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Biomedical subjects

K Radermacher

Publications and source records attributed to K Radermacher.

At least 19 recordsLinked to original sources
PubMed2006

Analysis of surgical management of calvarial tumours and first results of a newly designed robotic trepanation system.

This study was performed to evaluate the surgical strategy in patients with calvarial tumours, in order to design and modify a robot-assisted trepanation system. A total of 75 patients underwent craniectomy for the treatment of calvarial tumours during the 10-year period from 1993 to 2002. The patients' complaints, the size, location and histology of the tumour, and the various cranioplasty techniques used were analysed retrospectively. In a second procedure several craniectomies at typical locations according to the study's results were performed in a laboratory setting using a hexapod robotic tool, constructed at the Helmholtz-Institute, RWTH Aachen University, and plastic model heads. The workflow was documented and the reproducibility and the accuracy of the procedure were registered. A total of 83 surgical procedures were performed on 75 patients. The majority (87 %) of lesions treated surgically were located in the frontal, temporal and anterior parts of the parietal region. Histological examination revealed benign lesions in 66 % of the patients and dural involvement in 46 %. According to these results craniectomies were performed using the robotic system. Mean positioning accuracy of the robotic system while milling was 0.24 mm, with a standard deviation of 0.04 mm, and maximum error under 1 mm. Craniectomies leaving a 1-mm layer of the tabula interna intact to ensure a healthy dura were performed in several regions successfully. The majority of calvarial tumours, requiring surgical treatment in our patients, were located in cosmetically relevant areas in which drilling can be carried out with the robotic trepanation system. Consequently, the surgical approach had to be planned carefully in order to achieve a good cosmetic outcome.

Adolescent↗
PubMed2004

Evaluation of deformable models for femoral neck surgery.

OBJECTIVE: Using fluoroscopic images alone, it is difficult to guarantee that screws are positioned within the femoral head and neck. This study evaluates whether the introduction of deformable 3D models limiting the planning and navigation space is a helpful approach to minimizing the incidence of misplaced screws, thereby enhancing patient safety. BACKGROUND: Even though a screw may appear to lie within the femoral head and neck on fluoroscopic images, this may not, in fact, be the case. This is a particular problem for interventions such as fixation of a slipped femoral head or osteosynthesis of the femoral neck, where screws must be set close to the cortical bone without penetrating the joint or injuring the cortex of the femoral neck. METHODS: A system was developed which permits computer-based planning and navigation of screws for femoral neck fracture fixation based on fluoroscopic images. Different approaches were employed which either a) make use of a deformable model adapted to the femoral head/neck, constraining the screw positions within this model; or b) allow the user to position the screws with or without geometrical constraints on the X-rays while maintaining parallelism of the screws. All designs were evaluated and compared by 7 test users using integral projection X-rays calculated from the CT dataset. Results were checked using a 3D model of the bone, also calculated from the CT dataset. RESULTS: Positioning screws using the deformable model resulted in a significantly smaller distribution of screw tip locations and no penetrations into the hip joint, in contrast to the other approaches where up to 11% of screws were misplaced. CONCLUSIONS: Constraining the planning and navigation space by means of a deformable model allows better control of screw positioning and thus increases the chances of a successful intervention. In particular, CAS systems allowing for virtual fluoroscopy should consider supporting this planning approach.

Bone Screws↗
PubMed2003

Identification of milling parameters for manual cutting of bicortical bone structures.

Within the framework of the development of a new neurosurgical robot system, parameters of conventional manual neurosurgical bone milling had to be determined. These results were used as a reference for the design and validation of the robotic versus manual milling task. Bovine scapulae were used for the tests because their bicortical structure is similar to the bone structure of the skull. The exercise was to cut defined geometries that had been registered on the bone prior to the start of the milling operation. The geometries had to be milled with a depth of 3 mm, which corresponded to the radius of the ball of the cutter. Different parameters like tool position, rotary speed, temperature, forces and time were registered. Eleven experienced neurosurgeons with practical experience of 80-1200 skull operations participated in this study. First results show a large variation in depth along the line. The lateral deviation was up to 5 mm, the depth error up to 2.5 mm, the tool temperature was 22 degrees C to 65 degrees C, and rotary speed varied from 15,000 to 80,000 rpm. Registered forces had maxima of 16 N in the feed direction and 21 N normal to the surface; average forces were approximately 1-2 N.

