficients and tested
for agreement with CR using Bland-Altman methods (Giavarina 2015).
Results
Pearson’s correlation coefficients between the directly-measured and model-estimated
ligament strains using the six-segment model are presented in Figures 4.5 and 4.6. Ligament
strains estimated using the bone pins were significantly correlated to the directly-measured
ligament strains for the the inferior slip of the spring ligament (r = 0.99; p = 0.0008) and the
tibionavicular slip of the deltoid ligament (r = 0.99; p = 0.002), as well as nearly significant
correlations in the tibiocalcaneal slip of the deltoid ligament (r = 0.87; p = 0.06) and the
calcaneonavicular slip of the bifurcate ligament (r = 0.87; p = 0.05). Relatively weaker
correlations were noted for the superomedial slip of the spring ligament (r = 0.73; p = 0.16), the
calcaneocuboid slip of the bifurcate ligament (r = 0.68; p = 0.21), and the cervical ligament (r =
0.77; p = 0.13).
The CR values between the directly-measured ligament strains and the model-estimated
strains across the five loading conditions using the six-segment model are also presented in
Figures 4.5 and 4.6. CR values range from 1.2% at the calcaneonavicular slip of the bifurcate
ligament to 8.3% at the inferior slip of the spring ligament, which highlights the range of strain
magnitude differences between the model and the directly-measured values.
Using the four-segment model, the strains estimated using the bone pins and the skin
markers were compared, and Pearson’s correlation coefficients between the bone pin and skin
markers strain estimates are presented in Figures 4.7 and 4.8. Statistically significant correlations
were noted for both slips of the spring ligament (superomedial: r = 0.97, p = 0.008; inferior: r =
0.99, p = 0.002), the tibionavicular (r = 0.99; p = 0.002) and tibiocalcaneal (r = 0.99; p = 0.002)
slips of the deltoid ligament, the calcaneonavicular slip of the bifurcate ligament (r = 0.98; p =
66
0.005), and the cervical ligament (r = 0.94; p = 0.02). The CR values were also calculated and
are presented in Figures 4.7 and 4.8. The values range from 0.03 to 1.6, representing the
magnitude differences between ligament strains estimated by the bone pins and ligament strains
estimated by the skin markers.
Discussion
The primary purpose of the study was to validate the musculoskeletal model of the foot
by comparing the directly-measured ligament strains to the model-estimated ligament strains,
and the results of the study confirm the validation of the model. Significant correlations between
the directly-measured and model-estimated ligament strains indicate that the relationship
between arch collapse and ligament strain is adequately modelled for the ligaments on the medial
side of the foot in the musculoskeletal model. When the axial load applied to the tibia was
increased, the resultant arch collapse produced an increased strain response in the spring, deltoid,
bifurcate, and cervical ligaments. Similar estimated strain responses were noted in all the
modelled ligaments.
The magnitudes of the directly-measured and model-estimated strains are relatively
similar in some ligaments, such as the superomedial slip of the spring ligament, the
tibiocalcaneal slip of the deltoid ligament, the calcaneonavicular slip of the bifurcate ligament,
and the cervical ligament. However, in the remaining ligaments (inferior slip of the spring
ligament, tibionavicular and tibiotalar slips of the deltoid ligament, and calcaneocuboid slip of
the bifurcate ligament), the magnitudes are substantially different (Figures 4.5 and 4.6). These
results are quantified in the reported CR values. There are several possible explanations for this
discrepancy. First, the material properties of the soft tissues in the cadaver specimens may have
been altered by the freezing and thawing process, or due to drying out. Furthermore, while the
age of the specimens were unknown, often cadaver specimens come from elderly individuals.
67
Material properties of ligaments are known to change with age (Woo, Ohland, and Weiss 1990),
so it is possible that the age of the cadaver specimens affected the measured strain values. For
example, the directly-measured and model-estimated strains of the tibionavicular slip of the
deltoid ligament follow nearly identical strain responses, but the directly-measured strains are
consistently between 3.6-4.1% higher (Figure 4.6A). This may be due to altered material
properties of the soft tissues of the cadaver specimens, leading to higher strain magnitudes. Next,
assumptions made in the model may have influenced the estimated ligament strains. For
example, the directly-measured strains of the tibiotalar slip of the deltoid ligament exhibited
strains of up to 5.5%, while the modelled ligament displayed estimated strains of approximately
zero (Figure 4.6E). This is due to the inability of the model to directly measure talus motion.
Because of this limitation, motion of the talus was assumed to be identical to the motion of the
tibia in the frontal and transverse planes. Consequently, the low strain magnitudes estimated in
the ligament are due to sagittal plane motion of the ankle joint, which was minimal in the study.
The secondary purpose of the study was to compare the model-estimated strains using
bone pin markers and skin markers as a way to validate the use of skin markers for the model,
and the results support the use of skin markers. Correlations between the bone pin and skin
marker estimated strains were very high and were statistically significant for nearly all of the
ligaments (Figures 4.7 and 4.8). The tibiotalar slip of the deltoid ligament exhibited a Pearson’s
R correlation of 0.6, which is likely due to the model assumptions of the ankle and subtalar joints
described previously. Furthermore, CR values were generally low, indicating similar magnitudes
of ligament strains between the two methods of segment measurement. Estimations of ligament
strains using the bone pins and skin markers can be seen in Figures 4.7 and 4.8. It should be
noted that a possible limitation of the study was the static nature of the data collection. A main
68
source of error when using skin-mounted markers is due to skin movement artefact, in which the
skin moves relative to the underlying bones during dynamic movements (Nester et al. 2007;
Westblad et al. 2002). This artefact has been shown to be affected by type of movement, with
greater errors demonstrated in a cutting motion when compared to walking (Benoit et al. 2006).
