Within- and Between-Session Reliability of Pelvic Marker Placement and Posture in Lower-Limb Amputees
Bibliographic record
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. Layman's Abstract Accurately placing small reflective markers on the body is very important for correctly measuring how people move during three-dimensional (3D) gait (walking) analysis. However, this can be more difficult in people with lower-limb amputations (LLA) because their anatomy is different, they use artificial limbs, and body shapes can vary. This study looked at how consistently these markers can be placed on the pelvis in adults with unilateral LLA. Fourteen adults participated in two sessions spaced 3–13 months apart. We assessed the consistency of the marker positions comparing them within and between sessions. We found that pelvis marker placement was quite reliable when tested in the same session, but less consistent between sessions, especially for markers placed on the back of the pelvis. The overall body posture and trunk positions also varied more between sessions. Even so, the size of the differences was small, meaning that the results were still fairly reliable to extract information about the motion. Findings support reliable pelvis marker placement within sessions but highlight challenges across longer time periods. Multiple trial collections and standardised posture guidelines are recommended to improve long-term reliability. Article PDF Link: https://jps.library.utoronto.ca/index.php/cpoj/article/view/46063/34419 How To Cite: 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 Corresponding Author: Alexandra Withey,Affiliation: Affiliation: Department for Health, University of Bath, Bath, UK.E-Mail: anmw20@bath.ac.uk ORCID ID: https://orcid.org/0000-0001-9422-2306
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.008 | 0.021 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".