F. Portheine

Image guided Orthopedic Surgery using individual templates

Individual templates for Orthopedic Surgery provide a precise intraoperative reproduction of the geometries of work on bone planned preoperatively on the base of CT-image data. The general feasibility concerning the adaptation to different surgical applications has already been demonstrated in various in-vitro studies as well as within clinical application1,2,3,4,5. Within the framework of the European IGOS-project a demonstrator for image guided pelvis surgery as an exemplary clinical application will be developed. In contrast to initial feasibility studies with our first labtyp systems, the introduction into clinical routine induces additional constraints. To provide an adequate level of reliability and usability additional efforts are necessary especially concerning quality assurance, ergonomic design and standardisation of the related chain of image acquisition and surgical planning, manufacturing of individual templates and finally the intraoperative execution. Aspects of the integration into clinical routine as well as laboratory investigations concerning accuracy and integrated manufacturing are discussed.Individual templates for Orthopedic Surgery provide a precise intraoperative reproduction of the geometries of work on bone planned preoperatively on the base of CT-image data. The general feasibility concerning the adaptation to different surgical applications has already been demonstrated in various in-vitro studies as well as within clinical application1,2,3,4,5. Within the framework of the European IGOS-project a demonstrator for image guided pelvis surgery as an exemplary clinical application will be developed. In contrast to initial feasibility studies with our first labtyp systems, the introduction into clinical routine induces additional constraints. To provide an adequate level of reliability and usability additional efforts are necessary especially concerning quality assurance, ergonomic design and standardisation of the related chain of image acquisition and surgical planning, manufacturing of individual templates and finally the intraoperative execution. Aspects of the integration into clinical routine as well as laboratory investigations concerning accuracy and integrated manufacturing are discussed.

CT-Based Planning and Individual Template Navigation in TKA

Among the various modalities of alloarthroplasty of the knee joint the total endoprosthesis is the most often exe-cuted intervention in the world. Severe arthrosis and axial deformities up to 30o varus or valgus can thereby be equalized. Today’high quality standard of surgical treatment requires anatomically correct orientation and fitting of the implant aiming at optimal biomechanical functionality. Thus, the single components must be taken into account as well as functional changings of tension in the surrounding soft tissue.

User-interactive registration of bone with A-mode ultrasound

In this study, we investigated a registration technique based on a mechanically tracked A-mode ultrasound pointer for transcutaneous A-mode ultrasound pointer for transcutaneous, noninvasive palpation of bone surface. The principle has been exemplified for distal femur registration in total hip replacement surgery and has been evaluated in laboratory trials on a bone/soft-tissue model. Three different registration modes were demonstrated. Regarding clinical requirements, we constricted the areas of palpation to points and surfaces accessible through a minimal surgical portal in order to avoid additional trauma to soft tissue. Registration based solely on proximal surface points seems to be insufficient for clinical application. To avoid the invasive direct palpation of the condyles and epicondyles, we used the A-mode ultrasound pointer for noninvasive transcutaneous registration (Mode III). The resulting entire mean rms error was 0.59 mm (0.28/spl deg/), which is significantly better and more reliable than a registration exclusively in the proximal part of the femur. During the ultrasound registration process, the computer-based assistance tool gave visual feedback to the user to guide the alignment of the transducers beam axis to be perpendicular to the local bone surface. After five iterations, the final angle error of this approximation was in the range of /spl plusmn/2 degree and generally influenced by the contribution of the discretization angle error /spl Phi//sub DIS/. Based on the consideration of the thickness of the soft-tissue and the geometry of the ultrasound probe, it is suggested that this is a sufficient accuracy in order to ensure a reliable ultrasound-based digitization of the bone surface. The overall mean registration time using A-mode ultrasound, including palpation, and matching, seems to be tolerable. The algorithm and interface for user-interactive A-mode ultrasound-based registration seem to provide efficient support for robust and accurate registration.

Planung und Ausführung von orthopädischen Operationen mit Hilfe von Individualschablonen

ZusammenfassungOperative Eingriffe lassen sich unter Zuhilfenahme von dreidimensionalen (3D-) Rekonstruktionen der anatomischen knöchernen Strukturen, erstellt aus den Tomographiedaten eines Patienten, genau planen und simulieren. Hilfestellung bei der intraoperativen Umsetzung des zuvor Geplanten sowie bei der räumlichen Orientierung im Operationssitus können computergestützte Navigationssysteme oder Robotersysteme geben.Als preiswerte Alternative ohne große technische Anforderungen an Ärzte oder Operationspersonal wurde im Helmholtz-Institut Aachen das System der Individualschablonen entwickelt. Die aus der 3D-Rekonstruktion des eigens entwickelten Planungssystems DISOS bekannte negative Knochenoberfläche wird in den Schablonenrohling eingefräst. Intraoperativ kann die Schablone als Referenz zur räumlichen Orientierung, als Leitstruktur zur Schnittführung oder als Werkzeugführung dienen, um den Knochen entsprechend vorheriger Planung zu bearbeiten.Klinische und experimentelle Studien haben gezeigt, dass sich durch den Einsatz von Individualschablonen Operationszeiten sowie intraoperative Röntgenzeiten verkürzen lassen, ohne den herkömmlichen Operationsablauf wesentlich zu beeinflussen.AbstractOperational interventions can be planned and simulated accurately with the help of a three-dimensional reconstruction of the anatomical bone structures, created from the tomographic data of a patient. Computer-assisted navigation systems or robotic systems can assist the intraoperative realization of the planned intervention and may support the spatial orientation within the operational field.As an inexpensive alternative without the high excessive technical workload on the physicians or the surgical personnel, individual templates were developed in the Helmholtz Institute Aachen. In this approach the negative three-dimensional bone surface, known exactly from the 3D-reconstruction of the patients bone by the planning system DISOS, is milled into a small cubic block of polycarbonate. During the intervention, the template serves as a reference for the spatial orientation and as a tool-guide for cutting or milling of the bone according to the previous planning.Clinical and experimental studies have shown that operation times as well as intraoperative X-ray times can be shortened by the use of individual templates, while preserving the task sequence of the conventional operation procedures.

