T 5.1 CT EVALUATION OF FEMORAL COMPONENT ROTATION IN TKA: COMPARISON OF TIBIAL AXIS METHOD TO TRANSEPICONDYLAR LINE.

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1 T 5.1 CT EVALUATION OF FEMORAL COMPONENT ROTATION IN TKA: COMPARISON OF TIBIAL AXIS METHOD TO TRANSEPICONDYLAR LINE. Schulthess Klinik, Zurich, Switzerland. Lehigh Valley Hospital, Allentown, PA, USA Purpose: Accepted landmarks for determining femoral component rotation in total knee arthroplasty (TKA) include the posterior condyles, Whiteside s line, arbitrary three to four degrees of external rotation, and transepicondylar axis (TEA). All methods require anatomical identification, which may be variable. The purpose of this study was to radiologically evaluate femoral component rotation (CT analysis) based on a method that references to the tibial shaft axis and balanced flexion tension without identification of femoral anatomical landmarks. Methods: Out of a cohort of 3058 mobile bearing low contact stress TKA, CT scans of 38 randomly selected well functioning TKA were evaluated to determine femoral component positioning. Spiral CT scans of the femoral epicondylar region with four mm cuts were performed to accurately identify medial and lateral femoral epicondyles. Rotational alignment was measured in relation to the transepicondylar axis using CT-implemented software by two independent radiologists. Results: Mean femoral rotational alignment was parallel to the TEA (average 0.3 degrees internal rotation) ranging from six degrees internal to four degrees external rotation. All thirty-eight cases had satisfactory clinical results, range of motion of over 90, and showed perfect patello-femoral tracking and patellar congruency on axial views. Conclusions: Femoral rotation position based on tibial shaft axis and balanced flexion tension gap is patient specific, reproducible and results in predictable femoral rotational positioning and patella tracking. CT analysis in this study confirms that the tibial shaft axis method produces a consistent femoral component positioning that relates accurately to the TEA. Tibial shaft axis method avoids the need for arbitrary landmark identification, placing the femoral component predictably in an optimum position in relation to the tibia and patella. Address for correspondence: jgboldt@hotmail.com

2 T 5.2 A Modular and Universal Planning System for Navigation- and Robotic-Based Interventions in Alloarthroplasty and Large Bone Surgery S. Kuenzler 1, I. Gross 2, P. Knappe 2, S. Pieck 2, J. Wahrburg 2 and F. Kerschbaumer 1 1 Department of Arthritis Surgery, University of Frankfurt (Main), Germany. 2 University of Siegen, Germany. 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 alloarthroplasty. 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. Keywords: planning system, navigation, robotics, orthopedic surgery Address for correspondence: Prof. Dr. med. Fridun Kerschbaumer, Department of Arthritis Surgery, University of Frankfurt, Marienburgstr. 2, Frankfurt, Germany. kerschbaumer@em.uni-frankfurt.de Dr.-Ing. Juergen Wahrburg, University of Siegen, Hoelderlinstr. 3, Siegen, Germany wahrburg@zess.uni-siegen.de

3 T 5.3 Erste Erfahrungen mit dem Navigationssystem Galileo und dem Vario-Knie-System H. Dinges; H. Gramlich; A. Kiekenbeck Unzureichende Ausrichtung der Prothesenkomponenten führt zu signifikant erhöhter Lockerungsrate. Ziel der computergestützten Navigation ist eine exaktere Ausrichtung der Prothesenkomponenten auch bei schwierigen Situationen wie z.n. Umstellungsosteotomie oder Fraktur. Derzeit werden verschiedene Navigationssysteme für die Knieendoprothetik entwickelt. Hierbei lokalisiert eine 3d- Infrarotkamera Infrarotdioden, die mit festen Trägern am Femur, der Tibia sowie an den Werkzeugen bzw. Schnittlehren befestigt sind. Galileo der Fa. PI ist ein Freihandsystem, das ohne präoperative Planung auskommt. Intraoperativ wird mittels kinematischer Analyse das Hüftdrehzentrum bestimmt. Die weiteren anatomischen Bezugspunkte und Achsen werden mit einem navigierten Handzeiger in das System eingelesen. Als Besonderheit wird bei Galileo die Sägelehre für die femoralen Schnitte von einem rigide am Femur verankerten Roboterarm geführt. Es ist derzeit wohl das einzige System, bei dem die Sägelehre dem Knochen nicht direkt aufliegen muß. Dadurch können Folgefehler durch auf nicht exakten Sägeschnitten aufliegende Schnittlehren vermieden werden. Bisherige Studien konnten bereits für andere Systeme zeigen, daß mit der Navigation eine exaktere Ausrichtung der Komponenten möglich ist und insbesondere Ausreißer vermieden werden können. Wir berichten über unsere ersten Erfahrungen mit dem Navigationssystem Galileo zur Navigation der Vario Knieprothese, sowie über die Ergebnisse der ersten 30 navigierten Implantationen, die wir seit dem damit durchgeführt haben. Korrespondenzadresse: Orthopädische Klinik und Abteilung für Rheumatologie, Westpfalz-Klinikum Kaiserslautern/ Kusel, Akademisches Lehrkrankenhaus Johannes-Gutenberg-Universität Mainz

