Clavicle Fractures Due to Belt Loading in Rear-Seated Adolescent Occupants

 Principal Investigators: Jason Stammen, PhD, NHTSA; John H. Bolte IV, PhD, The Ohio State University; Kristy Arbogast, PhD, The Children’s Hospital of Philadelphia

 

Below is an executive summary of this project. Please note that this summary describes results and interpretation that may not be final. Final interpretation of results will be in the peer-reviewed literature.

 

Pictured clockwise left to right: CIREN case MADYMO reconstruction with scaled 6-year-old ATD model seated in 3-point belt with backless booster; FE age-matched pediatric clavicle with stress distribution resulting from ATD shoulder belt contact loading in MADYMO reconstruction; X-ray of clavicle fracture from corresponding CIREN case.

 

Little is known about the dynamic response of the adolescent occupant shoulder when seat belt restrained in a frontal or off-center crash. Pediatric clavicle fractures attributed to shoulder belt loading, while rare, provide a glimpse into how the belt-shoulder interaction changes with crash speed, the principal direction of force, restraint type, and belt anchor locations within the vehicle.

Investigating cases of clavicle fractures sustained by seat-belt-restrained pediatric occupants provides guidance for developing improved shoulder designs in child-sized anthropomorphic test devices (ATDs). The goals of the study were to determine the crash characteristics typically associated with clavicle fractures, with consideration for age-related differences in injury patterns and restraint conditions, and to estimate the level of force required to cause injury to the adolescent clavicle through paired match case reconstructions with a Hybrid III ATD model.

Real world crash data was collected from the National Highway Traffic Safety Administration’s Crash Injury and Research Engineering Network (CIREN) and the National Automotive Sampling System – Crashworthiness Data System (NASS-CDS). The data collected included age, seating position, type of restraint, extent of vehicle damage, crash velocity, and injuries.

Differences in injury patterns between front- and rear-seated occupants, as well as between adult and adolescent occupants, were observed in NASS-CDS data. Younger occupants appeared to have a greater risk of thoracic organ injuries, while older occupants tended to have more skeletal (rib, sternum, and clavicle) injuries due to the belt. Also, lumbar vertebral fractures were more common in younger occupants, reflecting the greater propensity for the lap belt to ride up on the occupant’s abdomen rather than fitting properly over the hips.

The data were further analyzed to identify patterns associated with clavicle fractures, including the presence of attendant serious head and thorax injuries. Four CIREN cases with a seat belt-induced clavicle fracture were selected, along with four cases without clavicle fracture matched to the injured cases by occupant, vehicle and crash characteristics. These eight cases were reconstructed using a combination of a computational modeling of the crash and a 3D finite element (FE) model of the clavicle created from real patient medical imaging. Vehicle- specific seat geometries and crash pulses were used to replicate the case information as closely as possible, and shoulder-belt contact forces obtained from the computer simulations were used as input to the FE clavicle, which had age-appropriate mechanical properties developed from literature studies. Differences in stress (the amount of force per area) magnitude between fracture and non-fracture cases were quantified with respect to both ATD shoulder forces and radiological fracture locations.

By drawing relationships between cases where the clavicle was injured and not injured, the researchers can provide guidance for improved ATD shoulder design, as well as loading thresholds indicative of clavicle fracture for vehicle and child seat design.

 

Co-investigators:
Caitlin Locey, BA and Matthew R. Maltese, PhD, The Children’s Hospital of Philadelphia; Rebecca Dupaix, PhD, The Ohio State University; Dan Parent, PhD, National Highway Traffic Safety Administration

Students:
Travis Jones and Rakshit Ramachandra, The Ohio State University

IAB Mentors:
Doug Longhitano, Honda R&D Americas Inc.; Rodney Rudd, National Highway Traffic Safety Administration; Julie Kleinert, General Motors Holdings LLC

 

About This Center

This Center is made possible through a grant from the National Science Foundation (NSF) which unites CHOP, University of Pennsylvania, and The Ohio State University researchers with R&D leaders in the automotive and insurance industries to translate research findings into tangible innovations in safety technology and public education programs.

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