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The influence of great toe valgus on pronation and frontal plane knee motion during running

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The Foot and Ankle Online Journal 13 (1): 7 Injury rates in running range from 19.4-79.3%, with injuries at the knee comprising 42.1%. Pronation and altered frontal plane knee joint range of motion have been linked to such injuries. The influence of foot structure on pronation and knee kinematics has not been examined in running. This study examined associations between great toe valgus angle, peak pronation angle and frontal plane range of movement at the knee joint during overground running while barefoot. Great toe valgus angle while standing, and peak pronation angle and frontal plane range of motion of the dominant leg during stance while running barefoot on an indoor track were recorded in fifteen recreational runners. There was a large, negative association between great toe valgus angle and peak pronation angle (r =-0.52, p = 0.04), and a strong positive association between great toe valgus angle and frontal plane range of motion at the knee joint (r = 0.67, p = 0.006). The results suggest that great toe position plays an important role in foot stability and upstream knee-joint motion. The role of forefoot structure as a factor for knee-joint injury has received little attention and could be a fruitful line of enquiry in the exploration of factors underpinning running-related knee injuries.
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The influence of great toe valgus on pronation and frontal
plane knee motion during running
by Richard Stoneham PhD1, Gillian Barry PhD1, Lee Saxby BSc2, Mick Wilkinson PhD1*
The Foot and Ankle Online Journal 13 (1): 7
Injury rates in running range from 19.4-79.3%, with injuries at the knee comprising 42.1%.
Pronation and altered frontal plane knee joint range of motion have been linked to such injuries.
The influence of foot structure on pronation and knee kinematics has not been examined in
running. This study examined associations between great toe valgus angle, peak pronation angle and
frontal plane range of movement at the knee joint during overground running while barefoot. Great
toe valgus angle while standing, and peak pronation angle and frontal plane range of motion of the
dominant leg during stance while running barefoot on an indoor track were recorded in fifteen
recreational runners. There was a large, negative association between great toe valgus angle and peak
pronation angle (r
= -0.52, p
= 0.04), and a strong positive association between great toe valgus angle  
and frontal plane range of motion at the knee joint (r
=
0.67, p
= 0.006). The results suggest that      
great toe position plays an important role in foot stability and upstream knee-joint motion. The role
of forefoot structure as a factor for knee-joint injury has received little attention and could be a
fruitful line of enquiry in the exploration of factors underpinning running-related knee injuries.
Keywords: great toe valgus; pronation; frontal plane knee range of motion; running
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Injury incidence in running ranges from 19.4-79.3%  
[1, 2]. The knee is the most injured site, comprising  
42.1% of all running-related injuries [2, 3].
Patellofemoral Pain Syndrome (PFPS) is the most
common running-related knee injury, followed closely
by Iliotibial Band Syndrome (ITBS) [3]. Altered
frontal plane hip and knee joint kinematics and  
pronation during the stance phase of running have    
been linked to these injury types, and differentiate
injured from uninjured runners [4-6]. Knee abduction,
femoral internal rotation, tibial external rotation, and
foot pronation, have been theoretically linked to
injury in a population of patients with PFPS [7]. As
such, interventions to normalise altered frontal plane
kinematics during running might be valuable for
rehabilitation of this type of knee injury. Interventions
have tended to focus on proximal areas linked to
altered knee kinematics. However, training studies to
increase hip abduction and external rotation strength
have not decreased hip or knee frontal plane peak
joint angles or joint excursions during the stance
phase of running [8-10]. Moreover, associations  
between hip strength and frontal plane hip and knee
peak angles and joint excursions while running and
jumping are weak [9, 11]. These findings suggest that  
proximally-based interventions are not effective at
altering lower extremity running mechanics and risk
of running related injury. Studies exploring the distal
end of the kinetic chain have utilised barefoot and
minimal footwear, and hip and foot muscle
1 - Department of Sport, Exercise and Rehabilitation, Northumbria University, UK
2 - LeeSaxby.com, Suffolk House, Louth, Lincolnshire, UK
* - Corresponding author: mic.wilkinson@northumbria.ac.uk
ISSN 1941-6806 doi: 10.3827/faoj.2020.1301.0007 faoj.org
The Foot and Ankle Online Journal 13 (1): 7
strengthening interventions to reduce surrogate
measures associated with injury at the knee and other
sites [10, 12-14]. Injury rates, however, remain high
[15]. The influence of foot structure on pronation and
knee joint kinematics in running has, by contrast,
received little attention.
