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Biomedical subjects

A Lahmer

Publications and source records attributed to A Lahmer.

10 recordsLinked to original sources
PubMed2001

[The importance to generate robot-assisted milled cavities for total hip replacement. A comparative experimental study: manual versus robotic preparation].

We present an experimental study to determine the effectiveness of computer assisted robotic bone preparation with regard to primary rotational stability in comparison to hand broaching. 5 different cementless stems were standardized implanted in synthetic femora and measured in a specially designed apparatus (displacement in 6 degrees of freedom). In addition the contact areas of the stems and the bone were visualized. The S-ROM- and ABG-stems were more stable in hand broached femora. The Osteolock-, G2- and Vision-2000-stems were more stable in the robot group. The mode of fixation of each implant could be characterized in relation to its position and its stiffness (primary rotational stability). The contact areas differed in some prosthesis in the way of preparation. The findings highlight the current difficulties in creating a perfect match of robotically milled cavity and stem geometry to achieve enhanced stability.

Arthroplasty, Replacement, Hip↗
PubMed2000

[VRATS--Virtual Reality Arthroscopy Training Simulator].

The subject of this paper is a highly interactive medical training system for arthroscopic surgery; this is based on computer graphics and virtual reality (VR) techniques and offers an alternative to conventional training methods. To provide the virtual environment, a realistic 3D representation of the knee joint is derived from 2D medical image data. The use of tracking techniques guarantees an intuitive handling of the surgical instruments. The system allows navigation via a virtual camera and interaction with the virtual anatomical structures. First approaches for the simulation of tissue deformation caused by collisions with the instruments are implemented. One important advantage over conventional training systems is the possibility of verifying the training progress. Work is in progress on the realization of tactile feedback with the aim of providing a higher degree of interactive realism.

Arthroscopy↗
PubMed2000

Planning system for computer assisted total knee replacement.

Total knee replacement (TKR) is a common orthopaedic surgical intervention and includes the removal of bone sections from the end of the femur and the top of the tibia for replacement by prosthetic components. Pain relief and functional improvement are predictable clinical results. But the accuracy of the alignment affects the surgical outcome and the longevity of the prosthesis. Hence, current total knee implantation systems attempt to align the knee joint in the mechanical axis for placement of the total knee components. These approaches use templates and plain radiographs for preoperative planning and alignment devices for bone cuts. To overcome the inherent inaccuracy of the presently used systems a computer-assisted planning system has been developed delivering the necessary control data for the intraoperative surgical robot system.

Arthroplasty, Replacement, Knee↗
PubMed1999

Computer assisted implantation of the femoral stem in THA - an experimental study.

Fourteen femoral stems were implanted either manually by an experienced surgeon or by a robot in fresh human cadaveric femora. The neck-shaft angle, the anteversion, the length of the femoral neck and the gap between stem and bone was measured in each specimen. Implantation by robot showed higher precision in reconstructing the true anatomic situation as well as providing a better press fit.

Arthroplasty, Replacement, Hip↗
PubMed1999

Computer-integrated revision total hip replacement surgery: concept and preliminary results.

This paper describes an ongoing project to develop a computer-integrated system to assist surgeons in revision total hip replacement (RTHR) surgery. In RTHR surgery, a failing orthopedic hip implant, typically cemented, is replaced with a new one by removing the old implant, removing the cement and fitting a new implant into an enlarged canal broached in the femur. RTHR surgery is a difficult procedure fraught with technical challenges and a high incidence of complications. The goals of the computer-based system are the significant reduction of cement removal labor and time, the elimination of cortical wall penetration and femur fracture, the improved positioning and fit of the new implant resulting from precise, high-quality canal milling and the reduction of bone sacrificed to fit the new implant. Our starting points are the ROBODOC system for primary hip replacement surgery and the manual RTHR surgical protocol. We first discuss the main difficulties of computer-integrated RTHR surgery and identify key issues and possible solutions. We then describe possible system architectures and protocols for preoperative planning and intraoperative execution. We present a summary of methods and preliminary results in CT image metal artifact removal, interactive cement cut-volume definition and cement machining, anatomy-based registration using fluoroscopic X-ray images and clinical trials using an extended RTHR version of ROBODOC. We conclude with a summary of lessons learned and a discussion of current and future work.

Algorithms↗
PubMed1999

[Computer-assisted surgery for hip endoprosthesis].