However, the pattern of error between skin-mounted markers and bone pins appears to be
inconsistent, as several studies have reported no systematic error patterns between the conditions
(Nester et al. 2007; Westblad et al. 2002).
Conclusions
The results of the current study show that the six-segment, modified musculoskeletal
model is satisfactorily able to estimate the ligament strain response due to arch collapse
following an axial load on the tibia. Furthermore, the comparison of the estimated ligament
strains between the bone pin model and the skin marker model showed that skin markers can be
used for the model. Therefore, it can be concluded that the model can be used in many different
scenarios, including on humans and in dynamic situations.
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Figures and Tables
Figure 4.1: The cadaver specimens were placed on the force platform underneath the pneumatic
actuator, which applied an axial load on the tibia.
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Figure 4.2: Bone pins with reflective marker triads attached to the end were inserted into the
calcaneus, talus, navicular, cuboid, 1st metatarsal, and hallux. In addition, skin marker triads
were placed on the calcaneus, navicular, and hallux.
72
Figure 4.3: The 11DOF model included six segments of the foot, including the calcaneus, talus,
navicular and cuneiforms, cuboid, metatarsals, and toes. In addition, the sesamoid bones were
separated from the metatarsals segment and modelled to rotate about the curvature of the first
metatarsal head as a function of the first MTP joint angle.
73
Figure 4.4: The 7DOF model included four segments of the foot, including the calcaneus, talus,
midfoot and forefoot, and toes. In addition, the sesamoid bones were separated from the
metatarsals segment and modelled to rotate about the curvature of the first metatarsal head as a
function of the first MTP joint angle.
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Figure 4.5: Directly-measured (blue line) and model-estimated (orange line) ligament strains
at each axial load for the A) spring – superomedial, C) spring – inferior, E) bifurcate –
calcaneonavicular, and G) bifurcate – calcaneocuboid ligaments. Bland-Altman plots for the
B) spring – superomedial, D) spring – inferior, F) bifurcate – calcaneonavicular, and H)
bifurcate – calcaneocuboid ligaments. The solid black lines represent the bias in the mean
differences between the measurements, the dotted lines represent the 95% limits of agreement,
CR represents the coefficient of repeatability, and CV represents the coefficient of variation.
0
4
8
12
0 250 500 750 1000
Str
ain
(%
)
Load (N)
0
4
8
12
0 250 500 750 1000
Str
ain (
%)
Load (N)
0
4
8
12
0 250 500 750 1000
Str
ain (
%)
Load (N)
0
4
8
12
0 250 500 750 1000
Str
ain
(%
)
Load (N)
r = 0.73 (p = 0.16)
r = 0.99 (p = 0.0008)*
r = 0.87 (p = 0.05)
r = 0.68 (p = 0.21)
A) B)
H) G)
F) E)
C) D)
75
Figure 4.6: Directly-measured (blue line) and model-estimated (orange line) ligament strains
at each axial load for the A) deltoid – tibionavicular, C) deltoid – tibiocalcaneal, E) deltoid –
tibiotalar, and G) cervical ligaments. Bland-Altman plots for the B) deltoid – tibionavicular,
D) deltoid – tibiocalcaneal, F) deltoid – tibiotalar, and H) cervical ligaments. The solid black
lines represent the bias in the mean differences between the measurements, the dotted lines
represent the 95% limits of agreement, CR represents the coefficient of repeatability, and CV
represents the coefficient of variation.
0
4
8
12
0 250 500 750 1000
Str
ain
(%
)
Load (N)
0
4
8
12
0 250 500 750 1000
Str
ain
(%
)
Load (N)
0
4
8
12
0 250 500 750 1000
Str
ain (
%)
Load (N)
0
4
8
12
0 250 500 750 1000
Str
ain
(%
)
Load (N)
r = 0.87 (p = 0.06)
r = 0.99 (p = 0.002)*
r = 0.81 (p = 0.1)
r = 0.77 (p = 0.13)
A) B)
H) G)
F) E)
C) D)
76
Figure 4.7: Model-estimated ligament strains using bone pins (orange line) skin markers
(green line) at each axial load for the A) spring – superomedial, C) spring – inferior, E)
bifurcate – calcaneonavicular, and G) bifurcate – calcaneocuboid ligaments. Bland-Altman
plots for the B) spring – superomedial, D) spring – inferior, F) bifurcate – calcaneonavicular,
and H) bifurcate – calcaneocuboid ligaments. The solid black lines represent the bias in the
mean differences between the measurements, the dotted lines represent the 95% limits of
agreement, CR represents the coefficient of repeatability, and CV represents the coefficient of
variation.
0
4
8
12
0 250 500 750 1000
Str
ain
(%
)
Load (N)
0
4
8
12
0 250 500 750 1000
Str
ain (
%)
Load (N)
0
4
8
12
0 250 500 750 1000
Str
ain (
%)
Load (N)
0
4
8
12
0 250 500 750 1000
Str
ain (
%)
Load (N)
r = 0.97 (p = 0.0008)*
r = 0.99 (p = 0.002)*
r = 0.98 (p = 0.005)*
r = 0.83 (p = 0.08)
A) B)
H) G)
F) E)
C) D)
77
Figure 4.8: Model-estimated ligament strains using bone pins (orange line) skin markers
(green line) at each axial load for the A) deltoid – tibionavicular, C) deltoid – tibiocalcaneal,
E) deltoid – tibiotalar, and G) cervical ligaments. Bland-Altman plots for the B) deltoid –
tibionavicular, D) deltoid – tibiocalcaneal, F) deltoid – tibiotalar, and H) cervical ligaments.
