







































McGrath M, Davies KC, Laszczak P, Rek B, McCarthy J, Zahedi S, Moser D. The influence of hydraulic ankles and microprocessor-control on the 
biomechanics of trans-tibial amputees during quiet standing on a 5° slope. Canadian Prosthetics & Orthotics Journal. 2019;Volume2, Issue2, No.2. 
https://doi.org/10.33137/cpoj.v2i2.33517 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 
 

 
 

 

 

 

 

 

ISSN: 2561-987X 

VOLUME 2, ISSUE 2 

 2019 

 

(ONLINE) 

R E S E A R C H   A R T I C L E 

All articles are permanently available online to the public without restrictions or subscription 

fees. All articles are free to be used, cited, and distributed, on condition that appropriate 

acknowledgment is included. Authors are the copyright holders of their original 

contributions and grant the Canadian Prosthetics & Orthotics Journal (CPOJ) a license to 

publish the article and identify itself as the original publisher. CPOJ articles are licensed 

under the Creative Commons Attribution 4.0 International License.   

 

CPOJ Website: https://jps.library.utoronto.ca/index.php/cpoj/index 

Editorial Office: cpoj@online-publication.com    

ISSN: 2561-987X 

CPOJ is a member of, and subscribes to the principles of, the Committee on Publication 

Ethics (COPE).   

 

 

https://doi.org/10.33137/cpoj.v2i2.33517
http://creativecommons.org/licenses/by/4.0/
https://jps.library.utoronto.ca/index.php/cpoj/index
mailto:cpoj@online-publication.com
https://publicationethics.org/about/our-organisation
https://publicationethics.org/about/our-organisation


 

 

  1 

 
OPEN  ACCESS 

THE INFLUENCE OF PROSTHETIC ANKLES ON THE STANDING BIOMECHANICS OF TRANSTIBIAL AMPUTEES 

Volume 2, Issue 2, Article No.2, 2019 

 

 

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

 

RESEARCH ARTICLE 

 

THE INFLUENCE OF HYDRAULIC ANKLES AND MICROPROCESSOR-CONTROL ON THE 
BIOMECHANICS OF TRANS-TIBIAL AMPUTEES DURING QUIET STANDING ON A 5° SLOPE  

 
McGrath M*, Davies KC, Laszczak P, Rek B, McCarthy J, Zahedi S, Moser D 
 

Blatchford Group, Unit D Antura, Bond Close, Basingstoke, RG24 8PZ, UK. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

INTRODUCTION   

Musculoskeletal health problems are prevalent among 

lower limb amputees.1–4 The consensus among 

biomechanists is that the inherent asymmetry of the body, 

along with reduced confidence and proprioception on the 

prosthetic side, leads to an unequal distribution of limb 

loading between the two limbs.2,3,5 Excessive dependence 

on the sound limb for support can have a degenerative 

effect on the joints. Osteoarthritis (OA) is common, with 

studies reporting incidences in up to 41% of trans-tibial 

amputee4,5 (TTA) community. Most often, OA presents in 

the sound knee joint, affecting between 12-66% of all lower 

limb amputees,2,3,6 however up to 23% are also affected at 

the sound hip.2,3 There are also consequences for the 

residual side through reduced loading. Osteoporosis (OP) 

and osteopenia have been reported to affect the residual 

limbs of approximately 90% of people with lower limb 

amputation.3,4 One research study found a mean reduction 

in bone density of 15% across lower limb amputees, 

compared to the intact limb.2 

Another consequence of loading asymmetry is low back 

pain (LBP). The rate of occurrence has been reported to 

be as high as 48-71% in the lower limb amputee 

population1,3,7–9 as a whole and 62% for TTAs,10 in 

particular. This figure is approximately double the 

estimated 28-30% of the general population that are 

affected by back pain.9,11 Research has also highlighted 

how quickly this problem can develop, with 60% of 

amputees reporting moderate to extreme back pain 

occurring within the first two years after amputation.10 

ABSTRACT 

BACKGROUND: Lower limb amputees have a high incidence of comorbidities, such as osteoarthritis, 

which are believed to be caused by kinetic asymmetries. A lack of prosthetic adaptation to different 

terrains requires kinematic compensations, which may influence these asymmetries. 

METHOD: Six SIGAM grade E-F trans-tibial amputees (one bilateral) wore motion capture markers 

while standing on force plates, facing down a 5° slope. The participants were tested under three 

prosthetic conditions; a fixed attachment foot (FIX), a hydraulic ankle (HYD) and a microprocessor 

foot with a ‘standing support’ mode (MPF). The resultant ground reaction force (GRF) and support 

moment for prosthetic and sound limbs were chosen as outcome measures. These were compared 

between prosthetic conditions and to previously captured able-bodied control data. 

RESULTS: The distribution of GRF between sound and prosthetic limbs was not significantly affected 

by foot type. However, the MPF condition required fewer kinematic compensations, leading to a 

reduction in sound side support moment of 59% (p=0.001) and prosthetic side support moment of 43% 

(p=0.02) compared to FIX. For the bilateral participant, only the MPF positioned the GRF vector 

anterior to the knees, reducing the demand on the residual joints to maintain posture. 

