Rib Geometry Explains Variation in Dynamic Structural Response:
Potential Implications for Frontal Impact Fracture Risk
Injury Biomechanics Research Center, The Ohio State University, 2063 Graves Hall, 333 W. 10th Ave, Columbus, OH 43210,
National Highway Trafﬁc and Safety Administration, Vehicle Research and Test Center, East Liberty, OH 43074, USA;
Department of Orthopaedic Surgery, University of Michigan, Biomedical Sciences Research Building, Ann Arbor,
MI 48109, USA
(Received 6 January 2017; accepted 5 May 2017; published online 25 May 2017)
Associate Editor Joel D. Stitzel oversaw the review of this article.
Abstract—The human thorax is commonly injured in motor
vehicle crashes, and despite advancements in occupant safety
rib fractures are highly prevalent. The objective of this study
was to quantify the ability of gross and cross-sectional
geometry, separately and in combination, to explain varia-
tion of human rib structural properties. One hundred and
twenty-two whole mid-level ribs from 76 fresh post-mortem
human subjects were tested in a dynamic frontal impact
scenario. Structural properties (peak force and stiffness) were
successfully predicted (p < 0.001) by rib cross-sectional
geometry obtained via direct histological imaging (total area,
cortical area, and section modulus) and were improved
further when utilizing a combination of cross-sectional and
gross geometry (robusticity, whole bone strength index).
Additionally, preliminary application of a novel, adaptive
thresholding technique, allowed for total area and robusticity
to be measured on a subsample of standard clinical CT scans
with varied success. These results can be used to understand
variation in individual rib response to frontal loading as well
as identify important geometric parameters, which could
ultimately improve injury criteria as well as the bioﬁdelity of
anthropomorphic test devices (ATDs) and ﬁnite element
(FE) models of the human thorax.
Keywords—Thorax, Rib, Cross-sectional geometry, Robus-
ticity, Fracture risk, Stiffness.
The human thorax is commonly injured in motor
vehicle crashes (MVCs), in which harmful loads can be
applied to the chest resulting in rib fractures.
fractures are often considered indicators of trauma
severity, because the greater the number of fractured
ribs, the higher the mortality and morbidity rates.
Despite advancements in occupant safety, rib fractures
are still highly prevalent in MVCs.
In order to
improve vehicle occupant protection against thoracic
injuries, researchers are continually striving to make
improvements to anthropomorphic test devices
(ATDs) and ﬁnite element (FE) models of the human
thorax. The bioﬁdelity of these tools can be improved
using speciﬁc data regarding the geometry, structural,
and material properties of human ribs, as the ribs are
the primary load bearing components of the thorax in
a frontal collision. Many researchers have attributed
variation in thorax and rib properties to age and sex,
however these variables only explain a trivial amount
of variation in individual rib properties and are poor
predictors of rib response and injury.
Both cross-sectional and gross geometry of the rib
may play a crucial role in determining the rib’s
response to loading.
Charpail et al.
mid-level ribs from ﬁve individuals in a dynamic
bending scenario and found a relationship between
mineral linear density (an index which represents rib
bone quality and gross geometry by dividing ash
weight by total curve length) and several mechanical
properties: maximum displacement, peak force, stiff-
ness, and work to fracture. Cormier et al.
each conducted 3-point bending tests on vari-
able locations of rib sections from four and six sub-
jects, respectively, and found differences in structural
properties to coincide with changes in cross-sectional
geometry. Due to the limited number of subjects used
in previous experimental studies, the applicability and
Address correspondence to Amanda M. Agnew, Injury Biome-
chanics Research Center, The Ohio State University, 2063 Graves
Hall, 333 W. 10th Ave, Columbus, OH 43210, USA. Electronic mail:
Annals of Biomedical Engineering, Vol. 45, No. 9, September 2017 (
2017) pp. 2159–2173
2017 Biomedical Engineering Society