4 T 5.4 Navigation in Knee Arthroplasty Rolf K. Miehlke, Hartmut Kiefer, Steffen Kohler, Jean-Yves Jenny, Werner Konermann Dept. for Arthritis Surgery, Centre for Orthopaedic Surgery and North-West German Centre for Rheumatology St. Josef-Stift, Sendenhorst, Germany INTRODUCTION Nowadays, longevity of total knee arthroplasties is very acceptable. Survivorship analyses demonstrate a success in a range of 80% to more than 95% over a period of more than ten years (1-4). However, long-term results largely depend, amongst other factors, on restoration of physiological alignment of the lower limb (5-11). Jeffery et al. (12) reported a three percent loosening rate over eight years when knees were correctly aligned whereas insufficient alignment lead to prosthetic loosening in 24 percent. Rand and Coventry (13) found a 90 percent survivorship rate at ten years when the mechanical axis was aligned in a range from nought to four degrees of valgus. Valgus position of more than four degrees or varus alignment resulted in only 71 percent and 73 percent of survivorship respectively. Recently, computer aided instrumentation systems (14,15) became available and preliminary results of small series were reported (16-17). The purpose of this study was to assess the accuracy of computer integrated instrumentation for knee alignment. MATERIAL AND METHOD The OrthoPilot represents a computer controlled image supported alignment system. A 3-D Optotrak camera localizes infra-red diodes fixed to rigid bodies within the surgical field. Thereby a spatial coordinate reference system is provided. The localizer is linked to a UNIX work station which performs the operative protocol using a graphical interface and a foot pedal. The rigid bodies are fixed to the bones by bi-cortical screws. An intraoperative kinematic analysis and various additional landmarks lead to definition of the centres of hip, ankle and knee joint and sizing of endoprosthetic components. With the use of LED-equipped alignment instruments the femoral and tibial resection planes are determined. The OrthoPilot navigation system is not dependant on CT data and no additional preoperative planning is therefore necessary. A prospective comparative multicentre study in five institutions, four in Germany and one in France, was carried out. 821 patients with primary tricompartimental knee arthroplasty using the SEARCH LC knee (B Braun AESCULAP) were included in the study. The OrthoPilot Navigation system was used in 555 cases and 266 knees were implanted with the use of conventional instrumentation. At the three months follow-up alignment was assessed using standardized one leg stance radiographs with regard to the mechanical axis and the femoral and tibial angels in the coronal plane. For the lateral femoral and tibial angels standard lateral x-rays were used. Prosthetic alignment was verified by an independent observer. RESULTS The radiographically assessed results were subdivided into three groups. An error of ± one degree in the radiographical measurements and small deviations caused by the play of surgical instruments have to be considered. With respect to the femoral and tibial angels in the ap and lateral view the group of very good clinical results was, therefore, defined in the range between ninty degrees and ± two degrees. Deviations of three and four degrees from the optimum were classified as being clinically acceptable. Aberrations of more than four degrees were classified as outliers. When measuring the mechanical axis deviations from fully precise femoral and tibial angels may add up. For this reason zero degrees ± three degrees were rated as a very good result, deviations of four to five degrees were considered to be acceptable and alignment beyond five degrees from the optimum was classified as an unsatisfactory result. Mechanical axis: 35.2% of the navigated cases were aligned at exactly zero degrees. This was achieved in only 24.4% of the manual cases. 88.6% of cases using navigation and 72.2% in the manual group showed zero degrees and varus or valgus angles of up to three degrees. 8.9% and 18.1% of cases respectively showed deviations of four or five degrees of valgus or varus alignment representing an acceptable clinical result. In only 2.5% of the navigation group aberrations of more than five degrees occurred. The rate of dissatisfying results was 9.8% in the manual group.

