A Subject-Specific Finite Element Model of Tilting Bone Anchor

A subject-specific finite element model was developed to simulate the complex mechanical interaction between a nonsymmetrical tilting anchor and bone. A heterogeneous voxel-based bone model was reconstructed from quantitative computed tomography (QCT) images of a human cadaveric humeri specimen. An anchor pull-out test was then performed on the same bone specimen, and the ultimate force of suture breakage, as well as the final radiographical configuration of the anchor inside the bone were recorded. In the finite element model, the bone was assumed to be an elastoplastic material with large deformation capability and strain-hardening behavior in the plastic region, and the anchor as a rigid material. A comparison of the model predictions with the results of the pull-out experiment indicated a very good agreement. At the ultimate pull-out force of 324 N, the model predicted a rotation angle of 53.8 degrees and an eyelet-to-bone surface distance of6.9 mm, which were close to the experimental results of 55.2 degrees of rotation and a 6.7 mm distance. It was concluded that the model could successfully simulate the complicated mechanical interaction between the anchor and bone, and provide a valuable tool for design optimization of the tilting anchors.