The solid black lines represent the bias in the mean differences between the measurements, the
dotted lines represent the 95% limits of agreement, CR represents the coefficient of
repeatability, and CV represents the coefficient of variation.
0
4
8
12
0 250 500 750 1000
Str
ain
(%
)
Load (N)
0
4
8
12
0 250 500 750 1000
Str
ain
(%
)
Load (N)
0
4
8
12
0 250 500 750 1000
Str
ain (
%)
Load (N)
0
4
8
12
0 250 500 750 1000
Str
ain
(%
)
Load (N)
r = 0.99 (p = 0.002)*
r = 0.99 (p = 0.002)*
r = 0.60 (p = 0.29)
r = 0.94 (p = 0.02)*
A) B)
H) G)
F) E)
C) D)
78
CHAPTER 5. EFFECTS OF LOW-DYE TAPING ON PLANTAR FASCIA STRAIN
AND FOOT KINEMATICS IN INDIVIDUALS WITH PLANTAR FASCIITIS
Jeff H. Mettlera, Erin Wardb, Timothy R. Derricka
a Department of Kinesiology, Iowa State University, 534 Wallace Rd, Ames, Iowa, 50011,
United States b Central Iowa Foot Clinic, 1302 Warford St, Perry, Iowa, 50220, United States
Modified from a manuscript to be submitted to Clinical Biomechanics
Abstract
The low-Dye taping method has been found to be effective at reducing pain and
increasing function in individuals with plantar fasciitis. While there are several proposed reasons
for this, the true reason for the reduction of pain following the taping procedure is unknown.
Therefore, the purpose of the study is to investigate the effect of the low-Dye taping method on
plantar fascia strain in individuals with plantar fasciitis. Fifteen adults with plantar fasciitis
participated in a repeated measures study, in which they walked barefoot at a self-selected speed
while untaped and while their pathological foot was taped using the low-Dye taping method.
Statistical Parametric Mapping (SPM) was used to compare plantar fascia strain between the two
conditions across stance phase. Significantly greater plantar fascia strain was found during the
untaped condition between 57-86% of stance phase (p = 0.008), which does not include the time
during stance phase when peak strain was reached. Post-hoc SPM analyses were conducted on
several foot joint motions to help explain the reported difference in plantar fascia strain, and the
low-Dye taping method reduced the amount of talonavicular joint dorsiflexion during 47-86% of
stance phase (p = 0.004), which represents a reduction in arch collapse. Finally, exploratory SPM
analyses were conducted on several secondary ligaments thought to assist the plantar fascia in
arch support. It was found that the low-Dye taping method reduced strains of the superomedial
and inferior slips of the spring ligament from 5-84% (p < 0.001) and 19-60% (p < 0.001) of
79
stance phase, respectively, and the 2nd and 3rd slips of the long plantar ligament from 70-85% (p
= 0.021) and 73-85% (p = 0.026) of stance phase, respectively. Our findings suggest that the
low-Dye taping method is effective at reducing pain in individuals with plantar fasciitis due to its
ability to reduce cumulative strain across the entire stance phase, which occurs due to the
reduction in arch collapse.
Introduction
Plantar fasciitis affects up to 10% of the population [1] and results in approximately one
million patient visits to office-based physicians and hospital outpatient departments each year
[2]. Unfortunately, the etiology of planter fasciitis is not well understood. While the etiology is
multifactorial in nature, the development of the disorder is believed to be caused by excessive
strain at the insertion of the plantar fascia on the calcaneal tubercle that produces microdamage
and/or inflammation [3–6]. Overpronation has often been cited as a risk factor for plantar
fasciitis [5,7,8], and the collapse of the medial longitudinal arch that occurs with pronation may
place an increased amount of strain on the plantar fascia [5]. Excessive pronation has been
reported in individuals with plantar fasciitis, although the measures were assessed visually [8].
Rearfoot eversion, a surrogate measure of pronation, has also been found to be altered in
individuals with plantar fasciitis. Although Chang et al. [9] reported no differences in peak
rearfoot eversion between healthy individuals and individuals with plantar fasciitis, they found
that individuals with plantar fasciitis displayed greater total rearfoot eversion when walking.
However, there have also been studies reporting no differences in rearfoot pronation between
individuals with plantar fasciitis and healthy controls [10,11]. Therefore, it is important to further
investigate the relationship between pronation and plantar fasciitis. Multi-segment foot models
are a valuable tool to accomplish this because they can be used to assess the complex interactions
of joint motions in the foot, as well as estimate strains of the plantar fascia and other ligaments
80
directly. While the plantar fascia provides much of the support of the medial longitudinal arch,
there are also several ligaments that have been shown to provide support under static conditions,
such as the spring ligament, portions of the deltoid ligament, long and short plantar ligaments,
bifurcate ligament, and cervical ligament [12–17]. However, more information is needed
regarding the role that these ligaments play in the support of the medial longitudinal arch during
dynamic activities.
