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Title: Plantar pressures and ground reaction forces during walking of individuals with
unilateral transfemoral amputation
Marcelo Peduzzi de Castro, PhD, MSc, PTa, b, *
Denise Soares, PhD a, b
Emília Mendes, MSc c, d
Leandro Machado, PhD a, b
a Center of Research, Education, Innovation and Intervention in Sport, Faculty of Sport,
University of Porto, Porto, Portugal
b Porto Biomechanics Laboratory, University of Porto, Porto, Portugal
c Department of Bioengineering, University of Strathclyde, Scotland UK
d Center of Professional Rehabilitation of Gaia - CRPG, Arcozelo, Portugal
* Corresponding author: Marcelo Peduzzi de Castro
Posta Addres: Laboratory of Biomechanics, College of Sports, University of Porto,
Porto, Portugal. Rua Dr. Plácido Costa, 91 - 4200.450, Porto, PORTUGAL.
Telephone: +351 225074791
Mobile: +351 932234823
Fax: +351 225 500 689
E-mail Address: marcelo.peduzzi.castro@gmail.com
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ABSTRACT
Objective: To describe and compare the plantar pressures, temporal foot roll-over, and
ground reaction forces (GRFs) between both limbs of subjects with unilateral
transfemoral amputation and with able-bodied participants during walking. We also
verify the relevance of a force plate and a pressure plate to discriminate changes in gait
parameters of subjects with limb loss.
Design: Cross-sectional study.
Setting: Biomechanics laboratory.
Subjects: 14 subjects with unilateral transfemoral amputation and 21 able-bodied
participants.
Methods: We used a force plate and a pressure plate to assess biomechanical gait
parameters while the participants were walking at their self-selected gait speed.
Main outcome measurements: We measured plantar pressure peaks in six foot regions
and the instant of their occurrence (temporal foot roll-over); and GRF peaks and
impulses of anterior-posterior (braking and propulsive phases), medial-lateral, and
vertical (load acceptance and thrust phases) components.
Results: The thrust, braking, and propulsive peaks, and the braking and propulsive
impulses were statistically lower in the amputated limb than in both the sound limb
(p<.05) and in able-bodied participants (p<.05). In the amputated limb, we observed
higher pressure peaks in the lateral rearfoot and medial and lateral midfoot, and lower
values in the forefoot regions compared to the other groups (p<.05). The temporal foot
roll-over showed statistically significant differences among the groups (p<.05).
Conclusions: The plantar pressures, temporal foot roll-over, and GRFs in subjects with
unilateral transfemoral amputation showed an asymmetric gait pattern, and different
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values were observed in both of their lower limbs as compared to able-bodied subjects
during walking. The instruments were able to determine differences between
participants in gait pattern, suggesting that both plantar pressure and GRF analyses are
useful tools for gait assessment in individuals with unilateral transfemoral amputation.
Due to the convenience of pressure plates, their use in the clinical context for prosthetic
management appears relevant to guide the rehabilitation of subjects with lower limb
amputation.
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INTRODUCTION
As a consequence of the absence of a natural limb, subjects with unilateral
transfemoral (TF) amputation often complain about pain in the sound limb (SL) [1].
They show a higher prevalence of osteoarthritis [2,3], scoliosis [4], and lumbar pain [5],
as well as lower bone mineral density [4] and reduction of the ability to perform all
desired tasks [6] compared to able-bodied (AB) subjects. Previous studies showed a
longer stance phase and higher ankle, knee and hip joint moments [7] and vertical
ground reaction forces (GRFs) [7-9] in the SL compared to the amputated limb (AL)
and AB subjects. These alterations in load distribution between lower limbs increase the
risk of injuries such as anterior cruciate ligament tears [10] and knee joint osteoarthritis
[3,9] in response to overload. Higher values for the step width [11] and displacement of
the center of pressure in both limbs of the individuals with lower limb amputation
compared to AB subjects have also been reported [12,13].
The prosthesis is limited in its mechanical functionality when the dynamic
movement changes, resulting in movement-specific compensatory mechanisms in the
residual joints and intact limb [14]. The alterations in gait features promoted by the
adaptation to a prosthetic limb may cause or reinforce physical impairments. During the
alignment process of the prosthesis and gait training in subjects with lower extremity
amputation, a prosthetic foot roll-over as close as possible to the physiological foot [15]
and bilateral symmetry [16] are pursued. This process is highly subjective and variable
[17], leading to the need for instruments able to easily and reliably provide quantitative
measurements of the gait of individuals with limb loss in order to help and improve the
rehabilitation process [17].
