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VOLUME 3, ISSUE 2 

 2020 

 

RESEARCH ARTICLE 

Bateni H. Postural sway in lower extremity amputees and older adults may suggest increased fall risk in amputees. Canadian Prosthetics & Orthotics Journal. 

2020;Volume 3, Issue 2, No.4. https://doi.org/10.33137/cpoj.v3i2.33804 

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https://doi.org/10.33137/cpoj.v3i2.33804


 

1 

Bateni H. Postural sway in lower extremity amputees and older adults may suggest increased fall risk in amputees. Canadian Prosthetics & Orthotics Journal. 
2020;Volume 3, Issue 2, No.4. https://doi.org/10.33137/cpoj.v3i2.33804 

 

 

 
RESEARCH ARTICLE 

 

POSTURAL SWAY IN LOWER EXTREMITY AMPUTEES AND OLDER ADULTS MAY SUGGEST 
INCREASED FALL RISK IN AMPUTEES 

 
Bateni H.* 
 

Physical Therapy Program, School of Allied Health and Communicative Disorders, Northern Illinois University, DeKalb, Illinois, USA. 
 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

INTRODUCTION   

Approximately 185,000 amputations occur in the United 

States per year, and about 2 million Americans currently live 

with a limb loss.1-3 The incidence of amputations per year 

ranges from 1.2 to 4.4 per 10,000 with a majority of 

amputations involving the lower limb.4 Falling is dangerous 

and debilitating, yet common, for individuals with lower 

extremity amputations.5 Nearly 50% of amputees 

experience an accidental fall within a year of their operation; 

over 40% of those falls result in serious injury, and over 19% 

require additional medical attention.6 As the amputee 

population ages, accidental falls become a greater problem. 

Increased rate of fall, reduced balance confidence, and 

increased fear of falling are reported following lower 

extremity amputation.7,8 Additionally, people with higher 

levels of amputation experience a higher rate of incidental 

falls.7,9  

Postural steadiness, as measured by quantification of 

postural sway during quiet standing on a force platform, has 

 
OPEN  ACCESS Volume 3, Issue 2, Article No.4, 2020 

 

 

Journal Homepage: https://jps.library.utoronto.ca/index.php/cpoj/index 

 

ABSTRACT 

BACKGROUND: Falls can be detrimental to overall health and quality of life for lower extremity 

amputees. Most previous studies of postural steadiness focus on quantification of time series variables 

extracted from postural sway signals. While it has been suggested that frequency domain variables can 

provide more valuable information, few current studies have evaluated postural sway in amputees using 

frequency domain variables.  

OBJECTIVE: To determine time and frequency domain variables of postural sway among lower extremity 

amputees vs. healthy young and older adult controls. 

METHODOLOGY: Participants were assigned to 3 groups:  lower extremity amputation (n=6), healthy 

young adults (n=10), and healthy older adults (n=10). Standing barefoot on a force platform, each 

individual completed 3 trials of each of 3 standing conditions: eyes open, eyes closed, and standing on 

a foam balance pad. Time and frequency domain variables of postural sway were computed and 

analyzed.  

RESULTS: Comparison of older adults, younger adults, and amputees on the three conditions of 

standing eyes open, eyes closed, and on foam revealed significant differences between groups. Mean 

mediolateral (ML) sway distance from the center of pressure (COP), total excursions and sway velocity 

was significantly higher for amputees and older adults when compared to young adults (p<0.05). 

Furthermore, power of sway signal was substantially lower for both amputees and older adults. When 

compared to that of older adults, postural steadiness of amputees was more affected by the eyes closed 

condition, whereas older adults’ was more affected when sensory and proprioceptive information was 

perturbed by standing on foam.   

CONCLUSION: Our findings showed that fall risk is greater in amputees than in young adults without 

amputation. Additionally, amputees may rely more heavily on visual information than proprioceptive 

information for balance, in contrast to older and young adults without amputation.   

. 

ARTICLE INFO 

Received: March 5, 2020 

Accepted: September 5, 2020 

Published: September 20, 2020 

CITATION 

Bateni H. Postural sway in lower 

extremity amputees and older 

adults may suggest increased 

fall risk in amputees. Canadian 

Prosthetics & Orthotics Journal. 

