Abstract
Introduction: In 1991 Berufsgenossenschaftliche Unfall-klinik Frankfurt am Main, Germany and Integrated Surgical Systems (ISS) in Sacramento, the developers of ROBODOC& #61650; established first contacts. Since that time, while studies in the United States were still going on the transition of ROBODOC& #61650; 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& #61650; 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& #61650; ROBODOC& #61650; creates a cavity for the implant according to the preoperative planning. The use of ROBODOC& #61650; 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& #61650; 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& #61650; 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& #61650; 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& #61650;-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& #61650;-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& #61650;. 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: Exclusion criteria for the use of the pinless system are severely disfigured post-traumatic cases, revision cases and cases with a non-titanium implant in the opposite leg because there are too many metal artifacts in the CT scan. We have seen no problems using the pinless system on patients with a cementless titanium implant in the opposite leg. There were cases in which the planned implant and the postoperative result showed some difference – mainly as a lateral or medial shift of the implant. We could identify an undetected bone motion and or poor verification as the cause of that shift. As a result several modifications were made to the system and a new system to measure bone is under development. The verification software has been changed so that a bad verification cannot be accepted anymore by the surgeon by mistake.
In revision cases the average age of patients with a cemented implant at time of revision was 65.5 years, with a cementless implant 53.9 years. The average time between primary THR and revision THR was 9.5 years for the cemented group and 7.5 years for the cementless group.
Intra- / postoperative complications were dislocation in 1 case, thrombosis / embolism in 1 case, fracture of the greater trochanter in one case and infection in two cases.
Conclusions: The major advantages of the pinless procedure are that only ONE operation is needed. It provides greater scheduling flexibility for the patient and the surgeon. Postoperative knee pain is eliminated in most cases. The costs per surgery are reduced. The surgical time and radiation exposure is the same as in the pin-based system. The system accuracy and reliability are equal to the pin-based system if the system is used properly. As we are using a spiral CT for the pinless cases, the radiation exposure is not higher than for the pin cases. The advantages of using ROBODOC& #61650; for revision THR are obvious. Optimized preoperative planning of the procedure is possible, the anteversion can be corrected, the fibrous membrane and sclerosis in the cavity are being removed by the cutter. The duration of the operation is greatly reduced compared to the traditional method of removing the bone cement manually. There is no risk of intraoperative fractures. A loose uncemented prosthesis can be replaced as well as a loose cemented implant. Postoperative weight bearing can be allowed immediately. The system has proved to be a great progress compared to the traditional method of Revision THR although a few hardware and software changes are still necessary. In December 2000 a new round of clinical trials was started in the U.S. for FDA approval of the pinless procedure. The first successful THR using the ROBODOC pinless-system in the U.S. was performed at Sutter General Hospital by Dr. Bargar in December 2000. This gives hope that the FDA approval will be on its way within the next year.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
