[
research report
]
MELISSA RABBITO, MSc, CPedC1 • MICHAEL B. POHL, PhD2 • NEIL HUMBLE, DPM3 • REED FERBER, PhD, CAT(C)4
Biomechanical and Clinical
Factors Related to Stage I Posterior
Tibial Tendon Dysfunction
P
osterior tibial tendon dysfunction (PTTD) is a progressive
and debilitating condition that is estimated to affect nearly 5
million people in the United States.7 In the early stages (stage I)
of the condition, PTTD is a common running-related injury.31
While the aetiology of PTTD has not been established, it is considered
multifactorial in nature and has generally been related to progressive
alterations in arch structure, muscular strength, and gait biomechanics.
Few studies have been conducted
to understand how arch structure may
play a role in the progressive nature of
PTTD.4,15,24 Williams et al36 conducted a
TTSTUDY DESIGN: Case control.
TTOBJECTIVES: To investigate differences in arch
height, ankle muscle strength, and biomechanical factors in individuals with stage I posterior
tibial tendon dysfunction (PTTD) in comparison to
healthy individuals.
TTBACKGROUND: PTTD is a progressive condition,
so early recognition and treatment are essential to
help delay or reverse the progression. However, no
previous studies have investigated stage I PTTD,
and no single study has measured static anatomical structure, muscle strength, and gait mechanics
in this population.
TTMETHODS: Twelve individuals with stage I PTTD
and 12 healthy, age- and gender-matched control
subjects, who were engaged in running-related
activities, participated in this study. Measurements of arch height index, maximum voluntary
ankle invertor muscle strength, and 3-dimensional
rearfoot and medial longitudinal arch kinematics
retrospective analysis of running injuries in runners with high and low plantar arch and reported that the low-arch
group had a 3-fold higher incidence of
during walking were obtained.
TTRESULTS: The runners with PTTD demonstrated
significantly lower seated arch height index (P =
.02) and greater (P = .03) and prolonged (P = .05)
peak rearfoot eversion angle during gait, compared
to the healthy runners. No differences were found
in standing arch height index values (P = .28), arch
rigidity index (P = .06), ankle invertor strength (P =
.49), or peak medial longitudinal arch values (P =
.49) between groups.
TTCONCLUSION: The increased foot pronation is
hypothesized to place greater strain on the posterior tibialis muscle, which may partially explain
the progressive nature of this condition. J Orthop
Sports Phys Ther 2011;41(10):776-784, Epub 12
July 2011. doi:10.2519/jospt.2011.3545
TTKEY WORDS: foot kinematics, gait,
tendinopathy
stage I PTTD compared to the high-arch
group. Dyal et al4 also reported that a
lower arch height was associated with the
symptomatic PTTD foot compared to the
uninvolved foot. In contrast, Shibuya et
al30 reported that radiographic and MRI
scans of patients with PTTD at various
stages showed damage to the spring
ligament, with a lower arch height only
present in patients with stages III and
IV PTTD. Thus reduced arch height may
be a predisposing factor related to stages
III and IV PTTD, while a more typical
arch height would be expected in stage I
PTTD. Moreover, stage I PTTD is characterized by tendon inflammation, with
no change in foot shape, while stage II
PTTD is characterized by the tendon’s
elongation and dysfunction, as the foot
develops adult acquired flatfoot disorder.13 Thus it can be hypothesized that
no differences in arch shape would be
expected for patients with stage I PTTD,
and, consequently, other factors, such as
reduced ankle muscle strength, should be
considered.
