THE INFLUENCE OF HYDRAULIC 
PROSTHETIC ANKLE ON WALKING OF A 
PERSON AFTER BILATERAL TRANSTIBIAL 
AMPUTATION – A CASE STUDY
VPLIV HIDRAVLIČNEGA STOPALA 
ZA PROTEZO NA HOJO OSEBE PO 
OBOJESTRANSKI TRANSTIBIALNI 
AMPUTACIJI – ŠTUDIJA PRIMERA
Sergeja Cergol1, dipl. ort. prot., dr. Matjaž Zadravec1, univ. dipl. inž. el., Veronika Podlogar1, mag. 
fiziot., prof. dr. Zlatko Matjačić1, 2, univ. dipl. inž. el., prof. dr. Helena Burger1, 3, dr. med.
1University Rehabilitation Institute, Republic of Slovenia, Ljubljana 
2Faculty of Electrical Engineering, University of Ljubljana 
3Faculty of Medicine, University of Ljubljana
Poslano: 9. 5. 2022
Sprejeto: 3. 7. 2022
Corresponding author/Avtorica za dopisovanje (HB): helena.burger@ir-rs.si
Abstract
Background:
Several articles about hydraulic ankles can be found in the 
PubMed bibliographic database, but we did not find any study 
about the influence of passive hydraulic ankle on walking up- 
and downhill in persons after bilateral transtibial amputation. 
The aim of our study was to assess this influence in a person 
after bilateral transtibial amputation.
Methods: 
The subject in our study was a 50-years old woman after 
bilateral transtibial amputation performed five years before 
the study due to complications of type I diabetes. Most meas-
urements were performed three times – on the admission day 
with the patient’s previous prostheses, after two weeks of 
training with the new prostheses with hydraulic prosthetic feet, 
and three months after discharge. We performed a structured 
interview, clinical tests, patient-reported outcome measures 
(PROMs) and kinesiological measurements during walking 
on flat, up- and downhill surfaces.
Results: 
While the patient reported subjective improvement on all 
questions of the structured interview and PROMs, we did 
not detect any objective improvement with clinical tests and 
Izvleček
Izhodišča: 
V bibliografski podatkovni zbirki PubMed je več člankov o 
hidravličnih stopalih za proteze, vendar nismo našli nobene 
študije o vplivu pasivnega hidravličnega stopala na hojo 
navkreber in navzdol pri osebah po obojestranski transtibialni 
amputaciji. V študiji smo želeli oceniti morebitni vpliv hidrav-
ličnega stopala na protezi pri hoji pacientke po obojestranski 
transtibialni amputaciji.
Metode: 
V raziskavo smo vključili petdesetletno žensko po obojestranski 
transtibialni amputaciji, opravljeni pet let pred raziskavo zaradi 
zapletov sladkorne bolezni tipa I. Večino meritev smo opravili 
trikrat – na dan sprejema z njenima prejšnjima protezama, z 
novima protezama s hidravličnim proteznim stopalom po dveh 
tednih vadbe in tri mesece po odpustu. Opravili smo struk-
turiran intervju, klinične teste, izpolnila je številne vprašalnike 
in naredili smo kineziološke meritve hoje po ravnem, po klančini 
navzgor in navzdol. 
Rezultati: 
Medtem ko je pacientka poročala o subjektivnem izboljšanju pri 
vseh vprašanjih strukturiranega intervjuja in na vseh vprašal-
nikih, s kliničnimi testi nismo ugotovili nobenega objektivnega 
Cergol, Zadravec, Podlogar, Matjačić, Burger / Rehabilitacija - letnik XXI, št. 1 (2022)
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INTRODUCTION
The main function of our lower limbs is to enable us safe and 
stable standing, walking and related activities, such as walking 
on different terrains, up and down stairs, jumping, running etc. 
After lower limb amputation, the functions of the amputated 
body part are replaced with a functions of prosthesis. For many 
years, prosthetic components were purely mechanical. The first 
fluid-controlled ankle was developed by Hans Mauch in 1950s (1). 