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The analysis of plantar pressures is considered clinically useful in identifying
anatomical deformities on the foot, in guiding the diagnosis and treatment of gait
disorders, and in preventing pressure ulcers [18,19]. The plantar pressure peak is the
main parameter used in plantar pressure analysis and reflects the highest pressure to
occur in a specific region of the foot during the stance phase. The instant of the pressure
peaks also can be calculated, allowing recognition of the sequence of recruitment of
different regions of the foot (loosely referred in the present study as temporal foot roll-
over). However, the validity of the plantar pressure analysis is not yet well established,
and its clinical applicability in the case of prosthetic feet is minimal. Geil and Lay [17]
investigated the capacity of a plantar pressure analysis system to identify alterations in
transtibial amputees’ prosthetic alignment for clinical purposes. These authors observed
that angular changes in the prosthetic alignment in the frontal plane produce predictable
shifts in the plantar pressures between lateral and medial foot regions, concluding that
plantar foot pressure analysis is a sensitive and feasible tool to help clinicians quantify
gait parameters and the way these parameters are influenced by the prosthetic alignment
[17].
Regarding the SL, although some studies have evidenced its overload during gait
[1,7-9], to the best of our knowledge, the identification of the plantar pressure
distribution pattern, temporal foot roll-over features, and specific overloaded regions
were not yet addressed. This information may help clinicians prevent plantar foot
injuries such as blisters, callosity, or skin ulcerations by avoiding the development of
regions with high pressure peaks, and may also guide gait training programs. The light-
weight plantar pressure plates could be a feasible and practical way to record these data.
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Information about mechanical stress can be obtained from vertical force analysis
[20]. The vertical GRF provides the global aspect of the vertical forces, while the
plantar pressure analysis informs about the distribution of this force along the plantar
surface of the foot [21]. The vertical GRF is related to joint contact forces and can
therefore provide insights about the development of some pathological conditions, such
as back pain and osteoarthritis [20]. Increased vertical forces represent a decreased
capacity of the musculoskeletal system in absorbing the body loading during gait [22]
and, as a consequence, express an increment on the likelihood of developing overuse
injuries [23]. The anterior-posterior GRF informs about the friction between the sole
and floor, relevant for assessing foot-related injuries (e.g. blister or ulceration) and
tendency to slip [24]. The medial-lateral GRF has been suggested to provide
information about gait balance [23]. The GRF are influenced by gait speed, where the
increase of speed promotes linear increases in the GRF peaks [25] and decreases the
GRF impulses [26]. In the present study, the GRF peaks and GRF impulses were
calculated. While the peak variables are widely used and inform about the highest forces
experienced by the body, the impulse variables provide complementary information
related to the amount of force received by the body during a given activity. Based on the
viscoelastic properties of the musculoskeletal tissues, the peak variables appear to be
more insightful in showing aggressive loads to the body. However, in terms of gait
pattern and long-term adaptations, the impulse variables might also provide valuable
information about the kinetic features of walking.
The GRFs provide global information about the vertical and shear stress forces,
whereas the plantar pressure analysis identifies the distribution of the vertical GRF over
the plantar foot surface [21]. The combination of both analyses provides more detailed
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and complementary information about specific features of forces acting on the
prosthetic and the sound limbs. Such information might be useful in verifying the
effects of adjustments in prosthesis components and different therapeutic approaches to
gait performance. Hence, the aim of this study is to describe and compare plantar
pressures, temporal foot roll-over, and GRF parameters between both limbs of subjects
with unilateral TF amputation and with AB subjects during walking. The plantar
pressure and GRF data were also analyzed in order to verify their relevance in
determining differences between participants in gait parameters of individuals with
unilateral TF amputation walking.
METHODS
This is a cross-sectional study with a convenience sample. This project was
approved by the ethical board from the Professional Rehabilitation Center of Gaia and
all participants freely signed an informed consent based on the Declaration of Helsinki.
Subjects
Two groups of participants were analyzed. For the experimental group, patients
with unilateral TF amputation were selected from the rehabilitation center’s database.
