The effect of footwear mass on the gait patterns of unilateral below-knee amputees
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Prosthetics and Orthotics International, 1989,13, 140-144
The effect of footwear mass on the gait patterns of
unilateral below-knee amputees
J. M. DONN, D. PORTER and V. C. ROBERTS
Department of Medical Engineering and Physics,
King's College School of Medicine and Dentistry, Denmark Hill, London
Abstract function during normal prosthetic use. The
This study reports an investigation into the advice regarding footwear for the amputee is
effect of shoe mass on the gait patterns of either non-existent, or that "the lighter the
below-knee (BK) amputees. Ten established footwear the better". Lighter footwear is often
unilateral BK, patellar-tendon-bearing thought to minimally affect the design
prosthesis wearers were assessed using a performance of the prosthesis, despite the fact
VICON system of gait analysis. Incremental that there is little published evidence of
masses of 50g (up to 200g) were added to the consideration of footwear in prosthetic design.
subjects' shoes and data captured as they In an early study of the effect of prosthetic
walked along a 15m measurement field. foot mass, Godfrey et al. (1977) described the
Coefficients of symmetry of various parameters effect of changing the foot mass of a prosthesis
of the swing phase (knee frequency symmetry, on above-knee amputee gait. Stride length and
swing time symmetry, maximum flexion to heel heel rise velocity were considered to be of
strike time symmetry) were measured and their major importance because of the pendular
correlation was tested with the patient's quality of the above-knee prosthesis. However,
preferrerd shoe mass and also their own shoe no significant differences of performance were
mass, all expressed as a proportion of body noted between the three different masses
mass. tested.
The subjects' 'preferred' shoe mass (139- Several authors have looked at the different
318g) showed the greatest symmetry in all the prosthetic feet available and their effects on
parameters examined (correlations 0.78-0.81 gait. Doane and Holt (1983) compared the
p
Footwear mass and BK gait patterns 141
weighing 460g. Consumer acceptance was the Method
final measure of the Seattle foot and the The mass of the shoe with which each patient
amputees' comments were noted. The relative arrived at the laboratory was recorded, as was
ability (compared with the use of other feet) to their body mass and the mass of the shoe the
run at different speeds and on different surfaces subject preferred during the tests.
was favourably commented upon, as was the The mass of shoes available commercially
extra push perceived at toe off. There was was tested and ranged from approx 250g (a light
however no mention of the effect of the mass of canvas shoe), to 460g (a heavy leather shoe).
the prosthetic foot. For the afternoon of the test the subjects wore a
pair of Drushoes*. This is a make of
A review of current prosthetic feet by orthopaedic footwear readily available in many
Edelstein (1988) commented on many areas, hospitals and often issued to amputees with
such as the ability to accommodate different their first prosthesis. Each Drushoe weighed
heel heights, the performance of the feet during
260g. Investigations were carried out with the
stance phase, the energy storing materials used,
unweighted shoes and then following the
and also their cost of production. Edelstein
sequential addition of plasticine (50g, 100g,
commented that to accommodate a change of
150g, 200g) to the front of each Drushoe. The
more than 0.5cm in heel height either higher or
plasticine was attached to the shoes as close to
lower, a change in the alignment of the
the ankle joint as possible to reduce any effect
prosthesis may be required, most designs of
on ankle moments to a minimum. The range of
prosthetic feet were able to accommodate
changes of up to 2-3cm, (this being achieved shoe mass (Drushoe plus extra mass) was thus
either by mechanically altering the alignment of 260-460g, effectively covering the 'normal'
the keel of the shoe to its heel, or by wedging range of shoe mass.
material under the heel, as in the Seattle foot). Kinematic information was obtained using
The new energy storing feet, for which superior the VICON 3-dimensional gait analysis system
performance is claimed, use a variety of consisting of four infra red cameras and a PDP
materials, from double carbon-fibre composite 11/23 computer. Foot switches were used in
in the Carbon Copy II foot, to acetyl polymer order to obtain accurate foot contact timing
and Kevlar fabric in the Seattle foot. The type information and thus swing phase times.
of shoes used in their assessments may have Each subject was required to wear shorts and
influenced the performance of the various feet reflective markers were placed on the subject's
but they were not mentioned. skin at the following anatomical landmarks on
the non-prosthetic side:
In the belief that many of these studies may 1 anterior superior iliac spine,
have overlooked a factor which may 2 greater trochanter,
significantly influence prosthetic use, this 3 lateral line of the knee,
present pilot study looks at the subject of 4 lateral malleolus,
footwear, specifically the effect of shoe mass on 5 headofthe fifth metatarsal.
the gait patterns of unilateral below-knee Markers were also placed at equivalent
amputees. positions on the prosthetic side. Marker
trajectories were recorded whilst the subjects
Subjects walked down at 15m walkway at their own
Ten unilateral BK amputees were assessed in comfortable pace. From these marker
this investigation. Nine were male, three trajectories information was obtained about
subjects having undergone left-sided ampu hip, knee and ankle joint angle variations in the
tations and seven right-sided amputations. sagittal plane, throughout the swing phase of
Body mass ranged from 57.0kg to 95.5kg with a one gait cycle on each side. Joint angles were
mean of 79.9kg (±14.6). All subjects were computed for the swing phase for both left and
patellar-tendon-bearing prostheses wearers and right sides. Each data set was normalised in
could walk at least 100m without the use of a time to 64 data samples using linear
walking aid. The subjects were all wearing interpolation. In order to compare the change
single-axis feet except one, who was wearing a
Quantum foot. * John D r e w (London) Ltd.