It did not enter clinical trial until the late 1970s, but due to seal 
leakage problems it was removed from the market (1). The interest 
in hydraulic ankles has been renewed in this millennium and 
today we have several commercially available devices. Their 
main advantage is that they permit much higher passive plantar 
(up to 50 degrees) and dorsal flexion than mechanical prosthetic 
ankles without fluid-control (1) and thus make it easier to ascend 
and descend slopes. Their performance was further improved by 
microprocessor control (MPC) (2-4).
In the PubMed bibliographic database, several articles about 
hydraulic ankles can be found, most of them are based on a 
small number of subjects after unilateral amputation; only three 
studies on non-MPC ankles include more than ten subjects (5-7). 
They found out that in subjects after unilateral transtibial ampu-
tation during level and decline walking with hydraulic ankles, 
there was reduced total mechanical work and metabolic energy 
expenditure (8), smoother and more rapid progression of centre 
of pressure (9, 10), the subjects chose faster walking speed (6, 
9, 10) and there was reduced risk of tripping of the prosthetic 
limb when ascending and descending the ramp (7). On the other 
hand, they didn’t find any difference in the torque at the distal 
end of the prosthetic socket during the single support phase, nor 
better socket comfort during walking at different slopes (11). 
One study included one bilateral amputee (5) and another study 
included three of them (12). They observed the largest increase 
in satisfaction in the bilateral amputees (12).
Selection of the most appropriate prosthetic components depends 
on the user’s health condition, functional status and user’s needs 
and wishes. In subjects after bilateral lower limb amputations, it is 
important to select components, which will allow stable standing 
and walking, but also comfortable walking on different terrains. 
When selecting the most appropriate components, the prosthetist 
has to find a balance between stability and function.
We did not find any study about the influence of passive hydrau-
lic ankle on walking up and downhill in subjects after bilateral 
transtibial amputation. Hence, the aim of our study was to assess 
this influence in a subject after bilateral transtibial amputation.
METHODS
Subject
We included a 50-year old woman after bilateral transtibial ampu-
tation performed five years prior to the study, due to complications 
of type I diabetes. She has had diabetes since she was eight years 
old, nowadays treated by an insulin pump. Since birth she is blind 
on her left eye. For the last 14 years, she has also had rheumatoid 
arthritis, treated with biological drugs. She had prostheses with 
silicone liners and energy-storing and realising (ESR) prosthetic 
feet (Epirus foot from Blatchford). She was using her prostheses 
whole day and was able to walk around 10.000 steps daily using 
one stick. In the last two years, she did not fall. Her main complaint 
was about difficulty at walking on uneven terrain and up and down 
hills. She has both uneven terrain and hills around her home and 
has to overcome them every day. During walking downhill, she 
had pain at the anterior distal part of both stumps, more severe 
on her left side.
Procedure
Most measurements were performed three times (Table 1). On 
the admission day (T1) they were performed with the patient’s 
previous prostheses. Immediately after measurements, she was 
fitted with new prostheses which had the same type but new 
silicone liners, the socket shape was a copy of the old one, so the 
only very small, probably clinically not important differences 
with kinesiological measurements.
Conclusions: 
Clinical tests and kinesiologic measurements did not confirm 
the subjective improvement felt by the patient. It is not pos-
sible to generalise our results to other subjects after bilateral 
transtibial amputation.
Keywords: 
bilateral transtibial amputation; passive hydraulic prosthetic 
ankle; walking downhill
izboljšanja, s kineziološkimi meritvami pa zelo majhne, verjetno 
klinično nepomembne razlike.
Zaključek: 
Klinični testi in kineziološke meritve niso potrdili subjektivnega 
izboljšanja, ki ga je občutila pacientka. Naših rezultatov ni 
mogoče posplošiti na druge osebe po obojestranski transtibialni 
amputaciji.
Ključne besede: 
obojestranska transtibialna amputacija; pasivno hidravlično 
protezno stopalo; hoja navzdol
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72
only difference was in the prosthetic feet – the new prostheses 
had hydraulic prosthetic ankles (Echelon foot from Blatchford). 