Patients who had been living with unilateral TF amputation for at least two years were
included, whereas those who had a prosthesis with electronically controlled knee or
prosthetic ankle with energy storing system, and/or who presented pain or lacked
independent walking (without the help of some kind of aid device) ability were
excluded. The AB participants were selected from the project of physical activity for
elderly developed at the university engaged in this study. They were excluded if they
presented any musculoskeletal impairment, limitation, or pain during walking.
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Fourteen subjects with TF amputation, 13 male and one female, with mean age
of 56.7 ± 11.7 years old and mean body mass of 71.4 ± 11.7 kg were enrolled in this
study. All participants had undergone the amputation more than nine years prior to the
experiment. Twelve amputations were traumatic, one from osteomyelitis complications,
and one from vascular disease; in these non-traumatic cases, the individuals did not
show any sign of co-morbidity or difficulty in gait related to the pathology that caused
the amputation. Twelve of the participants used a modular prosthesis of endoskeletal
type and two the exoskeletal type. Twelve prostheses had a prosthetic foot with
articulated ankle and two with fixed ankle; all of them presented a friction-controlled
knee joint, where 12 were uniaxial and two polyaxial. All prosthetic sockets were of
total contact type without the use of a pelvic suspension belt. All individuals had
concluded the adaptation and prosthesis alignment process, a process completed by the
same two technicians in all cases. Participants used their own shoes (standard classic
shoes), which were provided by the same manufacturer, and they were all of similar
type (not orthopedic shoes). Furthermore, the prosthesis was individually aligned for
these shoes. They had no special insole inside. The AB group was composed of six men
and 15 women with a mean age of 68.3 ± 9.4 years old and mean body mass of 66.0 ±
9.0 kg. They also wore their own shoes, which were their preferred ones and were of the
same type as the entire AB group (athletic shoes).
As a measure of the capacity and physical independence of the participants, the
questionnaire SF-36 v.2 was applied and the physical function domain was analyzed
[27].
Instruments
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We used a pressure plate (RsScan, Olen, Belgium) measuring 0.5 m x 0.4 m,
with a spatial resolution of 2.7 sensors/cm² operating at 300 Hz to capture pressure data.
To collect the GRFs, we used a piezoelectric force plate (Kistler Instruments AG,
Winterthur, Switzerland) operating at 1000 Hz. Both plates were calibrated before the
study, and they were synchronized by an external trigger that started them
simultaneously.
Data acquisition
We used the FootScan 7 gait 2nd generation software (RsScan, Olen, Belgium)
to acquire the pressure plate data (Figure 1), while SIMI Motion System® software
(SIMI Reality Motion Systems, Unterschleissheim, Germany) was used for data
acquisition of the force plate.
--Insert Figure 1--
Procedures
The pressure plate was positioned over the force plate and they were placed in
the middle of an 8 m walkway. Anti-slip mats were placed along the trajectory to avoid
unlevel ground cause by the pressure plate. The participants were familiarized with the
environment by freely walking over the walkway. During data collection, the
participants walked at their self-selected speed. They performed at least seven steps
(three before and three after stepping on the plate). The participants with amputation
performed six valid trials, three of them recording data from the AL and three from the
SL. The AB participants performed three valid trials with their right leg. The trial was
considered valid if the participants hit the plate with the entire foot over it and did not
alter their gait pattern. Alterations in the gait pattern such as step length or pace were
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assessed subjectively by visual inspection comparing the gait performed during the
familiarization time and the trials.
Data analysis and outcome measures
Data from the pressure plate (values of each sensor at each frame) and force
plate (three components of the GRFs) were exported to Matlab® 7.0 (MathWorks,
Massachusetts, USA), and a program for data processing and variable calculations was
developed. The shoe imprint (hereafter loosely referred to as foot) was divided into six
regions: in the longitudinal (anterior/posterior) direction, the boundary between rearfoot
and midfoot was located at 73% of foot length, measured from toes to heel, and that
between midfoot and forefoot was located at 45% along this length [28]. Each region
was further divided in two parts, 50% medial and 50% lateral.
