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VOLUME 4, ISSUE 1 

 2021 

 

RESEARCH ARTICLE 

Altenburg B, Ernst M, Maciejasz P, Schmalz T, Braatz F, Gerke H, Bellmann M. Effects of a prosthetic foot with increased coronal adaptability on cross-slope 

walking. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.7. https://doi.org/10.33137/cpoj.v4i1.35206 

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1 

Altenburg B, Ernst M, Maciejasz P, Schmalz T, Braatz F, Gerke H, Bellmann M. Effects of a prosthetic foot with increased coronal adaptability on cross-slope 
walking. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.7.  https://doi.org/10.33137/cpoj.v4i1.35206 

 

 

 
RESEARCH ARTICLE 

 

EFFECTS OF A PROSTHETIC FOOT WITH INCREASED CORONAL ADAPTABILITY ON CROSS-

SLOPE WALKING 

Altenburg B1*, Ernst M1, Maciejasz P2, Schmalz T1, Braatz F3, Gerke H4, Bellmann M1
 

 

1 Research Biomechanics, Ottobock SE & Co. KGaA, Göttingen, Germany. 
2 Clinical Research and Services, Ottobock SE & Co. KGaA, Duderstadt, Germany. 
3 Medical Orthobionics, Pivate University of Applied Sciences, Göttingen, Germany. 
4 Institute of Biomechanics and Orthopaedics, German Sport University Cologne, Köln, Germany. 

 

 

 

 

  

 

 

 

 

 

 

 

 
 

 

 

 

INTRODUCTION   

Real-life outdoor walking of persons with a lower limb 

amputation is continuously challenged by uneven ground, 

including bumps, obstacles, slopes and cross-slopes.  

 

 

 

 

 

Cross-slopes are especially demanding,1 since many 

sidewalks are generally tilted for water drainage and often 

intersected with driveways. Such tilted ground induces a 

functional leg length discrepancy, which is an apparent 

problem, in particular when the prosthetic limb is positioned 

hillside and is effectively too long. This requires the user to 

perform compensatory strategies during gait.2 Conversely, 

an adaptive prosthesis may diminish compensatory user 

effort. In  a  lower  limb prosthesis, the  prosthetic  foot  is a 

 
OPEN  ACCESS Volume 4, Issue 1, Article No.7. 2021 

 

 

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

 

ABSTRACT 

BACKGROUND: Walking on cross-slopes is a common but challenging task for persons with lower limb 

amputation. The uneven ground and the resulting functional leg length discrepancy in this situation 

requires adaptability of both user and prosthesis. 

OBJECTIVE(S): This study investigated the effects of a novel prosthetic foot that offers adaptability on 

cross-slope surfaces, using instrumented gait analysis and patient-reported outcomes. Moreover, the 

results were compared with two common prosthetic feet.   

METHODOLOGY: Twelve individuals with unilateral transtibial amputation and ten able-bodied control 

subjects participated in this randomized cross-over study. Participants walked on level ground and ±10° 

inclined cross-slopes at a self-selected walking speed. There were three prosthetic foot interventions: 

Triton Side Flex (TSF), Triton LP and Pro-Flex LP. The accommodation time for each foot was at least 

4 weeks. The main outcome measures were as follows: frontal plane adaptation of shoe and prosthetic 

foot keel, mediolateral course of the center of pressure, ground reaction force in vertical and 

mediolateral direction, external knee adduction moment, gait speed, stance phase duration, step length 

and step width. Patient-reported outcomes assessed were the Activities specific Balanced Confidence 

(ABC) Scale, Prosthetic Limb Users Survey of Mobility (PLUS M) and Activities of Daily Living 

Questionnaire (ADL-Q).   

FINDINGS: The TSF prosthetic foot adapted both faster and to a greater extent to the cross-slope 

conditions compared to the Triton LP and Pro-Flex LP. The graphs for the mediolateral center of 

pressure course and mediolateral ground reaction force showed a distinct grouping for level ground and 

±10° cross-slopes, similar to control subjects. In the ADL-Q, participants reported a higher level of 

perceived safety and comfort when using the TSF on cross-slopes. Eight out of twelve participants 

preferred the TSF over the reference. 

CONCLUSION: The frontal plane adaptation characteristics of the TSF prosthetic foot appear to be 

beneficial to the user and thus may enhance locomotion on uneven ground – specifically on cross-

slopes. 

 

ARTICLE INFO 

Received: December 2, 2020 

Accepted: June 8, 2021 

Published: June 25, 2021 

CITATION 

Altenburg B, Ernst M, Maciejasz 

P, Schmalz T, Braatz F, Gerke 

H, Bellmann M. Effects of a 

prosthetic foot with increased 

coronal adaptability on cross-

slope walking. Canadian 

Prosthetics & Orthotics Journal. 

2021;Volume 4, Issue 1, No.7.  

https://doi.org/10.33137/cpoj.v4i

1.35206 

KEYWORDS 

Cross-slopes, Transtibial, 

Amputation, Coronal Adaptation, 

Prosthetic Foot, Center of 

Pressure, External Knee 

Adduction Moment (EKAM) 

 

 

* CORRESPONDING AUTHOR 

Björn Altenburg, 

Research Biomechanics, Ottobock SE & Co. KGaA, Göttingen, 
Germany. 

