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Biomedical subjects

N Suhm

Publications and source records attributed to N Suhm.

At least 19 recordsLinked to original sources
PubMed2006

[Treatment of osteoporosis--the new role of the orthopaedic surgeon].

Fractures which are caused by falling from standing height or less are named "fragility fractures". These fractures may indicate neglected osteoporosis and will occur even more frequently in the future, due to the demographic change. This is why osteoporosis will become a challenge to our healthcare systems. For the orthopaedic surgeon treatment of osteoporosis was limited to fracture fixation in the past. As this approach is very focussed towards the fracture as the major complication of osteoporosis, there is a big potential for improvement. It is important to know that such patients suffering from a first fragility fracture are at high risk for being hit by a second or further fragility fractures. A fracture prevention programme should therefore become a mandatory requirement for these patients in the future. The orthopaedic surgeons will be the key players who should put this approach into effect. As we treat most patients with fragility fractures it is our privilege to identify those patients who will most likely benefit from fracture prevention.

Age Factors↗
PubMed2006

Augmentation of implant purchase with bone cements: an in vitro study of injectability and dough distribution.

Vertebroplasty is widely used to treat (augment) osteoporotic fractures of the spine. This technique--with or without metallic implants--might have more widespread indications, if the mechanics of the injection and distribution of the cement dough through cannulated instruments and implants were better understood. This study was performed to investigate injectability of calcium phosphate and acrylic bone cements through implant prototypes, which featured different perforated sleeve designs. Using a custom-made capillary rheometer, the forces needed to inject 10 mL of the cement dough through standard cannulas were measured in the first series of experiments. In the second series, plastic sleeves were attached to the rheometer, simulating the implant. In both series, the dough was injected into ambient laboratory atmosphere, and in the second series, cement distribution was analyzed by means of an optical system. Injection of cement dough through the cannulas required forces between 50 and 400 N in the case of acrylic cements and between 40 and 500 N in case of the calcium phosphate cements. Using different sleeves did not have a significant influence on the distribution of the cement dough around the sleeve. The amount of cement dough injected was reduced when a perforated implant was attached to the cannula. More material was delivered through the proximal holes of the implant, leading to a V-shaped distribution of the cement dough. Among topics to be investigated in future studies is determination of the injectability of cement dough into trabecular bone or bone-like structures.

Biocompatible Materials↗
PubMed2006

Augmentation of osteoporotic bone: effect of pulsed jet-lavage on injection forces, cement distribution, and push-out strength of implants.

Demographic change in the population leads to higher incidence of fragility fractures. Fracture fixation with standard implants may lead to implant cut-out due to reduced purchase. Augmentation of the bone stock with bone cements might overcome this problem. However, cancellous bone infiltration with the viscous cement dough reveals problems of fat embolism or high pressures during application of the cement. This study investigates the improved quality of bovine cancellous bone augmentation when pulsed jet-lavage is used for fat and marrow removal. Parameters such as injection forces, cement dough distribution through cannulated implants and mechanical strength of the fixation were applied for quantification. Injection of 5 mL of acrylic bone cement required significantly lower forces in the lavaged as compared to the untreated bone (50 N vs. > 300 N). Cement distribution was much more homogeneous and push-out forces significantly higher in the pretreated bone group (8.33 +/- 1.41 kN vs. 1.66 +/- 0.63 kN). The application of pulsed jet-lavage for fat removal prior to acrylic cement augmentation led to much more controlled outcomes of the augmentation. This seems to be a relevant step towards safe and efficient injection of bone cements into cancellous bone structures.

Bone Cements↗
PubMed2006

Biomechanical evaluation of a new augmentation method for enhanced screw fixation in osteoporotic proximal femoral fractures.