5 Femoral axis (coronal plane): In the navigation group 48.1% of cases showed an alignment at exactly 90 degrees which was the case in only 33.5% of the control group. Altogether, in 89.4% of the navigated cases a very good result was observed. In the conventionally instrumented cases only 77.1% very good results were found. There were 1.6% outliers beyond the limits of four degrees in the navigation group in comparison to 4.9% amongst the control cases. Femoral axis (sagittal plane): Very good results with up to two degrees of deviation from a ninety degree position were obtained in 75.5% of navigated cases and 70.7% of manual cases. 37.3% and 34.6% respectively showed an ideal alignment of exactly ninety degrees. Unsatisfactory results were observed in 9.5% of the navigated cases and 9.4% of the manual cases. Tibial axis (coronal plane): 58.7% of the computer assisted and 40.6% of the reference cases were exactly aligned at rectangles. All in all, in 91.9% navigated and only 83.5% manual cases a very good result was obtained. Only 1.1% outliers had to be observed in the navigation group whereas 3.4% unsatisfactory results were registered with manual technique. Tibial axis (sagittal plane): 44.3% of the navigated cases and only 26.7% of cases in the control group were aligned perpendicular to the dorsal tibial cortex, thus showing no posterior slope. Altogether, 81.3% could be classified as very good clinical results in the computer assisted group. The corresponding rate of the manual group was 69.9%. Equivalent values of 8.6% in the navigation group and 8.3% in the reference group were registered beyond the limits of four degrees deviation. The additional operation time for the use of the navigation system is calculated between eight and ten minutes after having passed through the learning curve. CONCLUSIONS Knee navigation facilitates proper alignment of endoprosthetic components and with the use of the OrthoPilot system results are clearly more favourable in comparison to conventional instrumentation technique. In addition, the data obtained from literature demonstrate that the use of this navigation system contributes to reducing outliers in number. With the learning curve the OrthoPilot alignment system proved to gain in reliability. Deviations from perfect alignment are still difficult to be classified into surgical or technical deficiencies. Many technical and software improvements which were introduced in the meantime will, in addition, contribute to reliability and time saving. Comparative studies with different navigation systems are not yet available. They might allow an even more profound insight into the possibilities and advantages or disadvantages of computer assisted knee alignment. LITERATURE (1) Knutson K, Lindstrand A, Lidgren L. Survival of knee arthroplasties, a nation-wide multicenter investigation of 8000 cases. J Bone Joint Surg. 1986; 68B: (2) Scuderi GR, Insall JN, Windsor RE, Moran MC. Survivorship of cemented knee replacement. J Bone Joint Surg. 1989; (3) Nafei A, Kristensen O, Knudson HM, Hvid I, Jensen J. Survivorship analysis of cemented total condylar knee arthoplasty. J Arthoplasty 11, 1996;07-10 (4) Ranawat CS, Flynn WF, Saddler S, Hansraj KH, Maynhard MJ. Long-term results of total condylar knee arthroplasty. A 15-years survivorship study. Clin Orthop 1993; 286: (5) Lotke PA, Ecker ML. Influence of positioning of prosthesis in total knee replacement. J Bone Joint Surg 1977;59-A:77-79 (6) Hood