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VOLUME 8, ISSUE 2 

 2025 
 

TECHNICAL/CLINICAL NOTE 

 

Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 

Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063  

 

 

  

 

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1 

Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 
Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063 

 

 

TECHNICAL/CLINICAL NOTE 

 

WITHIN- AND BETWEEN-SESSION RELIABILITY OF PELVIC MARKER PLACEMENT AND 

POSTURE IN LOWER-LIMB AMPUTEES 

Withey A1*, Cazzola D1, Tabor A2, Seminati E1 

1. Department for Health, University of Bath, Bath, UK. 
2. Faculty of Health and Applied Sciences, University of the West of England, UK. 
  
 

 

 

 

  

 

 

 

 

 

 

 

INTRODUCTION   

Correct placement of anatomical markers in three-

dimensional (3D) gait analysis is crucial for ensuring valid 

biomechanical outcomes. However, within- and between-

sessions variability in markers placement can introduce 

errors in kinematic movement analysis, especially in 

longitudinal studies where participants are monitored 

repetitive times across different sessions, such as in the 

monitoring of patients’ rehabilitation.1 Research has shown 

that human error in inconsistent markers placement can 

affect kinematic gait data in terms of average joint angles by 

up to 75%.1  

Together with marker placement, a correct static trial is a 

fundamental step in motion analysis, as it establishes 

segment lengths at the start of a measurement, which are 

essential for many kinematic and kinetic gait calculations.2,3 

It also provides a reference for the participant’s 

anthropometrics and anatomical alignment, which helps 

define body segment coordinate systems with respect to the 

ground, and it allows comparison of data across participants 

or trials by providing a standardized reference. Therefore, 

exploring the reliability of within- and between-session 

anatomical marker placement and static posture with 

respect to kinematic outcomes is an important area of study 

when designing longitudinal studies.  

While marker placement reliability has been well-

documented in the general population with skin marker 

placement variability (standard deviation) within 10 mm and 

12 mm for intra-evaluator and inter- evaluator, respectively,4 

limited research has examined its consistency in individuals 

with lower-limb amputation (LLA). This population presents 

unique challenges due to altered anatomy, soft tissue 

distribution, prosthetic limb interfaces and suspensions 

(especially for above knee amputations), and limb 

differences, all of which may influence marker placement 

precision and subsequent biomechanical interpretations. 

Moreover, a substantial proportion of individuals with LLA 

are overweight or obese, with prevalence rates ranging from 

28% to 48%.5,6 Excess subcutaneous fat can obscure 

* CORRESPONDING AUTHOR: 
 

Alexandra Withey, 

Affiliation: Department for Health, University of Bath, Bath, UK. 

E-Mail: anmw20@bath.ac.uk  

ORCID ID: https://orcid.org/0000-0001-9422-2306 

 

 
OPEN  ACCESS 

ABSTRACT 

BACKGROUND: Accurate placement of anatomical markers is essential for valid three-dimensional (3D) gait 

analysis, yet individuals with lower-limb amputation (LLA) pose unique challenges due to altered anatomy, 

prosthetic interfaces, and increased adiposity.  

OBJECTIVE: This study assessed within- and between-session reliability of pelvis marker placement and 

static posture kinematics in adults with unilateral LLA.  

METHODOLOGY: Fourteen adults with unilateral LLA (age: 58 ± 15 years, height: 174.6 ± 7.5 cm, body 

mass: 91.1 ± 27.7 kg, BMI: 29.6 ± 7.5 kg/m²; eleven transtibial, three transfemoral) participated in two 

sessions spaced 3–13 months apart. Reliability of marker distances and static posture kinematics were 

assessed using intraclass correlation coefficients (ICC) and standard error of measurement (SEM). 

FINDINGS: Within-session reliability of pelvis marker distances was good to excellent (ICC ≥ 0.78), whereas 

between-session reliability was lower (ICC as low as 0.14), particularly for posterior superior iliac spine 

markers. Pelvis kinematics demonstrated moderate reliability within sessions (average ICC ≈ 0.71), but trunk 

kinematics showed poor reliability. SEM values were low (<5°), suggesting acceptable absolute consistency 

despite variable ICCs, likely driven by postural changes and prosthetic factors.  