A biomechanical investigation on eight pairs of human cadaver proximal femurs was performed to evaluate the impact of a new augmentation method on the internal fixation of osteoporotic proximal femur fractures. The study focused on enhancing implant purchase to reduce the incidence of implant cut-out in osteoporotic bone. In a left-right comparison, a conventional hip screw fixation (control) was compared to the new cement augmentation method. After bone bed preparation through high pressure irrigation to remove fat, blood, and bone debris, the bones were augmented with low viscosity polymethylmethacrylate (PMMA) cement. Step-wise fatigue testing was performed by cyclically loading the femoral heads in a physiological manner, beginning at 1,500 N and increasing 500 N every 5,000 cycles to 4,000 N, and continuously monitoring head displacement. Failure was defined as >5.0 mm head displacement. The head displacement at 2,000 N was significantly smaller (p=0.018) for the augmented group as compared to the conventionally treated bones (0.09+/-0.01 mm vs. 0.90+/-0.32 mm; mean+/-SEM). The displacement rate at the second load step was significantly higher (p=0.018) for the conventionally treated bones as compared to the augmented ones. All of the nonaugmented specimens failed during testing, where 50% of the augmented specimens did not fail. The promising results of these experiments suggest that this new standardized irrigation/augmentation method enhances the implant anchorage and offers a potential solution to the problem of implant cut-out in osteoporotic metaphyseal bone.

Biomechanical Phenomena↗
PubMed2004

Fixation principles in metaphyseal bone--a patent based review.

Osteoporotic changes start in cancellous bone due to the underlying pathophysiology. Consequently, the metaphyses are at a higher risk of "osteoporotic" fracture than the diaphysis. Furthermore, implant purchase to fix these fractures is also affected by the poor bone quality. In general, researchers and developers have worked on three different approaches to address the problem of fractures to osteoporotic bone: adapted anchoring techniques, improved load distribution as well as transfer with angular stable screws, and augmentation techniques using bone substitutes. A patent-based review was performed to evaluate which ideas were utilized to improve fixation in osteoporotic, metaphyseal bone, especially in the proximal femur, and to analyze whether the concept had entered clinical use. Anchoring devices that are either extramedullary or intramedullary have a long clinical history. However, demanding surgical techniques and complications, especially in poor quality bone, are justification that such implants and their corresponding surgical techniques need to be improved upon. Expanding elements have been evaluated in the laboratory. The results are promising and the potential of this approach has yet to be fully exploited in the clinics. Internal fixators with angular stable screws open the door for many new anchorage ideas and have great potential for further optimization of load distribution and transfer. Augmentation techniques may improve anchorage in osteoporotic bone. However, the properties of bone substitute materials will need to be modified and improved upon in order to meet the demanding requirements. If we summarise the development process and the clinical use of implants to date, we have to clearly state that more factors than simply biomechanical advantage will determine the clinical success of a new fixation principle or a new implant. Instead, fracture treatment of patients with osteoporosis really needs an interdisciplinary approach!

Bone Nails↗
PubMed2003

[Fluoroscopy based surgical navitation vs. mechanical guidance system for percutaneous interventions. A controlled prospective study exemplified by distal locking of intramedullary nails].

The aim of this study was to directly compare mechanically based targetting and surgical navigation when applied for percutaneous osteosynthesis. The distal locking procedure of intramedullary nails was used as the clinical model for a controlled prospective study. A total of 50 patients were included in two groups. In group 1, the distal locking was done with a mechanical aiming device while in group 2 this was done using a fluoroscopy based surgical navigation system. The target parameters were the precision attained, the necessary operation and fluoroscopy times as well as the number and severity of intra-operative problems. The drill-bit failed to pass through the interlocking hole in one patient with mechanical guidance and in two patients with surgical navigation. The average procedure time for distal locking with mechanical guidance was 6.9 minutes compared with 37.6 minutes with surgical navigation. An additional 44 minutes were required before skin incision and after skin closure as setup time for the navigation system. There was no significant difference in the fluoroscopy time or in the number of intra-operative technical problems. Surgical navigation increased the demand for resources but failed to improve the precision of distal locking compared with mechanical guidance. Further clinical studies are required to determine to what degree these results, using a special model, relate to other applications.