2020;Volume 3, Issue 2, No.4. 

https://doi.org/10.33137/cpoj.v3i

2.33804 

KEYWORDS 

Amputation, Postural balance, 

Amputee, Prosthesis, Lower 

limb amputation, Postural sway 

 

* CORRESPONDING AUTHOR: 
Hamid Bateni, PhD  
Physical Therapy Program, School of Allied Health and 
Communicative Disorders, Northern Illinois University, DeKalb, Illinois, 
USA. 
E-mail: hbateni@niu.edu 
ORCID: https://orcid.org/0000-0001-9083-1817 
 

https://doi.org/10.33137/cpoj.v3i2.33804
https://jps.library.utoronto.ca/index.php/cpoj/index
https://doi.org/10.33137/cpoj.v3i2.33804
https://doi.org/10.33137/cpoj.v3i2.33804
mailto:hbateni@niu.edu
https://orcid.org/0000-0001-9083-1817


 

2 

Bateni H. Postural sway in lower extremity amputees and older adults may suggest increased fall risk in amputees. Canadian Prosthetics & Orthotics Journal. 
2020;Volume 3, Issue 2, No.4. https://doi.org/10.33137/cpoj.v3i2.33804 

ISSN: 2561-987X POSTURAL SWAY IN LOWER EXTREMITY AMPUTEES  
Bateni H. 2020 

 
CPOJ 

 
been used frequently as a method of assessment of static 

balance and postural control. Postural steadiness may be 

an indicator of the quality of balance and postural  

control.10-13 Literature has linked time series14,15 and 

frequency domain16-19 variables of postural sway to 

balance. Additionally, it is reported that state of anxiety and 

fear of falling impact postural sway.20,21 Anxiety and fear of 

falling are psychological conditions that can lead individuals 

to avoid participation in activities.7 Activity avoidance due to 

the fear of falling can lead to reduced quality of life related 

to reduced strength, endurance, and balance, and can 

increase the risk for further health problems, including falls, 

in patients with lower extremity amputations.22 

While most studies of postural steadiness focus on 

quantification of time series variables extracted from 

postural sway signals,23 others have suggested and utilized 

frequency domain variables of sway in parallel with time 

series variables to reveal more valuable information.11,12,19 

Analysis of frequency content of a signal reveals underlying 

changes that often are not observed in time series. For 

instance, in the absence of movement, agonist and 

antagonist muscles may still be actively working against 

each other. Additionally, in the inverted pendulum model, 

that was introduced by Maurer and Peterka,24 ankle stiffness 

and noise may be increased simultaneously. In these 

cases, time series variables, e.g. velocity and displacement, 

do not show any changes. Power spectral density however, 

would provide information of the underlying conditions. As a 

result, it is often suggested that both time and frequency 

domain variables should be evaluated in assessment of 

postural steadiness. The purpose of this study was to 

determine change in both time and frequency domain 

variables of postural sway among lower extremity amputees 

as compared to healthy young and older adult controls.  

METHODOLOGY 

Following approval of the Institutional Review Board 

(Northern Illinois University), a study was conducted to 

determine impact of lower extremity amputation on time 

series and frequency domain variables of postural sway. 

This study included 6 individuals with lower extremity 

amputation (2 unilateral trans-tibial [UTT], 1 bilateral trans-

tibial [BTT], 2 unilateral trans-femoral [UTF] and 1 unilateral 

hip disarticulation [UHD]) with the average age of 51 

(SD=16) years), 10 healthy young adults (age 25 (SD=1.6) 

years), and 10 healthy older adults (age 71.7 (SD=5.4) 

years). Amputee participants were included if they met the 

following criteria: a) were lower extremity amputees with 

more than one year of experience using a prosthetic limb, 

b) had a comfortable prosthetic limb about which they had 

no complaints, c) apart from lower extremity amputation, 

had no physical or mental disability that could potentially 

affect their balance, d) could ambulate without any 

assistance or use of an assistive device, and e) could stand 

upright independently for at least 10 minutes. Individuals 

with any visual deficits (apart from requiring corrective 

lenses) or vestibular deficits and those with a history of 

injury or surgery to the lower extremities within the past 6 

months were excluded from the study. Healthy young and 

older adults were recruited if they were able to stand upright 

independently for at least 10 minutes and ambulate without 

assistance. Those with any physical or mental condition that 

could potentially impact postural control were excluded. 

