Automated Preoperative Planning of Femoral Component for Total Hip Arthroplasty (THA) from 3D CT Images

The present paper describes a method for 3-dimensional (3D) automated preoperative planning of the femoral component (stem) in total hip arthroplasty (THA). Stem planning is formulated as a problem to determine the optimal parameters of position, rotation, and stem size, based on 3D surface models of host bone reconstructed from CT images, which includes the femur and femoral canal. An objective function that represents the fitness between the femoral canal and stem surfaces is defined. We also defined positional and rotational constraints derived from previous studies on femoral anatomy. Maximization is performed by the Powell method using initial values equally sampled within the possible solution space. We obtained parameters that maximize the objective function by exhaustive adjustment of the parameters. We applied the proposed method to 17 cases, and the proposed method was experimentally evaluated according to differences between planning results of the automated system and those of an experienced surgeon. Preoperative planning was also performed by a surgeon to evaluate performance of the automated system. The difference in stem size was less than 1 size in all cases, and the surgeon agreed with the planning results of the proposed method in 14 cases. In those 14 cases, mean errors of position and orientation were 3.2 mm and 4.6 deg., respectively. The proposed method thus appears applicable in preoperative planning of the stem.