42 Robotics
J. Bellemans
Summary
Today there is growing evidence that performing total knee arthroplasty using computer navigation can lead to a more accurate surgical positioning of the components and subsequent alignment of the knee prosthesis, com- pared with when a conventional operating technique without computer assistance and navigation is used.
These computer navigation systems are readily available and are being used more and more in daily practice.
The use of robotic technology could theoretically take this accuracy one level further, since it uses navigation in combination with ultimate mechanical precision, which could eliminate or reduce the inevitable margin of error during mechanical preparation of the bony cuts by the surgeon. In this chapter we report the experiences gained so far with robotic technology in knee arthroplasty surgery.
Introduction
The introduction of robotic technology into orthopedic surgery dates from the late 1980s and led to the first ro- bot-assisted hip replacement performed on a human pa- tient in 1992, with subsequent commercialization of the system in 1994 under approval of the European Union [1].
Although most of the initial research and development was performed by schools and centers in Germany, the enthusiasm has since spread out not only over the whole European continent,but also over North America and the rest of the world. Today, for example, robots are used not only in hip arthroplasty but also in knee arthroplasty and cruciate ligament surgery, with different commercial sys- tems available.
Generally speaking, robots can be categorized as pas- sive,active,or semiactive.Passive robots hold the guide or jig in the correct place, but the actual cutting or drilling is performed by the surgeon or the operator.Active robots not only hold the cutting tool; they also autonomously make the appropriate cuts. Semiactive robots combine both principles,whereby the robot guides the cutting tool within a predefined trajectory (e.g., a plane on the proxi-
mal tibia), within which the surgeon can work under the constraints provided by the robot.
Although a number of groups are now exploring the potential role of semiactive robots in knee arthroplasty, the systems that are commercially available for knee surgery today are active robots [2].Such active robots ob- viously require a high degree of safety and reliability and should give the surgeon adequate feedback about the on- going process,such as the cutting path with respect to the preoperative planning, cutting forces, bone motion, etc., in order to allow the surgeon to detect if something is going wrong and subsequently allow him to intervene if necessary.
Two systems that fulfill these requirements have been made commercially available for knee arthroplasty, i.e., the ROBODOC system (Integrated Surgical Systems, Davis, Calif.) and the CASPAR system (U.R.S. Ortho Ras- tatt, Germany). Both systems have a comparable applica- tion protocol, with similar performance characteristics.
Application Protocol
The process of robot-assisted knee arthroplasty basically consists of four steps: placement of the fiducial marker pins, spiral CT-scanning of the patient’s leg, preoperative planning and virtual implantation, and the actual surgi- cal implantation.
Placement of the Fiducial Markers.Just as in classical com- puter-navigated TKA,fiducial markers need to be applied to the femur and tibia. These markers are used by the ro- bot for spatial orientation and the necessary geometric calculations. These fiducial markers therefore need to be firmly fixed; this is usually achieved by double bicortical threaded pin fixation in a separate operation, which usu- ally takes about 15 min.
Spiral CT-Scan.With the pins in place, a spiral CT-scan is obtained.The femoral head,the knee joint,the ankle joint, and the pins are scanned, usually while the patient is still under spinal or epidural anesthesia. The average time for acquiring such a CT-scan is usually 20 min. In case the
operating theater is provided with on-site CT-scanning possibilities, both previous steps together with the actu- al robotic surgery can obviously be combined without having to displace and transfer the patient,which leads to a significant improvement in comfort for both the patient and the surgical team.
Preoperative Planning and Virtual Implantation.After the CT data have been transferred to the PC-based planning sta- tion, the necessary anatomical landmarks are identified at the level of the knee joint, as are the center of the femoral
head and the center of the ankle joint,which are used for de- termination of the mechanical and anatomical axes (⊡ Fig.
42-1). Subsequently, the calculation of the frontal, sagittal, and rotational alignment is performed by the system.
Next, the virtual implantation is performed on the screen by selecting a specific implant and size and posi- tioning it onto the corresponding bone while changing or playing with the component translation and/or rotation until a satisfactory position is achieved (⊡ Fig. 42-2).
Immediate graphical and numerical feedback on the alterations in alignment, as well as mediolateral and
⊡ Fig. 42-1.Determination of the anatomical landmarks
⊡ Fig. 42-2. Virtual implantation of the tibial component
presence of femoral notching, over- or undersizing of the component relative to the bone size, or restoration of posterior condylar offset can be assessed and corrected instantly (⊡ Fig. 42-3).