She received two weeks of physiotherapy training with the new 
prostheses. Functional training combined training of gait and 
daily activities. At the beginning, gait endurance and velocity 
on flat surfaces was trained; uneven surfaces, stairs and ramps 
followed. After two weeks of training, we performed the second 
measurement (T2), after which she was discharged home. The last 
measurement was performed three months after discharge (T3). 
Clinical tests
The 6-minute walk test (6MWT) is a generic timed test used to 
assess aerobic capacity and endurance, and to monitor prosthetic 
walking performance (13). It was performed according to the 
guidelines (14); the turnaround points were marked with cones. 
Verbal encouragement was standardised; the distance walked in 
6 min was recorded in meters. 
The 10-metre walk test (10MWT) was conducted on a 14 m walk-
ing path. The measurement started when the participant crossed 
the 2 m mark and stopped when she crossed the 12 m mark (15). 
The participant was instructed to walk as fast as possible but safely 
without running. Two consecutive trials were performed with fast 
speed, and the mean speed was calculated as the outcome (16). 
The L Test is as modification of the Timed Up and Go test (17). It is 
named after the L-shaped walking path. The time of an individual 
to stand up from a chair, walk for 3 m in a straight line, turn left 
for 90° at the first cone, walk 7 m in a straight line, turn for 180° 
at the second cone, walk back along the same path and sit down 
on the chair was measured with a manual stopwatch (in seconds, 
to the first decimal point). The participant was instructed to walk 
as fast as she was safely able to. Following the test demonstration 
by the therapist and one practice trial, two consecutive trials were 
measured with a 2minuste break between them. The mean was 
calculated as the outcome (18).
Table 1: Timetable of performed tests and outcome measures.
Tabela 1: Časovnica opravljenih testov in merjenj izida.
Test / outcome measure
Test / mera izida
T1 – at admission with 
the old prostheses
T1 – ob sprejemu s 
starima protezama
T2 – after 2 weeks of training 
with the new prostheses
T2 – po dveh tednih vadbe 
z novima protezama
T3 – after 3 months 
of use at home
T3 – po treh mesecih 
uporabe doma
Structured interview / 
Strukturirani intervju
x x 
Clinical tests / Klinični testi
6-minute walk test (m) x x x
10-metre walk test (m/s) x x x
L-test (s) x x x
One leg standing test 
(on prosthesis) (s)
left x x x
right x x x
AMPPRO-Bilateral x x x
PROMs / Vprašalniki
PMQ 2.0 x x
ABC x x
WAS x x
Numeric pain rating scale 
walking downhill
x x
Kinesiologic measurements / Kineziološke meritve
Flat 0.3 m/s x x x
Flat 0.6 m/s x x x
Uphill 0.3 m/s x x x
Uphill 0.6 m/s x x x
Downhill 0.3 m/s x x x
Legend: AMPPRO – Amputee Mobility Predictor, PROMs – patient reported outcome measures, PMQ – Prosthetic Mobility Questionnaire, ABC - Activities-specific 
Balance Confidence Scale, WAS - Walking Aid Scale.
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The one-leg stance test is described as a method of quantifying stat-
ic balance ability. It is a valid measure and is useful in explaining 
other variables of importance such as frailty and self-sufficiency 
in activities of daily living, gait performance and fall status (19, 
20). Test was performed with eyes open and hands placed on the 
hips. Participant had to stand unassisted on one leg - prosthesis, 
timed from the time the other foot leaved the ground till when 
the foot touched the ground again or the arms left the hips. The 
best time of five trials was used as a result (21).
Patient reported outcome measures (PROMs)
She filled in the Prosthetic Mobility Questionnaire (PMQ) 2.0 
(22, 23), the Activity-specific Balance Confidence (ABC) scale 
(24, 25), and the Walking Aid Scale (WAS) (26), all in the validated 
Slovene versions (23, 25, 26). Pain was assessed using the Numeric 
Pain Rating Scale (27).
