Validation of a method to accurately correct anterior superior iliac spine marker occlusion

Anterior superior iliac spine (ASIS) marker occlusion commonly occurs during three-dimensional (3-D) motion capture of dynamic tasks with deep hip flexion. The purpose of this study was to validate a universal technique to correct ASIS occlusion. 420 ms of bilateral ASIS marker occlusion was simulated in fourteen drop vertical jump (DVJ) trials (n=14). Kinematic and kinetic hip data calculated for pelvic segments based on iliac crest (IC) marker and virtual ASIS (produced by our algorithm and a commercial virtual join) trajectories were compared to true ASIS marker tracking data. Root mean squared errors (RMSEs; mean±standard deviation) and intra-class correlations (ICCs) between pelvic tracking based on virtual ASIS trajectories filled by our algorithm and true ASIS position were 2.3±0.9° (ICC=0.982) flexion/extension, 0.8±0.2° (ICC=0.954) abduction/adduction for hip angles, and 0.40±0.17 N m (ICC=1.000) and 1.05±0.36 N m (ICC=0.998) for sagittal and frontal plane moments. RMSEs for IC pelvic tracking were 6.9±1.8° (ICC=0.888) flexion/extension, 0.8±0.3° (ICC=0.949) abduction/adduction for hip angles, and 0.31±0.13 N m (ICC=1.00) and 1.48±0.69 N m (ICC=0.996) for sagittal and frontal plane moments. Finally, the commercially-available virtual join demonstrated RMSEs of 4.4±1.5° (ICC=0.945) flexion/extension, 0.7±0.2° (ICC=0.972) abduction/adduction for hip angles, and 0.97±0.62 N m (ICC=1.000) and 1.49±0.67 N m (ICC=0.996) for sagittal and frontal plane moments. The presented algorithm exceeded the a priori ICC cutoff of 0.95 for excellent validity and is an acceptable tracking alternative. While ICCs for the commercially available virtual join did not exhibit excellent correlation, good validity was observed for all kinematics and kinetics. IC marker pelvic tracking is not a valid alternative.