E-Mail: Bjoern.altenburg@ottobock.com 

ORCID ID: https://orcid.org/0000-0002-3484-4346 

https://doi.org/10.33137/cpoj.v4i1.35206
https://jps.library.utoronto.ca/index.php/cpoj/index
https://doi.org/10.33137/cpoj.v4i1.35206
https://doi.org/10.33137/cpoj.v4i1.35206
https://doi.org/10.33137/cpoj.v4i1.35206
mailto:Bjoern.altenburg@ottobock.com


 

2 

Altenburg B, Ernst M, Maciejasz P, Schmalz T, Braatz F, Gerke H, Bellmann M. Effects of a prosthetic foot with increased coronal adaptability on cross-slope 
walking. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.7.  https://doi.org/10.33137/cpoj.v4i1.35206 

ISSN: 2561-987X 
EFFECTS OF PROSTHETIC FOOT ON CROSS-SLOPE WALKING 

Altenburg et al. 2021 CPOJ 

 
central component which offers an individual adaptability, 

depending on the design and materials used.3  

Due to their carbon structure, common energy-storing-and-

returning (ESR) feet have a certain degree of flexibility, 

which allows for limited adaptation under load.3 It has been 

shown in different studies4-6 that a mechanical ankle joint 

can increase the range of motion in plantar and dorsiflexion 

and that a sophisticated microprocessor control can 

improve the adaptation to uneven ground.7-9 Most studies 

have focused on adaptations in the sagittal plane. Only a 

few studies have investigated prototype feet that adapt in 

the frontal plane.10,11 Many ESR feet are equipped with a 

split-toe feature that is thought to add flexibility in the frontal 

plane.3 However, it has not yet been shown that such foot 

design benefits individuals with lower-limb amputations 

walking on inclined ground. Moreover, few studies have 

investigated amputees’ gait on cross-slopes.12-14 Most 

recently, Villa et al. revealed compensatory strategies of 

lower-limb amputees during prosthetic swing when the 

prosthesis was positioned hillside.  

Individuals with transtibial amputation (ITTAs) showed 

increased hip and knee flexion in the residual limb for 

compensation and individuals with transfemoral amputation 

(ITFAs) increased hip hiking and vaulting.12 Such vaulting 

strategies of ITFAs were investigated in a previous article 

by Villa.13 Starholm et al.14 found that ITFAs use 

significantly more energy when walking on a surface 

moderately tilted in the frontal plane compared to walking 

with a tilt in the sagittal plane. They assume that when the 

prosthesis is on the slope side it becomes functionally too 

long and provokes a more energy consuming gait pattern. 

The existing literature shows that the most-investigated 

situation of cross-slope walking of amputees is walking with 

the prosthesis hillside, whereby the focus is placed on 

prosthetic swing, intact side stance and required 

compensatory strategies. 

Building on these approaches, this study focused on the 

biomechanics of the prosthetic stance phase in both cross-

slope conditions: foot positioned hillside (provokes 

eversion) and foot positioned valleyside (provokes 

inversion). The aim was to reveal the impact of the 

adaptability of the prosthetic foot on kinematics and kinetics 

of amputee gait on cross-slopes and to analyze the effects 

on balance and comfort by using self-reported outcome 

measures. The hypothesis was that a novel foot module 

with high frontal plane compliance enhances the locomotion 

of ITTAs on uneven ground. 

METHODOLOGY 

Participants 

Twelve ITTAs participated in the study. This randomized 

cross-over study was approved by the ethics committee of 

the medical faculty of the University of Göttingen, Germany. 

Inclusion criteria were as follows: active individuals (K-level 

3, 4)15,16 with unilateral transtibial amputation, at least 18 

months post-amputation, stable residual limb volume, 

stable gait pattern, aged 18 years or older. Exclusion criteria 

were as follows: body weight exceeding 125 kg, any 

conditions that severely influence performance and gait like 

cardiovascular diseases or present socket issues. In 

addition, ten able-bodied individuals were included as 

controls. All participants provided written informed consent. 

Prosthetic Feet 

Three ESR feet were investigated (Figure 1). The novel foot 

was the Triton Side Flex (Ottobock, Germany). The TSF 

features a dedicated joint for frontal plane adaptations. This 

joint unit enables ±10° rotation (inversion/eversion) against 

a progressive resistance that is provided by a torsion bar.17 

The rotational resistance increases towards the hard stop at 

10° and is not user specific. The unit is screwed on a carbon 

base with split toes. The overall weight (size 27, including 

Spectra sock and cosmetic cover) is 860 g. The build height 

(heel to top of the pyramid) is 109 mm. In addition, two 

reference feet were tested. The Triton LP (Ottobock, 

Germany) contains the same carbon base as the TSF with 

matching properties in terms of dimensions and basic 

flexibility. The overall weight is 690 g and the build height 

86 mm. The Pro-Flex LP (Ossur, Iceland) is a direct 

competitor of the Triton LP in the section of low profile ESR 

feet for active (K3 + K4) users. It features split toes as well, 

which are, however, asymmetrically designed. The overall 

weight (660 g) and build height (90 mm) are similar to the 

Triton LP.  

Workflow 

The study captured biomechanical data and patient-

reported outcomes. Each participant tested the TSF and 

one reference foot. The selection of the reference foot and 

the order of tests (start with the TSF or reference) were 

randomized. All prosthetic assembling was done by the 

same certified prosthetist. The bench alignment followed 

the manufacturers’ specifications and was reproducibly 

done using a PROS.A. Assembly (Ottobock, Germany)18 

followed by a static optimization19,20 on the L.A.S.A.R. 