Aged↗
PubMed2003

Adapting the fluoroscope to image-guided surgery.

Image-guided techniques have been well established in all surgical disciplines for years. To achieve an optimised work flow during image-guided surgery, the surgeon should be able to manipulate the visual feedback and therefore the imaging unit. C-arm fluoroscopy is the imaging modality routinely used for intraoperative imaging in orthopaedic surgery. The C-arm fluoroscope is positioned and handled by a radiographer on vocal commands, which means that the surgeon depends on external help to manipulate the visual feedback and the work flow is not optimised. The MEPUC interface adapts the C-arm fluoroscope to the needs of image-guided orthopaedic procedures. MEPUC is an acronym for Motorised Exact-Positioning Unit for C-arm. In the hardware component of the MEPUC a conventional C-arm fluoroscope is equipped with stepping motors. The software component allows the surgeon to control the motorised movements of the fluoroscope. The MEPUC interface enables the surgeon to position the C-arm fluoroscope independently in the operating room. Further advantages are achievable when the MEPUC interface is combined with surgical navigation, as this combination allows fully automatic reproduction of former projections. Clinical experience with the MEPUC interface suggests that the work flow for intraoperative imaging is improved and personal requirements reduced.

Fluoroscopy↗
PubMed2001

Intraoperative accuracy evaluation of virtual fluoroscopy--a method for application in computer-assisted distal locking.

Virtual fluoroscopy integrates intraoperative C-arm fluoroscopy as an imaging modality for surgical navigation. In the operating room, the conditions for application of virtual fluoroscopy may be impaired. In such situations, the surgeon is interested in an intraoperative check to decide whether the accuracy available is sufficient to perform the scheduled procedure. The test principle is to include an artificial landmark within the fluoroscopic images acquired for virtual fluoroscopy. As this landmark is fixed outside the patient, it can be touched with the referenced tool prior to performing the procedure. A mismatch between the actual tool position at the landmark and the virtual tool position as visualized on the computer screen allows estimation of the system's accuracy. The principle described was designed for detection of inaccuracies resulting from input of nonoptimal data to the navigation system. The method was successfully applied during computer-assisted distal locking of intramedullary implants, and the test principle might be adapted for other applications of virtual fluoroscopy.

Fluoroscopy↗
PubMed2001

Volumetric model determination of the tibia based on 2D radiographs using a 2D/3D database.

We present a new concept with mathematical background for the construction of a three-dimensional (3D) volumetric model of the human tibia based on two conventional orthogonal two-dimensional (2D) radiographic images. This approach is supported by a computer database containing a collection of 80 2D/3D image data sets of individual cadaveric tibiae. For each of these tibiae, the database contains digitized 2D orthogonal radiographic images in both anterior and lateral views, and the corresponding 3D CT data obtained by computerized tomography. To obtain a 3D model of a tibia for a given patient, shape matching is performed. The computer finds the most similar tibia to the patient's tibia among the 2D radiographic images in the database by applying a matching process. To improve accuracy, a 2D image warping procedure can be applied on the slices of the selected bone prior to 3D reconstruction. The warping process is controlled by the contour data of the two orthogonal views. We found that the 3D model thus achieved was useful for virtual preoperative planning and for simulation of the internal fixation of long bones.

Cadaver↗
PubMed2001

[Technology integration and process management. Concept and implementation of a new platform for simultaneous diagnosis and therapy of acutely ill and injured patients and for elective computer assisted surgery (CAS)].

Modern imaging and computer technology gain more and more importance in surgery. This is true for elective and emergency diagnosis and treatment. However integration of technology and optimization of process management is severely behind. A new diagnostic-therapeutic platform should balance this deficit. The platform is composed of a fully equipped operation room environment with integrated high end computer-tomography with navigation, a digital subtraction angiography and an OR- and imaging-table particularly developed for this set-up. The platform may be used for elective diagnosis, for diagnosis and therapy in polytraumatized patients in one and the same location (one stop shop) and for computer assisted surgery (CAS). Bringing the technology to the patient and not the patient to the technology can save time consuming and potentially dangerous transports and expensive personnel can be reduced. Navigation-technology and high quality intra-operative imaging expand the spectrum of minimally invasive surgery.

