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.

Objectives: A surgical robot (ROBODOC®) is used for total knee replacement. The same system has been in clinical use for total hip replacement at BGU Frankfurt since 1994 and since March 2000 TKR is another clinical application. The presentation intends to give an overview of the system and of the first experiences in clinical use.

Background: The outcome of conventional total knee replacement has always been very dependent on the surgeon’s individual skills and routine. The most common mistakes have been malpositionings and malrotations of the prosthesis, which postoperatively caused varus and valgus malalignments of the lower limb resulting in an incorrect mechanical axis.

The system permits a three-dimensional pre-operative planning of the correct axis and rotation as well as the correct implant size. The introperative cutting is entirely executed by the surgical robot according to the preoperative planning.

Design / Methods: The ROBODOC® Surgical Assistant System consists of three major components: The pre-operative planning workstation called ORTHODOC®, the surgical robot and the robot control unit that receives the preoperative planning data and controls ROBODOC®. Presently, four titanium pins have to be implanted at the beginning of the procedure, one in the proximal femur, one in the distal femur, one in the proximal and one in the distal tibia. These pins are the landmarks for the following procedures.

A CT scan is made of the femoral head, the distal femur and the proximal tibia including all the pins and the ankle. A rod is laid on the patient’s leg to detect the motion during CT scan. The CT data is being transferred to the ORTHODOC® workstation on an optical disk. The ORTHODOC® displays three orthogonal cross-sections of the bone on a high-resolution screen. A manipulation on one of the cross-sections is shown in nearly real-time on the other two cross-sections.

The first step is to find all the four pins on the CT scan and to check their position. The next step is to create a femoral and tibial axis using four markers (i.e. proximal and distal femur and proximal an distal tibia). The bone is then aligned along the axis. Once those steps have been performed and implant can be selected from an implant library. The femoral component is the first part of the planning. Once the correct size, alignment and rotation have been found the tibial component is added and adjusted. The final step is to select the tibial liner.

Once the planning is finished a synthetic x-ray can be created which shows the postoperative result and helps to determine if the correct axis was planned. After finishing the planning a transfer tape that can be loaded into the ROBODOC® is created. The patient’s leg is positioned using a special leg holder and thigh support plate.

The patient’s knee should be flexed to an angle of approximately 70 to 80 degrees, a gap of 1 to 2 mm should be achieved. The patient is prepared and draped in the normal manner. Surgery proceeds normally and the regular approach for TKA is used. Once the exposure is finished and the four pins are clearly accessible, two Steinmann pins are inserted, one in the femur and one in the tibia. The Hoffmann II Orthopedic Fixation System is used to connect the two Steinmann pins and to distract the knee joint.

Now the robot is moved to the OR table. The femur and the tibia must be rigidly fixated to the robot base. Following this two bone motion monitors are attached to the bone, one to the femur and one to the tibia.

The registration program is started. Using ROBODOC®’s ball probe the four pins have to be located, including the use of pin extenders so that the robot can find the patient’s position on the OR table by comparing the data to the preoperative CT data of that particular patient. First the femoral pins are found, then the tibial pins. If the registration is correct the cutter can be installed, the irrigation system is connected and the robot starts cutting the surface for the planned implant.

First the femur is prepared, then the tibia. The final cut is the cruciform in the tibia for which a special cutter is required. Should bone motion occur during any part of the cutting procedure the robot will stop and the pins have to be re-registered. Once the cutting is finished, the robot is moved away from the OR-table, the pins and fixators are removed an the surgeon inserts the planned implant manually – normally using the cementless tecnique. The surgery is finished the traditional way.

Fifty patients who had received total knee replacement using the ROBODOC® System were followed up and examined using a pre-defined protocol: 23 patients were male, 27 were female. All cases showed severe signs of osteoarthrosis. In 35 cases we saw a varus deviation, in 13 cases a valgus deviation, in two cases there was no deviation from the axis. four patients were post-traumatic cases, in one case a complex osteotomy had been performed.

In 38 patients the cementless technique was used, in eight cases the tibial component was cemented and in four cases both components were cemented due to poor bone quality.

We had an obvious learning curve, OR time went down from 130 minutes for the first procedure to 90 minutes average OR time. Due to the three-dimensional pre-operative planning of the correct axis and rotation we saw a good alignment of the femoral and tibial component in all cases. Besides the optimal size of the components could be selected for the patients in this group.

Results/Conclusions: The system permits a three-dimensional pre-operative planning of the correct axis and rotation as well as the correct implant size. Due to the exact cut surfaces the cementless technique can be used in the makority of cases. The patients are permitted full weight bearing immediately postoperatively. None of the templates or tools that are needed for manual TKR are necessary when the ROBODOC® system is used which means an immense reduction of surgical tools for that procedure. The OR-time is not significantly longer compared to traditional TKR.

The surgeon has total control of the procedure at all times and the procedure can be finished manually if necessary. Correct aligment and rotation are the known preconditions for durability in TKR. The present disadvantages of the system are soft tissue management including ligament balancing, the rigid fixation and the use of pins (markers).

By June 2001 about 280 surgeries have been performed using the system. The development of a pinless system is already on its way and clinical testings are abour to start at BGU Frankfurt.