Posture (Ottobock, Germany)21 and a final dynamic 

optimization to the prosthetist’s and participants’ 

satisfaction. The accommodation time for each foot was at 

least 4 weeks prior to performing the biomechanical 

assessments and patient questionnaires.  

Setup 

Gait analysis measurements were gathered using a motion 

capture system consisting of 12 Bonita cameras (Vicon, UK, 

sampling rate 200 Hz) and two force plates (Kistler, 

Switzerland, sampling rate 1000 Hz). A dedicated marker 

set with 39 passive markers was applied. This enables the 

https://doi.org/10.33137/cpoj.v4i1.35206
https://shop.ottobock.ca/en/Prosthetics/Lower-Limb-Prosthetics/Feet---Mechanical/1C68-Triton-side-flex/p/1C68
https://shop.ottobock.ca/en/Prosthetics/Lower-Limb-Prosthetics/Feet---Mechanical/1C63-Triton-LP/p/1C63
https://www.ossur.com/en-gb/prosthetics/feet/pro-flex-lp


 

3 

Altenburg B, Ernst M, Maciejasz P, Schmalz T, Braatz F, Gerke H, Bellmann M. Effects of a prosthetic foot with increased coronal adaptability on cross-slope 
walking. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.7.  https://doi.org/10.33137/cpoj.v4i1.35206 

ISSN: 2561-987X 
EFFECTS OF PROSTHETIC FOOT ON CROSS-SLOPE WALKING 

Altenburg et al. 2021 CPOJ 

 
assessor to distinguish between the different contributions 

to the frontal plane adaptations of the foot including joint 

adaptation, carbon base deformation and shoe/foot shell 

deformation.3 For this purpose, the shoe and foot shell were 

modified and antenna markers were mounted directly on the 

carbon base (Figure 1). During measurements, all 

participants wore the same model of shoe with defined 

marker positions. 

The studied situations were walking on level ground (using 

both force plates in the middle of the track) and walking on 

a 10° cross-slope, which was 8.5 m long and equipped with 

one force plate in the center. The participants were 

instructed to walk on the track at a self-selected, 

comfortable walking speed several times until eight valid 

recordings for each condition (level walking, four cross-

slope conditions: 10° prosthesis hillside, 10° intact side 

hillside, 10° prosthesis valleyside, 10° intact side valleyside) 

were captured. The inclusion or exclusion of each recording 

was determined by an assessor next to the track (inclusion 

criteria: steady state of walking in the middle of the track, 

entire foot on the force plate without obviously aiming for it 

and without specific step length adaptation). As the physical 

cross-slope setup remained the same for all cross-slope 

measurements, the starting point was adjusted for each 

individual subject and both walking directions were 

captured. For the healthy controls both sides were 

measured in equal distribution in order to generate 

comparative data in 3 different conditions (level, hillside, 

valleyside). 

In addition to the biomechanical measurements, 

participants completed a questionnaire evaluating 

amputees’ experience during 4 weeks or more of daily use. 

This questionnaire included the Activities-Specific Balance 

Confidence (ABC) Scale22 (16 questions), the Prosthetic 

Limb Users Survey of Mobility (PLUS-M) Scale23,24 (12-item 

short form) and a self-developed scale evaluating socket 

comfort and perceived safety in 40 situations of daily living 

(ADL-Scale). Among the situations evaluated with the ADL-

Scale, there were 9 standing situations, 11 walking 

situations potentially affected by medial/lateral flexibility, 8 

walking situations potentially unaffected by medial/lateral 

flexibility and 12 social activity situations. Both socket 

comfort and perceived safety were measured on a 

numerical rating scale from 0 (worst) to 10 (best). At the end 

of the study, participants were also asked which of the two 

tested feet they preferred for daily use. 

Data analysis 

Valid trials were further processed with VICON Nexus, 

customized VICON BodyBuilder (Vicon Motion System, UK) 

and MATLAB (R2018a, Mathwork Inc, US) scripts. The 

following spatiotemporal gait characteristics were 

considered: gait speed, step length, step width and stance 

phase duration. The lateral shoe markers, Figure 2 were 

used to automatically calculate these parameters with 

VICON Nexus.25 Furthermore, the following kinetic 

parameters were determined: ground reaction force in 

vertical (GRFv) and mediolateral (GRFml) direction; 

external knee adduction moment (EKAM), considered as 

EKAM peak (first maximum) and EKAM impulse (EKAM 

integral over duration of gait cycle (GC)).  

Figure 1: Experimental setup and prosthetic feet used. (A) shows 
the 8.5m cross-slope with a force plate embedded in the center of 
the track (shown step) and a typical participant (prosthesis is 
valleyside limb, intact side is hillside limb). (B) display the marker 
set for estimating the CoP (markers on toe and heel of shoe) and 
the adaptation to the tilt (shoe markers and antenna markers 
through a cutout in the shoe and foot shell, attached to the carbon 
base). (C) shows the prosthetic feet tested: Triton Side Flex (left), 
Triton LP (middle) and Pro-Flex LP (right). 