The use of computer-controlled robots for implanting cement-free prostheses requires exact preoperative planning on a three-dimensional graphics computer (ORTHODOC). For the first time ever, it has been possible to implement the three-dimensional plan using a computer-controlled robot working on patients. We assume that the considerably improved bone contact provided by the high-precision reaming process--an thus high primary stability--will lead to better incorporation in the bone. In experiments on dogs, in which cement-free hips had been implanted using computer-assisted robots, the animals showed much earlier and more uniform weight-bearing on the affected extremity than animals in a control group that had received conventional implants. In histological therms, the precise fit obtained by the ROBOCOC was accompanied by primary angiogenic healing patterns that all demonstrated labels during the first four weeks. The manually reamed comparators showed more pronounced fissure and defect healing, the healing patterns was irregular, and turnover activity was demonstrate.

Arthroplasty, Replacement, Hip↗
PubMed1998

[Increasing the quality of preoperative planning and intraoperative application of computer-assisted systems and surgical robots--an experimental study].

UNLABELLED: 14 human femurs were scanned by CAT and 3D reconstructed. In every specimen digital documentation of CCD and antetorsion (AT) angle was performed. With a special software package (Orthodoc) virtual preoperative planning for implantation of a cementless total hip alloplasty was undertaken. The specimens were randomised into two groups, one of which had manual and the other one robot implantation of the femoral component. After implantation all specimens were evaluated again by CAT and CCT and AT angle were documented again. The preoperative CCD angle was 126.7 degrees (SD = 4.0) in the manual group and 127.8 degrees (SD = 4.3) in the robodoc group. Postoperatively the angle averaged 131.9 degrees (SD = 0.8) in the manual group and 133.2 degrees (SD = 1.9) in the robodoc group. Significant differences were found for the AT angle in both groups. The preoperative AT angle in the manual group was 31.3 degrees (SD = 8.8), decreasing to 20.5 degrees (SD = 9.5) after implantation. In the robodoc group this angle was 30.9 degrees (SD = 8.0) before and 31.3 degrees (SD = 8.7) after implantation. The difference between pre- and postoperative AT angle averaged 10.8 degrees (SD = 6.4) in the manual group and only 0.4 degree (SD = 0.9) in the robodoc-group. CONCLUSIONS: With the technique used, preoperative planning in hip alloarthroplasty is much more accurate than with the conventional technique with plain X-ray. The virtual preoperative planning can be transferred to the intraoperative setting with high precision. These factors may lead to an increase in outcome quality.

Arthroplasty, Replacement, Hip↗
PubMed1997

[Computer-assisted robotics in hip endoprosthesis implantation].

The most important prerequisite for permanent fixation of an implant is primary stability. Osteointegration of the implant is a major goal in cementless total hip replacement (THR). This means direct contact between bone and implant leading to fixation of the implant in the bone without the interference of fibrous tissue. In addition to the design of the implant, the structure of the implant surface and the material of the implant, the specific operational technique plays a major role in permanent fixation. Only the conical fixation of femoral implants guarantees high primary stability in cementless THR. The type of fixation of the implant in the femoral cavity and the resulting load transfer from implant to bone has a decisive effect on the durability of the prostheses. In order to achieve optimal primary fixation of the implant, robot-assisted implantation of the cementless implant has been performed at the Berufsgenossenschaftliche Unfallklinik Frankfurt am Main since the summer of 1994. After preoperative planning at a three-dimensional graphic work station these data are transferred to the robot, which transforms the preoperative planning by milling the femoral cavity with the highest precision. So far this type of surgery has been performed on 300 patients. The encouraging postoperative results prompted us to install the second system of Robodoc at the Berufsgenossenschaftliche Unfallklinik Frankfurt.

Arthroplasty, Replacement, Hip↗
PubMed1997

[Computer-guided robot-assisted hip endoprosthesis].

Computer-guided robot-assisted surgery in cementless total hip replacement requires exact preoperative planning at the 3D workstation Orthodoc. Only the Robodoc procedure allows the precise execution of the preoperative plan in surgery. Robot-assisted surgery has been undergoing clinical evaluation at the Berufsgenossenschaftliche Unfallklinik, Frankfurt, since November 1994. In all 465 patients, the preoperative plan was successfully carried out intraoperatively. The high precision in reaming, leading to a superb bone implant contact, guarantees absolute initial stability and is likely to promote primary healing between implant and bone. The common and often published incidence of varus or valgus malpositioning and any fractures or fissures could be avoided through the use of Robodoc. Although immediate full-weight bearing was strongly recommended to the patients, no implant subsidence was seen in the treatment follow-up X ray studies.

Adult↗