CONCLUSION: Findings support reliable pelvis marker placement within sessions but highlight challenges 

for longitudinal consistency. Multiple trial collections and standardised posture protocols are recommended 

to improve long-term reliability. 

ARTICLE INFO 

Received: September 22, 2025 

Accepted: October 12, 2025 

Published: October 20, 2025 
 

CITATION 

Withey A, Cazzola D, Tabor A, 

Seminati E. Within- and between-

session reliability of pelvic marker 

placement and posture in lower-

limb amputees. Canadian 

Prosthetics & Orthotics Journal. 

2025; Volume 8, Issue 2, No. 2. 

https://doi.org/10.33137/cpoj.v8i

2.46063 

KEYWORDS 

Lower-Limb Amputation; Gait 

Analysis; Posture; Kinematics; 
Longitudinal Consistency; Marker 

Placement Reliability. 

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

Volume 8, Issue 2, Article No. 2. 2025 

 

 

https://doi.org/10.33137/cpoj.v8i2.46063
mailto:anmw20@bath.ac.uk
https://orcid.org/0000-0001-9422-2306
https://doi.org/10.33137/cpoj.v8i2.46063
https://doi.org/10.33137/cpoj.v8i2.46063
https://jps.library.utoronto.ca/index.php/cpoj/index


 

2 

Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 
Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X RELIABILITY OF PELVIC MARKERS AND POSTURE IN LOWER-LIMB AMPUTEES 

Withey et al., 2025 

anatomical landmarks, causing inconsistent marker 

placement and errors in joint kinematics.7,8 

Despite these known challenges, the reliability of pelvis 

marker placement among individuals with LLA remains 

largely unexplored, particularly in those with higher BMI. 

This study focused primarily on evaluating the test-retest 

reliability of pelvis  marker placements within- and between-

sessions in individuals with LLA, together with static trial 

posture variability for the pelvis and trunk segments. We 

expected pelvis marker placement to demonstrate 

reliability, with ICC values exceeding 0.70 across a diverse 

sample of participants with LLA and varying body mass 

index (BMIs). An intraclass correlation coefficient (ICC) 

value of 0.70 or higher is acceptable for internal consistency 

and reliability in this population.9-11 

METHODOLOGY 

Thirteen males and one female with unilateral LLA (age: 58 

± 15 years; height: 174.6 ± 7.5 cm; weight: 91.1 ± 27.7 kg; 

BMI: 29.6 ± 7.5 kg/m2) were recruited; eleven transtibial and 

three transfemoral (Table 1). Participants were classified per 

National Health Service (NHS) Body Mass Index (BMI) 

guidelines: seven as obese (BMI ≥ 30), two as overweight 

(BMI 25-29.9), and five as healthy weight (BMI < 25). Ethical 

approval was obtained (REC 23/EE/0090). 

Participants were recruited from the NHS Bristol Centre for 

Enablement and the Portsmouth Enablement Centre. 

Recruitment commenced in July 2023 and continued for 12-

months. Clinicians who were part of the participants’ routine 

care team identified eligible patients during assessment 

days according to the inclusion and exclusion criteria.  

Inclusion and exclusion criteria  

Participants were included if they were over 18 years of age, 

had a unilateral lower-limb amputation (above or below the 

knee), were newly fitted with a prosthesis (three months 

post-amputation) and were able to walk on level ground. 

Exclusion criteria were balance disorders, congenital lower-

limb absence, inability to provide consent for prosthetic use 

and individuals at serious risk of complications to the sound 

limb that could limit normal rehabilitation. These clinicians 

made the initial approach to potential participants and 

introduced the study. The primary investigator of this study 

(AW) then provided information sheets and informed 

consent forms to eligible participants. 

