Numerische Synthese überbestimmter Mechanismen

Der Freiheitsgrad einer räumlichen kinematischen Schleife kann im Allgemeinen mit Hilfe des Grübler-Kutzbach-Kriteriums bestimmt werden. Dieses gilt jedoch nur, wenn die durch die Gelenke eingebrachten Bindungen voneinander unabhängig sind. Sind die auftretenden Bindungen aufgrund spezieller geometrischer Eigenschaften voneinander abhängig, so kann dies zu weiteren Bewegungsfreiheitsgraden führen. In diesem Falle wird von überbestimmten Mechanismen gesprochen. Während für die kinematische Analyse überbestimmter Mechanismen allgemeingültige Ansätze existieren, beschränken sich die Syntheseverfahren meist auf spezielle Klassen überbestimmter Mechanismen. Im Folgenden wird ein Ansatz zur Synthese überbestimmter einschleifiger Mechanismen mit Schraubgelenken vorgestellt. Betrachtet werden kinematische Einzelschleifen mit n ≤ 6 Körpern und Schraubgelenken (nH-Schleife). Die Schleifenschließbedingungen können mit Hilfe der Schraubachsen der Gelenke als implizite Bindungen auf Geschwindigkeitsebene ausgedrückt werden. Für den Fall, dass die kinematische Schleife einen Bewegungsfreiheitsgrad von f = 1 aufweist, existiert eine einparametrige explizite Lösung der impliziten Bindungen, welche jedoch im Allgemeinen nicht analytisch gefunden werden kann. Aus diesem Grund werden die impliziten Bindungen auf Geschwindigkeitsebene durch eine Taylorreihe approximiert und die notwendige Bedingung des Rangabfalls der Koeffizientenmatrix mit Hilfe von reziproken Schrauben formuliert. Dies liefert notwendige Bedingungen für die endliche Beweglichkeit einer nH-Schleife. Es kann gezeigt werden, dass das Erfülltsein einer endlichen Anzahl dieser notwendigen Bedingungen hinreichend ist für die endliche Beweglichkeit der nH-Schleife. Dadurch können die gewonnenen Bedingungen für die numerische Synthese von nH-Mechanismen verwendet werden

Bifocal extra- and intradural melanocytoma of the spine: case report and literature review

Background: Spinal melanocytoma is one of the most infrequent space-occupying lesions of the central nervous system. To the best of our knowledge, this is the first report of primary bifocal intradural melanocytoma of heterogenous pathological grade to date. Case description: We report the case of a 43-year old patient with primary bifocal melanocytoma, clinically and radiologically resembling benign schwannoma. The patient presented with myeloradiculopathy of the left C3 dermatome. Magnetic resonance imaging of the upper spine revealed two space-occupying lesions with paraspinal extension, initially diagnosed as neurofibroma. Definitive histopathological classification of both lesions was melanocytoma. Both tumours were only partially removed due to adherence to surrounding structures. The patient underwent stereotactic external beam irradiation (EBR). Follow-up at 1year after surgery revealed no recurrence and the patient remained free of symptoms. The clinical, radiological and pathological features of this rare tumour entity are presented and the available literature is reviewed. Conclusions: Intradural melanocytoma, although exceedingly rare, requires a thorough work-up to exclude malignant melanoma. With only two previous reports of multifocal melanocytoma published in the literature, standard therapy has not yet been established and complete surgical removal remains the modality of choice. Patients should be closely monitored to detect local recurrence or malignant degeneration. EBR may be considered in cases where total excision is not achievable and reduces risk of local recurrence

Intraoperative low-field MR-guided frameless stereotactic biopsy for intracerebral lesions