We calculated two plantar pressure and 10 global GRF dependent variables. The
plantar pressure variables were calculated for all six foot regions and were (i) the
pressure peak (unit, N/cm2), which was defined as the peak of the average of all active
sensors in the region, and (ii) temporal foot roll-over—the instant of pressure peak—
(unit, % of the stance phase), which was defined as the moment of occurrence of the
pressure peak. The GRF variables were as follows (Figure 2):
- Stance phase duration – time from the first contact to toe off;
- Load acceptance peak (VLA-Peak) – first peak (highest value at the first half of
the curve) from the vertical GRF;
- Thrust peak (VT-Peak) – second peak (highest value at the second half of the
curve) from the vertical GRF;
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- Braking peak (APB-Peak) – lowest value (negative peak) from the anterior-
posterior GRF;
- Propulsive peak (APP-Peak) – highest value (positive peak) from the anterior-
posterior GRF;
- Medial-lateral peak (MLPeak) – the highest value from the medial-lateral GRF;
- Load acceptance impulse (VLA-Imp) – time integral from the first foot contact
until midstance (minimum between VLA-Peak and VT-Peak) from the vertical GRF;
- Thrust impulse (VT-Imp) – time integral from midstance to toe-off from the
vertical GRF;
- Braking impulse (APB-Imp) – time integral from the first contact to middle zero
from the anterior-posterior GRF;
- Propulsive impulse (APP-Imp) – time integral from the middle zero to toe-off
from the anterior-posterior GRF.
--Insert Figure 2--
The variables were calculated for the three groups under study. The GRFs were
normalized by body weight (the weight of the prosthesis was added to the body weight).
In the present study, an asymmetric pattern was considered present when statistically
significant differences were found between AL and SL in any variable [29].
Statistical analysis
The mean of the three repetitions of each group (AL, SL and AB groups) was
computed and statistical procedures were performed with these values. Data normality
was verified by the Shapiro-Wilk test and homogeneity of variances by the Levene’s
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test. The between-trial repeatability of all variables was verified by the intraclass
correlation coefficient (ICC). In order to compare the variables among the groups,
paired student’s t-tests (AL vs. SL) and independent student’s t-tests (SL vs. AB and
AL vs. AB) were used. As there was only one female in the experimental group, and in
the control group there were more females than males, we also used independent
student’s t-tests to compare males and females in the control group. The statistical
procedures were performed using SPSS software (SPSS Inc, Chicago, IL, USA) with an
α value set at 0.05.
RESULTS
All data showed normality of distribution and homogeneity of variance. The ICC
values were above 0.90 for all variables, indicating excellent inter-trial repeatability.
The AL showed shorter stance time compared to SL (AL= 0.88 ± 0.12 s vs. SL= 1.02 ±
0.12 s; p=.003) and higher stance time than AB (0.73 ± 0.10 s; p=.001), and the AB
participants also showed shorter stance time than the SL (p<.001). The values of the
questionnaire SF-36 were 62.8 ± 24.9 points for the subjects with lower limb
amputation and 82.3 ± 18 points for the AB participants. There was no statistically
significant difference between males and females in the control group for any parameter
(p<.05—these results are in appendix 1).
The pressure peaks showed statistically significant differences among the three
groups (AL, SL, and AB). The AL showed higher pressure peaks on the lateral rearfoot
and lateral midfoot compared to the AB group, and higher pressure peaks on the medial
midfoot than the AB and SL groups. No differences were found on the medial rearfoot
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among groups. The AL presented lower pressure peaks than AB on the medial forefoot
and also lower values than AB and SL on the lateral forefoot (Figure 3a).
The temporal foot roll-over also showed statistically significant differences
among the three groups (Figure 3b). In both rearfoot regions the instants of pressure
peaks occurred earlier in both AL and SL compared to the AB. In the medial midfoot,
the instants of pressure peaks occurred statistically significantly later in the AL
compared to the SL and AB, and in the lateral midfoot they occurred earlier in the SL
compared to the AL and AB. In the AL group, the instants of pressure peaks occurred
earlier in the lateral and medial forefoot compared to the AB.
--Insert Figure 3--
The three GRF components were statistically different among the groups. The
AL showed lower VT-Peak and VLA-imp, and lower braking (APB-Peak and APB-Imp) and
propulsive (APP-Peak and APP-Imp) forces than the SL and AB groups. For the MLPeak, the
AL showed higher values than the SL and AB groups. The SL presented higher VT-Imp
and APB-Imp and lower VT-Peak, APB-Peak, and VLA-imp than the AB participants (Table 1
and Figure 4).