Animals↗
PubMed2002

[Developing authoring tools for web-based multi-media orthopedics education modules].

In the framework of the EC-Project VOEU ("Virtual Orthopaedic European University"), authoring tools have been developed to support the implementation of online interactive courses for multimedia orthopaedic educational modules. Based on the pedagogical concept of case-based, problem-oriented learning, different user-interaction scenarios and Learning Objects (LOs) were analyzed and developed. Each LO acts as an interactive dialogue presenting one kind of question with certain rules and interactions. The multimedia course content entailing anamnesis, diagnosis and therapy is managed in a database and can be adaptively generated as certain LO with the help of Active Server Pages (ASPs). As an example, an interactive course on Developmental Dislocation of Hip has been implemented.

Computer-Assisted Instruction↗
PubMed2002

[Empirical studies of the reliability of surgical navigation systems].

A number of studies demonstrate the clinical relevance of systems for computer assisted surgery (CAS systems). As however studies on human error in medicine indicate, reliability of the results strongly depends on aspects of usability and error tolerance of the system. This paper presents studies which aim to assess these aspects of reliability of CAS systems. In a clinical study, interaction with a CAS system by 16 expert and novice surgeons was observed and assessed. From 133 recorded incidents 41% were rated to have significant impact on the clinical result or to inhibit successful completion of the task, which indicates a low degree of error tolerance of the system. These findings are supported by the results obtained from questionnaire, were learnability and error tolerance were judged to be not sufficient.

Attitude of Health Personnel↗
PubMed2002

[Minaro--new approaches for minimally invasive roentgen image based hip prosthesis revision].

The main objective of the MINARO project (Minimal Invasive NAvigation and RObotics) is the development of a modular intraoperative planning system for fluoroscopy based total hip revision surgery. Especially the distal cement removal can be a challenging problem. To avoid exhaustive x-ray imaging a navigation system should be used, nevertheless, the three-dimensional shape of the bone cement remains unclear. Our approach in the MINARO-project is to reconstruct the real shape of the bone cement by using just a few x-ray projections. First results show, that the reconstruction has an RMS-Error smaller than 0.5 mm using 6 x-ray projections.

Arthroplasty, Replacement, Hip↗
PubMed2002

[Development of a compact, semi-robotic platform for an electronic surgical microscope].

In the context of the development of a new, electronic microscope for surgical interventions a semirobotic motion platform for the spatial placement and fixation of a stereoscopic camera is currently being developed. Based on an inquiry about the medical, technical and user-requirements, different phases and characteristics concerning frequency, workspace, speed and accuracy of camera movement during an intervention have been specified. To meet these requirements, a differentiated concept for the platform has been developed including a serial structure for manual pre-positioning, a parallel robot for motor-movement during surgical work and different user-interfaces for suitable robot-control.

Equipment Design↗
PubMed2002

[Visual user guidance for registration based on A-mode ultrasound].

In this study we investigate the use of an A-Mode ultrasound probe tracked by a mechanical localizer system (MicroScribe 3D) for non-invasive transcutaneous palpation and registration of bone surface points. A CT of a femur-model has been scanned and subsequently 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 have been recorded and compared. The results for using an A-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 10 bone surface points of distal part of femur.

Arthroplasty, Replacement, Hip↗
PubMed2002

[CRANIO--development of a system for computer- and robot-assisted craniotomy].