A 

Valleyside 

Limb 

Hillside 

Limb 

B 

C 

https://doi.org/10.33137/cpoj.v4i1.35206
https://shop.ottobock.ca/en/Prosthetics/Lower-Limb-Prosthetics/Feet---Mechanical/1C68-Triton-side-flex/p/1C68
https://shop.ottobock.ca/en/Prosthetics/Lower-Limb-Prosthetics/Feet---Mechanical/1C63-Triton-LP/p/1C63
https://www.ossur.com/en-gb/prosthetics/feet/pro-flex-lp


 

4 

Altenburg B, Ernst M, Maciejasz P, Schmalz T, Braatz F, Gerke H, Bellmann M. Effects of a prosthetic foot with increased coronal adaptability on cross-slope 
walking. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.7.  https://doi.org/10.33137/cpoj.v4i1.35206 

ISSN: 2561-987X 
EFFECTS OF PROSTHETIC FOOT ON CROSS-SLOPE WALKING 

Altenburg et al. 2021 CPOJ 

 

The adaptation of the shoe and carbon base in the frontal 

plane and the mediolateral course of the center of pressure 

(CoP) with respect to the foot were specific biomechanical 

parameters used in the study. The relative adaptation of the 

shoe in the frontal plane was determined in three steps. 

First, the angle between the projected connection line of 

medial and lateral shoe markers in the frontal plane and the 

horizontal surface was calculated (shoe in Figure 2). Second, 

the adaptation of the shoe was calculated: 

'shoe=shoe+shank. Hereby shank represents the frontal 

shank angle (shank in Figure 2). Third, the relative adaptation 

of the shoe in the frontal plane was calculated by subtracting 

the adaptations found for level walking from the adaptations 

found for cross-slope situations: αshoe='shoe,cross-slope-

 'shoe,level. The calculations were performed in the laboratory 

coordinate system. The same calculation was carried out for 

the medial / lateral antenna markers, which were attached 

to the associated parts of the carbon base (αbase). It was 

assumed that these values represent the adaptation of the 

carbon base of the prosthetic foot.3 

 

The course of the CoP was estimated, first, by projecting 

the CoP of the force plate and the foot axis (defined by tip 

and heel marker on the shoe) to the surface and, second, 

by calculating the orthogonal distance of the projected CoP 

to the projected marker line (CoPdist in Figure 2).  

Statistics 

For each situation, individual means (calculated from single 

trials) and group means (calculated from individual means) 

of the analyzed parameters were determined. To compare 

the effects of the different prosthetic foot types (reference 

feet vs. TSF) for certain setups (level, 10° hillside, 10° 

valleyside) a paired T-test was performed. If the assumed 

normal distribution (Shapiro-Wilks test) was not given, a 

non-parametric Wilcoxon test was performed. To account 

for multiple testing, the alpha level was set to 1%. The 

statistical analysis was performed with IBM SPSS Statistics 

(IBM Corp., US). We did not conduct a statistical analysis of 

the effects of the cross-slopes angle within the groups, i.e. 

level vs 10° hillside vs 10° valleyside, nor did we consider a 

statistical comparison between ITTAs and control subjects. 

We did, however, perform a statistical analysis of the ABC, 

PLUS-M and ADL-Scale scores. The ADL scores were 

y 

y 

x 

z 

lateral 

medial 

lateral 

medial posterior 

anterior 

walking direction  

A B 

 
shoe

 

 
base

 

 
shank

 

 

Figure 2: Diagram to introduce the parameters used. (A) Shank and foot from frontal view: Markers, symbolized by circles, were projected in 

the frontal plane (y-z plane) to calculate shoe (medial and lateral shoe marker), base (medial and lateral antenna marker) and shank (virtual 

center of knee and ankle marker). These parameters were used to estimate the relative adaptation shoe and base to cross-slopes. The 
external knee adduction moment (EKAM) was calculated using the virtual center of the knee (blue marker, middle of lateral and medial knee 
markers) and the ground reaction force (using cross product in lab coordinate system). (B) foot from transversal view (lab coordinate system): 

CoPdist, the orthogonal distance between the CoP course (red-arrow line) and the foot axis (black-dashed line, defined by tip and heel marker), 
was calculated on the cross-slope surface. Note, the cross-slope surface is tilted (10°) relative to the shown transversal plane (x-y plane) 
shown above. 

https://doi.org/10.33137/cpoj.v4i1.35206


 

5 

Altenburg B, Ernst M, Maciejasz P, Schmalz T, Braatz F, Gerke H, Bellmann M. Effects of a prosthetic foot with increased coronal adaptability on cross-slope 
walking. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.7.  https://doi.org/10.33137/cpoj.v4i1.35206 

ISSN: 2561-987X 
EFFECTS OF PROSTHETIC FOOT ON CROSS-SLOPE WALKING 

Altenburg et al. 2021 CPOJ 

 
separately determined for each activity block (standing, 

walking – non-m/l, walking – m/l, and social activities) and 

each dimension (safety, comfort)  – resulting in eight ADL 

scores per person and tested foot. The individual scores of 

participants obtained with different feet were compared 

using the paired T-test.  

RESULTS 

Twelve ITTAs with activity level K3 (Medicare Functional 

Classification Level) or higher, participated in this study. 

Further detailed demographic data are shown in Table 1. In 

addition 10 control subjects (age: 29±7 years; weight: 83±15 

kg; height: 183±11 cm) were also recruited for the study. 

The spatiotemporal parameters provided in Table 2 showed 

no statistically significant differences between the TSF and 

reference feet for any condition. Gait speed and step width 

tended to decrease from level to slope conditions for all feet. 