There are several conservative treatment options for plantar fasciitis, including anti-
inflammatory methods such as NSAIDs or steroid injections, pain reduction methods such as
analgesics or foot pads, and mechanical methods [18]. Mechanical methods include custom
orthotics, over the counter shoe inserts, and night splints [19]. Orthotics are proposed to reduce
the symptoms of plantar fasciitis. This is possibly due to the orthotic helping to maintain medial
longitudinal arch height [20], as plantar fascia strain has been found to be the lowest when
wearing orthotics that maintain medial longitudinal arch height [21]. An alternative mechanical
treatment option is taping. While it is often used as a way to determine the potential success of
custom orthotics [22,23], taping can also be used as a treatment method [4,24]. Much like the
mechanism of orthotics, the low-Dye taping method is designed to control excessive foot
pronation by preventing medial longitudinal arch collapse [25]. It consists of an anchor strip of
tape that begins on the lateral aspect of the fifth metatarsal head, wraps behind the calcaneus, and
attaches on the medial aspect of the first metatarsal head. Then, a series of stirrups are applied on
the plantar aspect of the foot, beginning on the lateral side of the foot and attaching to the medial
side. Tension is applied to the tape during the application of the stirrups to oppose pronation. The
stirrups begin below the medial longitudinal arch and are applied on the plantar aspect of the foot
in a proximal direction until the plantar calcaneus is covered (Figure 5.1).
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Many studies have demonstrated the ability of low-Dye taping to reduce pain and
improve function in plantar fasciitis patients [18,26–28]. There are several proposed reasons for
this, including altered plantar pressures, altered surrounding muscular activity, or altered
kinematics. Research has reported a decrease in plantar pressures under the medial midfoot and
an increase in plantar pressures under the lateral midfoot following low-Dye taping [29,30],
which suggests this taping may help to support the medial longitudinal arch. Reductions in
tibialis posterior and tibialis anterior activity following taping have also been reported [31,32],
although the results are not consistent enough to make definitive conclusions. Finally,
individuals with plantar fasciitis have demonstrated increased medial longitudinal arch height
and reduced rearfoot eversion during static stance following a taping technique similar to the
low-Dye method [33]. Similar results have also been found in healthy individuals considered to
be excessive pronators [34,35].
There are few studies that have considered the effects of low-Dye taping on lower
extremity kinematics during gait, and none to the author’s knowledge have researched the effects
in a clinical population. A reduction in peak rearfoot eversion following low-Dye taping has
been reported in healthy subjects [36], although no significant differences in peak rearfoot
eversion during walking has also been reported [34,37]. Furthermore, Vicenzino et al. [38] and
Yoho et al. [39] both reported a significantly higher medial longitudinal arch height in healthy
subjects following low-Dye taping methods when compared to the untaped condition. At this
point, the kinematic effects of low-Dye taping on individuals with plantar fasciitis during
walking have not been investigated. Therefore, the purpose of the study is to determine the
effects of low-Dye taping on plantar fascia strain in individuals with plantar fasciitis during
walking. It was hypothesized that the low-Dye taping method would result in reduced levels of
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plantar fascia strain during walking in individuals with plantar fasciitis. Previous studies have
limited their kinematic analysis of the foot to medial longitudinal arch height and rearfoot
eversion. Therefore, an additional exploratory purpose of the study is to investigate the effects of
low-Dye taping on the kinematics of the foot using a multi-segment foot model. Finally, there is
limited knowledge regarding other ligaments besides the plantar fascia that help to support the
arch during dynamic activities. Therefore, the effects of low-Dye taping on strain during walking
in several ligaments of the foot will be investigated using the multi-segment foot model.
Methods
Participants
To investigate the effects of low-Dye taping on foot kinematics and ligament strains, data
were collected on individuals who currently had plantar fasciitis. Participants were included in
the study if they had been diagnosed by a physician, if they had been experiencing pain for at
least three months, if they had no arthritis or other concurrent lower extremity or back injuries,
and if they had received no steroid injections within the last three months. Other treatments such
as taping, shoe inserts, custom orthotics, and NSAIDs were acceptable. Treatment for the plantar
fasciitis patients must have been consistent for a period of three months before they were
allowed to participate in the study.
A power analysis using the results from Vicenzino et al. [38] was used to calculate the
required sample size for a repeated measures study assuming α=0.05 and β=0.20. The study
measured the effects of augmented low-Dye taping on the sagittal plane midfoot angle during
gait in seventeen healthy individuals. The results of the power analysis revealed that a sample of
ten participants was required to yield sufficient statistical power. Eventually, fifteen participants
with plantar fasciitis were recruited for the study (11 males, 4 females; age: 38.3±15.8yrs;
height: 1.8±0.1m; mass: 78.4±12.3kg).
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Data Collection Procedures
Following the informed consent procedure, participants were screened by a licensed
podiatrist to ensure they met the inclusionary criteria for plantar fasciitis. Static measures of arch
height index [38,40] and arch rigidity index [41] were obtained before taping the pathological
foot (10 right feet analyzed, 5 left feet analyzed). For plantar fasciitis patients who displayed
bilateral plantar fasciitis, the foot that displayed greater symptoms was used for analysis.
Statically, arch height index measures were taken while the participant stood with equal weight
on both limbs. The arch height index was calculated by dividing the arch height by the truncated
foot length, which is the distance from the posterior heel surface to the first metatarsophalangeal
(MTP) joint line. The same measures were taken while the participant sat in a chair with equal
weight on both limbs, and the arch rigidity index was then calculated by dividing the arch height
index during standing by the arch height index during sitting (standing AHI = 0.38±0.04, seated
AHI = 0.40±0.04, ARI = 0.95±0.03). Following the static measures, a standing calibration trial
was captured. A support was provided to the participant to allow them to offload their
pathological foot while keeping contact with the ground. Participants then walked overground on
the force platforms at a self-selected barefoot walking speed (untaped = 1.26±0.15m/s; taped =
1.25±0.16m/s) while kinematics and ground reaction forces were collected. Each participant
performed ten trials in each of two conditions: barefoot and barefoot with low-Dye tape on the
pathological foot. Participants were taped with rigid sports tape with zinc oxide adhesive (Henry
Schein, Inc., Melville, NY, USA) by a licensed podiatrist with extensive experience performing
the low-Dye taping method. The conditions were counterbalanced, and half the participants
started with the untaped condition while the other half started with the taped condition. Five
marker triads were placed on the calcaneus, navicular, cuboid, 1st metatarsal, and hallux of the
taped foot. A curved base of each triad was fitted to the bone. The triads were attached with
84
double-sided tape on the base and secured with athletic tape over the top. Anatomical markers
were placed on the sacrum, ASIS, greater trochanter, medial and lateral knee, and medial and
lateral malleoli, and tracking markers were placed on the thigh and shank on the taped side to
measure additional kinematics while walking during both conditions. Anthropometric
measurements and marker placements were performed by the same researchers for all
participants.