RW, Vanni M, Insall JN. The correction of knee alignment in 225 consecutive total condylar knee replacements. Clin Orthop 1981;160: (7) Bargren JH, Blaha JD, Freeman MAR. Alignment in total knee arthroplasty. Clin Orthop 1983;173: (8) Hvid I, Nielsen S. Total condylar knee arthroplasty. Acta Orthop Scand 1984;55: (9) Tew M, Waugh W. Tibial-femoral alignment and the results of knee replacement. J Bone Joint Surg 1985;67-B: (10) Jonsson B, Astrom J. Alignment and long-term clinical results of a semi-constrained knee prosthesis. Clin Orthop 1988;226: (11) Ritter MA, Faris PM, Keating EM, Meding JB. Postoperative alignment of total knee replacement its effect on survival. Clin Orthop 1994;299: (12) Jeffery RS, Morris RW, Denham RA. Coronal alignment after total knee replacement. J Bone Joint Surg 1991;73-B: (13) Rand JA, Coventry MB. Ten-year evaluation of geometric total knee arthroplasty. 1988;232: (14) Leitner F, Picard F, Minfelde R, Schulz HJ, Clinquin P, Saragaglia D. Computer assisted knee surgical total replacement. In: CVRMed-MRCAS. Troccaz J, Grimson E, Mösges R (Eds). 1997; , Springer (15) Delp SL, Stulberg SD, Davies BL, Picard F, Leitner F. Computer assisted knee replacement. Clin Orthop 1998; 354:49-56 (16) Picard F, Saragaglia D, Montbarbon E, Chaussard C, Leitner F, Raoult O. Computer assisted knee arthroplasty - preliminary clinical results with the OrthoPilot System. Abstract, 4 th International CAOS Symposium, Davos, Switzerland, 1999 (17) Miehlke RK, Clemens U, Jens J-H, Kershally S. Navigation in der Knieendoprothetik vorläufige klinische Erfahrungen und prospektiv vergleichende Studie gegenüber konventioneller Implantationstechnik, Z Orthop 2001; 139: Address for correspondence: Professor Dr. med. Rolf K. Miehlke, Abt. für Rheumaorthopädie, Orthopädisches Zentrum & Nordwestdeutsches Rheumazentrum, St. Josef-Stift, Sendenhorst, Germany miehlke@st-josef-stift.de,

6 T 5.5 Revisionschirurgie mit dem Navigationssystem beim Prothesenversagen Beate Wolke, M. Sparmann Die Knieendoprothetik stellt heute ein bewährtes Verfahren in der orthopädischen Chirurgie dar. Der Erfolg einer Knieendoprothesenimplantation hängt von verschiedenen Faktoren ab. Hierunter sind Patientenauswahl, Prothesendesign, Weichteilbalancing, Beinachse und Wiederherstellung der Gelenklinie zu zählen. Nach fast zwei Jahren klinischer Anwendung des Strykernavigationssystems und mehr als 350 Primärimplantationen blicken wir jetzt auf 41 Wechseloperationen in den letzten 14 Monaten zurück. Das Ziel der Anwendung des Navigationssystems bei Revisionsfällen war es zu analysieren, ob mit dem Navigationssystem die Gründe für ein Versagen der Knieendoprothese ermittelt werden können In allen Fällen klagten die Patienten über Schwellungen des Gelenkes, Ergüsse oder Schmerzen. 11 Patienten hatten Giving way Phänomene. 33 bicondyläre Oberflächenersatzprothesen und 8 Hemischlitten wurden revidiert. Das Navigationssystem wurde intraoperativ in der gleichen Technik wie bei der Primärimplantation eingesetzt. Zuerst wurden die Rigid Bodies fixiert. Die anatomischen Landmarken wurden erhoben. Die Oberflächendigitalisierung erfolgte auf der Prothesenoberfläche. Die initiale Kinematik wurde bezüglich der Beinachse und des Weichteilbalancing analysiert Anschließend wurde die Varus/Valgusposition bei liegender Prothese gemessen. Die Rotation wurde nach Explantation des Implantates ermittelt. 