[Computer-assisted prosthesis selection and implantation control]

Using CT-based 3D-data of human femora, it is possible to simulate the THR very realistically by a newly developed fit program. The evaluation of OP simulations of different prostheses systems on more than 200 femora showed that a large number of hip joints can only be reconstructed unsatisfactorily by standard stems regarding intramedullary fit and joint geometry. This could be minimized by optimized off-the-shelf prostheses, but there is still a remainder that can only be satisfactorily reconstructed by customized devices. The decision of choosing a standard or custom device for each individual case can be made by the same fit program using CT-data of the femur. Planning with conventional X-rays only shows major restrictions. With the results of our evaluation, "standard stems" have been developed respecting the fixation principles of our CTX-custom device system and with optimized head positions using statistical methods. The selection of the right size regarding the criteria of fixation and joint geometry is examined preoperatively with the help of the same fit program. If standard prostheses cannot fulfill the requirements, we see the indication for a custom-made stem. In this way the quality of custom-made prostheses can be transferred to the application of standard devices. The operative results confirm our expectations of the exact planning and implantation technique. The CTX combination system consisting of off-the-shelf stems and customized devices will reduce the costs for optimized techniques. In comparison with other new 3D-methods like robotics or navigation, our development has an advantage: this technology including the fit program is accomplished preoperatively in order to simplify the operative technique. In future, combinations of our advanced planning methods as well as implantations of custom prostheses using navigation systems and/or robotics seem to be possible and may be helpful for special cases.