The PMQ 2.0 is a Rasch-validated self-report 12-item questionnaire 
that examines different tasks of varying difficulty related to mobility 
in people with lower-limb loss (22, 23). The common stem of the 
items is “Over the past week, please rate your ability to do the 
following activities when using your prosthesis”. Each item is 
rated with a 5-response option scale (0, unable; 1, high difficulty; 
2, moderate difficulty; 3, little difficulty; 4, no problems). In PMQ 
2.0, all 12 PMQ items of the original version (22) are assessed, but 
the global score is calculated on 10 of them, using only the worst 
performance in each couple of locally-dependent items, representing 
the same task performed in two opposite directions (up/down stairs; 
up/down hill). Raw scores range from 0 to 40, with higher scores 
indicating better prosthetic mobility.
The ABC (24) is a self-report 16-item questionnaire that asks people 
to score their perceived level of balance confidence when performing 
various indoor and outdoor activities of daily living. The common 
stem of the questions is: “How confident are you that you can 
maintain your balance and remain steady when you...”. We use the 
original scoring (0= No confidence; 100 = Complete confidence).
The WAS quantifies the need for walking aids in four activities 
of increasing difficulty (walking indoors; walking on sidewalk 
and streets; walking up and down a steep hill; walking for up to 
2 hours) on a 5level ordinal scale: 0 – no walking aids; 1 – one 
cane or crutch; 2 – two canes or crutches; 3 – walker or rollator; 
4 – unable to perform the activity. The sum of the four scores is 
taken as the total score, with higher values indicating a greater need 
for walking aids (26).
Numeric Pain Rating scale (27) is an 11-point scale scored from 
zero (no pain) to 10 (the most intense pain imaginable). Patients 
verbally select a value that is the most in line with the intensity of 
pain they have experienced in the last 24 hours.
Kinesiological measurements
Kinematic data were captured using the Optitrack motion analysis 
system (Prime 13W, NaturalPoint Inc., US). Plug-in gait low-
er-body model with 16 reflective markers attached to the subject 
was used to calculate hip, knee and ankle angles, as well as step 
length, width and time. The subject walked on a custom-designed 
wide instrumented treadmill with force transducers (K3D120, 
ME Systeme GmbH, DE) placed underneath, from which ground 
reaction forces (GRF) and centre of pressure (COP) were obtained. 
Sampling frequency was 120 Hz for kinematic and 200 Hz for 
kinetic data. Uphill and downhill measurements were recorded 
on a sloped treadmill with the slope angle of 8.5 degrees (15 %). 
The subject walked uphill, downhill and on a flat positioned 
treadmill as outlined in Table 1, with each measurement lasting for 
approximately three minutes, from which 50 gait cycles were ex-
tracted on average. Kinematic and kinetic signals were segmented 
into strides (defined between two consecutive heel strikes of the 
same leg) for calculation of mean values and standard deviation. 
Spatio-temporal data on step length, width and time were statis-
tically analysed using one-way ANOVA separately for each leg. 
Figure 1: Bilateral transtibial amputee walking on a flat, uphill-sloped and downhill-sloped instrumented treadmill.
Slika 1: Oseba po obojestranski transtibialni amputaciji hodi po ravnem, navkreber in navzdol po tekočem traku, opremljenem z 
merilnimi napravami.
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In addition, post hoc multiple comparison tests were performed 
using Bonferroni correction. For safety, the patient was wearing 
a harness (Figure 1). In spite of the harness, while walking uphill 
she was holding a rope (Figure 1), and while walking downhill 
the hand of a physiotherapist (Figure 1, Table 2).
The study was approved by the Research Ethics Committee of 
the University Rehabilitation Institute, Republic of Slovenia 
(035-1/2021-1/2-2).
RESULTS
The results of the structured interview, clinical tests and PROMs 
are summarised in Table 3. The subject was wearing new pros-
theses the whole day and walked with them approximately 2000 
steps more that with the old prostheses. For half an hour, she was 
also able to walk without a stick or any additional walking aids. 
Otherwise, she was using one cane. She also walked with a cane 
Table 2: Additional support while walking on treadmill.
Tabela 2: Dodatna opora pri hoji na tekočem traku.