CONCLUSION: For trans-tibial amputees, loading on lower limb joints is affected by prosthetic foot 

technology, due to the kinematic compensations required for slope adaptation. MPFs with ‘standing 

support’ might be considered reasonable and necessary for bilateral amputees, or amputees with 

stability problems due to the reduced biomechanical compensations evident. 

CITATION 

McGrath M, Davies KC, Laszczak P, 

Rek B, McCarthy J, Zahedi S, 

Moser D. The influence of hydraulic 

ankles and microprocessor-control 

on the biomechanics of trans-tibial 

amputees during quiet standing on a 

5° slope. Canadian Prosthetics & 

Orthotics Journal. 2019;Volume2, 

Issue2, No.2. 

https://doi.org/10.33137/cpoj.v2i2.33

517 

 
KEYWORDS 

Prosthesis, Transtibial Amputees, 

Gait Analysis, Kinematic, Kinetic,  

Amputation, Microprocessor foot, 

Hydraulic ankle, Slope, Symmetry, 

Standing balance 

*CORRESPONDING AUTHOR 

Dr. Michael McGrath, 

Research Scientist–Clinical Evidence 

Blatchford Group, Unit D Antura, Bond Close, Basingstoke, RG24 8PZ, United Kingdom 

Email: mike.mcgrath@blatchford.co.uk 

ORCID: https://orcid.org/0000-0003-0195-970X 

 

DOI: https://doi.org/10.33137/cpoj.v2i2.33517 

ARTICLE INFO 

Received: December 31, 2019 

Accepted: February 20, 2020 

Published: February 24, 2020 

 

https://jps.library.utoronto.ca/index.php/cpoj/index
https://doi.org/10.33137/cpoj.v2i2.33517
https://doi.org/10.33137/cpoj.v2i2.33517
mailto:mike.mcgrath@blatchford.co.uk
https://doi.org/10.33137/cpoj.v2i2.33517


 

 

 McGrath M, Davies KC, Laszczak P, Rek B, McCarthy J, Zahedi S, Moser D. The influence of hydraulic ankles and microprocessor-control on the biomechanics of trans-tibial 
amputees during quiet standing on a 5° slope. Canadian Prosthetics & Orthotics Journal. 2019;Volume2, Issue2, No.2. https://doi.org/10.33137/cpoj.v2i2.33517 

 

2 

CPOJ 

 

McGrath et al. 2019 

 THE INFLUENCE OF PROSTHETIC ANKLES ON THE STANDING BIOMECHANICS OF TRANSTIBIAL AMPUTEES 

The alignment of the lower limb prosthesis is one factor 

key to achieving a ‘close-to-normal’ posture and gait with 

even distribution of loads between prosthetic and sound 

limbs. The position and movement of the body’s centre-of-

mass (COM), relative to the positions of the lower limb 

joints, influences the forces and moments acting at those 

joints.12,13 This in turn affects the muscular effort required 

to provide support.14 Typically, the alignment process 

within a clinic focuses on level ground ambulation. 

However, when walking or standing on uneven or sloped 

surfaces, the relative position of the body’s COM to the 

lower limb joints changes and thus the alignment of a 

prosthesis may become sub-optimal.15–18  

Part of the problem may be the prosthetic device. In 

conventional, energy-storing-and-return (ESR) feet that 

have a fixed attachment to the distal end of the prosthetic 

pylon, plantarflexion and dorsiflexion of the foot are 

achieved through deformation of the foot keel, which is 

often constructed of elastic elements and structures. If the 

foot cannot comply with sloped surfaces, compensatory 

movement of other joints may be required to ensure the 

foot is flat on the ground.19This is due to the reaction forces 

that are induced and act on the body as the keel deflects 

from a neutral unloaded condition. For unilateral TTAs, this 

often presents as increased residual knee flexion.20,21This 

action puts the body’s COM behind the knee joint centre, 

creating a flexion moment, which may require greater 

effort to resist. Not only does this increase the day-to-day 

energy consumption of the user, but it also has negative 

implications on their stability and sound limb dependence. 

Hydraulic ankles, which produce a viscoelastic response 

when loaded, allow a degree of damped movement 

proximal to the foot springs, ‘self-aligning’ with the ground 

and helping to maintain the body’s COM position relative 

to the lower limb joints.19,22 This action minimises 

undesirable biased forces and moments acting on the 

limb, thus it may also reduce the compensations needed 

to enable effective standing on uneven surfaces.19 

Previous work has used the ground reaction force (GRF) 

to determine the inter-limb load distribution during trans-

femoral amputee (TFA) standing tests.19 This approach, 

however, does not consider the loading at individual joints, 

which could provide greater insight into which joints are 

most at risk of OA development. Furthermore, since 

possible compensation strategies may vary between 

amputees,19 Winter’s concept of support moment23 may 

provide a more comprehensive and universal metric by 

which to measure the demand on a given limb to provide 

support. This is defined as the sum of the moments acting 

at the ankle, knee and hip, where extension moments 

make up the positive contribution to support and flexion 

moments provide a negative one.23 

This study expands on the previous work19 to focus on 

TTAs and, in particular, how differences in prosthetic foot 

and ankle technology can influence the way in which they 

stand on non-level ground. Two hypotheses were tested. 