--Insert Table 1 --
--Insert Figure 4--
DISCUSSION
This study was conducted to describe and compare plantar pressure and GRF
parameters between both limbs of individuals with TF amputation (AL and SL) and
with AB subjects during gait. As an indicator of physical function, the SF36
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questionnaire showed that the subjects with lower limb amputation have lower values
than their able-bodied counterparts. Nevertheless, these data indicate that they felt few
limitations to performing daily living activities involving physical function and,
therefore, the gait of both groups of participants appears suitable to be compared. We
observed an asymmetrical pattern in pressure peaks, temporal foot roll-over, and GRF
variables when the participants with TF amputation walked. Furthermore, statistically
significant differences in both SL and AL compared to the AB participants were also
identified. Both plantar pressure and GRF analyses were able to discriminate differences
in gait pattern among the groups. To the best of our knowledge, no studies presenting
values of plantar pressures on subjects with TF amputation are available in the literature
to compare with our results. Nevertheless, other studies analyzing the center of pressure
[12,13], GRFs [7,8,30], lower limb kinematics [30], and joint moments [7] also found
an asymmetrical pattern when subjects with TF amputation walked. However, it is not
clear whether these asymmetries are necessary (in both magnitude and pattern) to
promote safety during walking and compensate for the difficulties inherent to walking
with a prosthetic limb [31] or whether they should be reduced in order to promote a
kinetic gait pattern as symmetric as possible to decrease the injury risks caused by
overloading or unloading [9].
During shod walking at a medium speed, healthy older adults showed plantar
pressure peaks ranging from 10 N/cm2 (medial midfoot) to 23 N/cm2 (medial forefoot)
and 25 N/cm2 (central forefoot) [32]. In the current study, the plantar pressure peaks in
the AB group ranged from 8 N/cm2 (medial midfoot) to 18 N/cm2 (lateral rearfoot), in
the AL from 10 N/cm2 (lateral forefoot) to 25 N/cm2 (lateral rearfoot), and in the SL
from 13 N/cm2 (medial and lateral midfoot) to 18 N/cm2 (lateral rearfoot). Therefore,
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even with different plantar pressure systems—in-shoe [32] vs. pressure plate (present
study)—similar magnitudes of plantar pressures were observed. This increases the
external reliability of our findings.
A set of studied parameters provided information regarding the beginning of the
stance phase: pressure plate—medial and lateral rearfoot pressure peaks and their
instants of occurrence, and force plate—VLA-Peak, VLA-Imp, APB-Peak, and APB-Imp. The
present findings suggest that both instruments were able to identify differences between
the subjects with amputation and AB participants while they walked. Subjects with TF
amputation did not show a higher load acceptance peak (VLA-Peak) in the SL compared to
the prosthetic one, but they did present higher vertical GRF impulse (VLA-Imp). Thus, as
the impulse variables are influenced by the magnitude and duration of force application,
the longer time spent on the sound limb (compared to the prosthetic limb) is likely to be
the main reason for this behavior, which might play an important role in the higher
levels of knee pain and knee osteoarthritis observed in the SL [1-3].
Changes in the temporal foot roll-over in both lower limbs of subjects with
unilateral TF amputation compared to subjects without any amputation and an altered
plantar pressure distribution between the medial and lateral rearfoot region in the AL
were identified by plantar pressure analysis. Such events could not be identified by the
GRF analysis as it assesses the overall GRFs and ground reaction moments and,
therefore, does not provide any information about how the forces are being distributed
among different plantar foot regions.
The asymmetrical plantar pressure distribution and the changes in the temporal
foot roll-over in the AL might be a consequence of the absence of physiological knee
and ankle joints, which causes altered motor control of the prosthetic limb [33].
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Michaud et al. [34] found an increased pelvic obliquity during the prosthetic swing in
individuals with unilateral lower limb amputation, suggesting hip hiking. As a result,
earlier instants of pressure peaks at the beginning of the stance phase might occur due to
the prosthetic foot’s abrupt landing. Hip hiking was also evidenced by the lower APB-
Peak and APB-Imp observed in the AL compared to the SL and AB. It is possible that the
increased motion in the frontal plane (hip hiking) resulted in a more vertical landing
with the prosthetic foot, reflected in lower anterior-posterior forces (braking forces).
This also indicates difficulties in decelerating the prosthetic limb at the beginning of the
stance phase. The possible slower gait speed of the participants with TF amputation
may have also contributed to these lower braking peaks in the prosthetic limb. Sapin et
al. [30], corroborating our results, observed a lower capacity for braking in subjects
with TF amputation who used a single-axis prosthetic knee (that coordinates ankle and
knee flexion), and in those using other knee joints without a knee–ankle link.