Control subjects walked on average with higher gait speed, 

step length, and step width in all conditions (not statistically 

analyzed). 

The frontal plane adaptations of the studied feet and shoes 

in cross-slope conditions during stance are represented in 

Figure 3. For the TSF, a major and continuous adaptation 
from the beginning of mid stance was found, whereas the 

reference feet showed only minor adaptations after loading 

response, constantly increasing with progressing stance.  

The amount of measured adaptation at mid stance (30% 

GC) was significantly (p<0.01) higher with the TSF 

compared to the reference feet in all slope conditions  

(Table 3). The measured shoe adaptation showed similar 

characteristics with a smaller difference between the 

studied feet. The TSF reached the same amount of 

adaptation as the controls. 

The EKAM impulse was significantly reduced for the 

valleyside condition with the TSF. No differences were 

found for hillside and level walking (Table 3, Figure 4). EKAM 

peaks showed no differences in all conditions. Control 

subjects presented notably higher values of peak EKAM in 

all conditions. 

The CoP paths of the control subjects showed a medial shift 

when the foot in question was positioned valleyside, but a 

close grouping for the hillside position and level walking. 

The TSF produced a similar grouping for level and hillside 

conditions, but a lateral shift for the valleyside condition. 

ESR feet revealed a different CoP path pattern with a 

distinct laterally shifted curve for the hillside and a medially 

shifted curve for the valleyside condition. A comparison of 

ESR and TSF feet demonstrated significantly different CoP 

paths for all conditions (Table 3). 

GRFv showed no differences between the feet in all 

conditions. There was a trend towards an increased first 

maximum for the valleyside condition. GRFml differed 

significantly between the investigated feet in the valleyside 

condition (30% GC).  

The results of the patient-reported outcomes are shown in 

Table 4. They found significantly (p<0.05) higher ratings for 

the TSF foot for perceived comfort while standing and 

perceived comfort and safety while walking in situations 

potentially affected by medial/lateral flexibility (ADL Scale). 

All other ADL sub-scales, as well as ABC and PLUS-M, 

tended towards higher ratings when using the TSF foot, but 

did not attain statistical significance. As far as foot 

preference was concerned, eight participants preferred the 

TSF, three participants preferred one of the reference feet 

(1x Triton LP, 2x Pro-Flex LP), and one participant had no 

preference.   

 

Participant Age Weight (kg) Height (m) Gender K-Level Socket suspension Foot #1 Foot #2 

S01 51 69 1,83 m 3 Suction, One way valve TSF Triton LP 

S02 61 125 1,80 m 3 Soft socket, supracondylar  TSF Pro-Flex LP 

S03 38 88 1,68 m 4 Suction, one way valve Pro-Flex LP TSF 

S04 77 86 1,75 m 3 Pin lock TSF Pro-Flex LP 

S05 47 50 1,56 w 3 Suction, one way valve Pro-Flex LP TSF 

S06 59 86 1,78 m 3 Suction, one way valve TSF Pro-Flex LP 

S07 44 68 1,68 w 3 Suction, one way valve Triton LP TSF 

S08 52 78 1,77 m 3 Suction, one way valve TSF Triton LP 

S09 37 90 1,84 m 3 Suction, one way valve Triton LP TSF 

S10 64 99 1,88 m 3 Suction, one way valve Triton LP TSF 

S11 57 79 1,80 m 4 Suction, one way valve Pro-Flex LP TSF 

S12 47 97 1,83 m 4 Pin lock TSF Triton LP 

Mean 52,8 83,9 1,77      

SD 11,5 19,4 0,09      

Range 37-77 50-125 1,56-1,88      

 

Table 1: Demographic data of study participants with transtibial amputation and allocated prosthetic feet (randomized process). 

https://doi.org/10.33137/cpoj.v4i1.35206


 

6 

Altenburg B, Ernst M, Maciejasz P, Schmalz T, Braatz F, Gerke H, Bellmann M. Effects of a prosthetic foot with increased coronal adaptability on cross-slope 
walking. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.7.  https://doi.org/10.33137/cpoj.v4i1.35206 

ISSN: 2561-987X 
EFFECTS OF PROSTHETIC FOOT ON CROSS-SLOPE WALKING 

Altenburg et al. 2021 CPOJ 

 

 

Table 2: Spatiotemporal parameters of the TSF and reference feet for level walking and 10° cross-slope conditions. No statistically 
significant differences between foot types were found (p<0.01) 

Prosthetic foot Condition Gait velocity (m/s) Step length (m) 
Stance phase 
duration (% GC) 

Step width (m) 

TSF 

Level  1.27 ± 0.12 0.74 ± 0.05 60.7 ± 1.3 0.22 ± 0.03 

10° hillside 1.25 ± 0.14 0.75 ± 0.05 61.1 ± 1.2 0.21 ± 0.03 

10° valleyside 1.23 ± 0.13 0.71 ± 0.05 60.3 ± 1.3 0.20 ± 0.02 

Reference 

Level  1.27 ± 0.14 0.73 ± 0.06 61.3 ± 0.9 0.22 ± 0.02 

10° hillside 1.24 ±0.14 0.75 ± 0.06 61.1 ± 1.4 0.21 ± 0.02 

10° valleyside 1.25 ± 0.15 0.72 ± 0.07 60.7 ± 1.2 0.20 ± 0.03 

Controls 

Level  1.44 ± 0.15 0.79 ± 0.09 61.7 ± 1.1 0.27 ± 0.03 

10° hillside 1.42 ± 0.19 0.79 ± 0.08 61.8 ± 1.4 0.25 ± 0.04 

10° valleyside 1.43 ± 0.19 0.77 ± 0.08 60.8 ± 1.4 0.26 ± 0.03 

 

Table 3: Parameters of the prosthetic side for the different setups at the first maximum peak (GRFv, EKAM peak), whole GC (EKAM 

impulse) and at 30% GC (GRFml, αbase, αshoe, CoPdist). Statistically significant differences between foot types are marked bold (p<0.01) 

or bold and * (p<0.001). 

