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The most common reason for possible complications after total hip replacement (THR) surgery is improper positioning of the implant components within the hip joint. Systems for computer assisted planning and navigation during THR have been developed. However, these established modules focus on the acetabular implant component only; disrespecting the fact that proper implant functioning relies upon correct placement of both components relative to each other. Therefore, we developed an extension to the existing CT-based SurgiGATE-Prosthetics system (Medivision, Oberdorf, Switzerland) for planning and placing of the acetabular component to give the surgeon a tool, which can help him/her to also plan and insert the femoral implant. Preoperatively, the appropriate size and position as well as the orientation of both implants components were planned. Following navigated cup placement a dynamic reference base (DRB) was fixed to the thighbone and the registration procedure was executed. For the preparation of the femoral cavity a modular PPF rasp system (Biomet-Merck, Darmstadt, Germany) was developed. All surgical action was visualised graphically within the patient’s image data. In addition, the surgeon was provided with real-time information about the depth of tool insertion, antetorsion angle, varus/valgus deviation, and the postoperative change in leg length and lateralisation of the hip joint. After extensive validation and accuracy analyses performed on plastic models the presented system was used during one operation. An extended clinical study is currently being started. We expect that the developed application will help the surgeon to better plan the appropriate size and position of the both parts of a hip endoprosthesis and will supply intraoperative feedback of the position of the surgical instruments relative to the patients’ anatomy and to the preoperative plan. Safer and more accurate placement of the implants components during free-hand THR surgery may be expected from this technology.