Background: To present our intraoperative low-field magnetic resonance imaging (ioMRI) technique for stereotactic brain biopsy in various intracerebral lesions. Method: Seventy-eight consecutive patients underwent stereotactic biopsies with the PoleStar N-20/N-30 ioMRI system and data were evaluated retrospectively. Biopsy technique included ioMRI before surgery, followed by insertion of the biopsy cannula in the lesion, and ioMRI before and after biopsy. Statistical analysis was performed to compare subgroups using Excel and SPSS statistic software. Results: In all patients, stereotactic biopsy was possible, with a mean intraoperative surgery time of 86.2 ± 28.6min and a mean hospital stay of 11.6 ± 4.6days. In 97.4% (n = 76), histology was conclusive, representing 58 brain tumors and 18 other pathologies. Five patients were biopsied previously without conclusive diagnosis, and all biopsies were conclusive this time. Mean cross-sectional lesion size in MRI T1 with contrast (n = 64) was 6.9 ± 5.7cm2, and in lesions without T1 contrast enhancement (n = 14), T2 mean cross-sectional lesion size was 5.5 ± 3.9cm2. Mean distance from the cortex surface to the lesion was 3.4 ± 1.2cm. One patient suffered from a postoperative wound dehiscence; neither clinically or radiologically significant hemorrhage after surgery, nor intraoperative complications occurred. Conclusions: Low-field ioMR-guided frameless stereotactic biopsy accurately diagnosed different intracerebral lesions without major complications for the patients, and within an acceptable surgery time and hospital stay. In repeated non-conclusive biopsies in particular, low-field ioMRI offers a technique for arriving at a diagnosi

Intra-operative high frequency ultrasound improves surgery of intramedullary cavernous malformations

Intra-operative ultrasound (ioUS) is a very useful tool in surgery of spinal lesions. Here we focus on modern ioUS to analyze its use for localisation, visualisation and resection control in intramedullary cavernous malformations (IMCM). A series of 35 consecutive intradural lesions were operated in our hospital in a time period of 24months using modern ioUS with a high frequency 7-15MHz transducer and a true real time 3D transducer (both Phillips iU 22 ultrasound system). Six of those cases were treated with the admitting diagnosis of a deep IMCM (two cervical, four thoracic lesions). IoUS images were performed before and after the IMCM resection. Pre-operative and early postoperative MRI images were performed in all patients. In all six IMCM cases a complete removal of the lesion was achieved microsurgically resulting in an improved neurological status of all patients. High frequency ioUS emerged to be a very useful tool during surgery for localization and visualization. Excellent resection control by ultrasound was possible in three cases. Minor resolution of true real time 3D ioUS decreases the actual advantage of simultaneous reconstruction in two planes. High frequency ioUS is the best choice for intra-operative imaging in deep IMCM to localize and to visualize the lesion and to plan the perfect surgical approach. Additionally, high frequency ioUS is suitable for intra-operative resection control of the lesion in selected IMCM case

Introducing a nationwide registry: the Swiss study on aneurysmal subarachnoid haemorrhage (Swiss SOS)

Background: Aneurysmal subarachnoid haemorrhage (aSAH) is a haemorrhagic form of stroke and occurs in a younger population compared with ischaemic stroke or intracerebral haemorrhage. It accounts for a large proportion of productive life-years lost to stroke. Its surgical and medical treatment represents a multidisciplinary effort. Due to the complexity of the disease, the management remains difficult to standardise and quality of care is accordingly difficult to assess. Objective: To create a registry to assess management parameters of patients treated for aSAH in Switzerland. Methods: A cohort study was initiated with the aim to record characteristics of patients admitted with aSAH, starting January 1st 2009. Ethical committee approval was obtained or is pending from the institutional review boards of all centres. In the study period, seven Swiss hospitals (five university [U], two non-university medical centres) harbouring a neurosurgery department, an intensive care unit and an interventional neuroradiology team so far agreed to participate in the registry (Aarau, Basel [U], Bern [U], Geneva [U], Lausanne [U], St. Gallen, Zürich [U]). Demographic and clinical parameters are entered into a common database. Discussion: This database will soon provide (1) a nationwide assessment of the current standard of care and (2) the outcomes for patients suffering from aSAH in Switzerland. Based on data from this registry, we can conduct cohort comparisons or design diagnostic or therapeutic studies on a national level. Moreover, a standardised registration system will allow healthcare providers to assess the quality of car

Third-generation cephalosporins as antibiotic prophylaxis in neurosurgery: what's the evidence?