In the framework of the DFG project CRANIO, we are dealing with the problems of computer-assisted planning and robot-assisted realization of craniotomy, with optional skull reconstruction. A CT dataset was obtained from a phantom skull model and basic operation planning as well as different registration methods were performed. As one option it is possible to mill a contour on the skull or even to remove the entire area with a robot-guided microsurgical milling tool. In this context, work space tests were performed with a hexapod parallel robot. The milling of any contour geometry could be realized with different tool angles using the existing CRIGOS robot system without additional axes.

Computer Simulation↗
PubMed2002

[Adaptive planing model for osteosynthesis of femoral neck fracture].

To investigate how surgeons can be supported in planning of screws for femoral neck fracture fixation reducing incidents of misplaced screws, a system was developed which makes use of a deformable model to be adapted to the femoral head/neck. The accuracy and usability of the system was checked against planning support systems mimicking the conventional positioning of screws within bi-planar x-rays. All designs were evaluated and compared by N = 7 test user. Checking the rate of misplaced screws a) at the femoral neck yielded rates of 8% or up to 42%, b) at the femoral head yielded rates of 0% or up to 11% for model-based or conventional planning, respectively. It is thus suggested to constrain the planning and navigation space by means of deformable models of the bone.

Bone Screws↗
PubMed2002

[Technical principles for removal of femoral bone cements in hip prosthesis implant revision].

As the removal of femoral bone cement is one of the most challenging tasks in cemented total Hip Revision, a lot of different technical devices have been developed to aid the surgeon. All of their pros and cons are partly consequences of the specific system-design but mainly arise from the basic physical principles used. The known methods and devices as well as their data-handling have therefore been analysed, reduced to their principles according to the criteria of systematic engineering design and systematized in order to provide a better comparability and starting point for the development of new devices.

Arthroplasty, Replacement, Hip↗
PubMed2001

Computer-assisted orthopedic surgery with individual templates and comparison to conventional operation method.

STUDY DESIGN: Comparison was made of the accuracy of a pedicle bore performed by conventional technique and by using an individual template in the lumbar spine of cadavers. OBJECTIVES: The fixation of pedicle screws necessitates a high amount of surgical skill and experience to avoid lesions of nerves and vessels. By using individual templates in a cadaver study the goal was to prove the accuracy and efficiency of this less-invasive image-guided surgery in comparison with the conventional technique by fluoroscopy and computed tomographic (CT) scan. SUMMARY OF BACKGROUND DATA: Based on three-dimensional models generated from CT scans of the lumbar spine, precise preoperative planning of the position and trajectory of pedicle screws is possible. In comparison with other means of computer-assisted spine surgery with navigation systems, in which a time-consuming intraoperative matching of the bone surface structure is necessary, the use of individual templates enables the surgeon to reduce the operation time considerably. METHODS: Individual templates are customized on the basis of three-dimensional reconstructions of the bone structures extracted from CT image data and depending on the individual preoperative surgical planning, which uses the desktop image processing system for orthopedic surgery (DISOS). A desktop-computer-controlled milling device is used as a three-dimensional printer to automatically mold the shape of small reference areas of the bone surface into the body of the template. Postoperative CT scans were obtained and the accuracy of the pedicle bore rated by two independent observers. RESULTS: The preparation time with the individual template lasted slightly longer than with the conventional operation technique (555 seconds and 482 seconds, respectively). Fluoroscopic study took a mean time of 31.5 seconds, with the conventional operation technique and 5.5 seconds with the individual template. The assessment of the postoperative CT scans demonstrated a higher accuracy of the pedicle bore with the individual template. CONCLUSIONS: This cadaveric study has shown that overall operation time including the fluoroscopy time can be shortened by using the individual template for the pedicle bore. The individual template is an alternative to the computer-assisted navigation systems with a good cost-performance ratio without excessive technical workload on the physicians or the surgical personnel. Further investigations must be conducted to validate the clinical applicability of this system.

Bone Screws↗
PubMed2001

An automatic camera-holding system for gynecologic laparoscopy.

