Total hip replacement procedures are among the most frequent surgical interventions in all industrialized countries. Although it is a routine operationliterature reports that important parameters regarding for example cup orientation and leg length discrepancy often turn out to be not satisfying after surgery. This paper presents a novel concept to improve the reproducibility and accuracy for implantation of cup and stem prosthesis at exactly the desired locations. Existing computer- based commercial products either offer software solutions for just pre-operative planning, or imageless navigation systems that are only used during surgery in the operating theatre. The innovation of our approach is based on an integrated computer-assisted solution that combines pre-operative planning and intra-operative navigation to support THR procedures.

The software for pre-operative planning can process both, 3D CT images and standard 2D x-ray images. A custom-built navigation system using optical 3D localizing technology has been developed to transfer planning results to the OR. The main objective of our approach is to implant the artificial joint in a way to restore the natural anatomy of the joint before surgery as close as possible, or with exactly planned modifications. In particular, cup inclination, cumulative anteversion of cup and stem, CCD angle and lateral offset, centre of rotation, leg length discrepancy, and joint range of motion are considered. It is not necessary to determine numerical values for all of these parameters because our approach uses a unique procedure to record the natural anatomical situation by combining pre-operative planning and intra-operative navigation, and subsequently supports implantation of the prosthesis components by surgical navigation in order to restore this situation.

In case planar 2D x-ray images are used for pre-operative planning accurate scaling of these images is a prerequisite for exact determination of relevant parameters. The patient-specific scaling factor depends on the distance of the hip joint rotation centre from the x-ray detector or film. We have designed a low-cost localization system to be mounted close to the x-ray apparatus. It localizes the 3D position of the rotation centre by small motions of the leg and eliminates uncertainties of conventional methods that are caused by improper positioning of a calibration body.

Easy and robust setup and application have been key objectives for the development of our custom-built navigation system. Acquisition of intraoperative parameters for example includes the determination of the acetabular centre axis by localizing selected landmarks at the acetabular rim. Intra-operative parameters are combined with pre-operative parameters without needing sophisticated matching procedures with the pre-operative images.

A preliminary surgical workflow that will be detailed in the conference presentation has been designed for evaluation of the concept using sawbones models. Based on the promising results of our laboratory tests we have started to prepare first clinical experiments in close cooperation with surgeons.

Total hip replacement in Germany has been performed in 227293 cases in 2015 and tendency is increasing. Although it is a standard intervention, freehand positioning of cup protheses has frequently poor accuracy. Image-based and image-free navigation systems improve the accuracy but most of them provide target positions as alphanumeric values on large-size screens beneath the patient site. In this case the surgeon always has to move his head frequently to change his eye-focus between incision and display to capture the target values. Already published studies using e.g. IPod-based displays or LED ring displays, show the chance for improvement by alternative approaches. Therefore, we propose a novel solution for an instrument-mounted small display in order to visualise intuitive instructions for instrument guidance directly in the viewing area of the surgeon.

For this purpose a solution consisting of a MicroView OLED display with integrated Arduino microcontroller, equipped with a Bluetooth interface as well as a battery has been developed. We have used an optical tracking system and our custom-designed navigation software to track surgical instruments equipped with reference bodies to acquire the input for the mini-display. The first implementation of the display is adapted to total hip replacement and focuses on assistance while reaming the acetabulum. In this case the reamer has to be centred to the middle point of the acetabular rim circle and its rotation axis must be aligned to the acetabular centre axis by Hakki. By means of these references the actual deviations between instrument and target pose are calculated and indicated. The display contains a cross-hair indicator for current position, two bubble level bars for angular deviation and a square in square indicator for depth control. All display parts are furnished with an adaptive variable scale. Highest possible resolution is 0.5 degrees angular, 1 millimeter for position and depth resolution is set to 2 mm.

Compared to existing approaches for instrument-mounted displays, the small display of our solution offers high flexibility to adjust the mounting position such that it is best visible for the surgeon while not constraining instrument handling. Despite the small size, the proposed visualisation symbols provide all information for instrument positioning in an intuitive way.

