Pediatric injury biomechanics

1. Paediatric Injury Biomechanics.
3-Point Bending of Human Femurs
Forman J *, del Pozo de Dios E**, Symeonidis I***,
Duart J**, Kerrigan J*, Robert Salzar R*,
Balasubramanian S****, Segui-Gomez M **, Kent R*
*University of Virginia Center for Applied Biomechanics
**European Center for Injury Prevention
***I.L.M. University of Munich
****Children’s Hospital of Philadelphia

2. Disclosures
No Disclosures

3. Material Properties
Introduction
Medicine
Physics
Maths
Engineering

4. Material Properties
Introduction
Injury Biomechanics
“Identification / definition of impact
injury mechanisms”
“Quantification of biomechanical
response to impact”
“Determination of impact tolerance
levels”
“Development of injury
assessment devices”
“Techniques for evaluating injury
prevention systems”

5. Material Properties
Introduction
0-14 y-o
15-17 y-o
RTIs
“Leading mechanism of
fatal injuries in Europe”
“Mortality 0-19 y-o:
16.400 per year”
“Leading mechanism of
traumatic brain and
extremity injuries and
subsequent long-term
impairment”
European Report on Child Injury Prevention
WHO 2008

6. Material Properties
Introduction
Risk factors
Childrens
• Small stature
number / severity
• Cognitive development
• Capacity to evaluate
risks
Teenager
• risktaking behaviour
• peer influence

7. Material Properties
Introduction
Risk factors
• Public transportation
• Street and road design
• Safe areas to play & walk
• Roadside barriers
• Controlling vehicle speed
• Poor conspicuity

8. Material Properties
Introduction

9. Injury Prediction Challenges: Biological Variability
Material Properties
Introduction
Geometric and material changes that occur
throughout development may affect skeletal
Size
injury tolerance
Human Femur Cortical Bone Elastic
20
18
16
14
12
10
Modulus
0 20 40 60 80
Elastic Modulus (GPa)
Age
Reilly et al. 1974
Characteristics of cortical bone

10. Injury Prediction Challenges: Biological Variability
Material Properties
Introduction
Age & Injury tolerance
Bending strenght
Modulus of elasticity
Currey JD, Butler G.
The mechanical properties of bone tissue in children
JBJS-Am, 1975

11. Introduction
Injury Prediction Challenges: Biological Variability
Material Properties
Geometry
Anthropometry
Age
How do these effect
injury susceptibility?
How do we incorporate into injury
prediction tools?

12. Objective
“To investigate the roles of geometric and
material factors in the changes that occur in
long-bone fracture tolerance throughout
skeletal development”
“To study the contributing effects of
changes in bone geometry and other
characteristics”

13. Material & Methods
Dynamic 3-point Bending
Literature Search
•Report age and fracture moment
•Adjusted for presence of flesh

14. Material & Methods
Dynamic 3-point Bending
Literature Search
•Report age and fracture moment
•Adjusted for presence of flesh
New Tests
• Transplant and Tissue Donation Program of the
Government of Navarra (Spain)
• Approved University of Navarra School of Medicine
•European Center for injury Prevention (ECIP)
•Denuded femurs, medial-lateral bending

15. Material & Methods
Dynamic 3-point Bending
Femur Bending - Methods
Mid-shaft loading
Kerrigan JR, Drinkwater DC, Kam CY, Murphy DB, Ivarsson BJ,
Crandall JR, Patrie J
Tolerance of the human leg and thigh in dynamic latero-medial
bending
I.J.Crash, 9, 6, pages 607-623, 2004.

16. Material & Methods
Dynamic 3-point Bending
Cross-Sectional Geometry from CT Scans
CT slice at mid-shaft Thresholding Import to CAD

17. Material & Methods
Approx. Bending Axis
Max Distance
cmax
Centroid
Dynamic 3-point Bending
Cross-Sectional Geometry from CT Scans
Area Moment of Inertia
Ixx

18. Material & Methods
Dynamic 3-point Bending
Moment of Fracture (Mfx), may be related
to geometric factors (Ixx/cmax) and the
“other” factors (Sfx) of the bone and it may
change during growth
Analysis of the geometric and material factors.

19. Results
Literature
Search
Reference Number of
Tests
Age Range
(years)
Typical Loading
Rate (m/s)
Loading
Direction
Geometry
Information?
Ouyang et al.
2003
10 2-12
0.008
(500 mm/min)
A-P No
Ouyang J, Zhu Q, Zhao W, Xu Y, Chen W, Zhong S
Biomechanical character of extremity long bones in children
Chinese Journal of Clinical Anatomy, 2003

20. Results
New Tests 10 Tests; Age 1.3 – 20 Years
Age
(years) Gender Aspect Loading
Direction* Flesh? Ixx (mm4) Cmax
(mm)
Mfx
(Nm)
20 M R M-L No 28247 14.9 533
4 F R M-L No NA NA 78.5
2 M R M-L No 1190.6 6.57 65.5
19 M L M-L No 28314 14.5 528
19 M R M-L No 26625 14.2 512
4 F R M-L No 2215.65 7.75 84.8
2 M L M-L No 1092.7 6.56 61.4
1.33 M R M-L No 814.28 5.78 61.7
4 F L M-L No 2001.3 7.55 69.1
4 F L M-L No 1577.9 6.86 75.5

21. Results
0 5 10 15 20 25
600
500
400
300
200
100
0
Age
(Nm)
M
fx
Mfx vs age

22. Results
section modulus vs. age
0 5 10 15 20 25
2500
2000
1500
1000
500
0
Age
(mm3 )
/c
max
I
xx
Rapid increase through skeletal development

23. 0 200 400 600 800 1000 1200 1400 1600 1800 2000
550
500
450
400
350
300
250
200
150
100
50
I
xx
/c
max
(mm3)
Mfx (Nm)
Geometric Component vs. Mfx
•Constant Sfx
•Dependent only on
geometry
Results

24. Results
Other components vs. age
0 5 10 15 20 25
500
450
400
350
300
250
200
150
100
Age
(MPa)
S
fx
Little change
early in life

25. Discussion
New Test
Kennedy et al. 2004
Kerrigan et al. 2004
Funk et al. 2004
Kerrigan et al. 2003
Ouyang et al. 2003
“Fracture Tolerance Related
to Skeletal Development and
Aging Throughout Life:
3-Point Bending of Human
Femurs”
International Research
Council on Biomechanics of
Injury (IRCOBI)
Conference on the
Biomechanics of Impact.
Dublin 2012
Fracture Moment vs. Age
800
700
600
500
400
300
200
100
0 10 20 30 40 50 60 70 80
0
Age
Mfx (Nm)

26. Discussion
Fracture Moment vs. Age
800
700
600
500
400
300
200
100
0 10 20 30 40 50 60 70 80
New Test
Kennedy et al. 2004
Kerrigan et al. 2004
Funk et al. 2004
Kerrigan et al. 2003
Ouyang et al. 2003
0
Age
Mfx (Nm)
Increase in femur bending
tolerance during skeletal
development
Due to changes in
bone geometry
Decrease in femur bending
tolerance during advanced
age
Due to combination of…
- Geometry (decrease in
cortical bone thickness)
- Material and Other Factors
(e.g., ultimate stress)

27. Conclusion
“The fracture moment of pediatric specimens
ranged from 24-85 Nm”
“The resulting dataset exhibited a rapid increase
in fracture moment throughout skeletal
development attributable to changes in the
cross-sectional bone geometry during growth”

28. Acknowledgements
• Whitaker International Scholars Grant
European Center for Injury Prevention (ECIP)
University of Virginia
Center for Applied Biomechanics