The first was that TTAs would present with asymmetry in 

GRF distribution when using a fixed attachment foot, 

which would be reduced when using adaptive feet. The 

second hypothesis was that the fixed attachment foot 

would lead to increased lower limb joint moments, 

compared to adaptive feet. 

METHODOLOGY 

Prosthetic devices 

Three different prosthetic ankle/foot devices were 

evaluated in this study, each of which uses different 

prosthetic technology. The first was Espriti (FIX – 

Blatchford, Hampshire, UK), which is an ESR foot with a 

fixed attachment to the distal end of the prosthetic pylon. 

The second device was Echelonii (HYD – Blatchford, 

Hampshire, UK), which shares a common geometry with 

Esprit but with a hydraulic ‘ankle’ unit attached proximally. 

Plantarflexion and dorsiflexion of the foot are achieved 

through a combination of rotation of the hydraulic unit 

(allowing for 9° of damped movement) and the 

deformation of foot springs. The final device was Elaniii  
(MPF – Blatchford, Hampshire, UK), with a hydraulic 

system similar to Echelon, which includes microprocessor-

control. The hydraulic unit provides damped ankle flexion 

adapting in real time to slopes and changes in speed but 

when the device detects that the user is standing still, the 

hydraulic resistances to movement in the plantarflexion 

and dorsiflexion directions are increased to a high level. 

This change is intended to provide both ground adaptation 

and extra support when standing. The high resistance is 

such that it permits small natural alignment adjustments 

but does not 'lock' the ankle in a fixed position, which may 

or may not be optimal.  

Participants 

Six TTA participants volunteered for the study, the details 

of whom are listed in Table 1. Verbal participant information 

was given and signed consent was provided by each 

participant. An ethics review of the study followed the 

tenets of the Declaration of Helsinki and was approved by 

the institutional ethics review board. Each person was 

aged 18 or over and, at the time of testing, their residual 

limbs were in good health, free from infection or skin 

conditions. A consultant prosthetist determined a SIGAM 

mobility grade E or higher for all participants, meaning they 

were capable of negotiating environmental barriers, such 

as sloped ground and ramps, with no other walking aids. 

Each of the participants had experience using both fixed 

attachment and hydraulic ankle/foot devices. They had all 

initially been prescribed fixed attachment feet immediately 

post amputation and three (TT1, TT3 and TT4) still used 

this type of device as a running limb. At the time of testing, 

all participants had been using a hydraulic ankle or a 

microprocessor-controlled hydraulic ankle as their 

habitual, everyday device for at least 12 months. 

The data gathered during this study were compared to the 

same measurements gathered from a group of able-

bodied control participants in a previous study19 (27.4±2.9 

years, 66.8±10.3 kg). 

Gait lab setup 

A motion capture system was used to track the 

movements of participants (Codamotion, Charnwood 

Dynamics, Leicestershire, UK). This system uses active 

marker clusters, two three-dimensional infra-red cameras 

and two force plates (Kistler Group, Winterthur, 

Switzerland) positioned side by side on a 5° slope. The 

cameras collected data at a frequency of 200Hz, while the 

https://doi.org/10.33137/cpoj.v2i2.33517


 

 

 McGrath M, Davies KC, Laszczak P, Rek B, McCarthy J, Zahedi S, Moser D. The influence of hydraulic ankles and microprocessor-control on the biomechanics of trans-tibial 
amputees during quiet standing on a 5° slope. Canadian Prosthetics & Orthotics Journal. 2019;Volume2, Issue2, No.2. https://doi.org/10.33137/cpoj.v2i2.33517 

 

3 

CPOJ 

 

McGrath et al. 2019 

 THE INFLUENCE OF PROSTHETIC ANKLES ON THE STANDING BIOMECHANICS OF TRANSTIBIAL AMPUTEES 

force plate acquisition frequency was 500Hz. Body 

segment tracking and definitions of virtual markers were 

done using a conventional six-degree-of-freedom (6DoF) 

marker model24 similar to that used in a previous study.19 

The marker model was designed for able-bodied 

participants and required virtual markers at the medial and 

lateral malleoli. On the prosthetic limb, these were defined 

at the pivot point of the hydraulic units for the HYD and 

MPF devices. The similar geometry of the FIX device 

meant that corresponding locations could be 

approximated when that device was worn.19 

Table 1: Characteristics of the participants. Please note 

EchelonVT is a hydraulic ankle with an in-built vertical shock 

pylon/ torsion adaptor and EchelonVAC is a hydraulic ankle with 

an in-built mechanism for generating elevated vacuum 

suspension. 

