Defining Regional Variation in the Material Properties of Human Rib Cortical Bone and Its Effect on Fracture Prediction 2003-22-0012
This paper presents the results of dynamic material tests and computational modelling that elucidate the effects of regional rib mechanical properties on thoracic fracture patterns.
First, a total of 80 experiments were performed using small cortical bone samples from 23 separate locations on the rib cages of four cadavers (2 male, 2 female). Each specimen was subjected to dynamic three-point bending
resulting in an average strain rate of 5 ± 1.5 strain/s. Test coupon modelling was used to verify the test setup. Regional variation was defined by location as anterior, lateral, or posterior as well as by rib level
1 through 12. The specimen stiffness and ultimate stress and strain were analyzed by location and rib level. Second, these material properties were incorporated into a human body computational model. The rib cage was
partitioned into anterior, lateral, and posterior segments and the material properties were varied by location using an elastic-plastic material model. A total of 12 simulations with a rigid impactor were performed
including 2 separate material assumptions, original and modified rib properties for regional variations, 3 separate impactor velocities, and 2 directions, anterior and lateral. The data from the material tests for all
subjects indicate a statistically significant increase in the average stiffness and average ultimate stress for the cortical bone specimens located in the lateral (11.9 GPA modulus, 153.5 MPa ultimate stress) portion of
the ribs versus the anterior (7.51 GPa, 116.7 MPa) and posterior (10.7 GPa, 127.7 MPa) rib locations. In addition, the stiffness, ultimate stress, and ultimate strain for all subjects are significantly different by rib
level with each variable generally increasing with increasing rib number. The results from the computational modelling for both frontal and lateral impacts illustrate that the location and number of rib fractures are
altered by the inclusion of rib material properties that vary by region.
Joel D. Stitzel, Joseph M. Cormier, Joseph T. Barretta, Eric A. Kennedy, Eric P. Smith, Amber L. Rath, Stefan M. Duma, Fumio Matsuoka
Virginia Tech - Wake Forest, Toyota Motor Corp.
47th Stapp Car Crash Conference (2003)
Stapp Car Crash Journal Vol. 47, 2004-P-385