Experimental set-up 

A motion capture system (Qualisys, Sweden) with eight 

infrared cameras was used to detect retroreflective 

markers. The system was calibrated prior to data collection 

using a Qualisys calibration wand and L-frame, achieving a 

residual error of < 1 mm (0.70 ± 0.10 mm). Cameras 

recorded at a sampling rate of 200 Hz, and the global 

coordinate system was aligned with a fixed floor platform 

(600 x 400 x 35 mm). For each static trial described in 

session 1 and 2, the participants were asked to stand for 10 

seconds in the same anatomical reference position relative 

to the platform.  

Protocol 

Participants completed two motion capture sessions (≈ 45 

minutes each). In both sessions, a single evaluator with 

three years of experience in collecting 3D motion capture 

data and running sessions on individuals with LLA, applied 

nine pearl retroreflective markers (diameter: 15.9 mm) to the 

Table 1: Individual participants’ characteristics at session 1 and session 2. Mean values ± standard deviation (SD) are reported at the end of 

the table.  

Participant 
Limb-
loss 
level 

Cause of limb 
loss 

Sex 
Height 
(cm) 

Age (years) Mass (kg) 
Time since limb loss 

(weeks) 

Session 1 Session 2 Session 1 Session 2 Session 1 Session 2 

P01 TT Traumatic M 168 39 40 87 73 18.7 70.8 

P02 TT Vascular M 168 84 85 59 62 16.1 58.1 

P03 TF Sepsis M 160 70 70 59 62 19.4 32.0 

P04 TT Vascular M 173 75 76 91 90 34.7 87.6 

P05 TT Vascular M 179 48 49 111 106 27.3 53.3 

P06 TT Vascular M 185 43 44 97 105 14.1 66.8 

P07 TF Vascular M 179 53 54 68 78 11.4 50.3 

P08 TT Cancer M 178 46 47 110 94 14.1 52.7 

P09 TT Chronic pain M 173 42 42 108 107 19.9 59.8 

P10 TT Vascular M 183 46 46 162 134 31.4 43.8 

P11 TT Vascular M 185 69 69 105 101 19.3 59.2 

P12 TT Vascular M 175 72 73 69 74 18.0 70.1 

P13 TT Vascular M 173 67 68 69 73 13.4 59.4 

P14 TF Vascular F 165 54 55 80 83 15.1 67.0 

Average 175 ± 8 58 ± 15 58 ± 15 91 ± 28 89 ± 20 19 ± 7 59 ± 13 

 

https://doi.org/10.33137/cpoj.v8i2.46063
https://www.nhsinform.scot/healthy-living/weight-loss/understanding-healthy-weight/how-do-i-measure-my-body-mass-index-bmi
https://www.nhsinform.scot/healthy-living/weight-loss/understanding-healthy-weight/how-do-i-measure-my-body-mass-index-bmi
https://www.nbt.nhs.uk/bristol-centre-enablement
https://www.nbt.nhs.uk/bristol-centre-enablement
https://www.porthosp.nhs.uk/departments-and-services/portsmouth-enablement-centre


 

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Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 
Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X RELIABILITY OF PELVIC MARKERS AND POSTURE IN LOWER-LIMB AMPUTEES 

Withey et al., 2025 

pelvis and trunk: bilaterally on the anterior superior iliac 

spine (ASIS), posterior superior iliac spine (PSIS), and iliac 

crest (IC), plus spinous processes at S1, T12, and C7 

(Figure 1). Markers were affixed directly to the participants’ 

skin with double-sided adhesive tape to avoid movement 

relative to the underlying anatomical landmarks during 

motion capture. For the three transfemoral amputees, the 

pelvis markers were instead placed on the prosthetic 

suspension belt (TES Suspension Belt, Ortho Europe, UK). 

Each participant completed repeated sessions at 

approximately the same time of day to minimize within-

subject variability, however, session times were not 

standardized across participants due to the use of two 

clinics and room availability.  

• Session 1: 3-6 months post-amputation (3.9 ± 1.1 

months): One 10-second static standing trial (Static 1) 

was recorded. At this time, all participants had 

commenced rehabilitation and were able to ambulate 

safely with their prosthesis. 