S
u
b
je

c
t 

G
e
n

d
e

r 

S
IG

A
M

 
g
ra

d
e

 

A
g
e
 

(y
e
a

rs
) 

M
a
s
s
 (

k
g
) 

H
e
ig

h
t 
(m

) 

P
ro

s
th

e
ti
c
 

lim
b

 

H
a
b
it
u
a
l 

p
ro

s
th

e
s
is

 

TT1 Male F 42 51 1.65 Right EchelonVT 

TT2 Male F 24 60 1.70 Right Elan 

TT3 Male F 38 92 1.83 Right EchelonVT 

TT4 Male F 53 65 1.78 Left EchelonVAC 

TT5 Male F 45 92 1.77 Right Elan 

TT6 Female E 36 55 1.75 Both 2x Elan 
 

Data collection 

Participants were asked to wear tight fitting shorts and  

t-shirts to permit the accurate positioning of markers, 

reduce marker occlusions and minimise movement 

artefact. Each wore regular trainers and the same 

footwear was used for each prosthetic device tested.  

The testing protocol was based on that used in a previous 

study.19 Participants stood facing down a 5° slope and, 

when instructed, stepped forwards, placing one foot on 

each of the two adjacent force plates. Once on the force 

plates they were instructed to stand as naturally as 

possible. Multiple trials (minimum of three) were used to 

measure at least 30 seconds of standing per participant. 

This meant that no single prosthetic device was 

detrimentally affected by initial foot positioning and 

steadying when a participant first stepped onto the force 

plates.  

Each participant performed the testing protocol with each 

of the three prosthetic ankle/foot devices. Each device was 

fitted and aligned by the same experienced senior 

prosthetist and the order in which they were tested was 

randomised. Before data collection began with a new 

prosthetic device, the participants were given 30 minutes 

to acclimatise to the new foot. Since each participant was 

already experienced with both fixed attachment and 

hydraulic prostheses, this time was deemed sufficient. 

Regardless, testing would only proceed once both the 

participant and prosthetist were satisfied that they were 

capable of performing the protocol safely. 

Data processing and analysis 

In order to ensure only quiet standing was analysed, the 

actions of stepping on and off of the force plates needed 

to be excluded. The final 3 seconds of each trial were 

rejected and the preceding 10 seconds were extracted and 

used in the final analysis. 

All kinetic parameters were normalised by the participant’s 

mass so that data were comparable between participants. 

All data were processed and analysed with Visual3D v6 

x64 biomechanics analysis software (C-motion Inc., 

Germantown, MD, USA). 

Statistical analysis 

The data were assessed for normality using Shapiro-Wilk 

tests and for homogeneity of variance using Fligner-

Killeen tests. For normally distributed data, a one-way 

analysis of variance (ANOVA) was used to identify 

statistically significant differences between the different 

prosthetic ankle/foot technologies and post-hoc Tukey 

tests were performed for pairwise comparisons. For non-

normally distributed data, or for groups with heterogeneity 

of variances, Kruskal-Wallis tests were followed by post-

hoc Dunn tests. Statistical significance was defined as 

p<0.05. All statistical tests were performed using R v3.3.3 

(The R Foundation, Vienna, Austria). 

RESULTS  

Kinematic compensations 

There were no significant differences between the mean 

joint angles for unilateral participants between prosthetic 

conditions. The bilateral amputee, however, did present 

with clear kinematic compensations (Figure 1). The FIX 

condition required knee flexion in order to achieve foot-flat. 

Interestingly, for the HYD condition, knee flexion increased 

further (not significant) as the participant ‘rested’ on the 

mechanical dorsiflexion stops at the limit of the hydraulic 

range. The MPF condition allowed knee flexion to be 

reduced to a more upright posture (p=0.002 compared to 

FIX). Ta 

 

Figure 1: The kinematic strategies of the bilateral trans-tibial 

amputee participant using (a) FIX, (b) HYD and (c) MPF. 

Kinetics (bodyweight distribution) 

There were no statistically significant differences in the 

resultant GRF, or any of the three axial components, 

between the prosthetic conditions for the unilateral 

amputees. Differences in the mean prosthetic and sound 

values were all less than 3%. The prosthetic condition did 

not significantly influence GRF for the bilateral amputee 

either. 

https://doi.org/10.33137/cpoj.v2i2.33517


 

 

 McGrath M, Davies KC, Laszczak P, Rek B, McCarthy J, Zahedi S, Moser D. The influence of hydraulic ankles and microprocessor-control on the biomechanics of trans-tibial 
amputees during quiet standing on a 5° slope. Canadian Prosthetics & Orthotics Journal. 2019;Volume2, Issue2, No.2. https://doi.org/10.33137/cpoj.v2i2.33517 

 

4 

CPOJ 

 

McGrath et al. 2019 

 THE INFLUENCE OF PROSTHETIC ANKLES ON THE STANDING BIOMECHANICS OF TRANSTIBIAL AMPUTEES 

Kinetics (joint moments) 

Both prosthetic and sound support moments were 

significantly affected by prosthetic condition for the 

unilateral group (Figure 2a). Post hoc testing showed that, 

compared to FIX (0.27 ± 0.19 Nm/kg), both HYD (0.17 ± 

0.12 Nm/kg, p=0.038) and MPF (0.15 ± 0.12 Nm/kg, 

p=0.020) reduced prosthetic side support moment. Sound 

side support moment was also reduced by HYD (0.29 ± 

0.17 Nm/kg) compared to FIX (0.41 ± 0.23 Nm/kg, 

p=0.045). MPF reduced sound side support moment 

further (0.17 ± 0.16 Nm/kg), which was statistically 

significant compared to FIX (p=0.001) but not compared to 

HYD. 

