Robot milling system integrated design and finite element analysis of custom femoral prostheses

The long-term stability of cementless femoral prostheses is primarily affected by aseptic loosening, micromotion, and stress shielding, all of which are related to the force transfer of the prosthesis. These factors can compromise the osseointegration of the proximal prosthesis, leading to aseptic loosening within the femoral cavity. Due to the individual variability of the femur, the fit between the prosthesis and the femoral cavity during the design phase may differ from the fit achieved during the surgical procedure. Consequently, the force transfer of the prosthesis postoperatively may not align with the results obtained from finite element analysis conducted during the design phase, making it challenging to control the micromotion and stress shielding of the prosthesis. The design model of a custom femoral prosthesis is based on the CT reconstruction of the patient' femur. The fit of prosthesis within the femoral cavity during the design phase should match the fit during the surgical operation. Consequently, the results of finite element analysis conducted during the design phase can be used to control the force transfer of the prosthesis postoperatively. This approach helps to prevent improper micromotion and stress shielding of the proximal prosthesis, which can compromise the primary stability of the prosthesis within the femoral cavity, thereby facilitating the osseointegration of the proximal prosthesis.This paper proposes a novel technology that combines the design, finite element analysis, and manufacturing of custom prostheses. Specifically, a CAD/CAM/robot integration method is used to fabricate these prostheses. This innovative technology not only enhances the control of force transfer in custom prostheses but also reduces design and manufacture time while lowering costs. In conclusion, the finite element analysis of the custom prosthesis effectively manages force transfer, and the milling errors associated with the custom prosthesis are less than 1 mm.