Participants were asked to sign a consent form prior to 

participation in the study. 

A Kistler force platform (Kistler Co., Winterthur, Switzerland) 

was used to collect position data of the center of pressure 

(COP) at 100 Hz. A LabVIEW program (National Instrument, 

Austin, Texas) was developed to collect postural sway data. 

Participants were randomly assigned to three standing 

conditions: a) eyes open, b) eyes closed and c) standing on 

Airex 2.5” thick foam balance pad (Airex Corporation, 

Somersworth, NH). The conditions of eyes closed and 

standing of foam were included to estimate changes in 

postural steadiness when visual and sensory information 

are diminished. Considering that vestibular, visual, and 

sensory information are typically relied upon to maintain 

upright posture, deterioration of any of these sources of 

information may reveal information regarding our 

dependency on the lost source. Each test condition was 

repeated three times. Test orders were block randomized, 

with each condition presented once in each block. During 

the study, participants were instructed to stand straight and 

static with arms on their sides (bare feet, heels together, 5-

7 degrees of toe-out) on the force platform. Data was 

collected for 35 seconds (Fs=100). For the eyes-closed 

condition, researchers asked each participant to close his 

or her eyes and confirmed that eyes remained closed 

throughout the trial. While there were not any specific 

resting periods implemented between trials, participants 

were informed prior to the testing that they were welcome to 

request a rest time if they needed to. Additionally, during the 

trials participants were repeatedly asked if they wanted to 

rest. Several participants asked for the rest during the tests.  

Anteroposterior and mediolateral time series data were 

filtered through a fourth-order zero phase Butterworth low-

pass filter with cutoff frequency of 5 Hz. The first 8 seconds 

and last 2 seconds of data were cut off to remove any 

potential lead-in/lead-out effect. MATLAB and Toolbox 

Release 2012b (MathWorks, Inc., Natick, Massachusetts) 

were used to filter postural sway data and to compute 

variables of interest. SAS statistical software was used to 

conduct statistical analysis and to compare means between 

healthy adults and amputees. Time and frequency domain 

variables of postural sway were computed. Detailed 

explanation of computation methods for variables and 

equations are available in literature.11,12,25-28 Mean sway 

distance which represents the average sway from the mean 

position of the center of pressure was calculated for N data 

points as follows: 

https://doi.org/10.33137/cpoj.v3i2.33804


 

3 

Bateni H. Postural sway in lower extremity amputees and older adults may suggest increased fall risk in amputees. Canadian Prosthetics & Orthotics Journal. 
2020;Volume 3, Issue 2, No.4. https://doi.org/10.33137/cpoj.v3i2.33804 

ISSN: 2561-987X POSTURAL SWAY IN LOWER EXTREMITY AMPUTEES  
Bateni H. 2020 

 
CPOJ 

 

Mean sway distance =  
1

N
∑ √AP[n]2 + ML[n]2 

 
Similarly, total excursion of sway as the total distance COP 

travels was computed by summation of distance between 

two consecutive data points: 

Total excursion of sway

=  ∑ √(AP[n + 1] − AP[n])2 + (ML[n + 1] − ML[n])2

N−1

n=1

 

Velocity of the sway was calculated by dividing total 

excursion over the time: 

𝑉elocity of the sway =  
total excursion of sway

total time
 

Power of sway signal was computed as the integrated area 

of power spectrum, and 95% power frequency was 

determined as the point below which 95% of the total power 

is placed.12 

A linear mixed model with the random effects for subjects 

and subjects × condition was used to compare the means. 

The least square means for the three groups of 

amputees/older adults/young adults × condition and their 

pairwise differences were computed for this model. 

