Introduction: Three-dimensional (3D) gait analysis using optoelectronic stereophotogrammetry and force platforms is widely employed to assess joint loading and movement patterns [1]. However, marker-based motion capture systems are susceptible to measurement errors, particularly soft tissue artefacts (STA) arising from skin movement relative to the underlying bone [2]. These errors are even more pronounced in osteoarthritis (OA) research, where nearly 90% of participants have a body mass index (BMI) of 30 or higher, classifying them as obese [3, 4]. Accurate tracking of anterior pelvic anatomical landmarks is therefore crucial, especially in individuals with higher BMI. This study evaluated the impact of two methods for anterior pelvic landmark tracking on gait kinematics across different BMI
groups.
Methods: Twenty participants were evenly divided into two groups based on their BMI, classified as ”low BMI” (19–27.5 kg/m2) or ”high BMI” (>27.5 kg/m2). Each participant completed a 3D gait analysis on an instrumented treadmill using a modified CGM2.4 marker set, which included additional sacrum markers and pointer-based ASIS tracking. Two methods for anterior pelvic landmark tracking were compared: skin-mounted ASIS markers (ASIS𝑠) and pointer-based virtual ASIS tracking (ASIS𝑣). Their effects on the estimation of ASIS location, pelvic orientation, and hip joint centre (HJC) were
evaluated. Furthermore, intra-rater reliability of the pointer technique was assessed using intraclass correlation coefficients (ICC) and standard error of measurement (SEM), and the relationship between
BMI and pointing errors was analysed. The effect of using multiple pointer measurements on reliability was also examined.
Results: Data from twenty participants showed no statistically significant differences between ASIS𝑠 and ASIS𝑣 within the low BMI group. In contrast, the high BMI group exhibited statistically significant
and clinically relevant differences across all directions in ASIS trajectories, pelvic obliquity, and HJC estimation. A positive correlation was found between BMI and the mean absolute error in ASIS
dentification, with the largest deviations occurring in the anterior-posterior direction. Intra-rater reliability was generally high (ICC > 0.90); however, the medial-lateral direction within the high BMI group showed notably lower reliability, with ICC improving from 0.29 to 0.77 and SEM decreasing from 11.92 mm to 6.79 mm after averaging four pointer measurements.
Conclusion: Within the low BMI group, both ASIS𝑠 and ASIS𝑣 could be used for gait kinematics assessment. However, within the high BMI group, the two methods could not be used interchangeably due to statistically significant differences in ASIS tracking, pelvic orientation, and HJC estimation. ASIS𝑣 appeared to better estimate pelvic kinematics, as it was less affected by STA associated with skinmounted markers. Nevertheless, the accuracy and reliability of ASIS𝑣 require further validation using imaging techniques such as fluoroscopy, enabling direct measurement and potential correction of STA.