Data comparing foot structure in habitually-barefoot
and habitually-shod populations have reported
consistent differences in the spread/abduction of the
great toe from the other toes [16-19]. Based on
Newtonian physics, larger areas of support provide
greater stability. It has been suggested that an
abducted great toe position might be important for
controlling the direction of body weight during
running, secondary to improved stability of the foot
[20, 21]. Running is essentially a series of alternate
single-leg jumps, where multiples of bodyweight must
be supported and controlled using a spring-like action
of the supporting foot and limb [22, 23]. Early
research showed an active role of the toes, the great
toe in particular, from midstance to toe off in running
[24]. More recent data comparing habitually barefoot
to habitually shod populations suggested that the
abducted great toe position, characteristic of the
barefoot group, reduced peak forefoot pressures
during running by increasing the area of support [19].
Another comparative study from the same lab [25]
found larger ankle eversion and internal rotation
(which together comprise pronation) during the
landing phase of jumping in habitually shod
compared to habitually-barefoot participants,
attributing differences to the abducted great toe
position characteristic of the barefoot group.
Together, these studies suggest a link between great
toe position and foot and ankle stability in running,
and dynamic tasks with similar demands to running.
Given evidence of the link between pronation, altered
frontal plane motion at the knee joint and risk of knee
injury [7], there is a possible mechanistic link between
great toe position, pronation and frontal plane knee
joint kinematics.
Previous research suggests that the toes have a
stabilising function, and that great toe position
influences area of support in running, and the extent
of pronation in the landing phase of jumping. The
influence of great toe position on pronation and on
kinematics at the knee joint has not been examined in
running. The aim of this study was to examine
associations between great toe valgus angle, peak
pronation angle and frontal plane range of movement
at the knee joint during overground running while
barefoot, the latter being necessary to avoid toe
position being constrained by shoes.
Methods
Participants
With institutional ethics approval, 15 volunteers (ten
male, five female) participated. Mean and SD age,
stature and mass of all participants were 26±7 yrs,
1.71±0.01 m and 69±10.9 kg respectively. Inclusion
criteria were aged 18-45 years and participation in
endurance running more than once per week as part
of habitual-exercise regimes, with at least one run
longer than 30 minutes. Participants were excluded if
they had an injury to the lower limbs in the previous
six months, or any condition that could affect their
normal running gait.
Design
An observational design assessed the relationship
between great toe valgus angle relative to the first
metatarsal, peak pronation angle and frontal plane
range of movement at the knee joint of the dominant
leg during stance, while running barefoot on an
indoor runway. The barefoot condition was chosen as
it was the only way to ensure that the toe angle
recorded in standing was not altered by footwear
while running. Data were collected in a single visit.
Participants were provided with a short-sleeved
compression top and shorts to improve skeletal
representation in biomechanical modelling, and were
instructed to be well rested before testing. Reflective
markers were attached in ‘Plug-In gait’ and
‘Oxford-Foot Model’ formations to assess lower-limb
kinematics of the dominant limb. Participants were
habituated to running barefoot with a 30-minute,
self-paced run. After habituation, participants ran
over a 20-m runway where kinematic data were
captured by 14 optoelectronic cameras. Electronic
timing gates (Brower timing gates, Utah, USA) placed
in the data capture area (2.7m apart) were used to
record speed in each trial. The average running speed
was 2.48±0.38 m·s-1.
Copyright © 2020 The Foot and Ankle Online Journal
The Foot and Ankle Online Journal 13 (1): 7
Procedures
Great toe valgus angle
Participants stood barefoot on top of a 0.35-m high
platform covered in graph paper. The non-dominant
foot was placed on the platform first, aligning the
most posterior aspect with a horizontal reference line
on the graph paper. The dominant foot was
positioned next, shoulder width apart from the other
foot, and with the most posterior aspect on the same
horizontal reference line. The first metatarsal
proximal-and distal-dorsal protrusions, and the
central and dorsal point of the interphalangeal joint of    
the great toe were identified by palpation, and marked
using a permanent pen. A digital camera (CX240,
Sony, Japan) positioned 0.3m above the platform on a
tripod was aligned with the first metatarsophalangeal
joint, and the zoom was adjusted so that bony
prominences defining great toe angle were visible. A
still image was captured and saved for analysis of
great toe valgus angle.