There is a paucity of research regarding differences in ankle invertor muscle
strength for individuals with PTTD. Alvarez et al1 reported significant concentric
and eccentric ankle invertor strength reductions for the involved compared to the
uninvolved ankle. Following a 10-week
Research Associate, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada. 2Postdoctoral Fellow, Faculty of Kinesiology, University of Calgary, Calgary, Alberta,
Canada. 3Clinical Assistant Professor, Division of Podiatric Surgery, University of Calgary, Calgary, Alberta, Canada; Adjunct Assistant Professor, Faculty of Kinesiology, University
of Calgary, Calgary, Alberta, Canada. 4Associate Professor, Faculties of Kinesiology and Nursing, University of Calgary, Calgary, Alberta, Canada; Director, Running Injury Clinic,
Calgary, Alberta, Canada. This study received ethical approval from the Conjoint Health Research Ethics Board of the University of Calgary. Address correspondence to Dr Reed
Ferber, Faculty of Kinesiology, 2500 University Drive NW, University of Calgary, Calgary, Alberta, Canada T2N 1N4. E-mail: [email protected]
1
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strengthening program, the PTTD group
exhibited a 58% increase in strength,
concomitant with significant reductions
in pain. Houck et al8 also reported that
patients with PTTD exhibited 30% reduced ankle invertor strength compared
to age-matched controls. However, while
these 2 studies indicate that ankle invertor strength may be associated with
PTTD, the individuals with PTTD in the
aforementioned studies were at stages
II to IV of the condition, and no study
has investigated individuals with stage I
PTTD for potential differences in ankle
invertor strength. Because stage I PTTD
involves mild swelling to the tendon and
pain upon palpation, it is reasonable to
hypothesize that reduced force output
would be present in these individuals.
Few studies have investigated differences in gait biomechanics for individuals with PTTD. Ness et al23 reported
increased rearfoot eversion throughout
stance in patient with PTTD compared
to controls; however, all their study’s patients with PTTD had failed conservative
treatment and were scheduled for operative intervention. Tome et al32 also reported that individuals with stage II PTTD
demonstrated significantly greater peak
rearfoot eversion and a lower medial longitudinal arch (MLA) angle during walking. Finally, Houck et al9 investigated
patients with stage II PTTD and reported
increased rearfoot eversion compared to
controls. Thus, increased rearfoot eversion is present in individuals with stages
II to IV PTTD when walking; however,
no studies have investigated whether
increased rearfoot eversion is present in
stage I of the condition. Because PTTD
is a progressive condition, identifying if
potentially contributing factors related
to static foot structure, ankle invertor
muscle strength, and gait biomechanics may be present in individuals with
stage I PTTD could lead to interventions
aimed at early detection and prevention
of PTTD progression.
The purpose of this study was to investigate differences in arch height, ankle
muscle strength, and kinematic factors in
TABLE 1
Demographic Data
PTTD (n = 12)
Control (n = 12)
P Value
Age, y
30.3  7.9
28.5  8.6
.30
Weight, kg
65.7  11.5
68.9  12.8
.26
Height, cm
168.2  10.8
170.1  7.8
.32
BMI, kg/m2
23.2  3.4
23.7  2.8
.37
Abbreviations: BMI, body mass index; PTTD, posterior tibial tendon dysfunction.
*Values are mean  SD unless otherwise specified.
individuals presenting with stage I PTTD
in comparison to healthy individuals.
Compared to the control group, we hypothesized that the PTTD group would
demonstrate (1) no differences in static
arch height, (2) decreased ankle invertor muscle strength, and (3) greater and
prolonged peak rearfoot eversion and
lower peak MLA during the stance phase
of walking.
METHODS
Subjects
S
ubjects
were
recruited
through the Running Injury Clinic
at the University of Calgary and
various sports medicine clinics, including local practitioners such as pedorthists, podiatrists, and medical doctors.
All subjects were actively involved in
running and running-related sports and
provided informed, written consent. The
study protocol was approved by the Conjoint Health Research Ethics Board of the
University of Calgary.
A Canadian certified athletic therapist, who is also a Canadian certified
pedorthist, screened potential subjects
through a clinical assessment that included a detailed history, differential
diagnosis for other tendinopathies and
musculoskeletal injuries, muscle strength
testing, and manual palpations. Several
steps were taken to differentiate between
individuals with stages I and II PTTD.
Typically, individuals with stage I PTTD
exhibit signs of tendinopathy without
postural changes in the foot, whereas
those with stage II PTTD exhibit tendon
elongation, acquired flatfoot deformity,
and fixed rearfoot deformities.13 Moreover, with stage I PTTD, individuals generally exhibit pain superior and posterior
to the medial malleolus, whereas those
with stage II PTTD exhibit pain near the
distal insertions of the tendon. Thus a
clinical examination of passive rearfoot
eversion and midfoot mobility was conducted and location of pain was evaluated to initially screen potential subjects.