Diagnostic Imaging↗
PubMed2001

[Radiation exposure of the patient by intraoperative imaging of intramedullary osteosyntheses].

MATERIAL AND METHOD: 39 patients with pertrochanteric femur fracture (n = 32) or lower leg fracture (n = 7) were treated with closed intramedullary nailing. The related radiation exposure of the patients was calculated. RESULTS: Osteosynthesis of pertrochanteric fractures took less fluoroscopic time than osteosynthesis of lower leg fractures. The effective dose was 14 mSv for nailing osteosynthesis of proximal pertrochanteric fractures and less than 0.1 mSv for osteosynthesis of distal lower leg fractures. CONCLUSION: Radiation exposure of the patient due to intraoperative fluoroscopic imaging during osteosynthesis can be estimated based on the data given above. Intraoperative observations imply, consequent application of radiation protection by the orthopaedic surgeons may reduce intraoperative radiation exposure even more.

Female↗
PubMed2001

[Navigation systems for image-guided therapy: A review].

Navigation systems for image-guided therapy: A review. Navigation is visually interactive targeting based on the simultaneous display of instrument position and of the corresponding two- or three-dimensional image data sets. In this way it unifies anatomic information and therapeutic action. Medical navigation systems (MNS) can simulate realtime image guidance and thereby reduce radiation exposure as well as provide the full range of digital image processing during an intervention. Navigation is based on the tracking of medical instruments in space and the transformation of image, patient, and instrument coordinates into a common reference system. If the patient coordinate system is used as the common base, the process is called patient-based navigation (PBN). If, however, the imaging modality is present in the interventional suite and its reference system is used, modality-based navigation (MBN) results. MBN does not need pre-interventional registration and inherently provides intra-operative imaging. In neurosurgery MNS's have been well established since years. They are in use for frameless biopsies and for minimizing the access morbidity in deeply situated pathologies. Currently there is a fast expansion of navigation into other surgical disciplines, e.g., orthopaedic surgery. The clinical accuracy of an MNS is hard to determine since an independent method of measurement is mostly not available during surgery. Normally, a deviation of below one up to about 5 mm between the display of the MNS and the actual position of an anatomic structure is reported. So far there have been only very few prospective randomized clinical trials between conventional and navigated interventions.

Forecasting↗
PubMed2000

Surgical navigation based on fluoroscopy--clinical application for computer-assisted distal locking of intramedullary implants.

OBJECTIVE: Fluoroscopy is used to guide surgical instruments during orthopedic procedures. Radiation exposure and lack of spatial information are drawbacks of this method. Improvements are expected when fluoroscopy-based surgical navigation is used for intraoperative guidance, e.g., in computer-assisted distal locking of intramedullary implants. PATIENTS AND METHODS: The method was applied to 42 interlocking procedures during implantation of the short proximal femoral nail in 27 patients with pertrochanteric femoral fractures. Precision of interlocking, exposure time, operating time, and number of personnel required for computer-assisted distal locking were recorded. RESULTS: One misplaced interlocking screw was observed (2.3%), and contact between the drill bit and the nail during drilling was noticed in 8 cases (19%). The average exposure time was 16 seconds (range 4-42 seconds), and the procedure took an average of 43 min (range 20-70 min). The number of persons required for computer-assisted distal locking was reduced from three to one within the course of the study. CONCLUSIONS: Fluoroscopy-based surgical navigation provided precise intraoperative guidance for computer-assisted distal locking with minimal use of fluoroscopy. The complex system and related procedure times may be drawbacks in this application. Clinical studies are underway to define implants and surgical procedures where intraoperative guidance by fluoroscopy-based surgical navigation is beneficial for the patient and/or surgeon.

