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ACKNOWLEDGEMENTS
The authors would like to thank the donors for their generous gifts. Thank you to the Forensic Anthropology Center at Texas State University – San Marcos for the use of some their samples.
Lastly, thank you to all the members of the Skeletal Biology Laboratory and the Injury Biomechanics Research Center at OSU, especially Randee Hunter and Michelle Murach.
REFERENCES CITED
CONCLUSIONS
INTRODUCTION
As the elderly population continues to increase, understanding the etiology of
age-related bone loss becomes of increasing importance. Both trabecular and
cortical bone diminish with age. However, in the elderly, trabecular bone within
the rib is almost non-existent, while cortical bone loss is characterized by large
pores on the endosteal envelope, resulting in trabecularization of the cortex
(Zebaze et al., 2009).
Evidence suggests that bone loss occurs at a differential rate between the
pleural and cutaneous regions of the rib, though what drives this remains unclear.
This study examines the prevalence and location of cortical resorption via
porosity in the ribs of elderly individuals. Patterns of bone loss are explored by
sex, as well as by intra-individual comparison of the pleural and cutaneous
cortices of the rib.
Agnew, A.M., Moorhouse, K., Kang, Y.-S., Donnelly, B.R., Pfefferle, K., Manning, A.X., Litsky, A.S, Herriott, R., Abdel-Rasoul, M.,
Bolte, J.H. IV, 2013. The Response of Pediatric Ribs to Quasi-static Loading: Mechanical Properties and Microstructure. Ann.
Biomed. Eng. 41 (12), 2501–2514.
Rasband, W.S., ImageJ, U. S. National Institutes of Health, Bethesda, Maryland, USA, http://imagej.nih.gov/ij/, 1997-2014.
IBM Corp. Released 2013. IBM SPSS Statistics for Macintosh, Version 22.0. Armonk, NY: IBM Corp.
Zebaze, R., Ghasem-Zadeh, A., Bohte, A., Iuliano-Burns, S., Mackie, E., Seeman, E., 2009. Age-related bone loss: The effect of
neglecting intracortical porosity. Bone 44, S117–S118.
Mean%
SD%
Cutaneous)Cortex)
1.6957)
0.95887)
Pleural)Cortex)
0.8378)
1.36962)
Our results show that in elderly individuals, the cutaneous cortex undergoes higher rates of bone loss than the
pleural cortex of the rib. When coupled with previous work that found the same pattern in the ribs of juveniles
undergoing modeling drift (Agnew et al., 2013), this suggests a preferential preservation of the pleural cortex over
that of the cutaneous cortex throughout life. Future work should examine both juvenile and adult samples to
determine if this pattern holds through all decades of life and why.
MATERIALS AND METHODS
The sample is composed of 34 elderly individuals, 18 male and 15 female,
between 63–94 years of age (mean = 79.06, SD = 8.36 years). Complete cross-
sections were taken at the left, midshaft of the 6
th rib and slides prepared
following standard histological protocols. All slides were photographed at 40X
magnification and all data were collected using ImageJ.
Ribs were photographed and then digitally bisected into pleural and cutaneous
regions for data collection (defined by Imin). Variables collected are listed in
Table 1. All areas were manually traced and only those pores with an area 0.02
mm2 were included in the analyses (Fig. 1).
Normality tests indicated that %Porosity values were not normally distributed, so
log transformation was applied to normalize the data. Independent sample t-tests
were run to compare %Porosity values between the sexes. Then, paired sample
t-tests were used to compare %CuPorosity and %PlPorosity.
Variab le
Definition
Ct.Ar
Total area between periosteal and endosteal borders
Po.Ar
Total area of pores within cortex
%Porosity
(Po.Ar/Ct.Ar)*100
RESULTS AND DISCUSSION
Independent sample t-tests indicated no significant differences between males and females in the tested porosity
indices (Table 2). Samples were pooled for further analyses.
Paired sample t-tests indicated that the cutaneous cortex of the rib has a significantly higher %Porosity than the
pleural cortex (p = 0.001, Table 3)
Delimitating between cortex and trabeculae was a problem in this study (Fig. 2). Though we used traditional Ct.Ar
measurements, it must be noted that these measurements exclude trabecularized cortex, thus underestimating both
cortex size and the associated increase in porosity (Zebaze et al., 2009). This may account for seemingly higher
%PlPorosity values in some of the study samples. While the trend in increased %CuPorosity is strong enough to
remain evident despite this quantification issue, researchers should keep in mind that traditional cortical
measurements may be underestimating rates of cortical bone loss.
t"
df"
p"
Total)Cortex)
1.574)
31)
0.126)
Cutaneous)Cortex)
1.109)
31)
0.276)
Pleural)Cortex)
0.738)
28)
0.467)
Ta bl e 2 . I n de p en d en t t-test Between Males and Females
Table 1. Collected Variablesa
Fig. 1. Rib stained in basic fuchsin, illustrating data collection protocol. Red line
indicates delineation between pleural and cutaneous regions. Inset represents
two measured pores included in the analyses.
aEach variable was also collected and analyzed for the cutaneous and pleural halves of
the rib specifically.
Table 3. Paired Sample t-testa Means
at(29) = 3.524, p = 0.001*
Fig. 2. A. Discernable endosteal border for porous cortex. Rib stained in basic fuchsin.