RESULTS 

Comparison of older adults, younger adults, and amputees 

on the three conditions of standing eyes open, eyes closed, 

and on foam revealed significant differences between 

groups. Mean mediolateral (ML) sway distance from the 

COP was significantly increased by both amputation and 

aging (P<0.0001). Tukey-Kramer post hoc analysis 

revealed that amputees’ COP deviated a significantly higher 

distance from the central point than did COP of young 

participants (Figure 1), particularly with eyes closed 

(p=0.02). Similarly, older adults swayed a greater distance 

mediolaterally than did young adults (p=0.001). The 

difference between older adults and amputees however, 

was not statistically significant, even though this value was 

higher for older adults. Furthermore, the difference in total 

excursions of sway during static standing was also 

significantly different between the three groups (amputees, 

young adults, and older adults) (p<0.0001).  

Post hoc analysis showed greater total excursions among 

older adults when compared to young adults (p<0.05) 

(Figure 2). When older adults were compared to amputee 

participants, however, the value of excursions was 

significantly higher for amputees (p=0.0008) only when 

participants were standing eyes closed. Mean velocity of 

sway was different between groups (p<0.0001). Older 

adults showed higher velocity of sway when compared to 

young adults in all conditions of standing, i.e., eyes open 

(p=0.002), eyes closed (p=0.0005), and standing on foam 

(p=0.001). While amputees swayed at higher velocity than 

did young adults, their velocity of sway was still lower than 

older adults’ in eyes open and standing on foam conditions 

and slightly higher in eyes closed condition. These 

differences, however, were not statistically significant. 

When eyes were closed, amputees showed a substantially 

higher velocity of sway than did young adults (p=0.0008) 

(Figure 3). 

Velocity of sway also varied based on condition of standing 

for all groups (p=0.0176). Amputees’ sway velocity was 

greatest with eyes closed, followed by standing on foam, 

and least with eyes open. These differences in sway velocity 

for the amputee group were statistically significant only for 

eyes closed vs. eyes open (p=0.024). This pattern however, 

was different for older adults. Older adults showed their 

highest velocity of sway when standing on foam. There was 

no statistically significant difference in sway velocity for 

older adults with eyes closed vs. eyes open, or eyes closed 

vs. standing on foam. The difference in velocity of sway was 

significant, however, when foam standing was compared to 

eyes open (p=0.0446).  

Resultant power of sway signal was also significantly 

different between the three groups (amputees, young 

adults, and older adults) (p=0.0074) and between the three 

conditions of standing (p=0.025). No significant interaction 

between groups and conditions of standing was noted. 

When young and older adults were compared, Tukey-

Kramer post hoc analysis showed that older adults 

demonstrated a higher level of power. Although this 

difference was not significant for the eyes open condition, it 

was nearly significant for the eyes closed (p=0.05) and 

significant for standing on foam (p=0.0014) conditions. 

Power of sway signal for the amputee group was higher 

than for young adults and lower than for older adults under 

conditions of eyes open, eyes closed and standing on foam. 

This difference however, was not statistically significant. 

Further analysis of our data showed that the resultant 

mediolateral 95% power frequency was significantly lower 

for both amputees and older adults when compared to 

young adults (p<0.05) for eyes open and eyes closed 

conditions (Figure 4). Lower power of amputee and older 

adults however, was not significant compared to young 

adults for standing on foam condition.  

Since our amputee population consisted of both young and 

older adults, we performed a secondary analysis on our 

data, eliminating data for amputees under the age of 60. We 

anticipated that this change would lead to a more 

homogenous sample of amputees who were all older adults. 

Therefore, comparison of amputees with older adults and 

young adults may be more telling. As a result, the amputee 

group in our secondary analysis consisted of 3 amputees 

(age 62 (SD=3.8) years). Similar to our previous findings, 

we noticed that older amputees sway at a significantly 

higher level with eyes closed than do young adults 

(p=0.046), but the sway distance, although higher, does not 

differ substantially when compared to older adults without 

amputation (p>0.05). Furthermore, we noticed that even 

though older amputees performed significantly higher total 

excursion of sway when compared to young adults 

(p=0.001), their total excursion was not substantially 

https://doi.org/10.33137/cpoj.v3i2.33804


 

4 

Bateni H. Postural sway in lower extremity amputees and older adults may suggest increased fall risk in amputees. Canadian Prosthetics & Orthotics Journal. 
2020;Volume 3, Issue 2, No.4. https://doi.org/10.33137/cpoj.v3i2.33804 

ISSN: 2561-987X POSTURAL SWAY IN LOWER EXTREMITY AMPUTEES  
Bateni H. 2020 

 
CPOJ 

 
different from older adults in closed-eyes conditions.  