Data Analysis
Raw 3D coordinate data were low-pass filtered at 8 Hz and input into a custom Matlab
script (MathWorks, Inc., Natick, MA). The ground reaction force data were used to determine
stance phase, which was defined as a vertical ground reaction force greater than 20N. The six-
segment, modified musculoskeletal model [42] that was described in chapter four was utilized to
analyze the data and provide estimates of plantar fascia and ligament strains. Talus motion was
considered to be the same as calcaneus motion in the sagittal plane and considered to be the same
as leg motion in the frontal and transverse planes. This assumption allowed for a representation
of both subtalar and talonavicular joint motions, even when using skin markers which cannot be
placed over the talus. Movement of the model ankle joint using calcaneal and tibial markers was
limited to the sagittal plane, with frontal and transverse plane motions between these bones
attributed to the subtalar joint. A further modification of the model included the addition of four
slips of the long plantar ligament and one slip of the short plantar ligament (Figure 5.2), as both
have been found to provide support to the medial longitudinal arch [13,15].
Plantar fascia strain during stance phase was analyzed using one-dimensional statistical
parametric mapping (SPM) (spm1d, version M.0.4.7 for Matlab, http://spm1d.org). SPM is a
procedure that was originally developed to analyze cerebral blood flow in 3D PET and fMRI
images [43,44], but it has also been utilized to analyze spatiotemporal biomechanical data [45].
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SPM takes into consideration the time-dependent nature of biomechanical variables such as joint
kinematics or ligament strains and performs a statistical comparison across the entire
spatiotemporal profile, rather than analyzing a discrete time point. Specifically, plantar fascia
strain was compared between the untaped and taped conditions using an SPM two-tailed
dependent t-test. First, the SPM{t} statistic was calculated for each data point during the stance
phase of gait. Random field theory was then used to determine the critical threshold in which the
SPM{t} statistic must cross to be considered significantly different at the α = 0.05 level. Tests
for normality using the D’Agostino-Pearson K2 test. Violations of normality were defined by a
significant K2 test statistic at the α = 0.05 level. In cases where violations of normality occurred,
non-parametric SPM analysis was conducted.
To further investigate the effects of low-Dye taping on plantar fascia strain, post hoc
analyses were conducted. The multi-segment foot model was used to explore kinematic variables
to help explain differences in plantar fascia strain. SPM procedures were utilized to analyze the
sagittal plane kinematics of the ankle joint, talonavicular joint, tarsometatarsal (TMT) joint, and
MTP joint, as well as the frontal and transverse plane kinematics of the subtalar joint. Finally,
strains in the spring, deltoid, long plantar, short plantar, bifurcate, and cervical ligaments during
stance phase were analyzed using the same SPM procedures utilized for the plantar fascia.
Results
At initial contact, there was a small spike in plantar fascia strain, which indicates an
increased strain magnitude relative to the offloaded standing calibration trial. Following the
initial spike, strain reduced to approximately 1-1.5% during midstance. This is followed by a
much larger spike in strain magnitude during late stance that corresponds to the push-off phase
of the gait cycle (Figure 5.2A).
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Statistical parametric mapping revealed a significant difference in plantar fascia strain
between the untaped and taped conditions because the SPM{t} statistic crossed the critical
threshold at α = 0.05 (p = 0.008). More specifically, differences between plantar fascia strain
were present between 57-86% of stance phase, with lesser strain present in the taped condition
(Figure 5.2B).
Subsequent analyses revealed a significant difference in talonavicular joint motion
between the untaped and taped conditions (p = 0.004) from 47-86% of stance phase (Figure 5.3A
and 5.3B). The taped condition displayed a smaller degree of talonavicular joint dorsiflexion,
indicating a reduced amount of arch collapse in the taped condition. A significant difference was
also found in the transverse plane subtalar joint motion from 15-17% (p = 0.047) and 33-65% (p
= 0.013) of stance phase, with the taped condition exhibiting greater subtalar abduction (Figure
5.3C and 5.3D). Analyses of the ankle, TMT, MTP, and frontal plane subtalar joint revealed no
statistical differences between the conditions.
Exploratory investigation of ligament strains revealed several significant differences due
to the walking conditions. Both slips of the spring ligament displayed lower magnitudes of strain
during the taped condition. The superomedial slip displayed significantly lesser strain (p < 0.001)
during the taped condition from 5-84% of stance phase (Figure 5.4A and 5.4B), while the
inferior slip displayed significantly lesser strain (p < 0.001) during the taped condition from 19-
60% of stance phase (Figure 5.4C and 5.4D). Finally, the 2nd and 3rd slips of the long plantar
ligament displayed higher magnitudes of the untaped condition, with the 2nd slip exhibiting
significantly greater strain (p = 0.021) during the untaped condition from 70-85% of stance phase
(Figure 5A and 5B) and the 3rd slip exhibiting significantly greater strain (p = 0.026) during the
untaped condition from 73-85% of stance phase (Figure 5C and 5D). However, no significant
87
differences were found in the deltoid, 4th slip of the long plantar, deep component of the long
plantar, short plantar, bifurcate, or cervical ligaments.