Kinematics
Prior to habituation, anthropometric measures were
recorded for use in biomechanical modelling (stature
(mm), mass (kg), bilateral-leg length (mm), and knee
and ankle joint width (mm)). For assessment of
lower-limb joint kinematics, participants had a series
of markers (Ø=14mm) attached in ‘Plug-In gait’ and
‘Oxford-Foot Model’ formations. Anatomical
locations of the ‘Plug-In gait’ and ‘Oxford-Foot
Model’ were sacrum, bilateral anterior-and
posterior-superior iliac spines, the bilateral
distal-lateral thigh, bilateral femoral-lateral epicondyle,
the bilateral distal-lateral lower-leg, the bilateral lateral
malleoli, the left/right toe (dorsal aspect of the
second metatarsal head) and the calcaneus of the
non-dominant limb at the same height as the toe
marker. The following markers were placed on the
dominant limb only, lateral head of the fibula, tibial
tuberosity, anterior aspect of the shin, the medial
malleoli, the proximal aspect of the calcaneus, a ‘peg
marker’ extending from the most posterior aspect of
the calcaneus, the inferior aspect of the calcaneus,
sustentaculum tali, proximal and dorsal aspect of the
first metatarsal head, the medial and distal aspect of
the first metatarsal head, the proximal-and
distal-lateral aspects of the fifth metatarsal and the
medial aspect of the first phalanx. Fourteen
infrared-optoelectronic cameras (Vicon 10 xT20 and
2 x T40, Oxford, UK) captured kinematic trajectories
at 200Hz.
Data treatment
A trial was deemed successful when running speed
was ± 5% of the predetermined running speed from
the habituation run. Dominant limb data for peak
pronation angle and frontal plane range of motion at
the knee joint were exported to Microsoft Excel
(Microsoft, USA). Foot structure images were loaded
to Dartfish ClassroomPlus (version 7.0, Fribourg,
Switzerland) where great toe valgus angle was
measured using the angle tool. (Chicago, USA).
Statistical analysis
Statistical analysis was undertaken using JASP 0.10.2.
Following verification of assumptions of linearity and
uniformity of errors using Q-Q and residuals versus
predicted value plots respectively, linear regression
assessed associations between great toe valgus angle,
peak pronation angle and frontal plane range of
motion at the knee joint. Strength of associations
were judged against Cohen’s effect size categories for
Pearson’s r
i.e. small association
0.1-0.3; moderate     
association 0.3-0.5; large association 0.5-1.0 [26]
Significance was accepted at p
< 0.05.
Results
Mean and SD great toe valgus angle, peak pronation
angle and frontal plane knee range of motion were
9.5±6.1°, -5.2±6.6° and 6.2±2.2° respectively.
Association between great toe valgus and peak pronation angle.
There was a large, negative association of great toe
valgus angle and peak pronation angle during stance (r   
= -0.52, p
= 0.04). As great toe valgus angle increased  
(more positive = more valgus), peak pronation angle
decreased (more negative = increased pronation) (see
Figure 1). The regression equation showed a 0.59°
increase in peak pronation for every additional degree
of great toe valgus (95% CI 0.01 to 1.12°).
Copyright © 2020 The Foot and Ankle Online Journal
The Foot and Ankle Online Journal 13 (1): 7
Figure 1 Association between great toe valgus angle
and peak pronation angle during overground barefoot
running on an indoor track in 15 recreational runners.
Association between great toe valgus and frontal plane knee
range of motion.
Great toe valgus angle was strongly and positively
associated with frontal plane range of motion at the
knee joint (r
=
0.67, p
= 0.006). As great toe valgus    
angle increased, frontal plane knee range of motion
also increased (see Figure 2). The regression equation
showed a 0.24° increase in frontal plane knee joint
excursion for every one degree increase in great toe
valgus angle (95% CI 0.01 to 0.40°).
Figure 2 Association between great toe valgus angle
and frontal plane range of motion at the knee joint during
overground barefoot running on an indoor track in 15
recreational runners.
Discussion
The aim of this study was to examine associations
between great toe valgus, peak pronation and frontal
plane range of motion at the knee joint during
overground running. There was a strong, negative
correlation between great toe valgus angle and peak
pronation such that increased great toe valgus was
associated with a more negative peak pronation angle
(increased pronation). There was also a strong,
positive correlation between great toe valgus angle
and frontal plane range of motion at the knee joint
such that increased great toe valgus was associated
with larger knee joint excursions in the frontal plane.