This latter finding was not in agreement with our original 

findings. Pattern of changes in sway velocity was similar to 

our original analysis. We noticed that older adults showed 

higher velocity of sway when compared to young adults in 

all conditions of standing, i.e., eyes open (p=0.002), eyes 

closed (p=0.0006), and standing on foam (p=0.002). When 

eyes were closed, older amputees showed a substantially 

higher velocity of sway than did young adults (p=0.0013). 

The difference of sway velocity among older adults and 

amputee was not statistically significant.  

Figure 1: Comparison of mean distance from the mean center of 

pressure in mediolateral direction during static standing for three 

different conditions of eyes open, eyes closed, and standing on 

foam. Diamond shape and solid line indicate mean and median of 

the data respectively. Data presented for three groups of amputees 

(AM), older adults (OA) and young adults (YA). Asterisks (**) 

denote statistically significant differences (p<0.05). 

Our secondary analysis for the resultant power of sway 

signal showed a similar pattern as our original analysis. 

Resultant power of sway was significantly different between 

the three groups (amputees, young adults, and older adults) 

(p=0.009) and between the three conditions of standing 

(p=0.01). Older adults demonstrated a higher level of power 

when compared to young adults. This difference was not 

statistically significant for the eyes open condition and eyes 

closed conditions, but significantly higher for older adults 

when standing on foam (p=0.002). Power of sway signal for 

the older amputee group was higher than for young adults 

and lower than for older adults under conditions of eyes 

open, eyes closed and standing on foam. Analysis of the 

resultant mediolateral 95% power frequency showed that 

this value is significantly lower for both older amputees and 

older adults without amputation when compared to young 

adults (p<0.05) for eyes-open and eyes-closed conditions. 

This difference however, was not statistically significant 

when participants were standing on foam.  

Figure 2: Comparison of total excursion of sway for three different 

conditions of eyes open, eyes closed, and standing on foam. 

Diamond shape and solid line indicate mean and median of the data 

respectively. Data presented for three groups of amputees (AM), 

older adults (OA) and young adults (YA). Asterisks (**) denote 

statistically significant differences (p<0.05). 

Figure 3: Figure depicts mean velocity of sway for three different 

conditions of eyes open, eyes closed, and standing on foam. 

Diamond shape and solid line indicate mean and median of the data 

respectively. Data presented for three groups of amputees (AM), 

older adults (OA) and young adults (YA). Asterisks (**) denote 

statistically significant differences (p<0.05). Note variation of mean 

velocity when amputees and older adults are compared for the 

conditions of eyes closed versus standing on foam. 

We performed an additional analysis on our data by 

removing the two individuals with hip disarticulation and 

bilateral transtibial amputation and included only those with 

unilateral transfemoral and transtibial amputation for 

analysis. 

 

0

10

20

30

40

EYES OPEN EYES CLOSED STANDING ON FOAM

AM AMOAAMOAYA YA YAOA

**
**

**
**

**
**

M
e

a
n

 d
is

ta
n

c
e

 o
f 
s
w

a
y 

in
 m

e
d

io
la

te
ra

l d
ir
e

c
ti
o

n
 (

m
m

)

 

0

500

1500

2000

3000

AM AM AMOA OA OAYA YA YA

1000

2500

**
**

**
**

**
**

T
o
ta

l 
e
x
c
u
rs

io
n

s
 (

m
m

)

EYES OPEN EYES CLOSED STANDING ON FOAM

 

100

120

AM AMOAAMOA OAYA YA YA

0

20

40

60

80

**
**

**
**

**
****

**

M
e

a
n

 v
e

lo
c
it
y
 o

f 
C

O
P

 (
m

m
/s

)

EYES OPEN EYES CLOSED STANDING ON FOAM

https://doi.org/10.33137/cpoj.v3i2.33804


 

5 

Bateni H. Postural sway in lower extremity amputees and older adults may suggest increased fall risk in amputees. Canadian Prosthetics & Orthotics Journal. 
2020;Volume 3, Issue 2, No.4. https://doi.org/10.33137/cpoj.v3i2.33804 

ISSN: 2561-987X POSTURAL SWAY IN LOWER EXTREMITY AMPUTEES  
Bateni H. 2020 

 
CPOJ 

 

Figure 4: Comparison of 95% mediolateral power frequency of 

sway signal for three different conditions of eyes open, eyes closed, 

and standing on foam. Diamond shape and solid line indicate mean 

and median of the data respectively. Data presented for three 

groups of amputees (AM), older adults (OA) and young adults (YA). 