142 J. M. Dorm, D. Porterand V. C. Roberts
in joint angle values rather than the absolute Table 1. Symmetry coefficients for Subject 5.
magnitude, the mean angle value for each data
set was subtracted from all points in that set. A
Fast Fourier Transform was then performed in
order to obtain the power spectrum for each
angle waveform.
2 2 2 2
r--(Zxy-(Zxy)/N)lV{(Zx -((Sx) )lN)(2y -((2y) )lN)}
The subject's own shoe and their preferred
1 shoe mass was expressed as a proportion of
their body mass, to allow comparison of results
The Index of Symmetry was calculated as the between subjects. Table 2 shows this and also
correlation index using Equation 1 (above). In whether the subjects preferred heavier or
this equation x represents the amplitude of the lighter shoes than their own.
angle at each harmonic for the left hand joint,
Table 2. Body/shoe mass proportion related to
and y the amplitude at the same frequencies for preference.
the right hand joint. The coefficient was
calculated for the first ten frequency samples
with the exception of the first since the joint
angle offset had been previously removed. A
symmetry coefficient of 1.0 would represent
perfect symmetry, with the coefficients ranging
from 0-1, this is the same procedure as followed
by Hannah & Morrison (1984) and Pepino et al.
(1986). Symmetry Indices were calculated for
the hip, knee and ankle (Hip Frequency
Symmetry, Knee Frequency Symmetry, Ankle
Frequency Symmetry).
Swing time symmetry was calculated from the The shoe mass which indicated the most
swing phase times obtained from heel and toe symmetrical gait in each of the parameters
switch information. Left and right feet were looked at was also expressed as a proportion of
compared and a symmetry coefficient (SWTS) body mass (Table 3). The body to shoe
wasobtalned. proportion which gave the most symmetrical
The time taken from maximum knee flexion gait patterns for the subjects ranged from 146-
to heel strike was calculated from the knee joint 318.
angle vs swing time waveform. Again left and
Table 3. Symmetry — body/shoe mass proportion.
right were compared and a symmetry
coefficient (MF-HS) obtained.
Results
From the temporal and kinematic data
obtained, symmetry coefficients were calcu
lated for three parameters at each mass tested.
The three parameters were, Knee Frequency
Symmetry in the Swing Phase (KFSS), Swing
Time Symmetry (SWTS) and Maximum
Flexion to Heel Strike Time Symmetry (MF-
HS). Table 1 shows the information collected Since all shoe masses were expressed as a
for one subject and is typical of the data proportion of body mass a correlation between
collected on all ten. From this information the indices is possible. In order to achieve this the
shoe mass which gave the most symmetrical shoe mass which provided the optimum results
gait, as indicated by the three parameters, for each of the parameters was identified. A
could be identified and recorded. correlation was then tested between these shoe
Footwear mass and BK gait patterns 143
Table 4. Correlation coefficients.
masses and both the original shoe mass with
which the subject arrived, and with the shoe
mass which the subject preferred.
Table 4 shows the correlation coefficients
calculated for KFSS, MF-HS and a combination
of all three parameters looked at. The
correlation calculated for the swing period
parameters, used an average of the body to
shoe mass proportion which produced the most
symmetrical gait in each of the three
parameters (KFSS, SWTS, MF-HS), for each
subject.
Although the results showed that the
optimum shoe mass exhibited little correlation
with the subjects own shoe mass, it was
however significantly correlated with their
preferred mass in each parameter.
Discussion
Since changing footwear mass is most likely to
change the gait pattern in the swing phase, this
present study has been confined to only that
part of the gait cycle. During the swing phase of
the gait cycle the knee is flexing and then Fig. 1. Compound pendulum.
extending under pendular action. If the
prosthetic shank and foot act as a simple direction. By adding mass to the footwear, the
pendulum the natural frequency and therefore position of the centre of mass will however be
the period of swing would be unaffected by the shifted distally therefore increasing r and
pendulum mass (i.e. prosthetic foot and shoe) consequently altering q°, (the distance from the
but would be dependent only on the distance of knee joint to the centre of percussion). Note
that mass from the axis of rotation ie. the knee that the natural frequency of the pendulum is
joint. inversely proportional to qo, which in turn will
However, it can be argued that a prosthesis be affected as suggested, by the shoe mass.
may more realistically resemble a compound In this present study, evidence was found that
pendulum due to the mass being distributed altering the shoe mass changed the swing time,
throughout the stump, prosthetic shank and as shown by the swing time symmetry (SWTS).
foot, with the added restraints of muscular Components of gait symmetry, ie. knee
control of the knee. Figure 1 shows a prosthesis frequency symmetry, maximum flexion to heel-
represented as a compound pendulum, (Steidal strike time symmetry and SWTS have been
1971). The position of the plasticine mass, close examined to see how much the prosthetic side
to both the normal and prosthetic ankle joints altered and approximated to the natural side
prevents a significant shift in the centre of mass during the swing phase. The possible
of the shank and foot in an antero-posterior correlation between gait symmetry and the
144 J. M. Donn. D. Porter and V. C. Roberts
subjects' acceptance of the shoes has also been Ltd. Roehampton, formerly of Vessa Ltd. Also
examined. to the registered charity Action Research for
The lack of correlation between the subjects' The Crippled Child who sponsored J. D. for a
own shoe and symmetry could have been for Research Training Fellowship which enabled
two reasons. Either the subjects had received her to finish this work.
the wrong advice about their footwear (six out
of the ten subjects preferred walking with shoes
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With grateful thanks to Mr. J. M. Regan, introduction to mechanical vibrations. N e w York:
Senior Prosthetist, Chas Blatchfords & Sons John Wiley, 5 3 - 5 7 .You can also read