These changes were mostly due to different ankle kinetics. 

The ankle moments for FIX (0.25 ± 0.17 Nm/kg prosthetic; 

0.38 ± 0.25 Nm/kg sound) were significantly decreased by 

HYD (0.16 ± 0.13 Nm/kg prosthetic, p=0.009; 0.26 ± 0.19 

Nm/kg sound, p=0.034) and by MPF (0.18 ± 0.14 Nm/kg 

prosthetic, p=0.042; 0.21 ± 0.19 Nm/kg sound, p=0.004). 

Another statistically significant change was the reduction 

of sound hip moment by MPF (0.02 ± 0.05 Nm/kg) 

compared to FIX (0.08 ± 0.03 Nm/kg, p<0.001). When 

MPF was compared to HYD (0.06 ± 0.06 Nm/kg), the 

reduction approached significance (p=0.06). 

For the bilateral amputee, support moment for HYD (0.62 

± 0.03 Nm/kg) was significantly higher than both FIX (0.46 

± 0.08 Nm/kg, p=0.002) and MPF (0.28 ± 0.11 Nm/kg, 

p<0.001). MPF significantly reduced knee moments (-0.08 

± 0.09 Nm/kg) compared to both other conditions (FIX: 

0.08 ± 0.06 Nm/kg, p=0.003, HYD: 0.078 ± 0.01 Nm/kg, 

p=0.002). 

DISCUSSION  

The results of this study disproved the first hypothesis that 

TTAs would present with GRF distribution asymmetry 

when standing on a slope with a fixed attachment foot. 

However, the second hypothesis that the fixed attachment 

foot would increase joint moments, compared to adaptive 

feet, was found to be true. 

The observation that the TTAs in this study did not display 

any obvious inter-limb GRF asymmetry for any of the 

prosthetic technologies is in contrast to the findings of the 

previous research with TFAs,19 suggesting that the 

participants had the confidence to load their prosthetic 

limb. This, in the long-term, may help to reduce the 

likelihood of OP25 or LBP1 development. Furthermore, 

again in contrast to the TFA participants,19 unilateral TTAs 

did not present any significant differences in mean joint 

angles between prosthetic conditions. Upon closer 

inspection, this observation could be attributed to the inter-

participant variation and different strategies used to adapt 

their limbs to the gradient, some with knee flexion, some 

with hip flexion. This led to broad standard deviations, 

masking any trends. Additionally, compared to TFAs, it is 

possible that the extra control allowed by the residual knee 

joint meant that a foot-flat position could be achieved 

through greater foot spring deflection, with a reduced 

amount of knee flexion. 

These observations perhaps highlight the advantage of 

using the support moment metric for standing 

biomechanics and prosthetic alignment. The concept of 

support moment was devised by Winter23 as a metric for 

use in gait analysis to show the bodyweight support 

provided by a limb as a whole. This research used the 

same method of calculation applied to quiet standing. The 

advantage of this approach is that it gives greater insight 

into the demand on the joints and how it is affected by 

changing test conditions, rather than only the weight-

bearing load. Additionally, this metric is not sensitive to the 

compensation strategy used so it is not obscured by inter-

participant variability. For the unilateral TTAs, statistically 

significant changes were observed in both prosthetic and 

sound support moments. This shows that even though the 

participants were applying equal loads to their limbs, there 

was still an adverse effect on their sound side joints, which 

could be a risk factor in OA development.26,27 In the case of 

unilateral amputees, for example, the FIX condition 

presented a significantly higher demand on the sound 

ankle (p=0.004) and hip (p<0.001), compared to MPF. 

Consequently, the MPF presented the best scenario for 

the sound joints, as participants were able to align their 

joints to minimise the moments acting about them. 