B. Endosteal border degraded by cortical trabecularization.
A) B)
Cutaneous
Pleural
... There is a nonsignificant trend observed in this study, of osteon size decreasing as intracortical porosity increases, which supports the suggestion that the amount of viable cortex plays a role in defining osteon size. On the other hand, the greater influence of %Ct.Ar may result from the fact that highly trabecularized cortex is often excluded (and inconsistent) when defining rib cortical area (Dominguez and Agnew, 2014). Thus, while measuring conventions may render an accurate accounting of the greater part of cortical porosity uncertain, this deficit corresponds with a similar obfuscation of measured cortical area. ...
... While age accounted for comparable amounts of variation between the cortices, %Ct.Ar represented nearly twice the variance in On.Ar in the cutaneous cortex as in the pleural cortex. This may be explained by the suggestion that the pleural cortex of the ribs is preferentially conserved over the cutaneous cortex, a relationship that holds true throughout life (Agnew et al., 2013;Dominguez and Agnew, 2014) and was supported by the t-test comparisons of %Ct.Ar between cortices described above. The greater cortical loss (or lesser apposition) experienced by the cutaneous cortex likely acts as a constraint on osteon size, resulting in significantly smaller osteons when compared to those of the pleural cortex, a fact observed in this study. ...
Article
Previous research demonstrates the size of secondary osteons varies considerably between individuals, though what factors act in the delineation of osteon size remain uncertain. This study explores the influence of age, sex, percent cortical area (%Ct.Ar), percent cortical porosity (%Po.Ar), and loading environment on osteon area (On.Ar) in human ribs. The sample consisted of midshaft 6(th) ribs from 80 individuals, 6-94 years of age. T-tests demonstrated no significant differences in On.Ar between the sexes (p=0.383). Age showed a significant correlation with both %Ct.Ar and %Po.Ar, so a hierarchical regression model was used to control for the effects of age on the other variables. Results indicate that age is the most significant factor of those tested in this study, (p=0.004), with %Ct.Ar playing a much smaller but still significant role (p=0.014), while %Po.Ar had no significant influence on On.Ar (p=0.443). Age demonstrates an inverse relationship with On.Ar, while %Ct.Ar has a direct relationship with On.Ar. Significant differences in On.Ar between the pleural and cutaneous cortices are attributed to variation in %Ct.Ar of each cortex. Therefore, age and %Ct.Ar, account for the majority of osteon size variability in this study, although it is likely genetics play an important role as well. Understanding the biological mechanisms that act in remodeling and determine osteon size is essential for accurately addressing and interpreting histological findings, work that is invaluable in its implications for bone biology. This article is protected by copyright. All rights reserved.
... During the anterior-posterior rib bending, the cutaneous cortex will be subjected to tensile stress and the pleural to compressive stress, and the principle stresses and strains will line up along the long rib axis. It has also been shown that the cutaneous cortex is generally thinner (Agnew et al. 2018) and has more intracortical porosity (Agnew and Stout 2012, Dominguez and Agnew 2014 compared to the pleural cortex. Together this means that the fracture initiation will most likely be in tension on the cutaneous side and the first principle strain is a good candidate for fracture prediction in this load case. ...
Article
Full-text available
Objective: The current state of the art human body models (HBMs) underpredict the number of fractured ribs. Also, it has not been shown that the models can predict the fracture locations. Efforts have been made to create subject specific rib models for fracture prediction, with mixed results. The aim of this study is to evaluate if subject-specific finite element (FE) rib models, based on state-of-the-art clinical CT data combined with subject-specific material data, can predict rib stiffness and fracture location in anterior-posterior rib bending. Method: High resolution clinical CT data was used to generate detailed subject-specific geometry for twelve FE models of the sixth rib. The cortical bone periosteal and endosteal surfaces were estimated based on a previously calibrated cortical bone mapping algorithm. The cortical and the trabecular bone were modeled using a hexa-block algorithm. The isotropic material model for the cortical bone in each rib model was assigned subject-specific material data based on tension coupon tests. Two different modeling strategies were used for the trabecular bone. The capability of the FE model to predict fracture location was carried out by modeling physical dynamic anterior-posterior rib bending tests. The rib model predictions were directly compared to the results from the tests. The predicted force-displacement time history, strain measurements at four locations, and rotation of the rib ends were compared to the results from the physical tests by means of CORA analysis. Rib fracture location in the FE model was estimated as the position for the element with the highest first principle strain at the time corresponding to rib fracture in the physical test. Results: Seven out of the twelve rib models predicted the fracture locations (at least for one of the trabecular modeling strategies) and had a force-displacement CORA score above 0.65. The other five rib models, had either a poor force-displacement CORA response or a poor fracture location prediction. It was observed that the stress-strain response for the coupon test for these five ribs showed significantly lower Young’s modulus, yield stress, and elongation at fracture compared to the other seven ribs. Conclusion: This study indicates that rib fracture location can be predicted for subject specific rib models based on high resolution CT, when loaded in anterior-posterior bending, as long as the rib’s cortical cortex is of sufficient thickness and has limited porosity. This study provides guidelines for further enhancements of rib modeling for fracture location prediction with HBMs.
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