Biomechanical response of ribs under quasistatic frontal loading

The goal of the present study was to identify rib-level differences in fracture characteristics for individual ribs subjected to anterior-posterior loading.

Twenty-seven individual ribs were extracted from levels 2 to 10 from 3 postmortem human subjects (2 females and one male) and subjected to anterior-posterior loading at a quasistatic (2 mm/s) loading rate. The ribs were placed in a fixture that provided a pinned boundary condition at each extremity, and each specimen was loaded to failure. Reaction force and strains on the internal and external cortical surfaces of the ribs were measured.

Rib 2 was found to be 3 to 4 times stiffer than rib 3, whereas all other ribs were comparable in stiffness to rib 3. Fracture forces, fracture displacement, and work to fracture showed no clear rib-level trends, although the young male subject consistently exhibited higher fracture force and work values than the elderly female subjects for a given rib level. The cortical strains on the external surface of the rib remained in tension during the loading, whereas the internal surface strains were in compression. The data from the present study were compared to a similar study performed at dynamic loading rates (1.43-1.85 m/s). The quasistatic tests exhibited lower peak force and greater normalized fracture displacement than the dynamic tests, though the work was comparable between the 2 studies.

The present study is one of the few that focuses on testing the rib as an entire structure and can contribute to understanding of how the structural behavior of an individual rib contributes to the fracture tolerance of the overall thorax when undergoing frontal loading.