Computer Simulation↗
PubMed2000

A whole-body registration-free navigation system for image-guided surgery and interventional radiology.

RATIONALE AND OBJECTIVES: To develop and test an image-guided navigation system in which the base of reference is taken from the imaging modality, here, a helical CT scanner. METHODS: An optical digitizer together with a calibration device is used to measure the transformation matrix between the digitizer reference system and a CT reference system. During intervention, it tracks radiological and surgical tools with tool references. A specific software visually integrates the current tool position with the corresponding image information. In vitro accuracy tests were performed. RESULTS: With helical CT, freehand positioning accuracy was 1.9 +/- 1.1 mm (mean +/- SD) in vitro (n = 718). CONCLUSIONS: The navigation system developed by the authors appears to be feasible for radiological interventions as well as for minimally invasive surgery. It is not limited to a certain procedure, can be used in every region of the body, and is functional after imaging. Intraprocedural scans can be integrated immediately.

Equipment Design↗
PubMed1998

Limitations for three-dimensional ultrasound imaging through a bore-hole trepanation.

The intraoperative shift of neuroanatomical landmarks that serve as reference points is an unsolved problem in current neuronavigation. Monitoring the position of these landmarks requires repeated intraoperative imaging. We analyzed the effectiveness of a 3-D ultrasound system for imaging through a bore-hole trepanation. A tissue-mimicking ultrasound phantom and plastic pads with bore-holes were utilized for in vitro tests of the system. Reducing the diameter of the simulated bore-hole decreased the image quality and reduced the field of view. The multiple plane mode of the 3-D ultrasound system allows reconstruction of images in arbitrary imaging planes on the basis of intraoperatively acquired 3-D datasets. Selecting planes that are coplanar with preoperative MRI scans, we were able to identify neuroanatomical landmarks in the reconstructed ultrasound images. Repeated 3-D ultrasound during a procedure might, therefore, allow recognition of a shift of these landmarks.

Artifacts↗
PubMed1996

Ablation of neural tissue by short-pulsed lasers--a technical report.

The basis for most laser applications in neurosurgery is the conversion of laser light into heat when the incident laser beam is absorbed by the tissue. Irradiation of neural tissue with laser light therefore leads to its thermal damage. However, due to the diffusion of heat energy into the surrounding tissue, often there is thermal damage to neural tissue outside the area of the target volume. These are the characteristics of thermal laser/tissue interaction. In this paper we discuss how we used three different short-pulsed lasers to achieve non-thermal ablation of neural tissue. Three different short-pulsed lasers were used to generate ultrashort laser pulses in the picosecond to femtosecond range. The interaction of such laser pulses with tissue was predicted to be nonthermal. The short-pulsed lasers were used for the ablation of neural tissue using an in vitro calf brain model. The histopathological examination of the lesions revealed that the neural tissue had been removed very precisely without any sign of thermal damage to the surrounding tissue.

Animals↗
PubMedDate not supplied

Coronal acetabular fractures: the anterior approach in computed tomography-navigated minimally invasive percutaneous fixation.

PURPOSE: To demonstrate the technical feasibility of the anterior approach to the coronal roof component of carefully selected acetabular fractures in computed tomography (CT)-navigated closed reduction and percutaneous fixation (CRPF). METHODS: Four patients with nondisplaced or slightly displaced coronal fractures of the acetabular roof were treated with percutaneous screw fixation. Screws were implanted over guidepins placed under CT navigation. Mean clinical and radiological follow-up was 16 months. RESULTS: All screws could be placed as intended. There were no peri- or postoperative complications. Radiological follow-up showed primary osseous union. Clinical results were excellent according to a median Merle-d'Aubigné score of 18. CONCLUSION: Nondisplaced or slightly displaced coronally oriented fractures of the acetabular roof can be treated by minimally invasive percutaneous CT-navigated fixation through an anterior approach that does not endanger the sciatic nerve. Early clinical results are encouraging. Close cooperation between trauma surgeons and radiologists and careful selection of cases is mandatory.

Acetabulum↗