Characterization of the Pediatric Shoulder’s Resistance to Various Loading Conditions

Principal Investigator: John H Bolte IV, PhD, The Ohio State University

During side impact Motor vehicle collisions (MVC), the positions of the occupant’s head, neck, and thorax heavily depend on the biomechanical response of the shoulder.  In order to better understand the role of the shoulder in MVCs, it is essential to have a more biofidelic shoulder in pediatric anthropomorphic testing devices (ATD) to accurately simulate the occupant’s response to side-impact MVCs and design better safety measures. 

The objectives of this study were 1) to determine the pediatric shoulder’s resistance to medial and posteromedial loading conditions, and 2) to compare shoulder resistance by age groups. During this study, a custom linear force applicator was used to displace the volunteer’s shoulder and measure the applied forces. The applicator’s design enabled translational motions in all directions to ensure proper alignment and to allow loads to be applied in both medial and posteromedial directions.  The subjects were seated against a support wall, equipped with load cells, in order to limit rotation and translation of the subject and to determine the amount of load translated through the subject’s upper torso. A total of 39 pediatric volunteers between 4-18 years old were tested. This age range was selected to represent the 6 year old, 10 year old, and 5th percentile female ATDs. 

Medial testing resulted with minimal shoulder displacement at these low loads due to the clavicle acting as a strut and supporting the shoulder girdle.  Non-normalized data from all trials for each volunteer were averaged to calculate a mean stiffness curve for each subject, which were then averaged to calculate a mean curve and standard deviation for each age group.  This process was completed for both relaxed and tensed loading conditions. Shoulder stiffness was then calculated, showing increasing stiffness by age group.

Posteromedial Stiffness Values 

Bone maturation is likely one contributor to the increase in stiffness with age. The older the children are, the more ossified their bones become and thus more stiff. In children, especially under the age of 12, their bones are still largely cartilaginous, which may translate into greater compliance and lower stiffness of the shoulder. These findings may be used to build a more biofidelic shoulder in pediatric ATDs, ultimately helping to clarify how some injuries occur during side impact crashes.