Surface and speed
Površina in hitrost
T1 – at admission with 
the old prostheses
T1 – ob sprejemu s 
starima protezama
T2 – after 2 weeks of training 
with the new prostheses
T2 – po dveh tednih vadbe 
z novima protezama
T3 – after 3 months 
of use at home
T3 – po treh mesecih 
uporabe doma
Flat 0.3 m/s Nothing 2 hands 1 hand
Flat 0.6 m/s 1 hand 2 hands 1 hand
Uphill 0.3 m/s 2 hands 1 hand 1 hand
Uphill 0.6 m/s 2 hands 1 hand 1 hand
Downhill 0.3 m/s 2 hands 2 hands 2 hands
Table 3: Results of the interview, clinical tests and PROMs.
Tabela 3: Rezultati intervjuja in kliničnih testov ter dosežki na vprašalnikih.
Test / outcome measure
Test / mera izida
T1 – at admission with 
the old prostheses
T1 – ob sprejemu s 
starima protezama
T2 – after 2 weeks of training 
with the new prostheses
T2 – po dveh tednih vadbe 
z novima protezama
T3 – after 3 months 
of use at home
T3 – po treh mesecih 
uporabe doma
Structured interview / Strukturirani intervju
Daily time of wearing prosthesis Whole day Whole day
Time able to walk without any aid (min) 15 30
Self-reported daily walking (no. of steps) 10.000 12.000
Clinical tests / Klinični testi
6-minute walk test (m) 350 360 390
10-metre walk test – fast speed (m/s) 1.08 1.17 1.16
L-test (s) 29.1 28.1 28.5
One leg standing test (on prosthesis) (s)
left 0 0 
right 0 0
AMPPRO- Bilateral 40 40 43
PROMs / Vprašalniki
PMQ 2.0 (0 – 40) 21 28
ABC (%) 37 69
WAS (0 – 20) 9 5
Numeric pain rating scale walking downhill 7 0
Legend: AMPPRO – Amputee Mobility Predictor, PROMs – patient reported outcome measures, PMQ – Prosthetic Mobility Questionnaire, ABC - Activities-specific 
Balance Confidence Scale, WAS - Walking Aid Scale.
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Table 4: Spatio-temporal data from kinesiological measurements.
Tabela 4: Prostorsko-časovni podatki kinezioloških meritev.
Spatio-temporal data
mean (SD)/ Prostorsko-
časovni podatki
povprečje (SO)
T1 – at admission with the old 
prostheses/  
T1 – ob sprejemu s 
starima protezama
T2 – after 2 weeks of training 
with the new prostheses/ 
T2 – po dveh tednih vadbe 
z novima protezama
T3 – after 3 months of use at 
home/  
T3 – po treh mesecih 
uporabe doma
Flat 0.3 m/s / Ravna površina 0,3 m/s
Step length (m)
L 0.26 (0.03) 0.27 (0.03) 0.32 (0.03)**##
R 0.26 (0.03) 0.26 (0.04) 0.28 (0.04)*
Step width (m)
L 0.19 (0.02) 0.16 (0.03)** 0.14 (0.02)**##
R 0.19 (0.02) 0.16 (0.02)** 0.14 (0.02)**##
Step time (s)
L 0.86 (0.05) 0.89 (0.09) 1.01 (0.07)**##
R 0.88 (0.07) 0.87 (0.09) 0.98 (0.09)**##
Flat 0.6 m/s / Ravna površina 0,6 m/s
Step length (m)
L 0.44 (0.02) 0.42 (0.03)** 0.45 (0.02)##
R 0.45 (0.03) 0.47 (0.02)* 0.44 (0.03)##
Step width (m)
L 0.11 (0.02) 0.12 (0.02) 0.11 (0.02)
R 0.11 (0.02) 0.12 (0.02) 0.11 (0.02)
Step time (s)
L 0.71 (0.03) 0.72 (0.04) 0.73 (0.03)
R 0.78 (0.04) 0.76 (0.04) 0.75 (0.03)*
Uphill 0.3 m/s / Navkreber 0,3 m/s
Step length (m)
L 0.41 (0.02) 0.33 (0.03)** 0.38 (0.02)**##
R 0.38 (0.03) 0.34 (0.02)** 0.39 (0.02)##
Step width (m)
L 0.09 (0.02) 0.12 (0.02)** 0.11 (0.01)*##
R 0.09 (0.01) 0.12 (0.02)** 0.11 (0.01)**##
