Finite element simulation of locking compression plates for femur fracture treatment under different boundary conditions
Jalali J, König B, Wittkowske C, Nolte A, Eder M, Raith S, Volf A, Kovacs L
Objective: The incidence of femoral shaft fractures is reported as being 1 per 10,000 people. This rate increases to 3 per 10,000 people in male individuals younger than 25 years and elderly patients, above the age of 65 years. The locking compression plate (LCP) is a common tool in the treatment of femoral shaft fractures. In osteoporotic patients, stable fixation of the plate can be a challenge since the bone often lacks the desired stability. This may lead to a high complication rate due to the loosening of screws or breakage of the implant.
Method: Finite element simulation is a powerful method to predict the effects of varying parameters which cannot be easily varied in a laboratory environment. In this project, which is funded by BMWi, an automated workflow was developed to support surgeons in their decision of the appropriate implant dimensions and where to place the screws in order to achieve an optimal fracture healing and to prevent implant failure after a femoral shaft fracture. This workflow has been used for the simulation of a non-osteoporotic 22-year old female and a 68-year old male with osteoporotic bone. A virtual transverse femoral shaft fracture with a gap of 3 mm was created using the software Blender (Blender Foundation). The exact geometry of a distal femur LCP was provided by Synthes (Synthes GmbH) as triangulated surface data.
CT data were imported into the software Mimics (Materialise) and used for patient specific modeling of the inhomogeneous material properties of bone. Hounsfield Units (HU) were exported and assigned to elements of a finite element mesh. HU of bone were correlated with mechanical properties such as the Young’s modulus. A linear finite element analysis was performed with ANSYS Classic (Ansys Inc.).
Results and conclusion: The boundary conditions are one of the most important parameters influencing the outcome a of finite element simulation. Three different loading situations which all model the physiological loading following surgery were compared.
- Force application from distal
- Force application from proximal
- Forces derived from a muscoskeletal model using the software AnyBody (AnyBody Technology A/S)
With this workflow monocortical and bicortical screw fixations were compared in variable positions to determine biomechanical effects. The optimal screws position in terms of interfragmentary movement was validated among different variations.
This workflow has also the potential to be used in other anatomical regions.
Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2014). Berlin, 28.-31.10.2014. Düsseldorf: German Medical Science GMS Publishing House; 2014. DocWI60-1328
doi: 10.3205/14dkou441 , urn:nbn:de:0183-14dkou4411
Published: October 13, 2014
© 2014 Jalali et al.
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