Once selected, potential subjects were
screened according to specific inclusion
and exclusion criteria.11,13,14
Each subject was required to meet the
following inclusion criteria to qualify for
the PTTD group: (1) mild swelling and/or
tenderness posterior to the medial malleolus, (2) pain posterior and/or superior
to the medial malleolus, aggravated by
recreational activity, (3) pain that had
been present for at least 3 weeks, and (4)
participation in recreational running or
walking a minimum of 3 times per week
and 30 minutes per session. Subjects
were excluded from the PTTD group if
they met any of the following exclusion
criteria: (1) previous surgery on the affected foot, leg, or knee; (2) osteoarthritis
in the knee of the affected side; (3) fixed
rearfoot deformities; (4) recurrent ankle
sprains on the affected side; (5) ligament
tears or boney abnormalities of the affected foot; (6) a physical or medical
condition that contraindicated the testing protocol; (7) pregnancy; or (8) flexor
hallucis longus or flexor digitorum longus
tendinopathy.
In total, 15 individuals with PTTD
presented for consideration, 3 of which
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FIGURE 1. Arch height index measurement system.
FIGURE 3. Strength testing of the tibialis posterior
(A) Adjustable sliders were used to measure total
foot length, (B) truncated foot length, (C) and dorsal
height at 50% of total foot length.
were excluded from the study, 1 due to
incorrect location of pain (presentation
of lateral ankle pain), another who met
all the inclusion criteria but whose data
were deemed unusable after processing,
and a third due to multiple confounding injuries, including plantar fasciitis
and metatarsalgia. Based on a 0-to-10
visual analog scale, with 0 representing
no pain and 10 extreme pain, the PTTD
group reported an average pain score of
5 during running activity and 3.5 during
activities of daily living. The visual analog
scale has been established as a reliable
and valid measure of self-reported pain.29
No individuals with stage II PTTD were
screened, most likely because the sample
was recruited primarily from sports medicine clinics, which typically see patients
involved in recreational sports that demand a level of activity limited by stage
II PTTD.11,13,14
Control subjects (9 females and 3
males) were matched to individuals with
PTTD (9 females and 3 males), based on
age, gender, and body mass index (BMI),
and screened by the same exclusion criteria as those used to screen the PTTD
group. There were no statistical differences between groups for the variables
listed in TABLE 1 and other demographic
variables.
Structure
Arch height index (AHI) was measured
using a custom-built arch height index
measurement system2 (FIGURE 1). Two
boards were placed under the foot, 1
]
muscle using a strap and dynamometer.
Strength
FIGURE 2. Measurement of maximal passive rearfoot
eversion range of motion.
under the calcaneus and 1 under the
forefoot, to allow the midfoot to achieve
maximum deformation. AHI was defined
as the ratio of dorsum height at 50% of
total foot length, divided by the foot
length from the back of the heel to the
head of the first metatarsal (truncated
foot length).35 Seated AHI was obtained
with the subject seated, hips and knees
flexed to 90°, and approximately 10% of
total body weight on the foot. Standing
AHI was obtained with the subject standing, with equal weight on both feet. Arch
rigidity index (ARI) is defined as the ratio
of standing AHI divided by seated AHI.27
AHI and ARI were deemed appropriate
measurements of static foot structure,
as their reliability has been previously
demonstrated.2,35
Additionally, and to better understand
the anatomical structure of the foot, goniometric measurement of passive rearfoot range of motion was obtained. With
the subjects in a prone position, the
calcaneus was passively and maximally
everted by the therapist (FIGURE 2). The
mean  SD passive and maximal rearfoot
eversion for the subjects with PTTD was
6.5°  3.1° and 4.8°  2.0°, respectively.
Pilot testing was conducted on 7 control
subjects, and the test-retest reliability
for the measurement of passive rearfoot
eversion was r = 0.94.
To assess the strength of the ankle invertor muscles, the subjects were seated on
the ground, with their knee fully extended and their foot in a plantar-flexed and
inverted position (FIGURE 3). They were
instructed to use only their ankle invertor muscles to produce a force against the
stationary force dynamometer (Lafayette
Instruments, Lafayette, IN). During the
contraction, the investigator palpated
the tibialis anterior tendon to ensure
that this muscle was not being recruited.
The movements of subtalar inversion
and forefoot adduction were based on
strength testing, as described by Kendall et al,12 to best isolate the ankle invertor muscles. Four trials of ankle invertor
maximum voluntary isometric contraction were collected and the average of
these 4 trials was recorded. Force measurements from the dynamometer were
normalized to body mass.10 Pilot testing,
using the aforementioned 7 control subjects, indicated a test-retest reliability for
ankle invertor strength of r = 0.86.