Altered frontal plane hip and knee joint kinematics  
and pronation during the stance phase of running
have been linked to running-related knee injury, and
 
can differentiate injured from uninjured runners [4-6].
Knee abduction and foot pronation have also been
theoretically linked to patellofemoral pain [7]. In light
of this evidence, our results suggest that forefoot
structure might be an important but largely
unexplored factor in running-related knee injury.
As this is the first study to explore the association
between great toe valgus, pronation and frontal plane
knee joint excursions during running, there are no
studies with a similar approach for comparison.
Nevertheless, the strong relationships observed
broadly support findings from previous comparative
cross-sectional studies of habitually barefoot and
habitually shod participants that differed in forefoot
structure with respect to the spread/abduction of the
great toe [19, 25]. Shu et al. [25] observed larger ankle
eversion and internal rotation (which together
comprise pronation) in habitually shod compared to
habitually barefoot participants in the landing phase
of jumping. As running is essentially a series of
single-leg jumps, the strong association of great toe
valgus angle with peak pronation observed in running
in our study is not surprising. The reduced and more
evenly distributed forefoot peak pressures of
habitually barefoot participants reported by Mei et al.
[19] alludes to greater forefoot stability during the
period of stance when forces are highest. It is possible
that as the stability provided by the great toe
decreases with increasing valgus angle, instability of
the foot could manifest as higher peak pronation.
Increased forefoot instability with increased great toe
valgus is a plausible mechanism that could explain the
strong correlation of great toe valgus angle and peak
pronation that we observed. Increased postural
instability with great toe valgus [27] and with splinting
of the great toe into flexion [28] have been observed
in single-leg balance tasks. Though these studies
examined static balance and not the dynamic
single-leg balance characteristic of running, the
underpinning link between the area of the base of
support and subsequent stability could be assumed to
Copyright © 2020 The Foot and Ankle Online Journal
The Foot and Ankle Online Journal 13 (1): 7
be common to both. Instability at the foot could have
kinematic consequences further up the kinetic chain,
resulting in increased frontal plane motion at the
knee. The strong, positive association of great toe
valgus angle with frontal plane knee joint excursion
observed in the current study is consistent with this
suggestion. Moreover, the kinematic links between
pronation and frontal plane knee joint range, as well
as the link between these factors and running-related
knee injury suggested here have been suggested
previously elsewhere [7] and supported by previous
studies [4-6].
The main limitation of this study is that the
correlational design prevents any suggestion of a
causal link between great toe valgus, peak pronation
and frontal plane knee joint excursions. Another
limitation is that great toe valgus angle was measured
during static stance, not while running, so an
assumption that valgus angle remains relatively
unchanged when the foot is loaded during running is
implicit in the interpretation of the results. Previous
research, however, suffers from similar limitations,
comprising only comparative studies of foot and
ankle function and pressure distributions of groups
with mean abducted versus mean valgus great toe
positions. As such, a correlational study like this one
does add to the understanding of how foot structure
might relate to pronation and knee joint kinematics in
dynamic tasks like running by examining a
‘dose-response’ type association, in addition to the
‘with and without’ type evidence of previous
comparative studies. Moreover, there are plausible
mechanisms of action for both key findings in this
study, so the data provide both direct and mechanistic
evidence towards establishing a causal link [29]. A
logical next step for this area of research would be
randomised control trials where pronation and knee
kinematics are evaluated before and after an
intervention to alter great toe valgus angle in one
group, with the control group foot structure
remaining unchanged. Interventions could potentially
include corrective surgery or corrective devices that
reposition the great toe. Additional comparative
studies that measure knee joint kinematics during
running would, however, be a useful intermediate
step.
In summary, this study observed strong associations
between great toe position, peak pronation and
frontal plane range of motion at the knee joint during
over-ground barefoot running. The results suggest
that great toe position plays an important role in foot
stability and subsequent knee-joint motion. Both
pronation and frontal plane knee-joint motion have
been implicated in the etiology of knee injuries. The
role of forefoot structure as a factor for knee-joint
injury has received little attention and could be a
fruitful line of enquiry in the exploration of factors
underpinning running-related injuries.
This study formed part of a PhD program
collaboratively funded by Northumbria University
and VivoBarefoot. VivoBarefoot had no input to the
design, analysis or interpretation of studies or data, or
the preparation of this manuscript.