• Session 2: ≥ 3 months later; range 7–16 months (13.1 

± 2.7 months). Three 10-second static standing trials 

were recorded: 

o Static 2: Initial standing trial with full marker set. 

o Static 3: After removing/reapplying all markers 

except ICs (after 10-minute rest). 

o Static 4: After 12 walking gait trials (≈ 30 minutes 

after static 2), markers unchanged. 

IC markers were retained in Session 2 to provide a 

consistent reference point for calculating placement error 

when the remaining pelvic markers were reapplied. 

Data analysis 

Markers were labelled in Qualisys Track Manager 

(Qualisys, Sweden). OpenSim 4.5 was then used to create 

a skeletal model of the pelvis and trunk segments, which 

was scaled to each participant’s standing calibration trials 

for each session. The pelvis segment was defined by the 

bilateral ASIS and PSIS markers, with the IC markers used 

as additional references as mentioned previously. The trunk 

segment was defined using the spinous process markers at 

S1, T12 and C7. The 3D Euclidean distances were 

calculated between pelvis markers, including the distances 

between the ASIS and PSIS markers and the fixed iliac 

crest markers (Figure 1). Additionally, pelvis (relative to the 

global reference system) and trunk (relative to the pelvis 

segment) joint angles were calculated for the standing 

calibration trials. 

Statistical analysis 

The reliability of marker placement and pelvis and trunk 

kinematic parameters was assessed using the ICC from a 

two-way random model (ICC2,k) and standard error of 

measurement (SEM). ICC thresholds were considered: 

poor (< 0.50), moderate (0.50–0.75), good (0.75–0.90), and 

excellent (> 0.90).12 For this study, an ICC value ≥ 0.70 was 

deemed acceptable.9-11 This threshold has also been 

applied in previous research examining marker placement 

during gait analysis, a methodology closely related to the 

present study.10 Standard Error of Measurement (SEM) was 

calculated as the square root of the mean square error term 

from a repeated measures ANOVA.13 Pelvis and trunk angle 

errors (%) were calculated as the absolute difference in 

range of motion (ROM) between repeated measurements, 

expressed as a percentage of the ROM of the first 

measurement. This method was used for both within-

session comparisons (repeated trials within the same 

session) and between-session comparisons 

(measurements from different sessions). All analyses were 

performed in MATLAB® R2021b (MathWorks, Inc., USA). 

 

Figure 1: Marker placement positions is represented from the posterior view in the full body diagram on the left. Marker details and 3D 
Euclidean distances are listed and represented in the right side of the picture. 

Marker 
Number 

Marker 
Name 

Markers distances 

1 C7    a = LPSIS-RPSIS 

2 T12    b = LPSIS-LIC 

3 S1    c = LASIS-LIC 

4 LASIS    d = LASIS-RASIS 

5 RASIS    e = RPSIS-RIC 

6 LIC    f = RASIS-RIC 

7 RIC    g = LASIS-LPSIS 

8 LPSIS    h = RASIS-RPSIS 

9 RPSIS  

 

     Left view                           Posterior View 

    Right view                           Anterior View 

https://doi.org/10.33137/cpoj.v8i2.46063


 

4 

Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 
Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X RELIABILITY OF PELVIC MARKERS AND POSTURE IN LOWER-LIMB AMPUTEES 

Withey et al., 2025 

RESULTS 

Within-session results  

Within-session ICCs for pelvis marker distances (session 2, 

statics 2–4) ranged from 0.78–1.00, indicating good to 

excellent reliability, with the highest reliability coefficients 

measured for LASIS-RASIS and LASIS-LPSIS distances 

(Table 2; Appendix 1). ASIS–IC and PSIS–IC distances had 

SEMs < 4 mm (Table 3). Pelvis angles had ICCs averaging 

0.71 ± 0.19, with tilt and list both ≥ 0.70 (Appendix 2) and 

SEMs < 5°. Static trials 3 and 4 differed by < 0.5° for all 

pelvis angles. For trunk range of motion parameters, all 

parameters displayed SEM values below 5°, however trunk 

rotation showed the lowest ICC values (Table 2; Appendix 

3). 