Biomechanics
Three-dimensional walking data were
collected using an 8-camera motion
analysis system (Vicon Motion Systems
Ltd, Oxford, UK). All subjects were barefoot and fitted with 9-mm retroreflective markers, adhered to the skin at the
anatomical landmarks of the tibia, fibula,
and foot (FIGURE 4). A standing calibration of 1 second was obtained with the
feet 0.30 m apart and pointing directly
forward. Following the standing calibra-
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FIGURE 4. (A) Posterior and (B) medial view of marker placement. The markers at the tibial tuberosity and head of the fibula are not pictured. Abbreviations: BLSH, bottom
lateral shank; BMSH, bottom medial shank; D1MT, distal first metatarsal head; HLX, hallux; ICAL, inferior calcaneus; LCAL, lateral calcaneus; MCAL, medial calcaneus; MMAL,
medial malleolus; NAV, navicular tuberosity; SCAL, superior calcaneus; SUST, sustentaculum tali; TLSH, top lateral shank; TMSH, top medial shank.
tion, the subjects were provided a 1-minute warm-up walk on the treadmill at 1.2
m/s–1. Following the familiarization period, marker trajectory data were captured
at a rate of 120 Hz.
Ten continuous footfalls of the walking trial were selected for analysis. Raw
marker trajectory data were filtered using a fourth-order low-pass Butterworth
filter at 12 Hz. Anatomical coordinate
systems were created for the shank and
rearfoot using Visual 3D software (CMotion Inc, Germantown, MD). Only the
stance phase of gait was analyzed, and all
kinematic data were normalized to 100
data points. Stance phase was defined as
initial heel contact to toe-off and these
events were identified using the velocities of the superior calcaneal and hallux
markers.38
Cardan angles were used to calculate
3-dimensional angles for the rearfoot and
shank. Rearfoot eversion was expressed
as frontal plane motion relative the shank
segment. The MLA was calculated in a
manner similar to the method used by
Tome et al.32 The MLA was defined as
the angle subtended by 2 lines, one from
the marker on the medial aspect of the
calcaneus (MCAL) to the navicular tuberosity and the other from the head of the
first metatarsal (D1MT) to the navicular
FIGURE 5. Medial longitudinal arch angle calculation.
tuberosity (FIGURE 5).
Custom LabVIEW software (National
Instruments Corp, Austin, TX) was used
to calculate discrete kinematic variables
of interest, which included peak rearfoot
eversion, peak MLA, and the time of peak
rearfoot eversion.
Statistical Analysis
An a priori power analysis was conducted
using kinematic rearfoot data previously
published.23,32 Individuals with stage II
PTTD, compared to healthy controls, had
a significant difference in rearfoot eversion angle (PTTD, 10.4°  4.5°; control,
5.4°  3.6°). Using these values, the following calculation was used to estimate
the required number of subjects to adequately power this study: n = [2 SD2 (Za +
Zb)2]/2, where SD is the pooled standard
deviation, Za is the z score of alpha (.05), Zb
is the z score of beta (.80), and  is the dif-
ference between the 2 means.33 Applying
this calculation gives an estimation of 10
subjects per group, with a statistical significance of 0.05. Thus 12 subjects per group
was considered appropriate for the study.
The following biomechanical variables
obtained during walking were compared
between the PTTD and control groups:
(1) peak rearfoot eversion, (2) eversion
excursion, (3) time to peak rearfoot eversion, and (4) peak MLA. The following
anatomical and strength variables were
compared between groups: (1) seated
AHI, (2) standing AHI, (3) ARI, (4) passive rearfoot eversion range of motion,
and (5) ankle invertor strength. Because
the biomechanical and strength variables were associated with directional
hypotheses, independent 1-tailed t tests
were employed. Because no differences in
static arch height were hypothesized, independent 2-tailed t tests were employed.
All comparisons were conducted using
an alpha of .05, in SPSS, Version 17 (IBM
Corporation, Armonk, NY) software.
RESULTS
Structure
T
he PTTD group demonstrated
significantly lower seated AHI
(PTTD, 0.36  0.01; control, 0.38
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TABLE 2
research report
Static and Strength Measurements*
PTTD (n = 12)
Control (n = 12)
P Value
AHI seated
0.36  0.01
0.38  0.02
.02
AHI standing
0.34  0.01
0.35  0.02
.28
ARI
0.92  0.02
0.90  0.04
.06
AIS, N/kg
1.00  0.41
0.99  0.35
.49
Abbreviations: AIS, ankle inverter strength; AHI, arch height index; ARI, arch rigidity index; PTTD,
posterior tibial tendon dysfunction.