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... Footwear can, however, change the pressure application to different areas of the foot, influencing the direction of ground reaction force vectors relative to joints, and thus, the resulting joint moments [58]. Footwear can also influence stability of the runner while they are absorbing the forces of impact, influencing the direction of ground reaction force vectors and joint movements [59]. ...
... Over time, this excessive pronation of the rear foot on the forefoot breaks down the soft tissues of the foot resulting in a dysfunctional collapsed/flat arch (overly twisted foot plate) and knee injuries [107]. A recent study showing a strong correlation of great toe valgus angle with pronation and frontal plane knee movement [59], and the previously reported positive association of navicular drop with running injury [10] support this link. ...
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The foot is a complex structure with many articulations and multiple degrees of freedom that play an important role in static posture and dynamic activities. The evolutionary development of the arch of the foot was coincident with the greater demands placed on the foot as humans began to run. The movement and stability of the arch is controlled by intrinsic and extrinsic muscles. However, the intrinsic muscles are largely ignored by clinicians and researchers. As such, these muscles are seldom addressed in rehabilitation programmes. Interventions for foot-related problems are more often directed at externally supporting the foot rather than training these muscles to function as they are designed. In this paper, we propose a novel paradigm for understanding the function of the foot. We begin with an overview of the evolution of the human foot with a focus on the development of the arch. This is followed by a description of the foot intrinsic muscles and their relationship to the extrinsic muscles. We draw the parallels between the small muscles of the trunk region that make up the lumbopelvic core and the intrinsic foot muscles, introducing the concept of the foot core. We then integrate the concept of the foot core into the assessment and treatment of the foot. Finally, we call for an increased awareness of the importance of the foot core stability to normal foot and lower extremity function.
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The Foot and Ankle Online Journal 9 (2): 5 There has been and continues to be much debate about the merits and detriments of barefoot and minimal-shoe running. Research on causes of running-related injury is also characterised by equivocal findings. A factor common to both issues is the structure and function of the foot. Comparatively, this has received little attention. This perspective piece argues that foot function and in particular, how foot structure determines function, has largely been overlooked, despite basic principles of physics dictating both the link between structure and function and the importance of function for stability in locomotion. We recommend that foot shape and function be considered in the interpretation of existing findings and be incorporated into future investigations interested in running mechanics, injury mechanisms and the effects of footwear on both. s stated by evolutionary biologist EO Wilson, " everything in biology is subject to the laws of physics and chemistry and has arisen through evolution by natural selection " [1]. Applying this logic to the study of human locomotion, and in particular the structure and role of the foot, can bring clarity to the interpretation of many past and recent studies on barefoot-versus-shod-and minimal-shoe locomotion, and the associated benefits and risks. Using laws and undisputed theories as filters through which to interpret study outcomes can provide a context to equivocal findings and also suggest fruitful lines of future inquiry. The 'purpose' of the foot Assigning a purpose to a biological structure is often criticised as teleological. However, as Nobel Laureate Albert Szent-Gyorgyi [2] wrote " teleology resembles an attractive lady of doubtful repute whose company we cherish but in whose company we do not like to be seen ". Purpose provides the context without which many observations in nature make no sense. A teleological view is therefore adopted in this piece. In an upright biped, the purpose of the foot is to support and control the direction of the body weight as it falls forwards during the stance phase of locomotion [3-5]. With this and fundamental physics in mind, a reverse-engineering approach suggests a larger base of support, that is widest at the front, would serve both purposes.
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Background Recreational runners frequently suffer from chronic pathologies. The knee and ankle have been highlighted as common injury sites. Barefoot and barefoot inspired footwear have been cited as treatment modalities for running injuries as opposed to more conventional running shoes. This investigation examined knee and ankle loading in barefoot and barefoot inspired footwear in relation to conventional running shoes. Method Thirty recreational male runners underwent 3D running analysis at 4.0 m.s- 1. Joint moments, patellofemoral contact force and pressure and Achilles tendon forces were compared between footwear. Findings At the knee the results show that barefoot and barefoot inspired footwear were associated with significant reductions in patellofemoral kinetic parameters. The ankle kinetics indicate that barefoot and barefoot inspired footwear were associated with significant increases in in Achilles tendon force compared to conventional shoes. Interpretation Barefoot and barefoot inspired footwear may serve to reduce the incidence of knee injuries in runners although corresponding increases in Achilles tendon loading may induce an injury risk at this tendon.