Considering the SL, we observed an earlier occurrence of the pressure peaks in the
rearfoot and midfoot of the SL compared to the AB. This may reflect a strategy to
compensate for the lower stability in the late stance with the prosthetic limb. Thus the
stance with the SL was anticipated and the maximal weight bearing in the rearfoot and
midfoot also occurred earlier.
At the midstance phase, in which the medial and lateral midfoot pressure peaks
occur, higher values of pressure peaks and later instants of their occurrence were found
for both regions in the AL. These higher magnitudes of pressure might be caused by the
need for the subjects with TF amputation to block their prosthetic knee in extension
[35]. Moreover, at the midstance phase, the prosthetic knee tends to be in extension as
the line of action of the GRFs passes over or anterior to the center of the knee joint
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[31]. Pressure peaks for the AL were postponed in the midfoot regions, possibly to
spend more time in this phase, as subjects consider it the most stable phase of stance.
Considering the MLPeak, both AL and SL showed higher values compared to AB
participants. As subjects with TF amputation showed a higher vertical displacement of
the center of mass in order to block the knee in extension [8,35], one may expect a
larger body movement on the frontal plane [34] to smooth out this greater center of
mass vertical displacement, resulting in higher values of MLPeak, as found in the present
study. The significantly increased load the in SL [8,35], the hip-hiking pattern, and the
lower control of the AL for lowering the pelvis on the SL side before the initial foot
contact might also contribute to these higher magnitudes of MLPeak [36], which might
reflect gait instability.
We found at the late stance the most different behaviors among groups in
pressure peaks (medial and lateral forefoot peaks), temporal foot roll-over, and GRFs
(VT-Peak, VT-Imp, APP-Peak and APP-Imp). The AL displayed lower values in almost all of
these variables, and earlier instants of pressure peaks compared to the SL and AB
groups. Similar results were found in patients using a prosthetic limb, with or without a
knee-ankle link [30]. The plantar flexor muscles are responsible for plantar flexion
during the gait propulsion phase, and their absence implies the recruitment of the hip
flexors to lift the foot, anticipating the AL swing phase [33]. Therefore, the lower values
that we observed might be caused by the absence of these muscles [37]. Moreover, all
participants used a Solid-Ankle Cushioned Heel (SACH) foot. This foot includes a solid
ankle and a rigid keel that runs along the length of the prosthetic foot until the end of
the midfoot, with most of the forefoot mainly composed of flexible, rubber-type
material that does not provide any support or energy return.
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The higher GRF impulses, pressure peaks in the medial forefoot, and the longer
stance phase duration in the subjects with TF amputation suggest a significantly bigger
load in the SL during walking. Nolan et al. [8] analyzed four subjects with TF
amputation and found higher vertical GRF impulses in the SL compared to the AL and
AB groups, whereas a longer stance and a shorter swing phase in the SL were observed
in previous studies [8,13,35]. The subjects with TF amputation raise their body by
excessive plantar flexion of the sound foot in a well-known compensatory mechanism
ie, vaulting. This behavior could occurr as an adaptive mechanism to increase the foot
clearance of the prosthetic foot and to protect the residual limb (AL) by charging it with
load for less time [8]. Because mechanical forces are related to joint damage and
dysfunctions such as those found in osteoarthritis [3], this “protective pattern” in
subjects with unilateral TF amputation might be one of the causes for the high incidence
of dysfunction in the SL [3].
Pressure plates allow the collection of information related to the interface
between shoe sole and ground, while in-shoe pressure systems capture data related to
the plantar foot surface interface and the internal surface of the shoe. We chose a
pressure plate in this study for its convenience and ease of use for clinical purposes.
Moreover, the effect promoted by the deformable interface of the shoe could exert
major influence on pressure insole measurements [38]. The insole sensors could be
affected by the internal environment of the shoe, such as temperature, contour, and
humidity [39]. Furthermore, the presence of cables attached to the individuals,
necessary for in-shoe pressure systems, could prove to be another conditioning factor
affecting the gait pattern.
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The present study showed that both plantar pressures and GRF are sensitive to
detecting alterations in gait patterns when subjects with TF amputation walked.
However, using both instruments in a clinical context might be complex and expensive.