*Values are mean  SD unless otherwise specified.
TABLE 3
Biomechanical Variables*
PTTD (n = 12)
Control (n = 12)
P Value
Peak eversion, deg
6.0  4.6
2.9  2.6
.03
Eversion excursion, deg
6.6  2.9
5.9  1.5
.24
Time to peak eversion, percent stance
45.8  8.1
38.1  12.9
.05
Peak MLA, deg
12.5  8.0
13.0  9.4
.49
Abbreviations: MLA, medial longitudinal arch; PTTD, posterior tibial tendon dysfunction.
*Values are mean  SD unless otherwise specified.
 0.02; P = .02), no significant differences in standing AHI (PTTD, 0.34  0.01;
control, 0.35  0.02; P = .28), and no
differences in ARI (PTTD, 0.92  0.02;
control, 0.90  0.04; P = .06) values, as
compared to healthy controls (TABLE 2).
Strength
There was no difference in ankle invertor
strength between the 2 groups (PTTD,
1.00  0.41 N/kg; control, 0.99  0.35
N/kg; P = .49).
Biomechanics
The PTTD group exhibited significantly
greater rearfoot eversion (6.0°  4.6°; P =
0.03) compared to controls (2.9°  2.6°)
and significantly greater time to peak
eversion (45.8%  8.1%; P = .05) compared to controls (38.1%  12.9%) (TABLE
3, FIGURE 6). There were no between-group
differences in rearfoot eversion excursion
(PTTD, 6.6°  2.9°; control, 5.9°  1.5°;
P = .24) or peak MLA (PTTD, 12.5° 
8.0°; control, 13.0°  9.4°; P = .49) (TABLE
3, FIGURE 7).
FIGURE 6 shows the PTTD rearfoot in-
version/eversion curve to be in a more
everted position throughout the stance
phase of gait as compared to that of the
control group. Therefore, to better understand the significantly greater peak
eversion between groups, we conducted
a post hoc analysis of rearfoot angle at
heel strike and found that the PTTD
group landed in significantly less inversion (0.1°  2.5°; P = .01) compared to
controls (3.9°  2.7°). In addition, there
was a significant positive correlation between rearfoot angle at heel strike and
peak rearfoot eversion angle for both the
PTTD (r = 0.81; P = .02) and control (r =
0.86; P = .01) groups.
DISCUSSION
T
he purpose of this study was to
investigate differences in arch
height, ankle muscle strength, and
biomechanical factors in patients with
stage I PTTD in comparison to healthy
individuals. While PTTD is considered
a progressive condition, most studies
8-10,24,32
have focused on stage II of the
]
condition in subjects who were predominately overweight and relatively sedentary women, as opposed to patients with
stage I PTTD who were generally younger and active. To our knowledge, no study
has investigated these factors for stage I
PTTD.
The PTTD group demonstrated a
lower arch height in a seated position
but no differences in standing AHI measurements or ARI, compared to controls.
Because the differences in seated AHI
were minimal and no other structural differences were measured between PTTD
and controls, these findings support our
hypothesis and indicate that there were
no differences in static foot measures between groups. Moreover, the AHI values
for both the PTTD and control groups
fall within the normative  SD value
of 0.34  0.03 for a group of 100 recreational runners reported by Butler et
al,2 suggesting overall typical static arch
height measures.
Shibuya et al30 also reported no differences in talar declination angle, or
Meary’s angle, between individuals with
stage I PTTD and healthy controls, as
measured using radiographs. However,
these authors did not measure AHI, so
comparisons are difficult. Both Neville
et al24 and Houck et al8-10 measured AHI
in individuals with stage II PTTD and
found significantly lower values than in
healthy controls. Therefore, the results
of the current study suggest that arch
structure, while perhaps not a contributing factor in stage I PTTD, may be more
apparent in later stages of the condition.
In contrast to our hypothesis, there
were no differences in ankle invertor
strength between the 2 groups. These
results are in contrast to the findings of
Alvarez et al1 and Houck et al,10 who reported that individuals with PTTD exhibited significantly reduced ankle invertor
strength compared to healthy controls.
