Investigation of Repeat Anterior-Posterior Loading of...
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Investigation of Repeat Anterior - Posterior Loading of Human Ribs Akshara Sreedhar 1 , Yun-Seok Kang 1 , Jason Stammen 2 , Kevin Moorhouse 2 , Amanda Agnew 1 1 Injury Biomechanics Research Center, The Ohio State University 2 National Highway Traffic Safety Administration, Vehicle Research and Test Center INTRODUCTION ACKNOWLEDGEMENTS Thank you to all of the students and staff of the Injury Biomechanics Research Center. Thank you to the National Highway Traffic Safety Administration for sponsoring this work. We are especially grateful to OSU’s Body Donor Program, LifeLine of Ohio, and the anatomical donors for their generous gifts. MATERIALS & METHODS RESULTS & DISCUSSION • Thorax injuries, specifically rib fractures, are common in motor vehicle crashes and can lead to high rates of morbidity and mortality (Kent et al. 2008). In order to ultimately improve thoracic injury prevention measures, quantifying variation in rib response for all occupants is crucial. • Many studies have been conducted on single impacts of ribs in dynamic testing (Agnew et al. 2018) and on non-injurious quasi-static fatigue loading (Li et al. 2010). However, repeated dynamic test data for whole human ribs are lacking. • The goal of this study was to explore why some ribs did not fail during a dynamic impact to better understand differential fracture risk. Additionally, we investigated changes in structural properties between multiple impacts. CONCLUSIONS • Results from this study and future work in exploring complex loading mechanisms will be crucial in quantifying variation in rib response for a large population with the overall goal of identifying differential injury thresholds and preventing thoracic injuries in motor vehicle crashes. REFERENCES CITED - Kent, R., Woods, W., & Bostrom, O. (2008). Fatality Risk and the Presence of Rib Fractures. Annals of Advances in Automotive Medicine, 52(October), 73–82. Agnew, A., Murach, M., Dominguez, V., Sreedhar, A., Misicka, E., Harden, A., Bolte, J., Moorhouse, K., and Kang, Y.S. (2018). Sources of Variability in Structural Bending Response of Pediatric and Adult Human Ribs in Dynamic Frontal Impacts, Stapp Car Crash Journal, 62(November), 119-192. Li, Z., Kindig, M., Kerrigan, J., Untaroiu, C., Subit, D., Crandall, J., Kent, R. (2010). Rib fractures under anterior-posterior dynamic loads: Experimental and finite-element study, Journal of Biomechanics, 43(January), 228-234. • Three-hundred and seventy-two ribs from 204 post-mortem human subjects (72 females, 132 males, 4 - 108 years) were dynamically impacted in anterior to posterior loading (Fig. 1). Displacement was measured by a linear string potentiometer attached to the moving plate of the fixture. Force was measured in the direction of impact (X) by a 6-axis load cell behind the vertebral end of the rib. Strain gages attached at 30% and 60% of whole rib curve length on the cutaneous and pleural surfaces measured strain. Structural properties were calculated from force vs. displacement (F-D) curves (Fig. 2). • Eleven ribs did not fracture during initial impact and were subsequently impacted again. These ribs fell into three distinct cases according to impact velocity (1 m/s or 2 m/s) and failure or not during the second impact (Fig. 2). Figure 1. Dynamic A-P rib bending test that did not fail on first impact through loading and “unloading” X Y Time = 0 ms X Y Time = 43 ms X Y Time = 84 ms X Y Time = 243 ms Time = 449 ms X Y Between Subjects • Age was lower (4 - 30 years) than the fractured sample • Both sexes: 7 Males, 2 Females Structural Properties • Average structural properties in all cases for these 11 ribs were greater than the average of the sample of fractured ribs. Cross-Sectional Geometric Properties • Larger Ct.Th and Ct.Ar (Fig. 6) in these 11 ribs were found when compared to age- and sex-matched ribs from the fractured sample, and likely contributed to increased fracture resistance. Figure 