Microstructural Analysis of Osteon Orientation in Human Rib Cortical Bone

The orientation of osteons in cortical bone has been shown to correlate with the loading condition. The purpose of this study is to determine the orientation of osteons in the rib cage to better understand the behavior of the rib cage under mechanical load. A total of 37 rib specimens were removed from 21 rib locations from a male and female cadaver. Eight histological slides were created from each 5 mm rib section. A custom image analysis algorithm was created in Matlab to track the center of each osteon through the rib section. Results show 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.