The paper presents the design of a mechatronic assistance system which started from the novel concept to integrate an optical navigation system and a robotic arm, combining the specific advantages of each of the two components. The integrated system offers precise positioning and guiding of surgical instruments according to pre-operative planning. A unique feature results from its capability to track small motions of the patient in real time, eliminating the need to rigidly fix the anatomical structure to be operated. The robot arm can be regarded as a controlled machine actuator of a navigation system. Its operation is mainly controlled by interactive operating modes which are based on a versatile haptic interface. The system supports the surgeon in those parts of a procedure where human skills are limited, but always lets him take full control, for example by directly grasping and moving the arm at its wrist if he wants to push the arm aside.

In 2003 several clinical trials have been performed to demonstrate the technical and medical feasibility of the approach. Our mechatronic assistance system has been world’s first system to support the implantation of the acetabular cup in robot assisted hip surgery. The next steps have been concentrated on further developments in some key areas.

Improvements of the man-machine interface in order to make the operation of the system faster, easier, and more robust, extension of the system application also to the femoral part of total hip replacement, including support for resurfacing implants, investigation of novel tool systems for bone preparation and prosthesis implantation that fully exploit the advantages of mechatronic, slip-away-safe tool guidance, further improvements for less invasive operating techniques.

It has turned out that apart from proving the basic system functionality it is a time consuming task to design all system components in a way that they are robust and easy to handle to be acceptable for daily clinical application. After a partial redesign of the system architecture presently the implementation of improved modules to support both the acetabular and the femoral part in total hip replacement surgery by the mechatronic assistance system is in progress.

Computer-based preoperative planning of orthopaedic interventions will gain increasing importance due to the following trends.

Digitalisation of x-ray equipment and installation of PACS in hospitals for electronic distribution and archiving of diagnostic images, corresponding need of planning procedures which directly process the digital images on a computer, forensic aspects within the scope of growing demands on documentation and quality assurance.

This paper presents the modiCAS software framework as an example which has been developed to meet these requirements. It is characterised by specific features that greatly enhance computer-based pre-operative planning of total hip and knee replacement procedures. The planning process can be compiled such that it is controllable by just three control buttons on the computer screen. Thus planning can be done very efficiently and does not demand more time than conventional film-based procedures on a light-box.

The software uses 3D-templates of the implants. It facilitates more informative planning even if standard 2D x-ray pictures are used, for example by showing the anteversion of the cup prosthesis in hip replacement. In case of accurate and patient-specific scaling of the x-ray images important parameters can be determined such as the required size of the implants, as well as offset and leg-length corrections. Future versions of the software will have a link to navigation systems and robotic assistance systems to support intra-operative realisation of the preoperative planning.

The modiCAS software is a manufacturer-independent solution which is not limited to certain implant or PACS producers. Its integrated DICOM interface facilitates data input from all compatible modalities, and the storage of the planning results at the end of the procedure. The library of available implant templates already comprises the most common implants and is continuously updated.

Robotic systems for computer assisted surgery have gained a lot of initial interest and several systems to support surgical inventions have been developed over the past ten years. While almost all systems are tailored to specific applications, the technology used may be divided into different groups. One part of the proposed solutions is essentially based on industrial robots, whereas the part relies on specific designs for medical applications. A particular approach which will not be discussed in this contribution is represented by tele-manipulator systems like the daVinci system from Intuitive Surgical Inc. for cardiac applications, and robots for endoscope guidance in abdominal surgery. The operation of these systems is controlled manually by the surgeon based on the visual information of the operating area which he gets by endoscopic cameras.

Robotic application in computer assisted surgery, in contrast to tele-manipulator approaches, is based on pre-operative planning and intra-operative registration of the patient anatomy. They principally offer additional advantages compared to pure navigation systems, such as

No problems due to tremor or unintentional slipping of the tool. Surgery will exactly achieve pre-operatively planned targets, resulting in very good reproducibility

It is a major challenge for new solutions of surgical robot system to exploit this potential while avoiding the drawbacks some existing designs which have not gained wider clinical acceptance. The “added value” of robotic systems must be obvious. Important features to achieve this objectives include interactive operating modes which turn the robot into a powerful and versatile assistance system instead of fully automatic system operation.