Asterisks (**) denote statistically significant differences (p<0.05). 

Considering that static balance is mainly controlled through 

ankle and hip strategies,29 we attempted to create a more 

homogenized sample by removing two participants from the 

sample. We anticipated, unlike other participants, bilateral 

amputees may not have a chance to compensate for the 

loss of ankle strategy through the sound limb. Although 

inability to perform hip strategy in individuals with hip 

disarticulation is yet to be determined, we also excluded this 

participant to avoid any potential bias.  

Comparison of means and confidence limits for time and 

frequency domain variables showed almost a similar pattern 

as previous analysis. When older adults and young adults 

were compared with amputees, except for resultant power, 

amputees’ variables were closer to those of older adults 

than young adults (Figure 5). The mean of resultant power, 

however, was closer to the mean power of young adults 

than older adults (Figure 5E).  

Further analysis showed that participants with amputation 

swayed at a significantly higher velocity when compared 

with young adults (p=0.012) during eyes closed condition. 

On the other hand, amputees swayed at a significantly lower 

velocity when compared to older adults (p=0.015) during 

standing on the foam condition. Similarly, amputees total 

excursion of sway was higher than young adults in eyes 

closed trials (p=0.012) and less than older adults in trials of 

standing on foam (p=0.015). When power of sway signal 

during standing on foam condition were compared, 

amputee participant generated significantly less power 

during static standing comparing with older adults 

(p=0.002).  

 

Table 1: Table consists of demographic information on study 

participants. Participants are presented as non-amputees (NAM), 

right/left trans tibial (RTT/LTT), bilateral trans tibial (BTT), left 

Trans-femoral (LTF) and left hip disarticulation(LHD). Most study 

participants with amputation was using Dynamic Response (DR) 

prosthetic feet. 

Participant Gender Age 
Height 
(cm) 

Weight 
(Kg) 

Condition 
Res. 
Limb. 

Length 
Reason 

Prosthetic 
foot 

1 M 26 172 67.1 NAM -- -- -- 

2 M 29 171 60.3 NAM -- -- -- 

3 M 24 181 80 NAM -- -- -- 

4 M 24 188 76.1 NAM -- -- -- 

5 F 25 160 65.2 NAM -- -- -- 

6 F 25 153 58.4 NAM -- -- -- 

7 M 77 172.5 66 NAM -- -- -- 

8 F 72 166.6 68.8 NAM -- -- -- 

9 M 25 184.5 91.1 NAM -- -- -- 

10 M 24 187 75.3 NAM -- -- -- 

11 F 24 167.5 69.5 NAM -- -- -- 

12 F 24 159 68.3 NAM -- -- -- 

13 M 69 172 79.5 NAM -- -- -- 

14 F 68 167 62.9 NAM -- -- -- 

15 M 70 166 78.7 NAM -- -- -- 

16 M 77 174.5 86.9 NAM -- -- -- 

17 F 82 160.5 67.1 NAM -- -- -- 

18 M 65 174.8 104.4 NAM -- -- -- 

19 M 71 177.5 94.1 NAM -- -- -- 

20 F 66 157.6 82.1 NAM -- -- -- 

21 M 30 196 100.5 RTT 10 Trauma DR 

22 M 58 173.4 101 LTT 16.5 Trauma DR 

23 M 30 185.5 84.4 LTF 36 Trauma DR 

24 M 61 177 100.1 LTF 37 Disease DR 

25 F 60 160.51 84.9 LHD 0 Disease DR 

26 M 67 182.5 92.1 BTT 
20R / 
25L 

Disease SACH 

 

DISCUSSION  

It has been documented that mediolateral stability 

significantly correlates with the risk of falling in older 

adults.30 Winter et al. previously highlighted the importance 

of mediolateral sway during quiet standing.31,32 It has also 

been shown that mediolateral sway is increased in fallers 

when compared to non-fallers.33 Our results suggest that 

lower limb amputation significantly affects postural 

steadiness. Comparison of our finding with young and older 

adults also revealed important aspects of postural control in 

lower extremity amputees. To our knowledge, no other 

studies have compared postural stability of lower extremity 

amputees against that of young and older adults. Our 

results showed that while older adults swayed 

mediolaterally more than did amputees, the difference was 

not statistically significant. Both amputees and older adults, 

however, swayed significantly more than did young adults. 

