1. No category

CAD-BONE: Patient-specific prediction of
fracture risk and evaluation of bone
healing for realistic 3D oblique fractures
M. A. Pérez*, J. Alierta ♦, M. Remacha*, B. Seral-García♣, J. M. García-Aznar*
*Department of Mechanical Engineering, University of Zaragoza
♦ Ministry of Defense, Zaragoza, Spain
♣ Orthopaedic
Surgery, Lozano Blesa University Hospiltal, Zaragoza, Spain
Motivation: Why CAD-BONE?
Patient-specific predictions for bone treatments
http://cadbone.unizar.es/
Integration of patient-specific modelling, musculoskeletal
loading and simulation of adaptive bone remodeling
Motivation: Why CAD-BONE?
• CAB-BONE
project:
Patient-specific
predictions
for
bone
treatments
cadbone.unizar.es
Overview
o Motivation: Why CAD-BONE?
o Patient-specific predictions of the femoral fracture risk
o Bone healing on 3D oblique fractures
o Acknowledgements
Patient-specific predictions of femoral fracture
o Every year in Spain there are more than 70.000 hip fractures [1]
o Worldwide incidence of hip fractures in 2000 was estimated at 1.6
millions, and predictions for 2050 indicate 6.26 millions [2]
o Hip fracture is now a major cause of morbidity, mortality and
disability representing a significant economic cost
Can we predict of the
femoral fracture risk?
[1] Herrera et al. (2006); [2] Johnell and Kanis (2006)
Patient-specific predictions of femoral fracture
o Many studies focused on femoral fracture risk prediction using finite
element method [1,2]
o Real femur geometries with a limited number of patients [3]
Development of a 3D parametric model
of the proximal femur
CAD-Model
Abaqus
Density distribution
[1] Schileo et al (2014); [2] Munckhof and Zadpoor (2014); [3] Bessho et al (2009)
Parametric FE model
CAD-Model
Abaqus
Model parameters:
ND – neck diameter
HD – nead diameter
NL – neck length
OFF- distance of head center from femur axis
NSA – angle between femur and neck axis
AA – anteversion angle
Parametric FE model
Bone material properties
MIMICS
Real femurs segmentation
In order to quantify bone
material properties
Bone density
parametrization based
on the femur geometry
Hounsfield Units -> Bone density distribution
Parametric FE model
Bone material properties
MIMICS
Bone density
parametrization based
on the femur geometry
Hounsfield Units -> Bone density distribution
Model Validation: Real vs. Parametric
Real Stiffness (N/mm)
Evaluation of the real and parametric stiffness under a vertical load
Comparison of the bone density distribution between the real and its
corresponding parametric FE model: %Bone volume under a certain density
range
2500
2000
1500
y = 1,2203x - 343,77
R² = 0,978
1000
500
0
1000
1200
1400
1600
1800
Parametric Stiffness (N/mm)
[1] Schileo et al (2008)
In conclusion:
o Generic FE parametric model of the proximal femur
o Patient-specific prediction of fracture risk
2000
Overview
o Motivation: Why CAD-BONE?
o Patient-specific predictions of the femoral fracture risk
o Bone healing on 3D oblique fractures
o Acknowledgements
Bone healing on 3D oblique fractures
o
Every year thousands of oblique fractures happen (Randsborg et
al., 2013)
o
The most common treatment for these fractures is mechanical
fixation using implants, such as nails, plates, …
Can we predict the
healing outcome of
oblique fractures?
Phenomenological approach
o
Cohesive Elements
t: Stress vector with three components
tn (normal direction)
ts (shear direction)
tt (shear direction)
ε: Strains vector
δi: Separation in the i direction
h: Original thickness of the element
εn =
δn
h
,ε s =
δs
h
,ε t =
t n  K nn
 
t = ts  =  0

t   0
t 
0
K ss
0
0  ε n 
 
0  ⋅ ε s  = K ⋅ ε

K tt  ε t 
K: Stiffness matrix
δt
h
More details Alierta et al. 2014
Phenomenological approach
o
Definition of the main state variable
α (union degree)
α = 1: Totally successful bone healing
α = 0: Completely non-union or malunion
o
ti = K0i ⋅ α ⋅ ε i
i = n, s, t
K0i : Linear stiffness in a completely healed fracture gap along the direction i
More details Alierta et al. 2014
Phenomenological approach
o
Biological union (α ↑ ): Indirect healing
α= αc (cartilage) + αb (bone)
Immature
callus
Mature
callus
More details Alierta et al. 2014
Phenomenological approach
o
Biological union (α ↑ ): Direct healing
α= αb (bone)
More details Alierta et al. 2014
Phenomenological approach
Parameter
Mc
Maturation time for cartilage (days)
Value
4a
Mb
Maturation time for bone (days)
10b
αcmax
Maximum value of αc
0.3b
αbmax
Maximum value of αb
0.7b
tc
Cartilage formation time (days)
36b
th
Total healing time (days)
60c
Compression strain limit for cartilage formation
Compression strain limit for bone formation
- 0.6b
𝐿𝐿𝑠𝑠ℎ
𝑐𝑐
Shear strain limit for cartilage formation
0.25b
Shear strain limit for bone formation
Initial linear stiffness (MPa)
0.15b
ε0i (i=n,s,t)
εci (i=n,s,t)
Maximum strain at the linear region
0.3b
Maximum allowed strain
1b
𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐
𝐿𝐿𝑐𝑐
𝐿𝐿𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐
𝑏𝑏
𝐿𝐿𝑠𝑠ℎ
𝑏𝑏
K0i (i=n, s ,t)
- 0.25b
50d
a
Park (1998)
Estimated
c
Klein et al. (2004)
d
Bishop et al. (2003)
b
More details Alierta et al. 2014
Bone healing on 3D oblique fractures
o
A patient (male, 1.70m and 76 kg) presented a fracture in the right fibula and tibia,
which was treated with an intramedullary nail (8 mm diameter cannulated
EXPERTTM nail of 330 mm length)
Bone healing on 3D oblique fractures
o
FE Model (MIMICS and 3-Matic)
Ti-6Al-7Nb
E=114 GPA
ν= 0.3
Duda et al. 2001
Duda et al. 2001
Bone healing on 3D oblique fractures
o
FE Model
60% Medial
40% Lateral
• Locking bolts
• MPC (Multi-point
Constrains)
• Nail-bone friction
coefficient
µ=0.3
(Rancourt et al. 1990)
Bone healing on 3D oblique fractures
o
Simulated configurations
Bone healing on 3D oblique fractures
o
Union degree, α
Manufacturer
Specifications
Clinical
Evolution
Bone healing on 3D oblique fractures
Static
t= 0 days
t= 60 days
Dynamic
t= 0 days
σynail= 800 MPa
(Niinomi, 1998)
t= 60 days
In conclusion:
o Practical application of a FE-based phenomenological
model
o Help for surgeons to choose the most suitable
configuration to stabilize one patient specific oblique
fracture
Conclusions and Future Research
• CAB-BONE
project:
Patient-specific
predictions
for
bone
treatments
cadbone.unizar.es
Acknowledgements
o Spanish Ministry of Economy and Competitiveness through
research project DPI2011-22413
cadbone.unizar.es