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ESB 2013 Talk, 27 August 2013, Patras
Transcript of ESB 2013 Talk, 27 August 2013, Patras
How to build a femur model that is physiologically more accurate for finite element analysis purposes?
An intramedullary telescopic skeletal distractor: CHIVI version 0.x
Rıza Bayoglu, Fethi Okyar
Biomechanics Research Laboratory
Faculty of Engineering
19th European Congress of Biomechanics
25-28 August 2013 Patras, Greece
Finite-element analyzes conducted in the ADINA suite yield important information pertaining to the mechanical behavior of the prototype such as
the load transfer path, and strain distribution across system components
However, the accuracy of these results directly depends on how well the model, including the material properties, loading and boundary conditions, simulate the in-vivo setting in which an implanted nail will operate during its lifetime.
LOADING & BOUNDARY CONDITIONS
GEOMETRY & OTHER CONSIDERATIONS
Static coefficient of friction at the cortical bone-implant (Ti-6Al-4V) interface is taken as 0.3 [Nuno et al.]
Three major contributions
Bergmann et al (2001)
Heller et al (2005)
Spiers et al (2006)
constrained hip movement
What about the
"residual" reaction force at the newly added hip constraint?
How do we measure "more phsyiological"?
Optimizating muscle attachment locations so as to give minimum residual force at the hip constraint will consistently yield a physiologically more realistic femur model
The effect of optimization on the residual force
A decrease in the residual force by
11.1% (rigid-body), and 17.8% (deformable)
was obtained. Good for starters!
The effect of optimization on the implant design
The new muscle attachment locations are also tested on a bone-implant construct with three interlocking pins:
The effect of changing the location of the knee center
The center of the knee joint is accepted to lie within the intercondylar fossa. Why not to including that in our optimization?
As a first trial, we just try another point on the intercondylar fossa at a distance of 10 mm to the original.
Next candidate to be optimized: the knee-joint center
This point was found to contain a suitable degree of modeling uncertainty. We could shift it by 15 mm in the medial direction and still keep it within the intercondylar fossa region.
The residual reaction force was used as a modeling metric to be minimized.
An optimization procedure was led to minimize this metric by manipulating modeling uncertainties.
By minimizing the residual by 80%, the released load was then overtaken by the nail, leading to a stress increase of 44%.