5. Hierarchical exploration of why ribs did not fail 0 2000 4000 6000 8000 10000 12000 14000 Total Energy (N*mm) Total Energy by Rib First Impact Second Impact Case 1 Case 3 Case 2 Figure 3. Total energy (left) and peak strain (right) comparisons by rib and impact number 0 10000 20000 30000 40000 50000 Peak Strain (microstrain) Peak Pleural Strain by Rib First Impact Second Impact Case 1 Case 2 Case 3 Figure 4. F-D and strain time history for rib in Fig. 1 showing loading and “unloading” Figure 2. Schematic of rib responses for each impact organized by case scenarios. Data are cut at the time of peak strain for calculation of structural properties. Figure 6. Ex: Ct.Ar and Ct.Th comparison Failure No Failure • Total energy, force (peak and yield), and linear structural stiffness were generally lower for the 2 nd impact than the 1 st . • Total energy (Fig. 3) decreased after the first impact regardless of varied impact velocities. The second rib in Case 1 shows only a small difference in total energy between impacts. During the second impact, the displacement was greater than that of the first impact contributing to similar energy values despite lower peak forces. • No trend in peak strain (Fig. 3) was observed. For ribs in Case 1 strain rates were decreased by 0.1 strain/s during the 2 nd impact despite the same impact velocity. • Fig. 4 shows the complete loading and “unloading” cycle of both impacts corresponding to Fig. 1. The end of the loading cycle was determined by the peak strain. The loading behavior between impacts is different but shows similar “unloading” response for both impacts. • Fig. 5 explores the differences in these 11 ribs compared to the 362 fractured ribs. Microdamage accumulation may explain decreased structural properties during subsequent impacts. Despite potential microdamage, ribs in Cases 1 and 3 did not fracture during a 2 nd impact and therefore these individuals could be at lower risk for thoracic injuries in frontal impacts. 11 ribs did not fail on first impact and were impacted again Case 1 Same velocity (2m/s 2m/s) No failure during second impact (n=4) Case 2 Different velocity (1m/s 2m/s) Failure during second impact (n=3) Case 3 Different velocity (1m/s 2m/s) No failure during second impact (n=4)
Transcript of Investigation of Repeat Anterior-Posterior Loading of...
Investigation of Repeat Anterior-Posterior Loading of Human Ribs
Akshara Sreedhar1, Yun-Seok Kang1, Jason Stammen2, Kevin Moorhouse2, Amanda Agnew1
1Injury Biomechanics Research Center, The Ohio State University2National Highway Traffic Safety Administration, Vehicle Research and Test Center
INTRODUCTION
ACKNOWLEDGEMENTSThank you to all of the students and staff of the Injury Biomechanics Research Center. Thank you to the National Highway Traffic Safety Administration for sponsoring this work. We are especiallygrateful to OSU’s Body Donor Program, LifeLine of Ohio, and the anatomical donors for their generous gifts.
MATERIALS & METHODS
RESULTS & DISCUSSION
• Thorax injuries, specifically rib fractures, are common in motor vehicle crashes andcan lead to high rates of morbidity and mortality (Kent et al. 2008). In order toultimately improve thoracic injury prevention measures, quantifying variation in ribresponse for all occupants is crucial.
• Many studies have been conducted on single impacts of ribs in dynamic testing(Agnew et al. 2018) and on non-injurious quasi-static fatigue loading (Li et al. 2010).However, repeated dynamic test data for whole human ribs are lacking.
• The goal of this study was to explore why some ribs did not fail during adynamic impact to better understand differential fracture risk. Additionally, weinvestigated changes in structural properties between multiple impacts.
CONCLUSIONS• Results from this study and future work in exploring complex loading mechanisms will
be crucial in quantifying variation in rib response for a large population with theoverall goal of identifying differential injury thresholds and preventing thoracic injuriesin motor vehicle crashes.