Parameter GRFv (%bw) GRFml (%bw) αbase (deg) αshoe (deg) CoPdist (mm) 
EKAM 
peak 

(Nm/kg) 

EKAM 
impulse 
(Nm/kg*s) 

Level TSF 108 ± 11 4.4 ± 1.3 - - 9 ± 5 0.34 ± 0.12 0.09 ± 0.04 

Level reference 
feet 

108 ± 7 4.5 ± 1.2 - - 14 ± 7 0.32 ± 0.11 0.09 ± 0.04 

Level controls 111 ± 5 2.0 ± 0.8 - - 9 ± 6 0.49 ± 0.10 0.19 ± 0.05 

Hillside TSF 108 ± 13 4.2 ± 1.3 -8.8 ± 1.6 * -11.9 ± 0.8 13 ± 5 * 0.27 ± 0.13 0.08 ± 0.04 

Hillside reference 
feet 

109 ± 12 4.5 ± 1.1 -2.1 ± 0.6 * -10.7 ± 0.8 24 ± 5 * 0.26 ± 0.13 0.08 ± 0.04 

Hillside controls 107 ± 6 2.2 ± 0.8 - -12.0 ± 0.9 10 ± 7 0.38 ± 0.10 0.16 ± 0.06 

Valleyside TSF 112 ± 12 3.4 ± 1.5 7.9 ± 1.8 * 11.9 ± 2.0 13 ± 6 * 0.38 ± 0.14 0.11 ± 0.03 

Valleyside 
reference feet 

112 ± 11 2.4 ± 1.2 2.9 ± 1.0 * 10.6 ± 1.2 2 ± 5 * 0.40 ± 0.12 0.14 ± 0.03 

Valleyside controls 112 ± 7 1.2 ± 0.7 - 12.0 ± 1.0 5 ± 6 0.56 ± 0.16 0.22 ± 0.06 

 

Table 4: Summary of the scores in the patient-reported outcomes for reference feet and the TSF. Significant differences in a parameter 
are marked bold for the p values (p<0.05). 

Analyzed parameter: n 
Reference feet  

(mean ± SD) 
TSF  

(mean ± SD) 
p 

ABC (Balance confidence) 12 86.6 ± 8.6 89.2 ± 8.4 0.14 

PLUS-M (Mobility) 12 56.6 ± 7.3 57.3 ± 7.8 0.67 

ADL: Standing situations (9 questions) 

Perceived comfort 12 8.4 ± 1.0 9.1 ± 0.8 0.02 

Perceived safety 12 8.8 ± 0.8 9.2 ± 0.7 0.11 

ADL: Walking in situations potentially affected by the medial/lateral flexibility (11 questions) 

Perceived comfort 12 8.3 ± 1.1 8.9 ± 0.8 0.02 

Perceived safety 12 8.4 ± 1.1 9.0 ± 0.9 0.04 

ADL: Walking in situations potentially not affected by the medial/lateral flexibility (8 questions) 

Perceived comfort 12 8.3 ± 0.9 8.8 ± 0.8 0.11 

Perceived safety 12 8.4 ± 1.0 8.7 ± 1.0 0.34 

ADL: Social activities (12 questions) 

Perceived comfort 12 8.3 ± 1.0 8.9 ± 0.8 0.05 

Perceived safety 12 8.6 ± 0.9 8.9 ± 0.9 0.12 

 

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7 

Altenburg B, Ernst M, Maciejasz P, Schmalz T, Braatz F, Gerke H, Bellmann M. Effects of a prosthetic foot with increased coronal adaptability on cross-slope 
walking. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.7.  https://doi.org/10.33137/cpoj.v4i1.35206 

ISSN: 2561-987X 
EFFECTS OF PROSTHETIC FOOT ON CROSS-SLOPE WALKING 

Altenburg et al. 2021 CPOJ 

 

DISCUSSION 

The aim of this study was to investigate the effects of a 

novel prosthetic foot, with adaptability on cross-slope 

surfaces, using instrumented gait analysis and patient-

reported outcomes. 

Several results support the initial hypothesis that a foot 

module with easily accessible frontal plane adaptation can 

enhance locomotion on uneven ground. First, the early and 

extensive adaptation at the beginning of stance found in this 

study appears to be of importance and agrees with the 

findings of Yeates10 who suggested an improved balance 

on uneven ground derived from greater frontal adaptation in 

early stance. Here the TSF adapts both earlier (at loading 

response, 10% GC) and more extensively and keeps this 

adaptation until the end of stance (Figure 3). The users felt 

directly a different foot behavior when stepping on the cross-

slope and reported a higher level of perceived safety. With 

the common ESR split toe concept of the measured 

reference feet, the maximum adaptation occurs at the end 

of stance with maximum toe load. The absolute value of 

adaptation is not exactly known since the measured position 

of the antenna markers fixed on the carbon base always 

reflect a combined adaptation of rotation of the carbon base, 

toe shift and toe twist.3 Nevertheless, the timing of 

adaptation is not affected. The frontal plane adaptation of 

the shoes reveals similar characteristics as the carbon 

bases with constant values for the TSF, but increasing 

adaptation as stance progresses for standard ESR feet. 