Entwicklung eines klinischen Demonstrators für die computerunterstützte Orthopädische Chirurgie mit CT-Bildbasierten Individualschablonen

Bei der Planung von Eingriffen in der orthopadischen Chirurgie kann der Orthopade auf eine Vielzahl von bildgebenden Verfahren zuruckgreifen, wie z.B. CT, MR, Ultraschall und Rontgenaufnahmen. Die jungsten Entwicklungen im Bereich der computerunterstutzten Chirurgie bieten verschiedene Losungsansatze, um die hohe geometrische Genauigkeit der praoperativen Bildgebung und Planung fur eine ebenso prazise intraoperative Ausfuhrung zu nutzen. Am Helmholtz-Institut wurde dafur das Prinzip der Individualschablonen entwickelt. Hierbei werden individuell angepaste Schablonen auf Basis von CT-Daten praoperativ gefertigt, die intraoperativ eine prazise Werkzeugfuhrung fur die geplanten Knochenbearbeitung darstellen. Die Realisierbarkeit des Konzeptes fur verschiedene chirurgische Anwendungen wurde bereits in Laboruntersuchungen sowie in klinischen Applikationen demonstriert. Im folgenden werden Aspekte der Entwicklung eines integrierten klinischen Demonstrators zur chirurgischen Planung und Fertigung von Individualschablonen fur periacetabulare Umstellungsosteotomien dargestellt.

CRANIO—computer-assisted planning for navigated and robot-assisted surgery on the skull

Abstract Computer-assisted planning, navigation, and robotic craniotomy, with optional skull reconstruction using customized implants are of increasing clinical interest in craniofacial and neurosurgery. The aim of the CRANIO project presented in the first part of this paper is to develop a system that integrates the entire surgical process, from planning, customized implant manufacturing, optional robot programming, up to intraoperative navigation and robot-assisted execution. In the second part of the paper, we present new algorithms developed in the framework of CRANIO project. This work is especially related to the manipulation of 3-D geometry data of the skull for planning and definition of craniotomy. The results of our work are presented, together with results and objectives for further development.

Pelvic Osteotomy with Template Navigation

Various surgical techniques are used for the treatment of hip dysplasia in young people and adults. In contrast to acetabuloplasty in children, the position of the complete acetabulum is corrected. The repositioning serves to enlarge the weight bearing zone of the dysplastic acetabulum covering the femoral head, in order to reduce pressure on this area to physiological levels. The major goals of this therapy are relief from pain as well as preventing premature osteoarthritis with the necessity for artificial hip replacement. The basics of the biomechanics as well as diagnosis and indications are described and discussed in detail elsewhere [9,11]. Apart from the triple osteotomy according to Tonnis, practiced by our clinic since more than 15 years, particular mention should be made of the periacetabular osteotomy technique described by Ganz [3]. In contrast, the spherical osteotomy procedure of Wagner [12] has not become established due to the danger of acetabular necrosis.

An interface for the data exchange between CAS and CAD/CAM systems

Abstract In Computer Assisted Surgery (CAS), there is an increasing need for the data exchange between the planning system and external Computer Aided Design (CAD)/Computer Aided Manufacture (CAM) process to simulate the intraoperative execution or to verify and optimize the implant design. An interface for such data exchange was therefore implemented and integrated in the CAS system developed in our group. We also propose a simple, robust and fast algorithm for the voxelization of surface models with triangle meshes. The tools have been used successfully for the integration of standard geometry implant data for total knee arthroplasty. A surgical simulation and planning module for the robot assisted craniectomy will also use this interface to simulate intraoperative robotic milling and support the iterative design of the individual implant.

VISUELLE BENUTZERFÜHRUNG ZUR REFERENZIERUNG AUF BASIS VON A-MODE ULTRASCHALL

In Ms study we investigate the use of an AMode ultrasound probe tracked by a mechanical localizer System (MicroScribe 3D) for non-invasive transcutaneous palpation and registration ofbone surface points. A CT of a femur-niodel has been scanned and subsequenlly processed by segmentation and 3D-reconstruction. During the ultrasound registration, a Computer based assistance tool helped guiding the alignment of the ultrasound probe. Three different modes of registration have been compared. Process times for registration fiave been recorded and compared. The results for using an -Mode ultrasound System demonstrate a translation RMS accuracy of 0.58 mm. Mean ultrasound registration time has been measured to 108 sec. for palpation of W hone surface points ofdistal part offemur. Keywords— -Mode, ultrasound, registration, visual interface, man-machine-interaction

Computer- und Robotertechnik für die bildgeführte Orthopädische Chirurgie (Computer and Robot Technology for Image guided Orthopaedic Surgery)

Seit einigen Jahren hält die Computer- und auch Robotertechnologie in der Orthopädischen Chirurgie Einzug, wird jedoch teilweise sehr kontrovers diskutiert. Wo liegen Vorteile und Probleme der Automatisierungstechnik für den chirurgischen Einsatz? In diesem Beitrag sollen Möglichkeiten und Techniken im Überblick dargestellt werden. Entwicklungspotentiale insbesondere im Hinblick auf robotische Unterstützungssysteme sollen am Beispiel des CRIGOS-Parallelrobotersystems aufgezeigt werden.