Table 2: Reliability indices (ICC) of ASIS and PSIS marker 

placement Euclidean distances, and pelvis and trunk kinematic 

parameters. Values represent the range of ICCs observed within- 

and between-sessions across static trials. 

 

ICC: Intraclass correlation coefficient; ICC values of ≤ 0.70 are presented in 

bold. 

Between-session results 

Between-session reliability (session 1 vs. 2) showed lower 

ICCs (Table 2; Appendix 4), ranging from 0.14–0.76, though 

SEMs remained acceptable. The lowest ICC value (0.14) 

was for LPSIS–RPSIS distance. Left and Right ASIS 

distance had the highest SEM (5.5 mm), suggesting more 

variation across timepoints (Table 3), although kinematic 

measurements consistently reported very small SEMs. 

Pelvis and trunk parameters had low ICCs (Appendix 5 and 

Appendix 6), but SEMs remained <5° (Table 4). 

DISCUSSION 

This study assessed the within- and between-assessor 

reliability of pelvis marker placement and kinematics in 

individuals with LLA, a population with anatomical and 

practical challenges limiting accurate and consistent marker 

positioning. 

Within-session pelvis marker distances showed good to 

excellent reliability (ICCs ≥ 0.78), supporting use in a single-

day or repeated trials. Between-session reliability was lower 

(ICCs as low as 0.14), especially for PSIS markers, likely 

due to anatomical variation, prosthetic interfaces, and 

increased adiposity obscuring landmarks. In this context, 

“prosthetic interfaces” refers to the components of the 

prosthetic socket and suspension system that interface with 

the residual limb. These interfaces can alter the positioning 

or soft tissue conformation around the pelvis between 

sessions, especially for transfemoral amputees. Despite 

this, SEMs remained low (< 4 mm), indicating limited 

absolute error. 

The time gap between testing sessions 1 and 2 (ranging 

from three to six months post-amputation for the initial 

session to seven months or more for the follow-up) may 

have contributed to the observed inconsistencies. In 

addition, changes in static standing posture due to the 

prosthetic limb, body mass fluctuations (change of up to  

2.4 kg between sessions in the current study), prosthetic 

Measure Within-session ICC 
Between-

session ICC 

LASIS-LIC 0.78-0.81 - 

RASIS-RIC 0.78-0.97 - 

LPSIS-LIC 0.90-0.98 - 

RPSIS-RIC 0.82-0.91 - 

LASIS-RASIS 0.94–1.00 0.68–0.76 

LPSIS-RPSIS 0.80–0.97 0.14–0.34 

LASIS-LPSIS 0.95–1.00 0.68–0.71 

RASIS-RPSIS 0.97–0.98 0.59–0.67 

Pelvis tilt 0.79–0.95 0.23–0.23 

Pelvis list 0.81–0.91 -0.04–0.01 

Pelvis rotation 0.43–0.70 -0.17–0.41 

Trunk flexion/extension 0.75–0.85 -0.01–0.17 

Trunk lateral bending 0.74–0.95 0.15–0.32 

Trunk rotation 0.49–0.84 -0.13–0.29 

 

Table 3: Euclidean distances reported in mm as mean ± standard deviation and Standard Error of Measurement (SEM) calculated between 

and within sessions. 

Distance Static 1 Static 2 Static 3 Static 4 SEM (within) 
SEM 

(between) 

LASIS-LIC - 107.2 ± 26.0 118.0 ± 29.9 118.0 ± 29.4 2.4 - 

RASIS-RIC - 104.0 ± 26.3 102.3 ± 24.1 103.6 ± 25.7 2.6 - 

LPSIS-LIC - 195.1 ± 22.8 194.0 ± 24.2 194.2 ± 26.4 1.7 - 

RPSIS-RIC - 209.5 ± 26.3 209.4 ± 19.9 213.0 ± 20.3 2.0 - 

LASIS-RASIS 326.8 ± 59.7 326.9 ± 42.3 326.9 ± 47.0 327.9 ± 46.3 2.3 5.5 

LPSIS-RPSIS 81.6 ± 17.9 85.7 ± 15.1 88.5 ± 11.7 88.9 ± 11.1 1.3 2.7 

LASIS-LPSIS 257.7 ± 34.6 252.7 ± 29.4 256.2 ± 33.1 256.7 ± 32.9 1.3 3.6 

RASIS-RPSIS 259.5 ± 32.1 260.4 ± 28.6 259.0 ± 29.0 262.4 ± 28.5 1.2 3.6 

 

https://doi.org/10.33137/cpoj.v8i2.46063


 