22 Prothesen waren gelockert. Ein Rotationsfehler lag in 28 Fällen vor, ein Varus/Valgus Malalignment in 13 Fällen. Kombinierte Fehler waren dabei ebenfalls nachweisbar. In einem Fall war die Prothese korrekt positioniert. Das lateral unzureichende Weichteilrelease bei Valgusgonarthritis führte zu einer Bandimbalance und damit erhöhtem Polyethylenabrieb. Dieser Patient konnte durch einen ausgedehnten lateralen Release und Erhöhung des Polyethylens behandelt werden. Wegen Infektverdacht konnten 6 Prothesen nicht einzeitig gewechselt werden. Es ließ sich zeigen, dass die Malrotationen der Tibia- und Femurkomponenten zu veränderten Bandspannungen in den einzelnen Freiheitsgraden der Bewegungsanalyse und damit zu einer Kompromittierung des Roll/Gleitverhaltens führen. Laterale Instabilitäten sind häufig durch eine vermehrte Innenrotationsfehlstellung der Femurkomponente bedingt. Die Folge ist eine vermehrte Polyethylenbelastung. Aussenrotationsfehlstellungen des Tibiaplateaus führen zu einer stärkeren Beeinträchtigung des Prothesenlaufes als Fehlimplantationen in Innenrotation. Mit dem Stryker Navigationssystem können intraoperativ Positionsfehler der Prothese, Achsenfehler und Instabilitäten genau analysiert werden. Damit ist die Voraussetzung für eine Korrektur der Fehler gegeben.

7 T 5.6 Fluoroscopic-assisted navigation of the TKR with the Medtronic Viking System and with the Genesis II Frank W. Hagena, M. Kettrukat, R.M. Christ Auguste - Viktoria Klinik, Bad Oeynhausen, Germany The C-arm is routinely used introperatively to control the anatomic structures during osteotomies and during reposition and nailing of the femoral neck fractures. Fluoroscopic navigation has been introduced in spinal surgery and it is a widely accepted tool for pedicel screws. It has been proven that fluoroscopic imaging in two planes shows an adequate reproduction of the 3-dimensional anatomy and enables a realistic acquisition for computer-assisted navigation. This experience with the Medtronic system is now adapted for application as the Viking System for total knee replacement using the Genesis II knee arthroplasty. After experimental cadaver studies and critical evaluation the system was tested the first time in our clinic during live surgery. In the first series of 40 Genesis II TKR we could establish a high degree of accuracy and reproducibility with the fluoroscopic navigation. Several advantages using the fluoroscopic navigation can be shown: 1. The navigation offers an online documentation at each step during surgery 2. These data give a good background for further studies 3. Fluoroscopic assisted navigation needs only very short radiation exposure 4. Fluoroscopic imaging is superior to virtual pixels in other systems 5. There is no limitation to use fluoroscopic navigation in case of severe destruction of the knee or in case of severe contracture of the ipsilateral hip or ankle joint 6. The intraoperative and postoperative controls show a deviation of the alignment of less than 2 degrees. During the study we could find a reduction of the time of surgery. The examination of additional laxity tests at various degrees of flexion with the trial implants in situ give an assessment of the ligament stability. Fluoroscopic assisted navigation may be used during the routine TKR to be prepared for the difficult case and to avoid malalignment in the routine TKR. Further investigation i.e. in a prospective study may reveal the advantage of navigation in correlation to the clinical outcome and the survival rates of the TKR.