Discussion
The results of the study supported the hypothesis that the low-Dye taping method results
in reduced levels of plantar fascia strain in individuals with plantar fasciitis when walking. The
levels of plantar fascia strain estimated by the model ranged from approximately 0.5-1.5% strain
during midstance to nearly 6% strain during late stance. These values are similar to Caravaggi et
al. [46], who reported peak strain magnitudes that ranged between 3.5-6.0% in a group of healthy
individuals when using a rigid body model to estimate plantar fascia strains during walking. The
study conducted by Fessel et al. [47] also provides support to the strain values estimated by this
study’s model. In it, the researchers reported a mean peak plantar fascia strain value of 4.8%
when they used fluoroscopy to measure plantar fascia strains during walking.
It is believed that excessive strain in the plantar fascia produces microtears and
inflammation at the insertion of the plantar fascia on the medial calcaneal tubercle, which leads
to plantar fasciitis [3–6]. A reduction in pain following the application of low-Dye tape has been
shown in individuals with plantar fasciitis [18,26–28]. The results of our study revealed a
reduction of plantar fascia strain during the taped condition from 57-86% of stance phase, which
may help to explain the ability of the low-Dye taping method to reduce pain in individuals with
plantar fasciitis. Interestingly, there was no difference between the conditions at the time of peak
plantar fascia strain, which occurred at approximately 90% of stance phase. These results suggest
that the reduction in pain from the low-Dye taping method is not due to a reduction in peak
plantar fascia strain, but instead due to a cumulative reduction in strain across the entire stance
phase.
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The low-Dye taping method may also reduce pain in plantar fasciitis patients by affecting
the function of the windlass mechanism. Previous studies have demonstrated the function of the
windlass mechanism by showing that an increase in MTP joint dorsiflexion causes the plantar
fascia to wind around the metatarsal heads, which increases the tension of the plantar fascia
[46,48,49]. Additionally, it has previously been reported that plantar fascia strain is moderated
by both MTP joint motion and arch collapse [50,51]. The results of this study support the strong
relationship between the windlass mechanism and plantar fascia strain, as the rapid increase of
MTP joint dorsiflexion during late stance corresponds to a similar rapid increase of plantar fascia
strain. However, the rapid increase of plantar fascia strain during the push-off phase occurred
slightly later during the taped condition. This suggests that the arch support provided by the
taping method acts to delay the engagement of the windlass mechanism by keeping the
talonavicular joint closer to neutral. The relative slackness of the plantar fascia in the taped
condition due to the increased arch height requires a greater amount of MTP joint dorsiflexion to
engage the windlass mechanism. Furthermore, the reduction in talonavicular dorsiflexion angle
helps to explain the decreased magnitude of plantar fascia strain during midstance. Increased
arch collapse (represented in this study by an increased talonavicular dorsiflexion angle)
increases the total distance between the calcaneus and the hallux, which increases the overall
strain in the plantar fascia.
The reduced arch collapse demonstrated by the individuals with plantar fasciitis in our
study was supported by the results found by Vicenzino et al. [38] and Yoho et al. [39], who
reported similar results in healthy individuals. In addition to the significant reduction of
talonavicular dorsiflexion caused by low-Dye taping, the participants in the current study also
demonstrated significantly greater subtalar abduction. While electromyographic data were not
89
collected in the study, it is possible that the application of the low-Dye tape affected activity of
the tibialis posterior and peroneus brevis muscles. The tibialis posterior is a subtalar inverter,
while the peroneus brevis is an everter [52]. The action of the low-Dye tape to prevent subtalar
eversion may reduce activity of the tibialis posterior, thereby increasing the action of its
antagonist, the peroneus brevis. In contrast to these results, a previous study conducted by
O’Sullivan et al. [36] reported reduced subtalar pronation following low-Dye taping. However, it
is important to note that the authors utilized a different method of subtalar joint measurement,
which may explain the differences in results. Furthermore, pronation is a tri-planar motion used
to describe a combination of dorsiflexion, eversion, and abduction, but previous research has
shown that motions of the subtalar joint often do not occur in the tri-planar pattern mentioned
above during closed-chain activities [53,54].
The decrease in arch collapse following application of the low-Dye tape can also explain
the decreased strains of the superomedial and inferior slips of the spring ligament, as well as the
2nd and 3rd slips of the long plantar ligament. Both the spring ligament and the long plantar
ligament provide support to the medial longitudinal arch [12,16], and the current study shows
that an increase in arch collapse increases the strain in the spring and long plantar ligaments.
Research has shown that release of the spring ligament increased arch collapse by 14.9% [15],
and a finite element model has shown that tension in the long plantar ligament increased by 91%
following release of the plantar fascia [13]. The results of the current study provide further
evidence of the roles that the spring and long plantar ligaments play in the maintenance of medial
longitudinal arch support. However, caution must be taken when interpreting the results of these
ligaments, as statistically significant differences found when the strains are negative may have
90
little physiological significance. More research needs to be conducted to better understand the
true physiological strains of these ligaments during dynamic activities such as walking.
The current study demonstrates the ability of the low-Dye taping method to reduce
plantar fascia strain during walking during a short time. The long-term effects of the low-Dye
taping method were not considered in this study, so caution must be taken when interpreting the
results of the study. Additionally, several limitations of the study must be considered. First, the
inability to directly measure talus motion may have affected measurements of the subtalar and
talonavicular joints. Because markers cannot be placed on the talus bone, the model was
modified to attribute frontal and transverse plane motions of the ankle joint to the subtalar joint.