However, the difference in adaptation is smaller compared 

to the carbon base data. This suggests movement, like tilt 

between carbon base, foot cover and shoe, that is usually 

not detected with conventional marker placement on the 

shoes. Consequently, every shoe as well as every 

prosthetic foot cover contributes to the overall adaptation. 

The data for shoe adaptation shows an overshoot in value 

for the TSF and control subjects (12° value on a 10° cross-

slope). Load-dependent shoe-sole compression and a 

different shank orientation (by leaning to a side) when 

walking on cross-slopes are plausible reasons for this 

effect.  

The EKAM is a clinically relevant parameter, since its first 

peak has been positively associated with medial 

compartment knee osteoarthritis (OA).26-29 The EKAM 

impulse is also commonly studied in conjunction with OA29-

32 According to Chang et al.33, it might even be the more 

comprehensive indicator of cumulative medial compartment 

loading during gait. This study showed a significantly 

reduced EKAM impulse for the valleyside condition using 

the TSF, but no differences in EKAM peak (Table 3, Figure 

4A). However, compared to the clearly higher moments 

generated by the control subjects, the overall impact on OA 

risk appears negligible. Still, this effect of prosthetic side 

knee load reduction for valleyside conditions might increase 

in similar everyday life loading scenarios with higher gait 

speed or varying step width.34 In general, the clearly higher 

gait speed and wider step width of the control subjects has 

to be considered when comparing absolute knee loading. 

TSF Reference Feet 

E
v
e

rs
io

n
 

In
v
e

rs
io

n
 

Time [% gait cycle] Time [% gait cycle] 

R
e

la
ti
v
e

 f
ro

n
ta

l 
a

d
a

p
ta

ti
o
n

[°
] 

0 10 20 30 40 50 60 0 10 20 30 40 50 60 

-15 

-10 

-5 

0 

10 

15 

5 

Figure 3: Relative frontal adaptation on the cross-slope for Triton Side Flex (left) and reference feet (right) for 10% to 50% GC (main loading 

interval). The solid red (hillside) and solid blue (valleyside) curves show the adaptation of the prosthesis via the antenna markers (αbase). The 

grey (control subjects) and dashed (prosthetic side) curves show the adaptation determined by the markers on the shoes (βshoe).  

 

https://doi.org/10.33137/cpoj.v4i1.35206


 

8 

Altenburg B, Ernst M, Maciejasz P, Schmalz T, Braatz F, Gerke H, Bellmann M. Effects of a prosthetic foot with increased coronal adaptability on cross-slope 
walking. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.7.  https://doi.org/10.33137/cpoj.v4i1.35206 

ISSN: 2561-987X 
EFFECTS OF PROSTHETIC FOOT ON CROSS-SLOPE WALKING 

Altenburg et al. 2021 CPOJ 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A 

B 

C 

D 

TSF Reference Feet Controls 

varus 

valgus 

lateral 

medial 

medial 

lateral 

Time [% gait cycle] Time [% gait cycle] Time [% gait cycle] 

0 10 20 30 40 50 60 0 10 20 30 40 50 60 0 10 20 30 40 50 60 
0 

20 

40 

60 

80 

100 

120 

G
R

F
v
 [

%
b

w
] 

-8 

-6 

-4 

-2 

0 

2 

4 

6 

8 

G
R

F
m

l 
[%

b
w

] 

-10 

-5 

0 

5 

10 

15 

20 

25 

C
o
P

d
is

t [
m

m
] 

E
K

A
M

 [
N

m
/k

g
] 

-0.2 

-0.1 

0 

0.1 

0.2 

0.3 

0.4 

0.5 

Figure 4: Parameters for the different studied situations. (A) EKAM, (B) mediolateral CoP course, (C) mediolateral ground reaction forces and 
(D) vertical ground reaction forces. The left column shows the prosthetic side values for the reference feet, the middle column the prosthetic 
side values for the TSF foot and the right column show the control subjects. The blue curves indicate the valleyside situations, the red curves 
indicate the hillside situations and the black curves indicate level walking. The associated standard deviations are given as shared areas for 
the blue and red curves. 

https://doi.org/10.33137/cpoj.v4i1.35206


 

9 

Altenburg B, Ernst M, Maciejasz P, Schmalz T, Braatz F, Gerke H, Bellmann M. Effects of a prosthetic foot with increased coronal adaptability on cross-slope 
walking. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.7.  https://doi.org/10.33137/cpoj.v4i1.35206 

ISSN: 2561-987X 
EFFECTS OF PROSTHETIC FOOT ON CROSS-SLOPE WALKING 

Altenburg et al. 2021 CPOJ 

 
The CoP path shows clear foot-dependent differences 

(Figure 4B). It can be assumed that the additional joint of the 

TSF quickly adapts, similar to the subtalar joint of the control 

subjects, causing similarly grouped CoP paths for the TSF 

and control subjects. The limited adaptation capability of the 

low profile ESR feet forces a main load transfer towards the 

lateral rim of the foot base (hillside condition) or towards the 

medial rim (valleyside condition), respectively, causing 

clearly different CoP paths compared to the level walking 

condition. The authors assume that these deviations require 

more compensatory strategies by the user to safely walking 

on cross-slopes. The GRFml also showed a close grouping 

for the TSF and control subjects (Figure 4C). This effect 

might facilitate more predictable steps with less control 

effort on cross-sloped surfaces or similar terrain. 