Once the optimal positions for the components have been obtained, the milling area can be specified and adapted in order to avoid milling into the soft-tissue re- gions, thereby reducing soft-tissue trauma (⊡ Fig. 42-4).
Finally, all data are saved and stored onto a memory disc,
The whole process of programming and virtual im- plantation takes 15-20 min on average, but it is unani- mously appreciated as very enlightening to everyone be- ing trained in robot-assisted knee arthroplasty, not only with regard to computer-assisted technology, but also with respect to conventional day-to-day TKA surgery.
Surgical Implantation.A standard incision with medial parapatellar arthrotomy and lateral dislocation of the
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⊡ Fig. 42-3. Virtual implantation of the femoral component
⊡ Fig. 42-4. Determination and pre- setting of the milling areas indicated by the red linings
patella is performed. Next, the leg is flexed and rigidly connected to the robot by two transverse Steinman pins inserted through the proximal tibia and the distal femur.
These two pins are connected to a frame which is linked to the robot, while several retracting devices are mount- ed onto this frame for optimal exposure and soft-tissue retraction (⊡ Fig. 42-6). In order to detect and control undesired motion of the leg during the robotic surgery, reflective markers are attached to this frame as well. They are continuously monitored by an infrared camera sys- tem and will immediately stop the robot in case any type of undesired motion is detected.
Following verification of the fiducial markers, the ro- botic action is started by the surgeon. The robot uses a milling cutter to perform the bone resection, together
with constant water irrigation for cooling purposes and for cleaning the milling debris. The surgeon maintains control over the milling process by a manually held but- ton, which shuts off the robotic action as soon as the but- ton is depressed. At any stage during the procedure, the surgeon can switch to conventional implantation tech- niques if desired. Once the bone cuts are finished, the robotic frame is disconnected, components are inserted, and the surgery is finished.
Experiences and Results
Twenty-one robot-assisted TKAs were performed with the CASPAR system at our institution between 2000 and 2002, with a typical and intense learning curve not only for the surgeon, but even more for the nursing staff and the radiologists involved. Unlike any other new operating technique, this type of robotic surgery has indeed posed many more challenges during the learning process. Not only the important increase in operating time,but also the sense of helplessness towards computer technology and software disfunctioning (caused by the operator or not) have been a constant area of concern and frustration dur- ing the learning phase, which required an adequate dose of perseverance for the team to succeed.
The 21 patients were randomly selected from our pa- tient data base and underwent the robotic TKA surgery after prior consent, without any selection towards sever- ity of the deformity, presence of osteoporosis, range of motion, or any other parameter. Despite the difficult learning curve, excellent results were obtained in all cas-
⊡ Fig. 42-5. Finalizing the virtual to- tal knee implantation
⊡ Fig. 42-6. Operative setup using the Caspar System
of neutral alignment. In three cases the robotic process was aborted because of technical difficulties with re- cognizing the reflective marker positions, leading to a continuous error signaling on the screen. Each of these cases was successfully finished by converting to a con- ventional technique.
Experiences comparable to ours have been reported in the meantime by other groups. Siebert et al. recently published their results in 70 cases operated with the CAS- PAR system,with a mean difference between planned and obtained tibiofemoral alignment of 0.8°. Some outliers were noted, with a maximum of 4° compared with the planned alignment [3,4].An average operating time of 135 (80-220) min was necessary to perform the surgery.
Borner et al. recently reported their results with the ROBODOC system and the Duracon total knee prosthe- sis in their first 100 cases. The procedure needed to be abandoned in only 5% of the cases and the surgeons switched to a conventional technique due to technical problems. Alignment was within the 3° margin for all cases, and operating time was between 90 and 100 min after the initial learning curve [5].
Discussion
It is clear today that excellent results can be obtained with robot-assisted total knee arthroplasty. The reported sub- jective outcome seems to be at least comparable to that with conventional TKA in the short-term follow-up,while evidence exists that coronal plane alignment and overall component positioning is much better using robotic tech- nology compared with conventional TKA.
The advantages of robot assistance in surgery are the functional constraints that these systems can impose; i.e., increased precision is obtained by constraining the move- ment of the machining tool within well-specified mar- gins.Total knee arthroplasty requires accurate machining of the bone surfaces of the tibia and femur, and the accu- racy of the location and orientation of these surgical cuts is crucial to obtaining proper implant alignment, joint kinematics, and ligament balancing. Moreover, in ce- mentless TKA, the surface flatness of the cuts has to be sufficient to maximize the chances for bone ingrowth and successful long-term fixation of the components [6, 7].