 

Figure 2: The relative contributions of ankle, knee and hip 

moment to the total support moment for (a) unilateral trans-tibial 

amputees, (b) a bilateral trans-tibial amputee and (c) able-bodied 

control participants. Asterisks indicate statistical significance: 

*p<0.05, **p<0.01. Obelisks indicate effect size changes: 

†|d|>0.5, ††|d|>0.8. 

https://doi.org/10.33137/cpoj.v2i2.33517


 

 

 McGrath M, Davies KC, Laszczak P, Rek B, McCarthy J, Zahedi S, Moser D. The influence of hydraulic ankles and microprocessor-control on the biomechanics of trans-tibial 
amputees during quiet standing on a 5° slope. Canadian Prosthetics & Orthotics Journal. 2019;Volume2, Issue2, No.2. https://doi.org/10.33137/cpoj.v2i2.33517 

 

5 

CPOJ 

 

McGrath et al. 2019 

 THE INFLUENCE OF PROSTHETIC ANKLES ON THE STANDING BIOMECHANICS OF TRANSTIBIAL AMPUTEES 

In a modelling analysis of quiet standing, Winter 

highlighted that in the lower limbs, the ankle joint provided 

the greatest contribution to posture and balance.28 This 

was confirmed by the able-bodied control participants in 

this study where, of the individual joints, the greatest 

contribution to support was found at the ankle (Figure 2c). 

This trend was also present in the sound limbs of the 

unilateral amputees, highlighting the potential benefits of a 

prosthetic technology that could reduce the demand on the 

ankle joint while maintaining a comfortable standing 

posture. 

These observations are what makes the bilateral TTA 

participant such an interesting case study. The lack of any 

sound ankle – integral to maintaining posture28 – shifts the 

reliance to the knees or, indeed, the prosthetic technology. 

In this case, knee moments were affected by prosthetic 

condition. MPF was the only condition to produce negative 

knee moments. This indicated that the ground reaction 

vector had passed anterior to the knee joints. When 

prosthetists align devices in the clinic, this is one of their 

goals to achieve adequate balance with minimal muscular 

demand. The ability of a prosthetic ankle to adapt to 

changing gradients in this way is invaluable for a bilateral 

amputee, but extra prosthetic technology is required to 

compensate for the lack of a sound ankle. The HYD and 

MPF devices in this study have the same hydraulic range 

but, for the bilateral participant, increased knee flexion was 

only observed during the HYD condition. This was 

because the MPF devices provided “standing support”; 

initially adapting to the slope before increasing the 

resistance to ‘ankle’ movement when the sensors detected 

that the user was standing still. This held the MPF devices 

well-aligned, shifting the knee moment trend in-line with 

that observed for the able-bodied participants. 

Other work has sought to compare different types of 

prosthetic feet when standing on slopes, but the gradients 

used were higher than that in the current study (7° slope,20 

10° slope21 and 15° slope,29 respectively) so direct, 

quantifiable comparisons are challenging. However, 

similar trends were reported for the comparison of fixed 

attachment feet to feet with adaptive ankles. Reduced 

residual knee flexion was observed when using the 

adaptive feet, compared to fixed,20,21 affecting joint 

moments. Ernst et al.21 also noted the different strategies 

employed by participants to adapt to the slope and how 

this influences the variability of the measurements. 

It is worth acknowledging that the protocol of this study 

might have influenced the findings to some degree. 

Software limitations meant that recordings could only be 

performed for relatively short intervals. Future work might 

ask participants to stand for longer time periods, recording 

short intervals throughout that longer period. This would 

highlight whether differences between prosthetic 

conditions become more substantial as the participants 

become more fatigued. 

CONCLUSION 

This study has shown that unilateral TTAs are able to 

maintain approximate weight-bearing symmetry between 

their prosthetic and sound limbs while standing on sloped 

ground. However, the demand that is placed on their joints 

is dependent upon the ease in which they are able to 

maintain an upright posture. Hydraulic ankles allow self-

alignment, resulting in fewer kinematic compensations and 

reducing the moments on the sound joints. For bilateral 

TTAs, the combination of ankle adaptation and standing 

support provided by the MPF, represented the only 

condition under which the ground reaction vector was 

anterior to the knee joints. This suggests that MPF 

technology is particularly important for bilateral amputees, 

in order to protect the joints against excessive demand and 

the development of OA. 

ACKNOWLEDGEMENTS 

The authors wish to thank the participants for taking the time to 

volunteer for this study. 

DECLARATION OF CONFLICTING 

INTERESTS 

The authors are full time employees of the manufacturer of the 

prosthetic devices examined in this study. 

ETHICAL APPROVAL 

An ethics review of the study followed the tenets of the Declaration 

of Helsinki and was approved by the institutional ethics review 

board. 

AUTHOR CONTRIBUTION 

• Michael McGrath,  

Conceptualization, data collection, data analysis, manuscript 

preparation, review and editing. 
 

• Katherine C. Davies,  

Manuscript preparation, review and editing. 
 

• Piotr Laszczak,  

Data analysis, manuscript review and editing. 
 

• Beata Rek,  

Data analysis, manuscript review and editing. 
 

• Joe McCarthy, 

Conceptualization, data collection, manuscript review and 

editing. 
 

• Saeed Zahedi, 

Conceptualization, manuscript review and editing. 
 

• David Moser, 

Conceptualization, manuscript review and editing. 

SOURCES OF SUPPORT 

Blatchford provided financial support and prosthetic devices for 

this study. 