5 

Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 
Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X RELIABILITY OF PELVIC MARKERS AND POSTURE IN LOWER-LIMB AMPUTEES 

Withey et al., 2025 

discomfort, and fatigue, along with external factors like 

suspension systems or high BMI, may have affected 

consistent marker placement and segment orientation 

across sessions on a population level. These factors can 

obscure anatomical landmarks and cause marker 

displacement — especially over longer intervals between 

assessments — reducing the reliability of pelvis and trunk 

kinematics. This likely contributed to the high placement 

variability observed in our study (standard deviations: 11.1–

59.7 mm), which exceeds the 10–12 mm values reported in 

healthy individuals, where variability is primarily attributed to 

soft tissue artifact.4 In our case, marker placement also 

affected joint angles calculation during dynamic trials. 

Between-session pelvis errors were 18% (tilt), 20% (list), 

and 10% (rotation), versus within-session errors of 10%, 

7%, and 2%. Trunk angles showed even greater variability, 

with between-session errors of 22%, 34%, and 61%, and 

within-session errors of 6%, 18%, and 37%. Subtracting a 

standing baseline from pelvis and trunk kinematics could 

reduce the apparent variability in walking trials by 

accounting for inter-session or inter-trial differences in 

participants’ neutral posture. Because trunk angles were 

calculated relative to the pelvis, any variation in pelvic 

orientation during standing contributes directly to trunk 

angle variability. By referencing walking kinematics to a 

consistent static posture, between- and within-session 

errors in both pelvis and trunk angles might be reduced, 

particularly for rotational measures, as individual 

differences in habitual standing alignment would be 

removed. However, this approach would not eliminate 

variability due to marker placement, soft tissue artifact, or 

dynamic postural adjustments during gait. 

Trunk and pelvis kinematic analysis observed during the 

static trials revealed additional reliability concerns. Pelvis 

and trunk rotation angles showed low within-session 

reliability during session 2 (static 2 vs static 4), with ICCs of 

0.43 and 0.50, respectively. Because trunk angles were 

calculated relative to the pelvis, variability in pelvic 

orientation likely contributed to the greater variability 

observed in trunk rotation measures. Fatigue, particularly in 

the residual limb hip flexors, may prompt compensatory 

strategies such as increased pelvic rotation toward the 

sound limb to maintain static balance and reduce muscular 

effort during standing. Discomfort or pain within the 

prosthetic socket during repeated walking trials can further 

contribute to asymmetrical weight distribution and postural 

adjustments, leading to pelvis and trunk rotation toward the 

sound limb during the final static trial.  

Although SEM values for pelvis and trunk angles remained 

below 5° when comparing the 2 sessions, indicating good 

absolute reliability, ICC values were low (Table 4). This likely 

reflects variability in participants’ static postures between 

sessions, which can affect ICC due to its sensitivity to 

between-subject variance.14 While ICC captures the 

proportion of variance due to true individual differences, 

inconsistent baseline positioning can reduce its values 

despite reliable within-subject measurements. In contrast, 

SEM reflects the within-subject consistency of repeated 

measurements and is unaffected by between-subject 

variability.13 Thus, the low ICCs likely result from postural 

variability rather than poor reliability.  

It is also important to consider that the 5° threshold used to 

interpret SEM values is often applied in studies involving 

lower extremity joint angles which typically exhibit a much 

larger range of motion than the pelvis or trunk.10 Therefore, 

in these regions, even small absolute errors can be 

proportionally significant. Despite this, the consistently low 

SEM values observed still indicate good within-subject 

reliability and interpreting SEM alongside ICC offers a more 

complete assessment of measurement reliability.  

