Preliminary Investigation of the Mechanical Properties of Costal Cartilage and Costochondral Junction in Three-Point Bending

Abstract

Motor vehicle collisions (MVCs) are a leading cause of morbidity and mortality. The chest accounts for the second most cause of driver fatalities in frontal collisions. The skeletal thorax is composed of the ribs, costal cartilage, thoracic vertebrae, and sternum. Costal cartilage (CC) is a viscoelastic material which connects the ribs to the sternum. Costochondral junctions (CCJ) are primary cartilaginous joints which couple the costal cartilage to the ribs. These structures are commonly modeled only as transition regions between CC and rib in human body models (HBMs). However, the biomechanical response of the CCJ has not been implemented into these models or studied experimentally. The goal of this study is to investigate the structural properties of costal cartilage and the costochondral junction when loaded to failure in three-point bending. Thirty (n=30) total samples were harvested from nineteen (n=19) donors from ages 21 to 98 years (9 Male, 10 Female). 3rd, 4th, 5th, and 6th ribs and costal cartilage were harvested and isolated into CC only and Rib + CC groups to compare differences in cartilage and junction properties. Sixteen (n=16) CC only and fourteen (n=14) Rib + CC samples with the CCJ still intact were fabricated, prepared, potted, and tested in three-point bending. All samples were tested to failure in a three-point bending loading scenario at a constant rate of 30 mm/s. The force and displacement were calculated for the duration of each test. Ultimate force, ultimate displacement, ultimate moment, failure force, failure displacement, and failure moment were calculated for all but five (n=5) samples, which did not fail during the test. Only linear stiffness was calculated for these samples. The failure location along the testing span length was also calculated for the samples that failed successfully. The effects of sample type, age, and sex on the structural properties were statistically evaluated. Force and stiffness were not significantly affected by sample type, age, or sex. Females had significantly greater failure location compared to males. CC only samples had significantly greater ultimate and failure displacement than Rib + CC samples. Failure displacement and location had weak, negative correlations with age. These results demonstrate differences in the structural properties of costal cartilage and CCJ that can be quantified and implemented into Human Body Models (HBMs). Differentiating the two anatomical features in computational modeling may improve the accuracy and predictive ability of HBMs, which will lead to more effective vehicular safety designs and decreased MVC injuries and fatalities.