REFERENCES 

1. Ehde DM, Smith DG, Czerniecki JM, Campbell KM, Malchow 

DM, Robinson LR. Back pain as a secondary disability in persons 

with lower limb amputations. Arch Phys Med Rehabil. 2001; 82: 

731–734. https://doi.org/10.1053/apmr.2001.21962 

2. Kulkarni J, Adams J, Thomas E, Silman A. Association between 

amputation, arthritis and osteopenia in British male war veterans 

with major lower limb amputations. Clin Rehabil. 1998; 12: 348–

353. https://doi.org/10.1191/026921598672393611 

https://doi.org/10.33137/cpoj.v2i2.33517
https://doi.org/10.1053/apmr.2001.21962
https://doi.org/10.1191/026921598672393611


 

 

 McGrath M, Davies KC, Laszczak P, Rek B, McCarthy J, Zahedi S, Moser D. The influence of hydraulic ankles and microprocessor-control on the biomechanics of trans-tibial 
amputees during quiet standing on a 5° slope. Canadian Prosthetics & Orthotics Journal. 2019;Volume2, Issue2, No.2. https://doi.org/10.33137/cpoj.v2i2.33517 

 

6 

CPOJ 

 

McGrath et al. 2019 

 THE INFLUENCE OF PROSTHETIC ANKLES ON THE STANDING BIOMECHANICS OF TRANSTIBIAL AMPUTEES 

3.Burke MJ, Roman V, Wright V. Bone and joint changes in lower 

limb amputees. Ann. Rheum. Dis. 1978; 37: 252–254. 
http://dx.doi.org/10.1136/ard.37.3.252 

4.Hungerford DS, Cockin J. Fate of the retained lower limb joints 

in Second World War amputees. J Bone Joint Surg 1975; 57: 111. 

5. Norvell DC, Czerniecki JM, Reiber GE, Maynard C, Pecoraro 

JA, Weiss NS. The prevalence of knee pain and symptomatic 

knee osteoarthritis among veteran traumatic amputees and 

nonamputees. Arch Phys Med Rehabil. 2005; 86: 487–493. 
https://doi.org/10.1016/j.apmr.2004.04.034 

6.Melzer I, Yekutiel M, Sukenik S. Comparative study of 

osteoarthritis of the contralateral knee joint of male amputees who 

do and do not play volleyball. J Rheumatol. 2001; 28: 169–172. 

7.Smith DG, Ehde DM, Legro MW, Reiber GE, del Aguila M, 

Boone DA. Phantom limb, residual limb, and back pain after lower 

extremity amputations. Clin. Orthop. Relat. Res. 1999; 361: 29–

38. 

8. Ehde DM, Czerniecki JM, Smith DG, Campbell KM, Edwards 

WT, Jensen MP, Robinson LR. Chronic phantom sensations, 

phantom pain, residual limb pain, and other regional pain after 

lower limb amputation. Arch Phys Med Rehabil.2000; 81: 1039–

1044. https://doi.org/10.1053/apmr.2000.7583 

9. Ephraim PL, Wegener ST, MacKenzie EJ, Dillingham TR, 

Pezzin LE. Phantom pain, residual limb pain, and  

back pain in amputees: results of a national survey.  

Arch Phys Med Rehabil.2005; 86: 1910–1919. 
https://doi.org/10.1016/j.apmr.2005.03.031 

10. Kulkarni J, Gaine WJ, Buckley JG, Rankine JJ, Adams J. 

Chronic low back pain in traumatic lower limb amputees.  

Clin Rehabil. 2005; 19: 81–86. 
https://doi.org/10.1191/0269215505cr819oa 

11.Kulkarni J. Post amputation syndrome. Prosthet Orthot Int. 

2008; 32: 434–437. https://doi.org/10.1080/03093640802258637 

12. Blumentrttt S. A new biomechanical method for determination 

of static prosthetic alignment. Prosthet Orthot Int. 1997; 21: 107–

113. 

13. Blumentrttt S, Sghmalz T, Jarasch R, Schneider M. Effects of 

sagittal plane prosthetic alignment on standing trans-tibial 

amputee knee loads. Prosthet Orthot Int. 1999; 23: 231–238. 

14.Houdijk H, Fickert R, van Velzen J, van Bennekom C. The 

energy cost for balance control during upright standing.  

Gait Posture. 2009; 30:150–154. 

https://doi.org/10.1016/j.gaitpost.2009.05.009 

15. Vrieling AH, Van Keeken HG, Schoppen T, Otten E, 

Halbertsma JPK, Hof AL, et al. Uphill and downhill walking in 

unilateral lower limb amputees. Gait Posture. 2008; 28: 235–242. 
https://doi.org/10.1016/j.gaitpost.2007.12.006 

16. Vickers DR, Palk C, McIntosh AS, Beatty KT. Elderly unilateral 

transtibial amputee gait on an inclined walkway: a biomechanical 

analysis. Gait Posture. 2008; 27: 518–529. 
https://doi.org/10.1016/j.gaitpost.2007.06.008 

17. Bai X, Ewins D, Crocombe AD, Xu W. Kinematic and 

biomimetic assessment of a hydraulic ankle/foot in level ground 

and camber walking. PLOS ONE 2017; 12: e0180836. doi: 

10.1371/journal.pone.0180836 

18. Wirta RW, Mason R, Calvo K, Golbranson FL. Effect on gait 

using various prosthetic ankle-foot devices. J Rehabil Res Dev 

1991; 28: 13–24. 

