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.

In the framework of the modiCAS (Modular Interactive Computer Assisted Surgery) Project, which emerged from a collaboration of the University of Siegen and the University of Frankfurt in the fields of mechatronics and medicine, the development of a modular system to assist the surgeon during the whole planning and operation procedure has been started. A completely new realization of a planning system for bone surgery and alloarthroplasty is presented. Characteristics of the new system are generic interfaces for navigation, robotics and real-time data acquisition, graphic interactivity, documentation of each planning-step, a flexible wizard-guided concept and adaptable teaching modes. The system can be configured to any data source such as X-ray, CT, MRI, US with individual calibration. For planning, the data sources can be merged in any user defined way. In contrast to all existing planning systems the presented system can optionally be linked to navigation and robotic systems.

The software was realized to run platform-independent on any personal computer surrounding. We used commercially available software libraries for computer graphics and graphical user interface programming. The whole system consists of several modules which are closely linked together and support all major pre- and intraoperative steps of surgery. The user interface remains the same during the planning and the intervention. Preoperative planning is carried out on a totally new planning station comprising an interactive and intuitive graphic interface, while intraoperative features include interactive matching procedures, true real-time-capability and incorporation of navigation and robotics.

Initially we realized modules to support total hip allo-arthroplasty. The first application of the system is for a clinical trial on total hip alloarthroplasty. Planning is performed on the basis of radiographs and CT-datasets. Intraoperatively a navigation system and a robotic surgery system are used. Preliminary results show very precise and reproducible plannings that could be achieved in short time without special training of the clinician. Furthermore the unlimited intraoperative access to the whole planning dataset appeared to be very convenient to the surgeon because it allowed immediate response to unforeseen patient specific situations.

Future adaptations of the universal planning system will be total knee alloarthroplasty, spine surgery and trauma surgery. The existing system can easily be configured to any surgical procedure because the same basic functionality is used for all applications and only special configurative datasets have to be generated for each application.

The open architecture of the system enables easy integration of further input or output devices, an easy adaptation to different interventions, planning styles and operative techniques is possible.