Although each participant completed repeated sessions at 

approximately the same time of day to minimize within-

subject variability due to prosthetic discomfort or fatigue, 

session times were not standardized across participants, 

which may have contributed to between-subject variability 

in marker placement and segment orientation. Static 1 was 

used as the baseline measurement for marker placement; 

however, it is possible that marker positioning in this trial 

was not fully representative of the participant’s true 

anatomical alignment. Using an average of multiple static 

trials (e.g. static 1–3) might have provided a more stable 

baseline, potentially reducing variability in subsequent 

measures. 

Table 4:  Pelvis and trunk kinematics for the pelvis and the trunk segments, in degrees as mean ± standard deviation and Standard Error of 

Measurement (SEM) calculated between and within sessions. 

Pelvis/trunk kinematics Static 1 Static 2 Static 3 Static 4 SEM (within) 
SEM 

(between) 

Mean pelvis tilt 7.7 ± 13.1 -0.7 ± 6.3 0.6 ± 4.9 0.2 ± 5.9 0.54 1.50 

Mean pelvis list 1.1 ± 5.1 2.9 ± 3.4 2.3 ± 3.3 2.6 ± 3.4 0.31 0.84 

Mean pelvis rotation  3.1 ± 4.0 1.6 ± 3.0 0.1 ± 3.9 0.1 ± 3.5 0.57 0.75 

Mean trunk flexion  -0.3 ± 0.3 -0.2 ± 0.1 -0.2 ± 0.1 -0.2 ± 0.1 0.01 0.04 

Mean trunk list  -0.0 ± 0.1 -0.0 ± 0.1 -0.0 ± 0.1 -0.0 ± 0.1 0.01 0.01 

Mean trunk rotation  0.1 ± 0.2 0.0 ± 0.1 0.0 ± 0.1 0.0 ± 0.1 0.01 0.03 

 

 

https://doi.org/10.33137/cpoj.v8i2.46063


 

6 

Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 
Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X RELIABILITY OF PELVIC MARKERS AND POSTURE IN LOWER-LIMB AMPUTEES 

Withey et al., 2025 

CONCLUSION 

Overall, findings support the reliability of pelvis marker 

placement and posture within a session in LLA populations 

but highlight challenges for between-session consistency, 

relevant for longitudinal studies. To improve consistency, 

we recommend collecting multiple trials per session, 

documenting prosthetic configuration, and standardizing 

participant posture using photographs or guides. Static trials 

remain useful for estimating segment lengths but may 

reflect habitual or compensatory postures rather than 

neutral alignment. Researchers should account for this 

when interpreting static kinematics. Ultimately, reliable gait 

analysis in LLA populations requires careful marker 

protocols, posture control, and awareness of static 

calibration limitations across timepoints. 

ACKNOWLEDGEMENTS 

We thank the clinicians Dr Shigong Gou and Helen Harvey (Bristol 

Centre for Enablement), and Chantel Ostler (Portsmouth 

Enablement Centre) for their feedback developing the 

inclusion/exclusion criteria for the study. We also thank the 

physiotherapists Anne Harrill (Bristol Centre for Enablement) and 

Matthias Wright (Portsmouth Enablement Centre) for their help with 

identifying patients who meet the inclusion criteria and coordinating 

patient bookings, and all the patients who took part in the study. 

DECLARATION OF CONFLICTING INTERESTS 

The authors declare that they have no known competing financial 

interests or personal relationships that could have appeared to 

influence the work reported in this paper. 

 

CONSENT FOR PUBLICATION 

Informed written consent for publication of individual person’s data 

in this manuscript was obtained. 
 

AUTHORS’ CONTRIBUTION 

• Alexandra Withey: Conceptualization, Methodology, Writing - 

Original Draft, Writing - Review & Editing. 

• Dario Cazzola: Methodology, Writing - Review & Editing, 

Supervision. 

• Abby Tabor: Methodology, Writing - Review & Editing, 

Supervision. 