Ergonomic analysis of conditions prevailing during laparoscopy show that static holding work causes considerable problems. The surgeon's assistant is particularly affected, for example, by holding the endoscope optical system. To minimize strain for the entire operating team and to increase the range of activities that can be performed by the assistant, an automatic surgical camera-holding system was developed. Its value in clinical practice was tested in gynecologic laparoscopy, where it enabled the surgical team to work more comfortably.

Equipment Design↗
PubMed2000

[Planning and performance of orthopedic surgery with the help of individual templates].

Operational 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 patient's 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.

Arthroplasty, Replacement, Hip↗
PubMed2000

[CRIGOS: development of a compact robot for image-guided orthopedic surgery].

In this paper, we present a medical robot system dedicated to support the surgeon during challenging tasks within orthopedic interventions. The main goal of this work is to develop a system as technically simple as the surgical requirements allow to keep its cost and complexity to a minimum. Therefore, we primarily focus on calibrated X-ray imaging for image acquisition, an easy registration procedure and robotic execution using a positioning device with simple parallel kinematics. Examples of different orthopedic interventions using the compact robot system for image-guided orthopedic surgery (CRIGOS) are presented, as well as various modes of execution of the device.

Arthroplasty, Replacement, Knee↗
PubMed2000

Critical evaluation of known bone material properties to realize anisotropic FE-simulation of the proximal femur.

PURPOSE: In a meta-analysis of the literature we evaluated the present knowledge of the material properties of cortical and cancellous bone to answer the question whether the available data are sufficient to realize anisotropic finite element (FE)-models of the proximal femur. MATERIAL AND METHOD: All studies that met the following criteria were analyzed: Young's modulus, tensile, compressive and torsional strengths, Poisson's ratio, the shear modulus and the viscoelastic properties had to be determined experimentally. The experiments had to be carried out in a moist environment and at room temperature with freshly removed and untreated human cadaverous femurs. All material properties had to be determined in defined load directions (axial, transverse) and should have been correlated to apparent density (g/cm(3)), reflecting the individually variable and age-dependent changes of bone material properties. RESULTS: Differences in Young's modulus of cortical [cancellous] bone at a rate of between 33% (58%) (at low apparent density) and 62% (80%) (at high apparent density), are higher in the axial than in the transverse load direction. Similar results have been seen for the compressive strength of femoral bone. For the tensile and torsional strengths, Poisson's ratio and the shear modulus, only ultimate values have been found without a correlation to apparent density. For the viscoelastic behaviour of bone only data of cortical bone and in axial load direction have been described up to now. CONCLUSIONS: Anisotropic FE-models of the femur could be realized for most part with the summarized material properties of bone if characterized by apparent density and load directions. Because several mechanical properties have not been correlated to these main criteria, further experimental investigations will be necessary in future.

Anisotropy↗
PubMed1999

CRIGOS: a compact robot for image-guided orthopedic surgery.

The CRIGOS (compact robot for image-guided orthopedic surgery) project was set up for the development of a compact surgical robot system for image-guided orthopedic surgery based on user requirements. The modular system comprises a compact parallel robot and a software system for planning of the surgical interventions and for supervision of the robotic device. Because it is not sufficient to consider only technical aspects in order to improve in clinical routine the therapeutic outcome of conventional interventions, a user-centered and task-oriented design process has been developed which also takes human factors into account. The design process for the CRIGOS system was started from requirement analysis of various orthopedic interventions using information gathered from literature, questionnaires, and workshops with domain experts. This resulted in identification of conventional interventions for which the robotic system would improve the medical and procedural quality. A system design concept has been elaborated which includes definitions of components, functionalities, and interfaces. Approaches to the acquisition of calibrated X-rays will be presented in the paper together with design and evaluation of a first human-computer interface. Finally, the first labtype parallel robot based on low-cost standard components is presented together with the first evaluation results concerning positioning accuracy.

Humans↗