To analyze the role of third-generation cephalosporins as prophylactic antibiotics in neurosurgery. We reviewed the literature for data from randomized controlled trials (RCTs) on third-generation cephalosporins compared to other antibiotic regimen in neurosurgery. End point of the RCTs was the occurrence of surgical site infections (SSIs)--data were pooled in a fixed-effects meta-analysis. Five randomized controlled trials enrolling a total of 2209 patients were identified. The pooled odds ratio for SSIs (overall) with third-generation cephalosporins prophylaxis in the five RCTs was 0.94 (95% CI, 0.59-1.52; P=0.81). No significant difference between third-generation cephalosporins and alternative regimen was identified. When analyzing organ SSIs (osteomyelitis, meningitis, and others intracranial infections) in data derived from four RCTs (1596 patients), third-generation cephalosporins failed to show superiority (pooled odds ratio 0.88; 95% CI 0.45-1.74; P=0.72). Third-generation cephalosporin antibiotic prophylaxis fails to show superiority over conventional regimens regarding both incisional and organ related SSIs in neurosurgery

Ruptured rathke cleft cyst mimicking pituitary apoplexy

Rathke cleft cysts (RCCs) are benign cystic lesions of the sellar and suprasellar region that are asymptomatic in most cases. Occasionally, compression of the optic pathway and hypothalamo-pituitary structures may cause clinical symptoms, such as headaches, visual deficits and endocrinopathies. Acute presentation caused by hemorrhage into an RCC have been described in the literature, and the term "Rathke cleft cyst apoplexy" has been coined. We present the case of a 32-year-old man with acute onset of meningitis-type symptoms and imaging findings resembling hemorrhagic pituitary tumor apoplexy. In retrospect, clinical symptoms, intraoperative appearance, and histologic examination were compatible with the diagnosis of nonhemorrhagic rupture of an RCC. Thus, the clinical presentation of "Rathke cleft cyst apoplexy" is not necessarily caused by hemorrhage

Biomechanical Assessment of Mobile-Bearing Total Knee Endoprostheses Using Musculoskeletal Simulation

The purpose of this computational study was to analyze the effects of different mobile-bearing (MB) total knee replacement (TKR) designs on knee joint biomechanics. A validated musculoskeletal model of the lower right extremity implanted with a cruciate-retaining fixed-bearing TKR undergoing a squat motion was adapted for three different MB TKR design variants: (I) a commercially available TKR design allowing for tibial insert rotation about the tibial tray with end stops to limit the range of rotation, (II) the same design without end stops, and (III) a multidirectional design with an additional translational degree-of-freedom (DoF) and end stops. When modeling the MB interface, two modeling strategies of different joint topologies were deployed: (1) a six DoF joint as a baseline and (2) a combined revolute-prismatic joint (two DoF joint) with end stops in both DoF. Altered knee joint kinematics for the three MB design variants were observed. The commercially available TKR design variant I yielded a deviation in internal-external rotation of the tibial insert relative to the tray up to 5° during knee flexion. Compared to the multidirectional design variant III, the other two variants revealed less femoral anterior-posterior translation by as much as 5 mm. Concerning the modeling strategies, the two DoF joint showed less computation time by 68%, 80%, and 82% for design variants I, II, and III, respectively. However, only slight differences in the knee joint kinematics of the two modeling strategies were recorded. In conclusion, knee joint biomechanics during a squat motion differed for each of the simulated MB design variants. Specific implant design elements, such as the presence of end stops, can impact the postoperative range of knee motion with regard to modeling strategy, and the two DoF joint option tested accurately replicated the results for the simulated designs with a considerably lower computation time than the six DoF joint. The proposed musculoskeletal multibody simulation framework is capable of virtually characterizing the knee joint dynamics for different TKR designs