REFERENCES CITED- Kent, R., Woods, W., & Bostrom, O. (2008). Fatality Risk and the Presence of Rib Fractures. Annals of Advances in Automotive Medicine, 52(October), 73–82. Agnew, A., Murach, M., Dominguez, V.,
Sreedhar, A., Misicka, E., Harden, A., Bolte, J., Moorhouse, K., and Kang, Y.S. (2018). Sources of Variability in Structural Bending Response of Pediatric and Adult Human Ribs in Dynamic Frontal Impacts, Stapp Car Crash Journal, 62(November), 119-192. Li, Z., Kindig, M., Kerrigan, J., Untaroiu, C., Subit, D., Crandall, J., Kent, R. (2010). Rib fractures under anterior-posterior dynamic loads: Experimental and finite-element study, Journal of Biomechanics, 43(January), 228-234.
• Three-hundred and seventy-two ribs from 204 post-mortem human subjects (72females, 132 males, 4 - 108 years) were dynamically impacted in anterior to posteriorloading (Fig. 1). Displacement was measured by a linear string potentiometerattached to the moving plate of the fixture. Force was measured in the direction ofimpact (X) by a 6-axis load cell behind the vertebral end of the rib. Strain gagesattached at 30% and 60% of whole rib curve length on the cutaneous and pleuralsurfaces measured strain. Structural properties were calculated from force vs.displacement (F-D) curves (Fig. 2).
• Eleven ribs did not fracture during initial impact and were subsequently impactedagain. These ribs fell into three distinct cases according to impact velocity (1 m/s or 2m/s) and failure or not during the second impact (Fig. 2).
Figure 1. Dynamic A-P rib bending test that did not fail on first impact through loading and “unloading”
X
Y Time = 0 msX
Y Time = 43 msX
Y Time = 84 msX
Y Time = 243 ms Time = 449 msX
Y
Between Subjects• Age was lower (4 - 30 years)
than the fractured sample• Both sexes: 7 Males, 2 Females
Structural Properties• Average structural properties
in all cases for these 11 ribswere greater than the averageof the sample of fractured ribs.
Cross-Sectional Geometric Properties
• Larger Ct.Th and Ct.Ar (Fig. 6)in these 11 ribs were foundwhen compared to age- andsex-matched ribs from thefractured sample, and likelycontributed to increasedfracture resistance.
Figure 5. Hierarchical exploration of why ribs did not fail
0
2000
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6000
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Tota
l Ene
rgy
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m)
Total Energy by Rib
First Impact Second Impact
Case 1 Case 3Case 2
Figure 3. Total energy (left) and peak strain (right) comparisons by rib and impact number0
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Peak Pleural Strain by Rib
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Figure 4. F-D and strain time history for rib in Fig. 1 showing loading and “unloading”
Figure 2. Schematic of rib responses for each impact organized by case scenarios. Data are cut at the time of peak strain for calculation of structural properties.
Figure 6. Ex: Ct.Ar and Ct.Th comparison
Failure
No Failure
• Total energy, force (peak and yield), andlinear structural stiffness were generallylower for the 2nd impact than the 1st.
• Total energy (Fig. 3) decreased after thefirst impact regardless of varied impactvelocities. The second rib in Case 1 showsonly a small difference in total energybetween impacts. During the secondimpact, the displacement was greater thanthat of the first impact contributing to similarenergy values despite lower peak forces.
• No trend in peak strain (Fig. 3) wasobserved. For ribs in Case 1 strain rateswere decreased by 0.1 strain/s during the2nd impact despite the same impact velocity.
• Fig. 4 shows the complete loading and“unloading” cycle of both impactscorresponding to Fig. 1. The end of theloading cycle was determined by the peakstrain. The loading behavior betweenimpacts is different but shows similar“unloading” response for both impacts.
• Fig. 5 explores the differences in these 11ribs compared to the 362 fractured ribs.Microdamage accumulation may explaindecreased structural properties duringsubsequent impacts. Despite potentialmicrodamage, ribs in Cases 1 and 3 did notfracture during a 2nd impact and thereforethese individuals could be at lower risk forthoracic injuries in frontal impacts.
11 ribs did not fail on first impact and were impacted again
Case 1Same velocity (2m/s 2m/s)
No failure during second impact (n=4)
Case 2Different velocity
(1m/s 2m/s)Failure during
second impact (n=3)
Case 3Different velocity
(1m/s 2m/s)No failure during
second impact (n=4)