For the hillside conditions, there were no foot-dependent 

differences found for EKAM and GRFml, despite clear 

differences in frontal plane adaptation, COP paths and 

reported advantages while using the TSF. It can be 

assumed that the functional leg length discrepancy (35 mm 

longer prosthetic side on 10° cross-slope, 20 cm step width) 

is a major problem to overcome for the user that presumably 

requires higher control and energetic efforts. According to 

Walsh et al.,2 leg length discrepancies greater than 5 mm 

require compensatory strategies during gait. The additional 

joint in the TSF allows for an effective shortening of about 5 

mm in this condition which is a small proportion of the 

estimated 35 mm leg length discrepancy but seems to 

positively impact perceived comfort and safety. Still, it did 

not translate into the measured parameters EKAM and 

GRFml. 

The patient-reported outcomes favored the TSF. However, 

it is noticeable that all ratings were found to be close to the 

maximum scores of the scales with relatively small 

differences between the feet tested. It has to be considered 

that all participants were active ambulators with highly 

functional components in their current prostheses and did 

not report major limitations in their everyday lives. They 

were all considered high-functioning, safe walkers. 

Nevertheless, statistically significant differences were found 

in 3 scales. It is believed that the increased perceived safety 

of the TSF is based on the fast adaptation at low loading 

and the resulting consistent GRFml (Figure 4C) on sloped 

surfaces. The reduced control effort may lead to diminished 

movement in the residual limb-socket interface and could be 

the reason for the increased perceived comfort. The 

preference question at the end of the study revealed, on the 

one hand, a clear preference by 8 of the 12 participants for 

the TSF. On the other hand, interesting arguments for its 

rejection were offered by the other participants. Two 

participants preferred the Pro-Flex LP because it was 

perceived to provide a more comfortable rollover. One 

participant preferred the Triton LP since he had an unstable 

knee and could not stabilize it in the frontal plane when 

using the TSF. This may hint at a possible contraindication 

for fitting such adaptive foot components that warrants 

further study. 

Study limitations 

Due to the long accommodation time (at least 4 weeks) for 

the test prosthesis, a blinding of the foot condition was not 

practicable, which introduced a potential bias in favor of the 

novel foot (expectation). The use of two different reference 

feet and grouping them into one reference is a limitation in 

methodology since it is to be assumed that both reference 

feet do not perform identically. The healthy control 

population was not an exact match to the experimental 

population in terms of age. This may impact gait 

characteristics. 

CONCLUSION 

This is the first study analyzing prosthetic side loading 

during cross-slope walking of individuals with transtibial 

amputation which has provided new quantitative results. 

Although the obvious problem of a functional leg length 

discrepancy during cross-slope walking cannot entirely be 

solved by the novel foot studied, the results suggest an 

improved frontal plane adaptability of the prosthetic foot. In 

particular a comprehensive adaptation starting at low 

loading in early stance may enhance locomotion on cross-

slopes such as uneven ground.  

ACKNOWLEDGEMENTS 

We would like to thank the anonymous reviewers for their 

valuable and constructive feedback. 

DECLARATION OF CONFLICTING 

INTERESTS 

Mr. Björn Altenburg, Dr. Michael Ernst, Dr. Pawel 

Maciejasz, Dr. Thomas Schmalz and Dr. Malte Bellmann 

are full time employees of Ottobock SE & Co. KGaA. 

AUTHOR CONTRIBUTION 

• Björn Altenburg: study design, prosthetic fittings, gait 

lab measurements, data interpretation, draft 

manuscript.  

 

• Michael Ernst: gait lab measurements, biomechanical 

data analysis, data interpretation, draft manuscript.  

 

• Pawel Maciejasz: preparation, evaluation and analysis 

of the outcome measurements. 

 

• Thomas Schmalz: supervision, revise manuscript. 

 

• Frank Braatz: supervision, revise manuscript. 

 

• Henrik Gerke: gait lab measurements, biomechanical 

data analysis. 

https://doi.org/10.33137/cpoj.v4i1.35206


 

10 

Altenburg B, Ernst M, Maciejasz P, Schmalz T, Braatz F, Gerke H, Bellmann M. Effects of a prosthetic foot with increased coronal adaptability on cross-slope 
walking. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.7.  https://doi.org/10.33137/cpoj.v4i1.35206 

ISSN: 2561-987X 
EFFECTS OF PROSTHETIC FOOT ON CROSS-SLOPE WALKING 

Altenburg et al. 2021 CPOJ 

 
 

• Malte Bellmann: study design, supervision, data 

interpretation, revise manuscript.  

 

SOURCES OF SUPPORT 

None. 

ETHICAL APPROVAL 

This randomized cross-over study was approved by the 

Ethics Committee of the Medical Faculty of the University of 

Göttingen, Germany. All participants provided written 

informed consent. 

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walking. Canadian Prosthetics & Orthotics Journal. 2021;Volume 4, Issue 1, No.7.  https://doi.org/10.33137/cpoj.v4i1.35206 

ISSN: 2561-987X 
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