 

0

2

4

6

8

10

AMOA OA OAYA YA YAAM AM

**
** **

**
**

**

EYES OPEN EYES CLOSED STANDING ON FOAM

9
5

%
 m

e
d

io
la

te
ra

l 
p

o
w

e
r 

fr
e

q
u

e
n
c
y
 (

H
z
)

https://doi.org/10.33137/cpoj.v3i2.33804


 

6 

Bateni H. Postural sway in lower extremity amputees and older adults may suggest increased fall risk in amputees. Canadian Prosthetics & Orthotics Journal. 
2020;Volume 3, Issue 2, No.4. https://doi.org/10.33137/cpoj.v3i2.33804 

ISSN: 2561-987X POSTURAL SWAY IN LOWER EXTREMITY AMPUTEES  
Bateni H. 2020 

 
CPOJ 

 

This variation, coupled with others’ findings relating sway to 

falls, supports the conclusion that both older adults and 

lower limb amputees are prone to falling. Our study finding 

is in agreement to those of Buckley et al,34 who reported 

increased sway distance in a group of 6 trans-tibial/trans-

femoral amputees.   

Similarly, total excursions of the center of pressure was 

higher for both older adults and amputees. When standing 

was challenged by a compliant (foam) surface, we noticed 

greater total excursions of sway in older adults, when 

compared to other conditions. Further analysis of sway 

velocity augmented this finding.  

Velocity of sway is recognized as one of the most important 

variables of sway analysis that can determine effects of 

aging on balance.12 Our results showed that older adults 

and amputees sway at a significantly higher velocity than do 

young adults (p<0.0001). Our post-hoc analysis did not 

reveal any significant difference in sway velocity between 

amputees and older adults. We also noted that with both 

amputees and older adults, the sway velocity increased 

when the condition was changed from eyes open to either 

eyes closed or standing on foam. It is particularly 

interesting, however, that the pattern of velocity is different 

between amputees and older adults when evaluating the 

three standing conditions. The two conditions of eyes 

closed and standing on foam are primarily designed to 

diminish visual and somatosensory/proprioceptive 

information, respectively, to the postural control system. It 

has been well documented and also seen in our own data 

that loss of any one of these sources of information for 

postural control leads to an increased sway and sway 

velocity in static standing.35 In our study, when amputees 

and older adults were compared, amputees swayed most 

when their eyes were closed, whereas older adults swayed 

more when they were standing on foam. Amputees’ sway 

velocity with eyes closed was significantly more than with 

eyes open (p=0.024); whereas, sway velocity did not 

increase significantly from eyes open to foam standing 

(p=0.19). On the other hand, for older adults, increase of 

sway velocity was significant when eyes open was 

compared to foam standing (p=0.044), while the increase in 

sway velocity was not significant when eyes open was 

compared to eyes closed (p=0.59). Both groups had 

 

AM OA YA
MDISTX

0

5

10

15

m
m

Conditions

a- eyes open

b- eyes closed

c- standing on foam

AM OA YA

m
m

2

0

20

40

60

80

100

POWER

X103

AM OA YA

m
m

/s

0

10

20

30

40

50

MVELO

AM OA YA

H
z

0

2

4

6

PFREQ95

AM OA YA

m
m

0

25

50

75

100

125

TOTEX

X10

A B

C D

E

Figure 5: Graph depicts mean values and 95% confidence limits for amputee group (AM), older adults (OA) and young adults (YA). Data 

represents amputee participants with unilateral transtibial and transfemoral amputation (n=4). A: Variables presented are mean distance of 

sway in mediolateral direction (MDISTX); B: mean velocity of COP (MVELO); C: Total excursions (TOTEX), D: 95% mediolateral power 

frequency (PFREQ95); E: Resultant power of sway (POWER). 

