Optimization Technique and FE Simulation for Lag Screw Placement in Anterior Column of the Acetabulum

Abstract

This paper presents an optimization technique for determining the lag screw placement in the anterior column of the acetabulum, and investigates new method for generating accurate finite-element (FE) model for biomechanics analysis. For prepare once measure, an accurate hemi-pelvis model is reconstructed from the volume-of-interest extracted from computed-tomography (CT) data, and the initial position of the lag screw is determined by traditional manual like method. Then, an objective function, for improving the placement of lag screw, is build by adaptive sampling the weighted distance of screw to the acetabulum boundary according to surgical requirement, and the two end points of the lag screw are modified iteratively to reduce the objective value. 30 hemi-pelvis models are tested by the optimization technique, and the statistical measure data are provided according to new anatomic reference landmarks for clinical use. In the second part, FE method is employed to evaluate the optimization result. To generate accurate and high quality FE model, a semi-automatic FE preprocessor specifically adapted to the pelvis anatomy is developed. The produced volume mesh has a very regular mesh structure and achieves a smooth change of element size transition. The final simulation stress distribution pattern justifies the placement of the lag screw in the anterior column of the acetabulum.