Within- and between-session reliability of pelvic marker placement and posture in lower-limb amputees

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.

This study assessed within- and between-session reliability of pelvis marker placement and static posture kinematics in adults with unilateral LLA.

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).

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.

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.