19. McGrath M, Laszczak P, Zahedi S, Moser D. Microprocessor 

knees with “standing support” and articulating, hydraulic ankles 

improve balance control and inter-limb loading during quiet 

standing. J Rehabil Assist Technol Eng. 2018; 5: 

2055668318795396. https://doi.org/10.1177/2055668318795396 

20. Thomas-Pohl M, Villa C, Davot J, Bonnet X, Facione J, 

Lapeyre E, Bascou J, Pillet H. Microprocessor prosthetic ankles: 

comparative biomechanical evaluation of people with transtibial 

traumatic amputation during standing on level ground and slope. 

Disabil Rehabil Assist Technol. 2019; 1–10. 
https://doi.org/10.1177/2055668318795396 

21.Ernst M, Altenburg B, Bellmann M, Schmalz T. Standing on 

slopes – how current microprocessor-controlled prosthetic feet 

support transtibial and transfemoral amputees in an everyday 

task. J NEUROENG REHABIL. 2017; 14: 117. doi: 

10.1186/s12984-017-0322-2. 

22.De Asha AR, Johnson L, Munjal R, Kulkarni J, Buckley JG. 

Attenuation of centre-of-pressure trajectory fluctuations under the 

prosthetic foot when using an articulating hydraulic ankle 

attachment compared to fixed attachment. Clin Biomech. 2013; 

28: 218–224. https://doi.org/10.1016/j.clinbiomech.2012.11.013 

23. Winter DA. Kinematic and kinetic patterns in human gait: 

variability and compensating effects. Hum Movement Sci.1984; 3: 

51–76. 

24. Charnwood Dynamics Ltd. Odin Feature Guides. Codamotion 

Wiki, https://codamotion.com/wiki/product-guides/odin-feature-

guides/ (2019). 

25. Sherk VD, Bemben MG, Bemben DA. BMD and bone 

geometry in transtibial and transfemoral amputees. J Bone Miner 

Res. 2008; 23: 1449–1457. https://doi.org/10.1359/jbmr.080402 

26. Royer TD, Wasilewski CA. Hip and knee frontal plane 

moments in persons with unilateral, trans-tibial amputation.  

Gait Posture. 2006; 23: 303–306. 
https://doi.org/10.1016/j.gaitpost.2005.04.003 

27. Lemaire ED, Fisher FR. Osteoarthritis and elderly amputee 

gait. Arch Phys Med Rehabil.1994; 75: 1094–1099. 
https://doi.org/10.1016/0003-9993(94)90084-1 

28. Winter DA, Patla AE, Prince F, Ishac M, Gielo-Perczak K. 

Stiffness Control of Balance in Quiet Standing. J Neurophysiol. 

1998; 80: 1211–1221. https://doi.org/10.1152/jn.1998.80.3.1211 

29.Kaluf B, Duncan A, Bridges W. Comparative Effectiveness of 

Microprocessor-Controlled and Carbon-Fiber Energy-Storing-

and-Returning Prosthetic Feet in Persons with Unilateral 

Transtibial Amputation: Patient-Reported Outcome Measures. J 

Prosthet Orthot. 2020: Online Ahead of Print. doi: 

10.1097/JPO.0000000000000288 

MANUFACTURERS’ DOCUMENTATION 

i http://www.blatchfordus.com/products/esprit 

ii http://www.blatchfordus.com/products/echelon 

iii http://www.blatchfordus.com/products/elan 

 

 

https://doi.org/10.33137/cpoj.v2i2.33517
http://dx.doi.org/10.1136/ard.37.3.252
https://doi.org/10.1016/j.apmr.2004.04.034
https://doi.org/10.1053/apmr.2000.7583
https://doi.org/10.1016/j.apmr.2005.03.031
https://doi.org/10.1191/0269215505cr819oa
https://doi.org/10.1080/03093640802258637
https://doi.org/10.1016/j.gaitpost.2009.05.009
https://doi.org/10.1016/j.gaitpost.2007.12.006
https://doi.org/10.1016/j.gaitpost.2007.06.008
https://doi.org/10.1177/2055668318795396
https://doi.org/10.1177/2055668318795396
https://doi.org/10.1016/j.clinbiomech.2012.11.013
https://doi.org/10.1359/jbmr.080402
https://doi.org/10.1016/j.gaitpost.2005.04.003
https://doi.org/10.1016/0003-9993(94)90084-1
https://doi.org/10.1152/jn.1998.80.3.1211
http://www.blatchfordus.com/products/esprit
http://www.blatchfordus.com/products/echelon
http://www.blatchfordus.com/products/elan

