Total Hip Replacement - From Scan to Simulation

Computational simulation has become a key tool in Biomedical research. Its effectiveness relies on the ability to rapidly generate accurate patient-specific models. This study presents an example of the efficient conversion of 3D digital images directly into highly accurate, robust and analysis ready computational models. In this case a patient specific model of an implanted total hip replacement is generated from medical CT for in-silico evaluation of mechanical performance.

Characteristics:

  • Based on in vivo patient data
  • Segmentation tools to aid separation of multiple, interconnecting parts
  • Six structures meshed simultaneously with conforming interfaces
  • Inhomogeneous material properties assigned
  • Contact surfaces defined between stem-cement and head-cup
  • FE analysis performed directly on generated mesh using Abaqus® and Ansys

Image Processing

The subject of the study was a 42yr old male patient with a total hip replacement. A CT scan was performed using a Siemens Somatom 16. The resolution of the scans produced was 0.77x0.77x1mm. On import to ScanIP, the images were resampled, reducing computational cost while maintaining suitable model accuracy for the study. A metal artefact reduction filter was applied to reduce the image artefacts produced by the implant.

Mesh Generation

Robust, accurate meshing of the multipart segmentation was achieved using the Simpleware Freemesher. This gave smooth, conforming interfaces with high mesh quality. Contact surfaces were defined at the stem-cement and head-cup interfaces. Material properties were automatically assigned to bone from the CT images. Uniform material properties were assigned to the metal and cement components.

Simulation

The generated mesh was exported directly to both Ansys and Abaqus®. The stain response of the system to a static load was analysed. The influence of different interface conditions at the cup-implant and implant-cement interfaces were investigated, utilising the contact surfaces defined in the +FE module for rapid and repeatable model setup. The proximal and distal boundaries were fixed using node sets defined in +FE.

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