effects of implant stiffness on bone resorption and stress shielding
DESCRIPTION
Femur ImplantTRANSCRIPT
Studying the effects of Implant stiffness on bone implant interface failure and bone remodeling
B.Tech ProjectbyMohit Raut11ME33021
INTRODUCTION
Femur Bone
• Longest, Strongest and the heaviest bone in the
human body
• In most of the daily activities such as running,
jumping etc. , entire weight of the body is
supported by the femur
• It contains two distinct morphological types of
bone namely ,Cortical and Cancellous
FEM Model
FEM-model developed from X-ray scans of femur prosthesis.
Bone and implant are modelled using PLANE183 element, a higher order 2-D, 8-node element with quadratic displacement behaviour
Cortical Bone (purple) has E=7Gpa.
Cancellous Bone (red) has E=1Gpa.
Bone and implant interface contact is defined by CONTA172 and TARGET189 elements in ANSYS.
FAILURE CRITERION
• Finding Bone Implant Interface Failure by Hoffman number (FL).
• Lower the FL, less the probability of failure. FL is calculated for each interface node
(Hoffman, 1967)
BONE REMODELING
Bone has the capability to adapt its structure (external geometry and internal
structure) in response to change in mechanical loading by bone apposition
(formation) and bone resorption (loss)
(Weinans et al 1992)
BONE REMODELING
BONE REMODELING
Finding change of density (bone remodeling) for each element:
BONE REMODELING
Density considerations and Relationship between density and Young’s modulus:
(Zhang et al 2010)
FORCE CALCULATIONS
FLOWCHART OF BONE REMODELLING
RESULTS Maximum Node Interface Stress before remodeling occurs. Stress shielding due to high stiffness visible
0 20 40 60 80 100 1200
2
4
6
8
10
12
14
16
YOUNG'S MODULUS vs MAX INTERFACE STRESS
YOUNG'S MODULUS in GPA
MAX
INTE
RFAC
E ST
RESS
in M
Pal
RESULTS Average change in density for elements after one time step. Bone resorption increases with stiffness.
0 20 40 60 80 100 1200
1
2
3
4
5
6
YOUNG'S MODULUS vs ∆ρ (% of initial value)average(for 1st time)
YOUNG'S MODULUS in GPA
∆P A
VERA
GE(fo
r 1st
tim
e)
RESULTS
Maximum Hoffman number (FL) was calculated for three time steps for implant with 36 GPa(flexible) and 110 GPa (titanium) for each interface node.Probability of failure increases with time due to bone remodelling.
1 2 3 40
2
4
6
8
10
12
14
7.29
9.5
11.2
12.3
4.16
5.46.3
7.1
Hoffman Number vs Loop Number
FlexibleTitanium
Loop Number
Hoffm
an N
umbe
r
CONCLUSIONS
• Bone Resorption increases the chances of the bone-implant interface failure as Hoffman Number (FL) increases after
each time step.
• Bone Resorption increases as stiffness of implant is increased.
• Flexible implants should be used in young patients who have higher bone density than older people
Thank You