However, these authors investigated persons with a mean age of 50 and 61 years,
respectively. Our subjects were classified
as having stage I PTTD, were 30 years
old on average, and were regularly ac-
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12
10
8
6
4
Rearfoot Angle, deg
tive in either running, exercise walking,
or running-based sports for a minimum
of 30 minutes per day, 3 times per week.
Thus the similarities in ankle invertor
muscle strength between the PTTD and
controls in the current study seem reasonable, considering that both groups
were involved in regular physical activity and those with PTTD exhibited only
minor swelling and pain to the posterior
tibialis region.
In support of our hypothesis, the
PTTD group exhibited greater peak
eversion while walking, compared to
the control subjects, which is similar to
the findings of previous studies involving stages II to IV PTTD.9,23,28,32 Moreover, those with PTTD demonstrated
approximately 4° less inversion at heel
strike compared to controls, and a significant positive association was found
between rearfoot angle at heel strike and
peak rearfoot eversion angle. These data
suggest that the PTTD group exhibit altered rearfoot kinematics throughout the
entire stance phase of gait. It is possible
that greater rearfoot eversion is associated with early identification of the PTTD;
however, prospective studies are necessary to answer this question.
Interestingly, when calculated with
respect to the amount of passive maximal rearfoot eversion, the PTTD group
utilized 92% of their available rearfoot
range of motion, reaching a peak eversion value of 6° out of 6.5° of available
range of motion. In contrast, the control
group used only 60% of their available
eversion range of motion, reaching 2.9°
out of a possible 4.8°. These results are
similar to those reported by Youberg
et al,37 in which healthy subjects used
68.1% of their available passive rearfoot
eversion range of motion while walking.
Thus the results of the current study suggest that individuals with stage I PTTD
exhibit atypical and excessive pronation
mechanics. While speculative, these data
also suggest that they may be at risk for
ligamentous damage, which is consistent
with the progressive nature of PTTD.
Although both groups reached the
2
0
–2
25
50
75
100
–4
–6
–8
–10
Percent of Stance
Control ± SD
PTTD
FIGURE 6. Representative rearfoot eversion patterns for posterior tibial tendon dysfunction (orange) and controls
(blue, shaded area is standard deviation) during the stance phase of gait. Positive values indicate rearfoot
inversion, negative values eversion.
peak eversion in the first half of stance,
the PTTD group reached peak eversion
at 45.8% of the stance phase as compared
to 38.1% of stance for the control group.
These findings are in contrast to the data
by Tome et al,32 who reported that individuals with PTTD reached peak eversion
earlier in the stance phase compared to
controls. Thus, we postulate that the increased rearfoot eversion measured in
the present study places greater strain
on the posterior tibialis muscle, which
may partially explain the progressive nature of this condition. While no strength
deficits were found in the PTTD group,
other elements of muscle control, such
as improper activation timing,6,21,22 lack
of eccentric control,17,18,25,26 and atypical
fiber recruitment,16 may contribute to
the altered rearfoot eversion. Future research is necessary to better understand
the interrelationship of muscle function
and biomechanical movement patterns.
Because the posterior tibialis muscle
is a major invertor and stabilizer of the
MLA, we also expected a greater MLA
value (lower arch) in those with PTTD
while walking. However, no differences
in MLA angle between the groups were
measured, which is consistent with the
finding of no difference in standing AHI
between groups and no differences in
strength. These results are in contrast
to those of Tome et al,32 who measured
the difference between standing MLA,
normalized to subtalar neutral position,
as compared to the peak MLA value in
gait. Because we did not obtain MLA
values in a subtalar neutral position, we
are not able to directly compare our results to those of Tome et al.32 In addition,
the present study was limited, in that the
vertical height of the medial calcaneal
marker from the plantar surface was not
standardized, which might have masked
between-group differences.