Recent work by our group has shown that a milling ro- bot can achieve this necessary high precision.The surface flatness of tibial bone cuts prepared by a robot-assisted procedure ranged between 0.15 and 0.29 mm,versus 0.16- 0.42 mm during conventional surgery using an oscillat- ing saw [8-10].
This advantage of robot-assisted surgery is clinically important, since the maximal distance between the bone
case with conventional sawing a depression of the middle aspect of the prepared surface was noted; this was never seen in the robot-assisted cases [10].
Finally, temperature rise during the robot-assisted procedures can be controlled by altering or adapting the milling speed, which is another advantage over conven- tional bone preparation using a power saw,whereby a rise in temperature is frequently generated and may exceed the critical threshold of 44°-47°C, beyond which bone damage is known to occur, leading to compromised ce- mentless or even cemented fixation [6, 7, 10, 11].
These last-mentioned advantages of robotic TKA over conventional surgery also speak for robotic systems as compared with contemporary navigation systems.
Although current navigation systems are significantly improved in comparison to the first-generation systems, which were beneficial to the surgeon mainly in improv- ing frontal plane alignment, they still require the use of standard old-fashioned types of bone preparation meth- ods with a well-known margin of imprecision.
The latest generation of navigation systems also have a number of important advantages over robotic systems, however. The versatility that is allowed during the actual procedure,for example,is an important benefit compared with the virtual implantation that is performed with the current robotic systems and that leaves the surgeon with no or very limited adaptations possible during the actual in vivo surgery, at least not without abandoning the ro- botic procedure and switching to conventional surgery.
Also, latest-generation navigation systems allow for on- line and numerically quantified assessment of soft-tissue status and subsequent soft-tissue balancing, a feature which, again, is not readily available with the current ro- botic systems. Finally, today’s navigation systems are much cheaper than the currently available robotic sys- tems, not only in purchase costs but also with regard to operational costs related to the disposable ancillaries that are required for each procedure.
With the decreased complexity and greater user friendliness for radiology and operating room staff, nav- igation systems have therefore been much more popular than robots so far in the minds of surgeons and hospital administrators. The recent problems with regard to the distribution and sale of the CASPAR systems (financial problems and stipulations of the manufacturing compa- ny) have further added to the reluctance and reservation of many orthopedic surgeons to select robotic technolo- gy when performing orthopedic surgery.
Furthermore, some less encouraging data have recently been published on total hip replacement with active systems such as the ROBODOC, demonstrating higher complication rates compared with conventional total hip arthroplasty, more specifically with regard to
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dislocation rate, amount of muscle damage, duration of surgery, and revision rate [12].
It is for these reasons that most laboratories and companies involved in orthopedic robotics have started focusing more and more on semiactive robotic systems, which may combine to a better extent the surgical versa- tility and adaptability of navigation systems with the ad- vantages of almost perfect machining and bone prepara- tion offered by robotic systems. Such semiactive robots would theoretically be much cheaper and more user- friendly than the current active robot systems, and there- fore would be more successful in daily application.
References
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2. Van Ham G et al (1998) Machining and accuracy studies for a tibial knee implant using a force-controlled robot. Comput Aided Surg 3:123-133
3. Mai S et al (2004) Clinical results with the robot assisted Caspar System and the Search-Evolution Prosthesis. In: Stiehl JB, Konermann WH, Haaker RG (eds) Navigation and robotics in total joint and spine surgery.
Springer-Verlag, Berlin Heidelberg New York Tokyo, pp 355-361 4. Siebert W et al (2002) Technique and first clinical results of robot-assisted
total knee replacement. Knee 9:173-180
5. Borner M et al (2004) Clinical experiences with Robodoc and the Dura- con Total Knee. In: Stiehl JB, Konermann WH, Haaker RG (eds) Navigation and robotics in total joint and spine surgery. Springer-Verlag, Berlin Heidelberg New York Tokyo, pp 362-366
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Acta Orthop Scand 70:1-35
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perature rise, milling forces and surface flatness in view of robot-assisted total knee arthroplasty. Int Congress Series 1230:300-306
11. Eriksson R et al (1984) the effect of heat on bone regeneration: an exper- imental study in the rabbit using the bone growth chamber. J Oral Maxillofac Surg 42:705-711
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