Step time (s)
L 1.30 (0.07) 1.10 (0.06)** 1.31 (0.08)##
R 1.35 (0.07) 1.15 (0.06)** 1.26 (0.07)**##
Uphill 0.6 m/s / Navkreber 0,6 m/s
Step length (m)
L 0.55 (0.02) 0.48 (0.02)** 0.51 (0.02)**##
R 0.52 (0.02) 0.51 (0.02) 0.50 (0.02)**#
Step width (m)
L 0.08 (0.01) 0.11 (0.02)** 0.11 (0.01)**
R 0.08 (0.01) 0.11 (0.02)** 0.11 (0.01)**
Step time (s)
L 0.86 (0.02) 0.80 (0.03)** 0.82 (0.02)**##
R 0.91 (0.03) 0.86 (0.03)** 0.86 (0.03)**
Downhill 0.3 m/s / Navzdol 0,3 m/s
Step length (m)
L 0.28 (0.03) 0.26 (0.04)** 0.26 (0.03)**
R 0.26 (0.03) 0.26 (0.04) 0.28 (0.03)**##
Step width (m)
L 0.15 (0.03) 0.16 (0.03) 0.15 (0.02)
R 0.15 (0.02) 0.16 (0.02)* 0.15 (0.02)
Step time (s)
L 0.92 (0.08) 0.89 (0.07) 0.94 (0.08)##
R 0.89 (0.08) 0.82 (0.10)** 0.86 (0.07)#
Legend: L – left; R – right; SD – standard deviation
Legenda: L - levo; R - desno; SD - standardni odklon
Note: * (p < 0.05) and ** (p < 0.01) indicate a statistically significant difference compared to T1; # (p < 0.05) and ## (p < 0.01) indicate a statistically significant 
difference between T2 and T3.
Opomba: * (p < 0,05) in ** (p < 0,01) označuje statistično značilno razliko v primerjavi s T1; # (p < 0,05) in ## (p < 0,01) označuje statistično značilno razliko med T2 in T3.
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during the 6MWT. While walking down she had no more pain 
in her stumps. On the Numeric Pain Rating Scale, she assessed 
pain while walking downhill as seven for the old and as zero for 
the new prostheses.
The main findings from the spatio-temporal results are significant 
narrowing of step width and consequently slight prolongation of 
step length and step duration at slow flat walking (0.3 m/s). When 
walking uphill at both speeds (0.3 and 0.6 m/s), we observed 
significant step widening between old and new prostheses. Flat 
walking at 0.6 m/s and downhill walking (0.3 m/s) showed no 
significant differences between using old and new prostheses 
(Table 4). There was also no difference in the need for additional 
support (Table 2). 
DISCUSSION
While the patient reported subjective improvement on all questions 
of structured interview and PROMs, we did not measure any 
objective improvement with clinical tests and with kinesiology 
we observed only very small, probably clinically not important 
differences.
To our knowledge, there is neither minimal detectable change 
(MDC) nor minimal clinically important difference (MCID) 
estimated either for the number of steps walked per day or for 
the Walking Aids Scale. However, both measures indicated a 
tendency of improvement. There are also no MDC or MCID 
estimates for pain in people with limb loss, but for all other pop-
ulations the MCID is between 1.0 and 2.2 (27). The difference of 
7 points reported by our patient is therefore a clinically important 
improvement. This decrease in pain is probably due to greater 
range of motion of hydraulic prosthetic feet, especially plantar 
flexion, because while walking on a flat surface she did not have 
any pain even with the old prostheses. 