The use of surgical navigation in computer assisted or image guided procedures requires the precise measurement of the spatial position of surgical instruments. Investigations of several physical principles have turned out that two technologies are best feasible for application in clinical routines:

optical technology,

Available systems based on either principle deliver measurement information for the 3D-position of a surgical instrument, expressed by the x-y-z coordinates of its tip, and for its 3D-orientation, described by the direction of the instrument axis towards the tip. It is therefore common terminology to describe such measurement systems as 3D/6D digitizing or localizing systems.

The presentation will describe basic principles of both technologies, including their main technical features and the design of key components such as rigid bodies for optical systems and sensor coils for electromagnetic systems. The survey includes an overview of known challenges and problems, and how commercial systems cope with these. A comparison of both technologies outlines the advantages and drawbacks in different applications as well as possible future improvements. It leads to the conclusion that both technologies will co-exist for the foreseeable future.

The first generation of surgical robots which has been used in orthopaedics was characterized by automatic performance of certain tasks like milling of bone cavities or planes. These systems have not been successful as their application and operation suffered from a number of unacceptable drawbacks. Presently computer assisted surgery is dominated by surgical navigation systems where position and orientation of manually guided instruments are visualized on a computer screen as an overlay to the picture of the anatomical structure.

However, new concepts of surgical robots make the benefits of using robotic systems more evident. Such robots do not operate automatically but are designed as assistance systems which support the surgeon by interactive operating modes. Compared to manual instrument guidance in pure navigation they offer several additional advantages some of which are particularly valuable to support less or minimal invasive operating techniques. No problems due to tremor or unintentional slipping of the tool. Precise drilling or reaming by stable tool guidance, surgery will be exact and reproducible to achieve pre-operatively planned targets, to overcome the ergonomic problems, such as difficult hand-eye-coordination and frequent changes of viewing direction. The application of interactive assistance robots in orthopaedic and trauma surgery is illustrated by describing exemplary procedures.

This paper illustrates the concept of a versatile surgical assistance system which combines an optical navigation system and a robotic arm. The integrated system offers precise positioning and guiding of surgical instruments according to pre-operative planning. A unique feature results from its capability to track small motions of the patient in real time, eliminating the need to rigidly fix the anatomical structure to be operated. The modular system architecture facilitates the adaptation of a common basic hardware platform to various surgical applications by adding associated software modules as well as appropriate surgical tools mounted to the robotic arm. The arm can be regarded as a controlled machine actuator of a navigation system. Its operation is mainly controlled by interactive operating modes which are based on a versatile haptic interface. The system supports the surgeon in those parts of a procedure where human skills are limited, but always lets him take full control, for example by directly grasping and moving the arm at its wrist if he wants to push the arm aside.

The use of surgical navigation in computer assisted or image guided procedures requires the precise measurement of the spatial position of surgical instruments. Investigations of several physical principles have turned out that two technologies are best feasible for application in clinical routines: a) optical technology, b) electromagnetic technology. Available systems based on either principle deliver measurement information for the 3D-position of a surgical instrument, expressed by the x-y-z coordinates of its tip, and for its 3D-orientation, described by the direction of the instrument axis towards the tip. It is therefore common terminology to describe such measurement systems as 3D/6D digitizing or localizing systems.

The presentation will describe basic principles of both technologies, including their main technical features and the design of key components such as rigid bodies for optical systems and sensor coils for electromagnetic systems. The survey includes an overview of known challenges and problems, and how commercial systems cope with these. A comparison of both technologies outlines the advantages and drawbacks in different applications as well as possible future improvements. It leads to the conclusion that both technologies will co-exist for the foreseeable future.

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 allo-arthroplasty. 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.