Comparison of two alternative technical marker sets for measuring 3D pelvic motion during gait

When using motion capture to measure pelvic motion, situations in which the anterior superior iliac spines (ASISs) or posterior superior iliac spines (PSISs) are obscured from view require that an alternative technical marker set be used to track the pelvis. The current study evaluated the accuracy and temporal similarity (i.e., cross-correlation) of two alternative pelvic models compared to the standard pelvic model during gait. The first alternative model used markers placed on the ASISs and iliac crests (ASIS-IC), while the second alternative model used markers placed on the PSISs and iliac crests (PSIS-IC). Both alternative models demonstrated an acceptable degree of accuracy in the sagittal, frontal, and transverse planes (root-mean-square error <1.4° in all planes). The temporal similarity between both alternative models and the standard model was "very strong" in the frontal and transverse planes. In the sagittal plane, the temporal similarity was also "very strong" for the PSIS-IC model and "strong" for the ASIS-IC model. Although statistically significant differences were found between the two alternative models for some of the variables, the practical significance of these findings is generally questionable considering the magnitude of the differences. These results suggest that both alternative models are suitable alternatives to the standard pelvic model for tracking pelvic motion. However, consideration would need to be paid to the spatial resolution and temporal resolution requirements, as well as the specific plane(s) of movement that are deemed most important, for a particular investigation if one of these alternative models is to be used.