As using a pressure plate does not require an elaborate laboratorial set up, it is cheaper
and more practical than using a force plate (i.e., pressure plates are smaller and lighter
than force plates), its use for analyzing different aspects of gait training and prosthesis
alignment is suggested. Moreover, data regarding AB subjects can be used to guide the
interpretation of data from patients with lower limb amputation, providing some
indications about the plantar foot regions that should be more or less used by AB
subjects while walking. However, this interpretation should be made with caution, and
data from AB subjects are not suggested to be a template that should be matched.
Angular changes between the pylon and the socket in the frontal plane during
prosthetic alignment shift the plantar pressure in a lateral/medial direction [17]. This
information could be used during prosthesis alignment to identify an imbalance of
pressures between medial and lateral plantar foot regions. After that step, alterations in
prosthesis alignment could be tested and the clinician could use data from AB subjects,
gait symmetry, or any other criteria in agreement with the aim of intervention to
improve the gait pattern. Future studies on the influence of specific muscle
strengthening, special insoles or shoes, gait training, and prosthesis components on
pressure distribution would provide a vast amount of quantitative information for
rehabilitation purposes. Such findings could be used to verify the most appropriate
approach to diminish gait asymmetry to an optimum level.
Limitations
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The adopted walking speed in this study was the one at which the subjects felt
most comfortable (self-selected). Thus, an identical gait speed for the subjects with TF
amputation and AB participants was not warranted. Based on the differences in duration
of the stance phase between the experimental and control groups, it is plausible to
assume the participants with TF amputation walked slower than their able-bodied
counterparts. A previous study [40] assessing AB subjects observed similar plantar
pressure peaks between slow and normal self-selected gait speeds. In Taylor et al.’s [40]
study, the duration of the stance phase for slow gait speed was 0.82 ± 11.1 s and for
normal gait speed was 0.70 ±5.2 s. The differences in the duration of stance phase
between groups in our study were only slightly higher (AB = 0.73 ± 0.10, AL= 0.88 ±
0.12 and SL 1.02 ± 0.12) than in the aforementioned study [40]. Therefore, we believe
that the possible differences in gait speed between groups had only small effects on the
plantar pressure parameters. On the other hand, the GRF peaks increase linearly with
increasing gait speed [25], and the GRF impulses decrease with increasing gait speed
[26]. Thus, the comparisons between the GRF parameters from the AL and SL with
those from the AB should be made with caution. Our subjective analysis of gait speed
during data collection was that the participants with TF amputation walked slightly
slower than the AB participants. We adopted the self-selected gait speed in order to
prevent disturbances in gait patterns—caused by restricting speed with treadmills or
using a metronome—and ensure normal walking.
Other limitations should also be considered in the present study. The distribution
between men and women among the participants was not homogenous. However, we
did not observe any difference between able-bodied males and females for any
parameter. Putti et al. [41] also reported that there are no differences in plantar pressure
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parameters between genders. Only the right lower limbs of the AB participants were
assessed; however, similar GRFs and plantar pressures have been shown between limbs
[42,43]. The shoe types were different between groups (TF amputees and AB
participants). Using new shoes or ones different from those usually worn could alter the
prosthesis alignment and gait pattern. In order to preserve a situation as real as possible
while causing the least interference in gait patterns, the participants were asked to use
their own shoes, which were of similar type inside the groups. Finally, the clinical
usefulness of the analyses used in the present study—GRFs and, mainly, plantar
pressures—as tools to guide and follow the rehabilitation process must be interpret with
caution, as there was no follow-up to verify the effects of intervention (i.e. gait training
or changes in prosthesis alignment) using these instruments.
CONCLUSION
The participants with unilateral TF amputation showed an asymmetrical plantar
pressure distribution and GRF patterns. In terms of plantar pressure distribution,
temporal foot roll-over, and GRFs, both lower limbs from the participants with TF
amputation (AL and SL) were different from the AB subjects. The GRFs suggest a
significantly increased load in the SL, whereas the plantar pressure analysis suggests a
higher recruitment of the lateral rearfoot and medial and lateral midfoot regions, and a
lower recruitment of the medial and lateral forefoot on the AL compared to the SL and
AB groups. Both systems seemed to be able to discriminate between the lower limbs of
individuals with unilateral TF amputation. The pressure plate seems to be a useful and
sensitive instrument for gait evaluation of subjects with limb loss.