A study that inserted bone pins in the foot to measure ankle and subtalar joint motion found that
plantarflexion/dorsiflexion occurred mainly around the ankle joint, while inversion/eversion and
abduction/adduction occurred equally across both joints [55]. However, it must be noted that the
study was only conducted on three participants, and the researchers concluded that the
assumption is appropriate for some individuals. While the visual recreation of the walking trials
with the musculoskeletal model appeared reasonable, it is possible that the inability of the model
to measure true motions of the subtalar joint affected the estimated strain magnitudes of the
plantar fascia and other ligaments. However, the similarity of the plantar fascia strain magnitudes
in the current study to strain magnitudes reported in other studies [21,46] provides support to the
validity of the current model. Another limitation of the study was the use of markers mounted on
the skin to represent the underlying motion of the foot bones, as previous research has reported
significant kinematic differences between bone pins and skin markers [56]. However, the
validation results reported in chapter four support the use of skin markers to represent the bones
of the foot during walking.
91
Conclusions
The results of this study show that the low-Dye taping method is effective at reducing
plantar fascia strain during walking. While it does not reduce the magnitude of peak plantar
fascia strain, it causes the increase in strain due to activation of the windlass mechanism to occur
later in the stance phase. The reduction in plantar fascia strain can be attributed to the significant
positive effect that the low-Dye taping method has on arch collapse, represented by talonavicular
motion in this study. Finally, this study shows that support to the medial longitudinal arch is
provided by both the spring and long plantar ligaments.
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Figures and Tables
Figure 5.1: The low-Dye taping procedure is designed to prevent medial longitudinal arch
collapse. Reprinted from “Arch-taping techniques for altering navicular height and plantar
pressures during activity,” by T. Newell, J. Simon, and C. Docherty, 2015, Journal of Athletic
Training, 50(8), 827. [57]
96
Figure 5.2: The model described in chapter four was modified to include the long plantar
ligament and short plantar ligament.
97
Figure 5.2: A) Mean plantar fascia strain during stance phase across all participants during
untaped (black line) and low-Dye taped (blue line) walking conditions. B) The critical threshold
of 2.716 was exceeded from 57-86% of stance phase, indicating significantly lesser (p = 0.008)
plantar fascia strain during the taped condition.
A) B)
98
Figure 5.3: A) Mean sagittal plane talonavicular angle and C) mean transverse plane subtalar
angle during stance phase across all participants during untaped (black line) and low-Dye taped
(blue line) walking conditions. B) For the talonavicular joint, the critical threshold of 2.535 was
exceeded from 47-86% of stance phase, indicating significantly lesser (p = 0.004) talonavicular
joint dorsiflexion during the taped condition. D) For the subtalar joint, the critical threshold of
2.213 was exceeded from 15-17% and from 33-65% of stance phase, indicating significantly
greater (p = 0.047 and p = 0.013, respectively) subtalar joint abduction in the taped condition.
C) D)
A) B)
99
Figure 5.4: Mean strain of the A) superomedial and C) inferior slips of the spring ligament
during stance phase across all participants during untaped (black line) and low-Dye taped (blue
line) walking conditions. B) For the superomedial slip, the critical threshold of 2.339 was
exceeded from 5-84% of stance phase, indicating significantly lesser (p < 0.001) strain during
the taped condition. D) For the inferior slip, the critical threshold of 2.783 was exceeded from
19-60% of stance phase, indicating significantly lesser (p < 0.001) strain in the taped condition.
C) D)
A) B)
100
Figure 5.5: Mean strain of the A) 2nd and C) 3rd slips of the long plantar ligament during stance
phase across all participants during untaped (black line) and low-Dye taped (blue line) walking
conditions. B) For the 2nd slip, the critical threshold of 2.823 was exceeded from 70-85% of
stance phase, indicating significantly greater (p = 0.021) strain during the untaped condition. D)
For the 3rd slip, the critical threshold of 2.864 was exceeded from 73-85% of stance phase,
indicating significantly greater (p = 0.026) strain in the untaped condition.
C) D)
A) B)
101
Appendix: Institutional Review Board Approval
102
103
CHAPTER 6. GENERAL CONCLUSIONS
Summary
The overall purpose of this dissertation was to investigate strains in the plantar fascia and
other ligaments that help to support the medial longitudinal arch with a specific goal to provide
insight into the injury mechanism of plantar fasciitis.
The first study examined several environmental factors thought to influence plantar fascia
strain. The effects of speed, incline, and shoe stiffness on peak plantar fascia strain during
walking were analyzed in healthy participants using a four-segment musculoskeletal model. It
was found that increased speed caused an increase in peak plantar fascia strain, while incline and
shoe stiffness did not affect peak strains. Furthermore, the study examined the interaction
between metatarsophalangeal (MTP) joint motion and arch collapse to help explain the results, as
both have been found to moderate plantar fascia strain [1–3]. The function of the windlass
mechanism was demonstrated; the results showed that MTP joint dorsiflexion during the push-
off phase contributed to an increase in plantar fascia strain. However, the MTP joint dorsiflexion
was accompanied by an increase in arch height, which contributed to a decrease in the plantar
fascia strain, thereby resulting in no significant differences in peak plantar fascia strain between
inclines or shoe stiffnesses.
The second study was conducted to validate a six-segment musculoskeletal model of the
foot that was created to generate estimations of ligament strains. In addition to the plantar fascia,
several ligaments also provide support to the medial longitudinal arch and help to control
motions such as excessive pronation [4–7]. Because of their contribution to arch support, these
ligaments may influence the magnitude of the load placed on the plantar fascia, which may be a
factor in the development of plantar fasciitis. The spring, deltoid, bifurcate, and cervical
104
ligaments were dissected on seven cadaver specimens, and strains were directly measured using
a manual digitizer and estimated using the musculoskeletal model while an axial load was placed
on the tibia. While there were some limitations to the results, strong correlations were reported in
several ligaments. Furthermore, many ligaments exhibited low coefficients of repeatability.
