Model Comparison for Defining the Trunk for Dynamic Testing in a Motion Capture Lab

Evaluation of trunk stability is common during return-to-activity assessments. While the use of motion capture for assessment of movement quality is also becoming more popular, it is critical that the trunk is modeled similarly across participants. The purpose of this study was to determine how adjusting marker placement at the sternum, cervical, and thorax locations for purposes of defining the trunk segment influences trunk kinematics. Sagittal plane trunk angles of 18 participants were computed for a comprehensive set of trunk model variations during standing, gait, and a drop vertical jump. Comparisons included variations from a single marker set altered at the sternum, cervical, and thorax locations. Intraclass correlation coefficients were computed per trunk marker combination to determine agreement with the recommended marker set. Agreement ranged from poor to excellent across all 3 tasks with the worst agreement observed during gait and across the sternum marker variations. Alternatively, few discrepancies were observed between the 2 cervical marker locations or during the drop vertical jump task. Consistent and reliable modeling of the trunk is critical for return-to-activity evaluation. The recommended model for defining the trunk segment includes marker placements on the jugular notch, xiphoid process, and first and 10th thoracic spinous processes.