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Biomedical subjects

J A K Ohnsorge

Publications and source records attributed to J A K Ohnsorge.

10 recordsLinked to original sources
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

[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↗
PubMedDate not supplied

[Accuracy of fluoroscopically navigated drilling procedures at the hip].

AIM: Many orthopaedic procedures require an accurate drilling in bone. The outcome is frequently dependent on the geometric accuracy of this surgical step. The precision of such a procedure can be improved with the help of fluoroscopic navigation. Reliability, accuracy and benefit of this new method for the patient, as well as for the surgical staff, need to be analysed. METHOD: In a standardised in vitro trial, the drilling of a 5 mm spherical lesion implanted in an artificial femoral head was performed using a navigated drill-guide and a navigated drill. In groups A and B, the distance of the tip of the drill to the center of the lesion was analysed in a 3D CT-generated model and in macroscopic cross section. Additionally, in group B the actual direction of the drill canal was measured. RESULTS: The mean distance in group A was measured to be 1 mm, with all results ranging between 0 and 2.5 mm. In group B the planned direction of the canal was reproduced with a deviation of 0 degrees to 7 degrees, the target only being missed by a mean distance of 2.5 mm and a maximum of 3.5 mm. Compared to the macroscopic and 3D-CT findings, the correlation of the data calculated by the navigation system was accurate up to a difference of 4 degrees or 2 mm. CONCLUSION: The fluoroscopically assisted freehand navigation used during the drilling of bone led to a high accuracy of three-dimensional tip placement while reducing radiation exposure to a minimum. It represents a promising and efficient application for a variety of procedures in orthopaedic surgery.

Artifacts↗
PubMedDate not supplied

[Computer-assisted retrograde drilling of osteochondritic lesions of the talus with the help of fluoroscopic navigation].

AIM: Due to the narrow access to the talar dome and the proximity of osteochondritic lesions to the joint surface, the therapeutic retrograde drilling often requires multiple attempts and repeated intraoperative X-ray-control. The advantages of a fluoroscopy-based computer-assisted navigation system regarding efficient planning and easy performance of the ideal drill path are evaluated in respect to accuracy and radiation exposure, as well as to time requirements. METHOD: A 5 mm spherical target was subcortically implanted in the medial aspect of the talar dome of 16 human cadaver specimens. Free-hand drilling was performed using the FluoroNav TM system in one group and conventional repetitive C-arm control in the other. The computed evaluation of the operative results was realized in a CT-generated 3D-model with the help of the DISOS planning and calculation program. The distance of the tip of the drill to the center of the lesion was measured, as well as X-ray exposure and total operating time. RESULTS: The CAS procedure missed the lesion only once. The mean deviation of the computer-guided drill path was measured to be 2 mm, whereas the conventional method led to a mean distance of 5 mm from the target. Conventional drilling failed to reach the target in 5 cases, violating the articular cartilage twice. Navigation reduced the traditionally required multiple attempts of the intervention to just one drill canal and reduced radiation time to 25 %. Despite the increased technical preparation required, the navigated procedure only exceeded the conventional operating time by 2 minutes. CONCLUSION: Thanks to the significantly increased accuracy, fluoroscopic navigation offers a high degree of safety and efficacy for this minimally invasive procedure. The operation can easily be performed successfully causing only minimal collateral damage to the bone, preserving the joint surface. The inherent risks of the retrograde drilling of osteochondritic lesions are lower with navigation, while the radiation exposure of the patient and the staff is significantly reduced.

Cadaver↗
PubMedDate not supplied

[Minimally-invasive computer-assisted fluoroscopic navigation for kyphoplasty].

AIM: The transpedicular placement of a hollow needle into vertebral bodies for kyphoplasty requires utmost accuracy and thereby permanent multiplanar X-ray control. Facing the increasing number of vertebral compression fractures, the aim of this work was the implementation of computer-assistance to optimise the issue. Prior to clinical implementation, experimental trials were undertaken to analyse the quality-improving options of the technique. METHOD: The virtual image of the planning and the puncture were correlated with the postoperative X-ray image of the needle. The real canal in the bone was then correlated with the preoperative planning in a CT-based 3D model and differences were calculated. As a measure of accuracy the deviation of the needle from the ideal intruding vector and the distance between its top and the centre of a predefined target were scrutinised and related to the indications of the navigation system. Operating time, radiation exposure and general applicability were additionally assessed. All data were compared with those of a conventional control group. RESULTS: Planning and navigation could be executed with high accuracy. With an exactly transpedicular approach, neural structures were safely circumnavigated without once missing the target. In the control group the distance fault was up to 9 mm. The navigated drilling differed from the ideal trajectory by 1 degrees to max. 4 degrees. Conventional C-arm control led to a divergence of 4 degrees to 8 degrees . Radiation exposure could be reduced through computer assistance by 76 % to a fourth of the conventionally resulting amount and the pure operating time thereby decreased by 40 %. The inconvenient course of repeated positioning of the C-arm was overcome. CONCLUSION: In challenging cases of deteriorated anatomy and difficult radiomorphologic orientation, especially of the lower thoracic spine, the CAOS-procedure succeeds in finding the optimal pedicular approach to the vertebral body, helps to avoid collateral damage and minimises the overall risk of the procedure. High accuracy and reduced radiation exposure justify the clinical use of fluoroscopic navigation for transpedicular instrumentation.

