Microstructural and Mechanical Properties of Human Ribs

Abstract

The direction of osteons in cortical bone has been shown to be well correlated with the strongest loading direction of the bone as a whole. Therefore, determining the orientation of osteons in the rib cage is an important step in understanding the behavior of the rib cage under mechanical load. A total of 37 specimens were removed from several rib locations from a male and female cadaver. Eight histological slides were created from each 5 mm long section. Image analysis included the use of a computer algorithm created in Matlab to track the center of each osteon throughout the rib section. Analysis of the results showed variations in the osteon direction between samples taken from the anterior, lateral and posterior surfaces of the rib cage. The average offset angle between the osteon direction and the rib axis was determined to be 4.1, 3.2 and 1.9 degrees for the anterior, lateral and posterior surfaces respectively. The average offset angle for the anterior specimens was significantly higher than that of the posterior rib specimens (P=0.01) The lateral specimens also showed a significantly higher average offset angle than the posterior rib specimens (P=0.01). The results indicate a trend in osteon offset angle between the three locations studied. The offset angle is highest in the anterior region, then decreases in the lateral and is lowest in the posterior regions of the rib cage.

Determining the risk of injury from an automobile collision to the thorax requires knowledge of the properties of the skeletal components that comprise the thorax. The purpose of this study was to investigate the strength of human ribs subjected to dynamic three-point bending. A total of four human cadavers were utilized by removing 16 rib sections from the right side of each thorax. One or two sections were removed from a single rib at the lateral, anterior and posterior locations of the thorax. The strain rates resulting from the dynamic loading ranged from 0.5 to 5.44 strains per second. Three-axis strain gage rosettes were used for one series of tests showing small variation of the principal strain axis from the direction of bending. For all subjects, the anterior specimens failed at a significantly lower peak stress than the lateral (p=0.01) and posterior (p=0.01) specimens. The average elastic modulus from all tests was 22 GPa. The average peak stress for all specimens was 115 MPa, with an average peak strain of 11,460 microstrain.