For ABC, there is also no MDC or MCID estimated for people 
with limb loss. For patients with Parkinson disease, MDC is 
13 (28); the difference in our patient was much higher. The cut 
point for risk of falling for non-specific population and people 
with vestibular problems is 67 % and for those with Parkinson 
disease it is 69 % (28). Our patient had a huge improvement on 
ABC score and moved from the area of high risk for falling to the 
cut point. This does not mean that she cannot fall using the new 
prostheses, but the risk of falling is much lower with hydraulic 
prosthetic feet and with that also risk for further injuries.
MCID for PMQ 2.0 is 8 points (29), while our patient reported 
an improvement of 7 points. That is certainly an improvement in 
self-reported mobility, because MDC for PMQ 2.0 is 5 points (29), 
which is just below the clinical importance.
The difference of 40 metres on the 6-minute walk test is probably 
not clinically important. MCID estimates vary from 34.4 m (30) 
for stroke patients up to 147.5 m for patients at least two years 
after unilateral lower limb amputation (30). For most disabilities, 
the MCID is around 50 metres (13).
The difference in walking speed of 0.08 m/s may represent a small 
clinically relevant change, as the MCID is 0.05 m/s for older 
adults and 0.06 m/s for stroke patients (31). We found no data 
for people with limb loss, not even unilateral. The difference is 
smaller than any reported clinically substantial difference, which 
is at least 0.13 m/s (31). 
The difference of one second on the L Test is in the range of the 
measurement error. In outpatient experienced prosthesis users, 
the MCID of the L Test was 4.5 s (32) and the minimal detectable 
change (MDC) ranged from 2.2 to 3.2 s (33). The difference of 3 
points on the AMPPRO is also in the range of measurement error, 
as the MDC for AMPPRO is 3.4 points (31).
Compared to walking speed of subjects with bilateral transtibial 
amputation (34), we decided for slow and very slow walking 
speeds on the treadmill. The reason for such decision was that 
we did our measurement on treadmill and not during over-ground 
walking as was the case in a comparable study (34). Compared 
to their results, our slow walking speed was very slow, while our 
fast-walking speed was still slow. We also did not find any study 
measuring walking parameters while walking up and downhill.
The differences observed in spatio-temporal parameters were 
small, so probably clinically not important. To our knowledge, 
there are no MDC or MCID estimates for spatio-temporal walking 
parameters.
While walking on flat treadmill at speed of 0.6 m/s, step width was 
similar to that of healthy subjects (34) and much narrower than 
in other subjects after bilateral transtibial amputation (34). That 
might suggest improved balance and confidence during walking 
with hydraulic prosthetic feet. The reason might also be increased 
additional support during the second measurement. While walking 
uphill, all measured differences were very small, much smaller 
than standard deviations estimated in a comparable study (34). 
While walking uphill at both walking speeds, our subject used 
the longest and the narrowest steps of all three conditions. The 
additional support that she needed while walking uphill decreased 
from two to one hand already at the first measurement with 
hydraulic prosthetic feet. That might suggest higher confidence 
when walking uphill and even better confidence when walking 
with hydraulic prosthetic feet.
When walking downhill, the patient was able to walk at 0.3m/s 
only, so this was the most difficult condition for her. Even after 
using hydraulic prosthetic feet for three months, she still needed 
additional support with both hands.
In spite of a carefully prepared protocol, our study has several 
limitations. The main limitation is that we did not anticipate that 
the patient might need additional support while walking, and 
consequently we allowed her various forms of support in different 
conditions and at different measurement times. Furthermore, 
the study was performed on one patient only. We do not have 
many highly active patients with bilateral transtibial amputation, 
so for us a study on a larger number of subjects would be very 
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difficult to perform. We did also not take into account some other 
aspects where we might have found some changes, such as energy 
expenditure and cognitive demand, but our primary focus was 
the ability to walk downhill, which was also the major problem 
of our patient while using the old prostheses. On the other hand, 
our study demonstrated that the acclimatisation period to different 
prosthetic feet might be even longer than two weeks.
CONCLUSION
While the patient reported subjective improvement on all questions 
of the structured interview and on the PROMs, we did not measure 
any objective improvement with clinical tests and with kinesiology, 
we observed only very small, probably clinically not important 
differences. It is not possible to generalise our results to other 
subjects after bilateral transtibial amputation.
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