• Elena Seminati: Conceptualization, Methodology, Writing - 

Review & Editing, Supervision. 

All authors read and approved the final manuscript. 
 

SOURCES OF SUPPORT 

This study has funding through the University Research 

Studentship Award (URSA) awarded by the University of Bath. The 

funders had no role in study design, data collection and analysis, 

decision to publish, or preparation of the manuscript.  

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7 

Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 
Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X RELIABILITY OF PELVIC MARKERS AND POSTURE IN LOWER-LIMB AMPUTEES 

Withey et al., 2025 

APPENDIX 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pelvis Marker Distances Across Static Comparisons Within Sessions 

 

 

 

 

 

Appendix 1: Individual pelvis marker distances across sequential static posture comparisons within sessions. Each subplot displays LASIS-

RASIS, LPSIS-RPSIS, LASIS-LPSIS, RASIS-RPSIS with corresponding intraclass correlation coefficients (ICC) to indicate measurement 

reliability. 

 

https://doi.org/10.33137/cpoj.v8i2.46063


 

8 

Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 
Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X RELIABILITY OF PELVIC MARKERS AND POSTURE IN LOWER-LIMB AMPUTEES 

Withey et al., 2025 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pelvis Angles Across Static Comparisons Within Sessions 

 

 

 

 

 

Appendix 2: Individual pelvis angles across sequential static posture comparisons within sessions. Each subplot displays pelvis tilt, list, and 

rotation with corresponding intraclass correlation coefficients (ICC) to indicate measurement reliability. 

 

https://doi.org/10.33137/cpoj.v8i2.46063


 

9 

Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 
Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X RELIABILITY OF PELVIC MARKERS AND POSTURE IN LOWER-LIMB AMPUTEES 

Withey et al., 2025 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Trunk Angles Across Static Comparisons Within Sessions 

 

 

 

 

 

Appendix 3: Individual trunk angles across sequential static posture comparisons within sessions. Each subplot displays trunk 

flexion/extension, lateral bending, and rotation with corresponding intraclass correlation coefficients (ICC) to indicate measurement reliability. 

 

https://doi.org/10.33137/cpoj.v8i2.46063


 

10 

Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 
Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X RELIABILITY OF PELVIC MARKERS AND POSTURE IN LOWER-LIMB AMPUTEES 

Withey et al., 2025 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pelvis Marker Distances Across Static Comparisons Between Sessions 

 

 

 

 

Appendix 4: Individual pelvis marker distances across sequential static posture comparisons between sessions. Each subplot displays 

LASIS-RASIS, LPSIS-RPSIS, LASIS-LPSIS, RASIS-RPSIS with corresponding intraclass correlation coefficients (ICC) to indicate 

measurement reliability. 

 

https://doi.org/10.33137/cpoj.v8i2.46063


 

11 

Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 
Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X RELIABILITY OF PELVIC MARKERS AND POSTURE IN LOWER-LIMB AMPUTEES 

Withey et al., 2025 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pelvis Angles Across Static Comparisons Between Sessions 

 

 

 

 

Appendix 5: Individual pelvis angles across sequential static posture comparisons between sessions. Each subplot displays pelvis tilt, list, 

and rotation with corresponding intraclass correlation coefficients (ICC) to indicate measurement reliability. 

 

https://doi.org/10.33137/cpoj.v8i2.46063


 

12 

Withey A, Cazzola D, Tabor A, Seminati E. Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees. Canadian 
Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 2, No. 2. https://doi.org/10.33137/cpoj.v8i2.46063 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X RELIABILITY OF PELVIC MARKERS AND POSTURE IN LOWER-LIMB AMPUTEES 

Withey et al., 2025 

 

 

 

 

 

 

 

 

 

 

Trunk Angles Across Static Comparisons Between Sessions 

 

 

 

 

 

 

Appendix 6: Individual trunk angles across sequential static posture comparisons between sessions. Each subplot displays trunk 

flexion/extension, lateral bending, and rotation with corresponding intraclass correlation coefficients (ICC) to indicate measurement reliability. 

 

https://doi.org/10.33137/cpoj.v8i2.46063