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22
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27
Table 1. Between group comparison of ground reaction force variables
Variables
Group
Mean
SD
Comparison
P
CI
lower
CI
upper
VLA-Peak
(%BW)
AL
101.6
5.7
AL vs. AB
.994
-5.2
5.2
SL
103.7
4.8
SL vs. AB
.396
-2.9
7.0
AB
101.6
7.1
AL vs. SL
.239
-5.7
1.6
VT-Peak
(%BW)
AL
97.9
5.3
AL vs. AB*
<.001
-19.2
-7.1
SL
104.4
7.2
SL vs. AB*
.042
-13.3
-0.3
AB
111.1
9.0
AL vs. SL*
.013
-11.2
-1.7
APB-Peak
(%BW)
AL
-7.12
2.3
AL vs. AB*
<.001
6.0
11.1
SL
-12.3
3.4
SL vs. AB*
.023
0.5
6.2
AB
-15.6
3.8
AL vs. SL*
.003
2.1
8.2
APP-Peak
(%BW)
AL
7.4
2.8
AL vs. AB*
<.001
-12.1
-6.3
SL
16.4
1.8
SL vs. AB
.881
-3.1
2.7
AB
16.6
4.1
AL vs. SL*
<.001
-12.0
-6.5
MLPeak
(%BW)
AL
8.17
2.1
AL vs. AB*
< .001
1.6
4.1
SL
7.5
2.2
SL vs. AB*
.002
0.9
3.4
AB
5.3
1.0
AL vs. SL
.283
-0.7
2.1
VLA-Imp
(%BW.s)
AL
27.3
3.7
AL vs. AB*
<.001
-11.8
-6.6
SL
32.4
2.1
SL vs. AB*
<.001
-6.2
-2.0
AB
36.5
3.0
AL vs. SL*
<.001
-7.0
-3.2
VT-Imp
(%BW.s)
AL
33.8
7.3
AL vs. AB*
.011
4.4
16.3
SL
47.9
10.1
SL vs. AB*
<.001
17.6
31.4
AB
23.4
7.8
AL vs. SL*
<.001
-19.8
-8.5
28
APB-Imp
(%BW.s)
AL
2.02
1.1
AL vs. AB*
.016
-1.6
-0.2
SL
4.4
1.0
SL vs. AB*
<.001
0.8
2.2
AB
2.9
0.7
AL vs. SL*
<.001
-3.2
-1.5
APP-Imp
(%BW.s)
AL
1.5
0.6
AL vs. AB*
<.001
-2.1
-1.2
SL
3.1
1.1
SL vs. AB*
.002
-2.6
-0.7
AB
3.1
0.6
AL vs. SL
.973
-0.7
0.7
AL = amputated limb; SL = sound limb; AB = able-bodied; SD = standard
deviation; CI lower = lower bound of 95% confidence interval; CI upper =
upper bound of 95% confidence interval. * = significant difference between
groups with p<.0.5.
29
Figure 1. Distribution of the plantar pressures, as acquired by FootScan 7 gait 2nd
generation, of one participant from one group.
30
Figure 2. Ground reaction force dependent variables.
Figure 2 legend:
VLA-Peak – Load acceptance peak; VT-Peak –Thrust peak; APB-Peak – Braking peak; APP-
Peak – Propulsive peak; MLPeak – Medial-lateral peak; VLA-Imp – Load acceptance
impulse; VT-Imp – Thrust impulse; APB-Imp – Braking impulse; APP-Imp – Propulsive
impulse.
31
Figure 3. (A) Plantar pressure peaks and (B) Temporal foot roll-over—instant of the
plantar pressure peaks for the three groups.
32
Figure 3 legend:
Equal symbols in the groups represent statistically significant difference between *
Amputated limb and Sound limb, † Amputated limb and Able-bodied and between #
Sound limb and Able-bodied with p<.05.
33
Figure 4. Ground reaction forces (GRF) of all tests and all participants. (A) Anterior-
posterior GRF, (B) Medial-lateral GRF, and (C) Vertical GRF.
Figure 4 legend:
Equal symbols in the groups represent statistically significant difference between *
Amputated limb and Sound limb, † Amputated limb and Able-bodied and between #
Sound limb and Able-bodied with p<.05. As all the MLPeak were in the same direction
(positive values) and, only some participants showed negative values at the edge of the
curve (first or last 20% of the stance phase), we have opted to present graphically only
absolute positive values of the medial-lateral GRF.
