Defining Anterior-Posterior Motion of the Shoulder Girdle
Principal Investigator: Laura Boucher, PhD, The Ohio State University
In a motor vehicle crash, serious injuries to the thorax and head are in part related to displacement and motion of the shoulder girdle. Currently, the shoulder complex of the 3-year-old anthropomorphic test device (ATD), or crash test dummy, may not fully capture the movement of the child caused by the interaction with the child restraint system (CRS) harness. By understanding how the shoulder and clavicle move, we can better predict the kinematics of the child and the relation to injuries to the thorax, cervical spine, and head.
This study aimed to quantify the amount of anterior and posterior displacement in the clavicle and T1 vertebra and the role of chest clip position and harness tightness on CRS-restrained children.
Data were collected from 23 children, 2-4 years old, after obtaining IRB approval and parental consent. Skin-mounted motion capture markers were placed on each child’s sternum, spinous process of T1, distal end of the right clavicle, right acromion process (of scapula), and right deltoid tubercle (of humerus). Anatomical segments were digitized using 3D motion capture software. Following instrumentation, each child was seated and asked to stretch as far as they could while holding onto a hand-strap connected to a dynamometer. The maximum anterior and posterior passive clavicle displacement was then quantified.
Children were then placed in a 5-point CRS and asked to stretch forward, while clavicle and T1 displacements was measured in four CRS conditions: proper harness tightness and chest clip position, proper harness tightness with low chest clip position, loose harness with proper chest clip position, and loose harness with low chest clip position. Each CRS testing condition was repeated three times. Anthropometry, maximum anterior and posterior clavicle displacement, and CRS scenarios were repeated using a 3-year-old ATD for comparison.
The anthropometry of the volunteers was similar to the ATD in most measurements, including height, weight, chest circumference, arm circumference, and seated height. Results indicated that maximum anterior and posterior displacement of the distal clavicle was 1.98 cm and 3.19 cm, respectively. The ATD moved significantly less, with anterior displacement of 1.38 cm and posterior displacement of 0.39 cm. Volunteer data from the CRS conditions revealed that clavicle displacement and T1 displacement in all conditions was significantly greater than the ATD. Interestingly, the position of the chest clip appeared to play a large role in the amount of displacement possible, even if the harness was loose.
These data provide the first glimpse into the amount and the ratio of anterior and posterior movement of the clavicle and how the clavicle and T1 move in different CRS conditions. These data may benefit future 3-year-old ATD shoulder designs or influence computer models. Understanding clavicular movement relative to chest clip position will help to better predict the effect of impacts on thorax, cervical spine, and head excursion in motor vehicle crashes.
The 3-year-old ATD under-predicts the amount of quasi-static clavicle movement compared to volunteers in correct and incorrect CRS harness and chest clip conditions.
Top: Images of the four CRS conditions tested in the study, where PropHarnNorm = proper harness tightness and chest clip position; PropHarnLow = proper harness tightness with low chest clip position; LsHarnNorm = loose harness with proper chest clip position; and LsHarnLow = loose harness with low chest clip position.
Bottom: Clavicle displacement results for each CRS condition depicting that the volunteers (red) had greater movement compared to the ATD (black).
Project Team Members: John H. Bolte IV, PhD, The Ohio State University; John Borstad, PhD, PT, The Ohio State University
Students: Karolina Ostapkiewicz, The Ohio State University; Saskia Richter, The Ohio State University; Jared Seidel, The Ohio State University
IAB Mentors: Eric Dahle, Evenflo Company Inc.; Phil Przybylo, Evenflo Company Inc.; Jack Jensen, General Motors Holdings LLC; Taft Jones, Graco Children’s Products Inc.; Jerry Wang, Humanetics Innovative Solutions Inc.; John Combest, Nissan Technical Center North America Inc.; Hiromasa Tanji, TK Holdings Inc.; Jason Gainey, Volkswagen Group of America