Therefore, the model was deemed appropriate to use in the subsequent study.
The final study examined the effects of the low-Dye taping method on plantar fascia
strain during walking in individuals with plantar fasciitis. The study also utilized the six-segment
musculoskeletal model to estimate the effects of the low-Dye taping method on ligament strains.
The low-Dye taping method helps to support the arch, and research has shown it is effective at
reducing pain and improving function in individuals with plantar fasciitis [8–11]. It was found
that the taping method reduced plantar fascia strain during midstance, although there was no
reduction of peak plantar fascia strain. The function of the windlass mechanism was also affected
by the taping method. The rapid increase of plantar fascia strain during the push-off phase
occurred slightly later, which suggests that the arch support provided by the taping method acts
to delay the engagement of the windlass mechanism by reducing talonavicular joint dorsiflexion.
Consequently, the increased arch height in the taped condition required a greater amount of MTP
joint dorsiflexion to overcome the relative slackness of the plantar fascia and engage the
windlass mechanism. The musculoskeletal model also revealed a significant decrease in spring
ligament and long plantar ligament strain during the taped condition. As both ligaments have
been shown to provide support to the medial longitudinal arch [4,12], these results suggest that
these ligaments may play a role in the development of plantar fasciitis by affecting the
magnitude of the load placed on the plantar fascia. However, more research needs to be
105
conducted on these tissues, as there is very little published information on the behavior of the
ligaments in the foot during dynamic activities.
Significance and Future Directions
In summary, this dissertation provides information about the plantar fascia strain
response under several different conditions. The results from this dissertation that examined
effects of speed, incline, shoe stiffness, and taping on plantar fascia strain affirm the contribution
of the windlass mechanism to plantar fascia strain, as both MTP joint motion and arch collapse
interact to influence plantar fascia strain magnitudes during walking. Furthermore, the spring and
long plantar ligament provide support to the medial longitudinal arch, and the way they influence
the magnitude of strains in the plantar fascia needs to be investigated further. Finally, the results
suggest that it may be the accumulation of strain rather than peak strain that plays a role in the
development and perpetuation of plantar fasciitis. This finding has implications, both in our
understanding of the disorder and in the treatment of the disorder. Further research is necessary
to better understand the plantar fascia strain response, as it is hoped that understanding the role
of plantar fascia strain in the etiology of plantar fasciitis will enable effective treatment and
prevention of the disorder.
References
[1] K.A. McDonald, S.M. Stearne, J.A. Alderson, I. North, N.J. Pires, J. Rubenson, The role
of arch compression and metatarsophalangeal joint dynamics in modulating plantar fascia
strain in running, PLoS One. 11 (2016) e0152602.
[2] D.L. Riddle, S.M. Schappert, Volume of Ambulatory Care Visits and Patterns of Care for
Patients Diagnosed with Plantar Fasciitis: A National Study of Medical Doctors, Foot
Ankle Int. 25 (2004) 303–310.
[3] R.E. Carlson, L.L. Fleming, W.C. Hutton, The Biomechanical Relationship Between The
Tendoachilles, Plantar Fascia and Metatarsophalangeal Joint Dorsiflexion Angle, Foot
Ankle Int. 21 (2000) 18–25.
106
[4] R.F. Ker, M.B. Bennett, S.R. Bibby, R.C. Kester, R.M. Alexander, The spring in the arch
of the human foot, Nature. 325 (1987) 147–149.
[5] K. Tao, W.T. Ji, D.M. Wang, C.T. Wang, X. Wang, Relative contributions of plantar
fascia and ligaments on the arch static stability: A finite element study, Biomed. Eng.
(NY). 55 (2010) 265–271.
[6] C.K. Huang, H.B. Kitaoka, K.N. An, E.Y.S. Chao, Biomechanical Evaluation of
Longitudinal Arch Stability, Foot Ankle Int. 14 (1993) 353–357.
[7] H.B. Kitaoka, T.-K. Ahn, Z.P. Luo, K.-N. An, Stability of the arch of the foot, Foot Ankle
Int. 18 (1997) 644–648.
[8] D.M. Lynch, W.P. Goforth, J.E. Martin, R.D. Odom, C.K. Preece, M.W. Kotter,
Conservative treatment of plantar fasciitis. A prospective study, J. Am. Podiatr. Med.
Assoc. 88 (1998) 375–380.
[9] J.A. Radford, K.B. Landorf, R. Buchbinder, C. Cook, Effectiveness of low-Dye taping for
the short-term treatment of plantar heel pain: A randomised trial, BMC Musculoskelet.
Disord. 7 (2006) 64.
[10] K.B. Landorf, J.A. Radford, A.-M. Keenan, A.C. Redmond, Effectiveness of low-dye
taping for the short-term management of plantar fasciitis, J. Am. Podiatr. Med. Assoc. 95
(2005) 525–530.
[11] M.R. Hyland, A. Webber-Gaffney, L. Cohen, S.W. Lichtman, Randomized controlled trial
of calcaneal taping, sham taping, and plantar fascia stretching for the short-term
management of plantar heel pain, J. Orthop. Sport. Phys. Ther. 36 (2006) 364–371.
[12] J.L. Crary, J. Marcus Hollis, A. Manoli, The effect of plantar fascia release on strain in the
spring and long plantar ligaments, Foot Ankle Int. 24 (2003) 245–250.