Decompression, Surgical↗
PubMedDate not supplied

[epiDRB--a new minimally invasive concept for referencing in the field of computer-assisted orthopaedic surgery].

AIM: Optoelectronic navigation for computer-assisted orthopaedic surgery (CAOS) is based on a firm connection of bone with passive reflectors or active light-emitting diodes in a specific three-dimensional pattern. Even a so-called "minimally-invasive" dynamic reference base (DRB) requires fixation with screws or clamps via incision of the skin. Consequently an originally percutaneous intervention would unnecessarily be extended to an open procedure. Thus, computer-assisted navigation is rarely applied. Due to their tree-like design most DRB's interfere with the surgeon's actions and therefore are at permanent risk to be accidentally dislocated. Accordingly, the optic communication between the camera and the operative site may repeatedly be interrupted. The aim of the research was the development of a less bulky, more comfortable, stable and safely trackable device that can be fixed truly percutaneously. METHOD: With engineering support of the industrial partner the radiolucent epiDRB was developed. It can be fixed with two or more pins and gains additional stability from its epicutaneous position. The intraoperative applicability and reliability was experimentally tested. RESULTS: Its low centre of gravity and its flat design allow the device to be located directly in the area of interest. Thanks to its epicutaneous position and its particular shape the epiDRB may perpetually be tracked by the navigation system without hindering the surgeon's actions. Hence, the risk of being displaced by accident is minimised and the line of sight remains unaffected. CONCLUSION: With the newly developed epiDRB computer-assisted navigation becomes easier and safer to handle even in punctures and other percutaneous procedures at the spine as much as at the extremities without an unproportionate amount of additional trauma. Due to the special design referencing of more than one vertebral body is possible at one time, thus decreasing radiation exposure and increasing efficiency.

Equipment Design↗
PubMedDate not supplied

[Special surgical technique of minimally invasive total knee replacement].

AIM: Due to the initial disappointing experience with minimally invasive knee arthroplasty, many surgeons still prefer the conventional technique. Sharing technical details, personal insights and results may help abbreviate the individual learning curve towards successful MIS. METHOD: Based on the experience of over 250 minimally invasive knee arthroplasties an operative algorithm was developed and evaluated to assure optimal realization of a gentle joint replacement using a mini-mid-vastus incision. Short-term results were compared to those of the conventional technique with particular regard to pain, use of analgesic medication, flexion of the knee and achievements at physiotherapy. RESULTS: In comparison to the conventional procedure, MIS produced significantly better results regarding pain and function during early rehabilitation and did not affect the perfect positioning of the implants. The morphine-equivalent dose was less than a half on day 2 after operation. Flexion on days 1 and 3 was 70 degrees and 75 degrees respectively. 80 degrees were obtained after 4 days and after 6 weeks flexion was at an average of 115 degrees . In contrast, results of the conventional control group were notably worse, with 50 degrees and 65 degrees on days 1 and 3, 80 degrees being obtained on day 6 only and a mean flexion of 100 degrees after 6 weeks. CONCLUSION: The special surgical technique of minimally invasive knee arthroplasty accelerates and facilitates the rehabilitation of the patient and thereby defines a new quality standard.

Algorithms↗
PubMedDate not supplied

[Reduction of spondylolisthesis by temporary adjacent segment distraction].

AIM OF THE STUDY: Multiple instrument systems are currently available for the reduction of spondylolisthesis, where posteriorly oriented tensile forces are directly acting on the slipped vertebra. The aim of this clinical study was to evaluate the clinical efficacy of a new indirect reduction manoeuvre applied to the lumbar spine. METHOD: A total number of 32 patients (14 female, 18 male) suffering of spondylolisthesis were reduced by transpedicular instrumentation during June 2001 until October 2003. The cranial adjacent vertebra was temporarily instrumented and the reduction of the slipped vertebra was facilitated by the application of traction on the instrumentation leading to tension of the longitudinal ligaments. Posterior transforaminal lumbar interbody fusion (TLIF) or anterior lumbar interbody fusion (ALIF) was then carried out according to the degree of degenerative shortening of the anterior long. spinal ligament. On the last follow up (average 32 month postoperatively; min.: 22 month) both the reduction of the spondylolisthesis and the ossification of the interbody fusion was evaluated radiologically. Physical function and patients satisfaction was measured by means of the SF 36 questionnaire. RESULTS: The dislocation was reduced in all cases (81% on average). At the time of the last follow up bony fusion was depicted on the radiographs in all 32 patients. A distinct improvement in all categories of the SF 36 (in 5 out of 8 categories statistic significant) could be demonstrated. CONCLUSION: Temporary intraoperative instrumentation of the cranial adjacent segment proofs to be a simple an effective method for the sufficient reduction of spondylolisthesis.

Adult↗