Aseptic loosening is the primary cause of cementless femoral
prosthesis failure and is related to the primary stability of the cementless femoral
prosthesis in the femoral cavity. The primary stability affects both the osseointegration and the long-term stability of cementless femoral
prostheses. A custom cementless femoral
prosthesis can improve the fit and fill of the
prosthesis in the femoral cavity and decrease the micromotion of the proximal
prosthesis such that the primary stability of the custom
prosthesis can be improved, and osseointegration of the proximal
prosthesis is achieved. These results will help to achieve long-term stability in
total hip arthroplasty (THA). In this paper, we introduce an integrated CAD/CAM/robotic method of milling custom cementless femoral
prostheses. The 3D reconstruction model uses femoral CT images and 3D design software to design a CAD model of the custom
prosthesis. After the transformation matrices between two units of the robotic system are calibrated, consistency between the CAM software and the robotic system can be achieved, and errors in the robotic milling can be limited. According to the CAD model of the custom
prosthesis, the positions of the robotic tool points are produced by the CAM software of the CNC machine. The normal vector of the three adjacent robotic tool point positions determines the pose of the robotic tool point. In conclusion, the fit rate of custom pig femur stems in the femoral cavities was 90.84%. After custom femoral
prostheses were inserted into the femoral cavities, the maximum gaps between the
prostheses and the cavities measured less than 1 mm at the diaphysis and 1.3 mm at the metaphysis.