Microstructural And Mechanical Properties Of Human Ribs Joseph

These ribs were chosen for comparison in order to match the loading directions used by
Yoganandan and Pintar (1998). The difference in elastic moduli between previous work
and the current work exemplifies the importance of dynamic analysis of biological tissue.
The effects of rib curvature on the strength of the rib were found to be minimal.
The change in stress values in a curved beam is a function of its radius of curvature (R) and
its depth (d) in the plane of bending. These parameters were investigated for the F1 female
subject and similar geometry was assumed to be present in the other subjects. This is a
reasonable assumption because the male subjects were larger so one would expect the
radius of curvature to increase. Therefore, the F1 subject represents the worst case for the
effects of rib curvature. The ratio R/d defines the significance of the curvature of a beam
and was determined for all specimens removed from the F1 subject. An R/d value of 8
represents the limit to which straight-beam theory applies with minimal errors that are on
the order of 4% to 5% (Young 1989). The average depth for all subjects was: 0.17 in. for
subject F1, .20 in. for subject F2, 0.24 in. for subjects M1 and 0.26 in. for subject M2. The
average radius of curvature (R) for the F1 subject was 6.28 inches. The average of the R/d
values for the F1 subject was 38, therefore the influence of rib curvature was assumed to be
negligible for all subjects because of similar geometry.
An interesting finding during this investigation was the strength of the periosteum
surrounding the ribs. In many of the rib fracture tests, the cortical bone would fail
corresponding to a drop in the load, but the periosteum would continue to provide structural
stability to the rib around the fracture location. This finding indicates that a more detailed
analysis of the periosteum should be considered.
45