Analysis of titanium induced CT artifacts in the development of biomechanical finite element models

X-ray computerized tomography (CT) is capable of providing detailed information about the geometry and mineral density of skeletal structures. Such accurate data are of great interest in studying the effects of orthopaedic implants on bone adaptive behaviour in vivo. Metallic implants, however, generate artifacts, typically seen as starburst streaking. These artifacts can degrade the capabilities of CT images to provide accurate information about the geometry and mineral density of bone structures. The aim of this work was to investigate the possibility of developing finite element models (FEM) of the human femur after hip joint arthroplasty using CT images acquired directly after surgery. The capability of modern CT scanners to accurately reconstruct the cross-section geometry of titanium alloy hip joint prosthetic stems was primarily investigated. A new measuring procedure dealing with the geometry of real stems was developed and its accuracy assessed. Secondly, the artifacts generated by a prosthetic stem on the radiological density of the bone were analysed, and their effects on the assessment of FEM material properties were evaluated. Results showed that CT images provide accurate information on metal stem geometry. An average error of 0.45 mm was estimated in the reconstruction of stem cross-section geometry. Concerning bone density estimation around the implant, it was observed that the effect of metal artifacts on tissue density becomes zero at a distance of 2 mm from the implant.