https://doi.org/10.33137/cpoj.v3i2.33804


 

7 

Bateni H. Postural sway in lower extremity amputees and older adults may suggest increased fall risk in amputees. Canadian Prosthetics & Orthotics Journal. 
2020;Volume 3, Issue 2, No.4. https://doi.org/10.33137/cpoj.v3i2.33804 

ISSN: 2561-987X POSTURAL SWAY IN LOWER EXTREMITY AMPUTEES  
Bateni H. 2020 

 
CPOJ 

 
corrected visual acuity of 20/20 with no known sensory 

deficits or physical or mental conditions that could 

potentially affect their balance. This may indicate that 

amputees are more dependent on visual information, 

whereas older adults are more dependent on 

somatosensory and proprioceptive information, to control 

their balance. The increased dependency of lower extremity 

amputees on visual input is also reported by Arifin et al.36,37 

in a sample of trans-tibial amputees, although no 

comparisons were made between amputees and young or 

older adults in this study.    

Also compared were the resultant mediolateral 95% power 

frequency among the study participants. The 95% power 

frequency is an estimate of the extent of the spectral content 

and indicates the frequency below which 95% of the 

integrated area of power spectrum resides. More detailed 

definition and method of calculation is explained 

elsewhere.12,38 Power spectral density is known to indicate 

the underlying mechanism of postural control.12 Therefore, 

the study suggests that the underlying mechanism of 

postural control for both amputees and older adults changes 

when eyes were closed, but not when they were standing 

on foam.  

Limitations 

There are several limitations acknowledged with respect to 

the generalizability of the study results. First, the study 

involved a small number of amputee participants: 6 

individuals with lower extremity amputation and 20 healthy 

controls. Although the findings suggest that amputees have 

an increased risk for falls and that they may rely heavily on 

visual input for postural control, replication should be sought 

with a larger sample. It is to be noted that the original 

sample included both young and older adults. In the 

secondary analysis, however, the data of amputees older 

than 60 years was only included. Although this change 

made the study sample more homogenous, it reduced the 

sample size even more. Additionally, all amputee data was 

combined, regardless of the level of amputation or, in the 

case of one participant, bilateral vs. unilateral amputation. 

As a result, this combination may have affected the results, 

but the level of this impact is yet to be investigated. 

Considering that in the inverted pendulum model of postural 

control, as suggested by Maurer and Peterka,24 postural 

sway is substantially controlled at the ankles. In fact, in a 

study of 8 unilateral trans-femoral amputees, Hlavackova et 

al.39 showed that the sound limb is most responsible for 

sway velocity when compared with the amputated side. In 

the current study, participants had different levels of 

amputation with the common characteristics that they were 

all missing their ankle. Nevertheless, further studies with a 

larger and more homogenous sample would be warranted 

to compare postural sway data between individuals with 

lower extremity amputation at different levels.     

CONCLUSION 

The results of this study suggest that lower limb amputation 

significantly affects postural steadiness. Additionally, it was 

noted that mediolateral postural sway and velocity of sway 

of lower limb amputee participants of this study were slightly 

less than those values for older adults. Furthermore, while 

both amputees and older adults represent a diminished 

postural steadiness, older adults’ steadiness is challenged 

more when standing on the foam, while amputees’ 

steadiness is more challenged when standing with eyes 

closed. It appears that when older adults and amputees are 

compared, most likely older adults are more dependent on 

their sensory information, while amputees are more 

dependent on their visual information.   

 

ACKNOWLEDGEMENTS 

The author would like acknowledge the help of Ms. Lisa 

Blackmer (SPT–Northern Illinois University) for her 

assistance with manuscript preparation and editorial 

contributions. The author would like to acknowledge the 

help of physical therapy students at Northern Illinois 

University with data collection in this study. 

DECLARATION OF CONFLICTING 

INTERESTS 

Author do not have any conflict of interest to disclose.   

SOURCES OF SUPPORT 

N/A 

ETHICAL APPROVAL 

This study approved (HS11- 0407) by  the Institutional Review 

Board, Northern Illinois University. Participants were asked to sign 

a consent form prior to participation in the study. 

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