EUROPEAN EXPERIENCE WITH AN OPERATIVE ROBOT FOR PRIMARY AND REVISION TOTAL HIP – A SUMMARY OF MORE THAN 3800 CASES AT BGU FRANKFURT

Abstract

Introduction: In 1991 Berufsgenossenschaftliche Unfall-klinik Frankfurt am Main, Germany and Integrated Surgical Systems (ISS) in Sacramento, the developers of ROBODOC established first contacts. Since that time, while studies in the United States were still going on the transition of ROBODOC to Germany was initialized. In 1992 the first successful robotic THR was performed at Sutter General Hospital in Sacramento, California. While there was still no FDA approval for the system in the United States, the first successful robot-assisted total hip replacement using a 3 pin-based system was performed at BGU Frankfurt in August 1994. Preoperatively three titanium pins had to be implanted in the greater trochanter and the medial and lateral femoral condyle. Afterwards a CT- scan is taken, the CT data is loaded into the preoperative planning station ORTHODOC and the implant can be planned using three-dimensional CT data. The planning data is saved on a transfer tape and loaded into the ROBODOC ROBODOC creates a cavity for the implant according to the preoperative planning. The use of ROBODOC for total hip surgery has become a standard procedure at BGU. OR-time went down to an average of 90 minutes per case and it was also possible to change the system from 3 to 2 pins, which not only helped to save a considerable amount of time during surgery but also reduced the postoperative knee pain in our patients. In 1998 the Pinless System was introduced. Instead of using pins a 3-D-surface model of the proximal and distal femur is created that is matched intraoperatively with the actual bone. Clinical relevance: The advantages of the ROBODOC system are well known nowadays. The robot guarantees precise transformation of the preoperative plan during surgery. Femur fractures, a common complication in cementless total hip replacement, can be avoided. ROBODOC proved to be a reliable and safe technology that can be handled by a trained surgeon without permanent on-site support. Materials and methods: By March 2001 more than 3800 robot-assisted primary and revision THRs have been performed at BGU Frankfurt. The results we have found in those 3800 patients were supported by a dog study at the Small Animal Clinic in Auburn, Alabama that was performed in 1995 comparing a ROBOT GROUP to a HANDBROACHED group of male greyhounds. There were no fractures found in the ROBODOC GROUP, no nerve palsies were found, the gait analysis was superior and there was closer alignment of the prosthesis to strong cortical bone. The ROBODOC-System contains a REVISION SOFTWARE which enables to plan and execute total hip revision surgery with ROBODOC&#61650. The greatest problem in Revision THR is the complete removal of bone cement without damaging healthy bone structures. In many cases the transfemoral approach is the only way to completely remove all existing bone cement. Postoperatively weight bearing is not allowed for 6 – 8 weeks. Using the ROBODOC-Revision-System two titanium pins need to be implanted preoperatively as there is no femoral neck left that could be used for surface matching. The next step is to take a CT scan of the femur and the data transfer to ORTHODOC. The program uses a special technique to enhance the CT images so that all existing bone cement in the cavity and around the old prosthesis is clearly visible and can be distinguished from bone structures. Besides, metal artifacts caused by the existing prosthesis are minimized. four points of interest are marked: Top of implant, top of bone, base of implant and base of cement. A cutting path can be planned to remove all the existing bone cement. The next step is the planning of the new prosthesis. The prosthesis can be adjusted in any direction until a satisfactory position is reached. Intraoperatively, after the pin finding procedure, the robot mills out the existing bone cement and creates a new cavity for the planned implant. The surgeon now implants the new prosthesis. Results: Ex