The biomechanical results of the current study provide support for PTTD being a progressive condition. For example,
the stage I PTTD group exhibited a 3.1°
increase in rearfoot eversion compared to
controls, whereas Tome et al32 reported
that patients with stage II PTTD demonstrated a 6.2° increase compared to
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35
30
MLA Angle, deg
25
20
15
10
5
0
0
25
50
75
100
Percent of Stance
Control ± SD
PTTD
FIGURE 7. Representative medial longitudinal arch (MLA) patterns for posterior tibial tendon dysfunction (orange)
and controls (blue, shaded area is standard deviation) during the stance phase of gait. Values closer to 0 indicate
arch deformation.
controls. Moreover, while discrete values
were not reported, Ness et al23 provided
data showing that an approximately 10°
increase in rearfoot eversion throughout
the stance phase of gait could be observed in individuals with stage II PTTD
compared to controls. Thus, increases in
frontal plane rearfoot kinematics appear
to be associated with PTTD severity. Interestingly, a strong positive association
was found between rearfoot angle at heel
strike and peak rearfoot angle in the current study. Ness et al23 reported a similar
eversion offset throughout stance. These
results suggest that individuals with
PTTD exhibit altered rearfoot kinematics throughout the stance phase of gait,
regardless of stage I or II of the condition.
Moreover, the lack of differences in MLA
between groups for the present study and
a reported 8° change in MLA for stage II
PTTD32 suggest that stage I PTTD may
not involve midfoot or forefoot changes
in walking kinematics, whereas these
factors may be apparent in stage II and
beyond.5,7,34 Thus, PTTD progression may
be best understood by rearfoot kinematic
measures during stage I, whereas altered
midfoot and forefoot kinematics may
play a role in stage II and beyond.19,20 Finally, the results of the current study also
suggest that patients with stage I PTTD
exhibit similar arch structure and ankle
invertor strength as compared to healthy
controls and that these variables may not
be associated with early identification of
the condition.5,34 In contrast, individuals
in the more severe stages of the PTTD
progression generally exhibit marked differences in arch height, strength, and gait
kinematics.20,24
Several limitations are acknowledged.
First, this study did not include the classically defined PTTD demographic of
sedentary women over the age of 40,
who are diabetic or obese.13,14 However,
the use of a younger, more active population is supported by previous research
demonstrating PTTD that is a common
injury among runners.31,36 It is also possible that stage I PTTD is distinct and
only associated with tendon overload
]
due to the altered rearfoot mechanics reported in the current study. In contrast,
tendon overload in stages II to IV PTTD
may be associated with other factors,
such as obesity, altered MLA and rearfoot mechanics, as well as neuromotor
and muscular strength deficits. Second,
due to the placement of markers directly
on the skin, participants had to undergo the biomechanical analysis barefoot,
and foot kinematics have been shown to
be different between barefoot and shod
gait.3 Third, the examiner responsible
for determining inclusion/exclusion criteria, data collection, and analysis of the
data was not blinded to group allocation.
However, a different clinician initially
screened all patients over the phone,
and all subjects were assigned a research
number to blind the examiner during
statistical analysis and to help minimize
potential bias. As well, the present investigation was designed as a case control
study; yet we sought to theorize about
the interrelationships between variables.
In addition, we powered the study based
only on potential differences in rearfoot
eversion. Thus future research, involving
multiple covariates, with a sample size
calculated considering a variance inflator
factor, is necessary to better understand
the multifactorial nature of biomechanical, strength, and structural factors for
patients with PTTD.
CONCLUSION
T
he results of the current study
suggest that runners with stage I
PTTD are likely to present with normal inversion ankle muscle strength, significant differences in rearfoot pronation
during walking gait, and no differences
in foot posture as compared to healthy
controls. The increased foot pronation is
hypothesized to place greater strain on
the posterior tibialis muscle, which may
partially explain the progressive nature
of this condition. Future investigations
should be directed towards assessing the
effects of rehabilitation programs for individuals in the early stages, to shed light
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on the clinical and biomechanical factors
that can be altered to prevent PTTD progression. t
KEY POINTS
FINDINGS: Runners with stage I PTTD
exhibited significant differences in
rearfoot pronation during walking
gait, along with normal inversion ankle
muscle strength and foot posture, as
compared to healthy controls.
IMPLICATION: The increased foot pronation is hypothesized to place greater
strain on the posterior tibialis muscle,
which may partially explain the progressive nature of this condition.
CAUTION: This study involved a group of
healthy runners that does not represent the classic PTTD demographic of
middle-aged, sedentary women with
diabetes and obesity, which are often
identified as primary risk factors.
ACKNOWLEDGEMENTS: This work was support-
ed in part by research grants from the Alberta
Innovates: Health Solutions and the Olympic
Oval High Performance Fund at the University of Calgary, and through a charitable
donation from SOLE Inc.
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