Comparison of compression and torque measurements of self-tapping and pretapped screws

The choice of an internal fixation system for maxillofacial surgery is made difficult because of lack of information with respect to functional load. This study attempted to clarify some of the controversy with respect to maxillofacial use of these implants. Maximal compressive force to torque values were measured in standardized bone thicknesses of 1, 2, 3, and 4 mm. The screws tested were pretapped AO 1.5-, 2.0-, 2.7-, and 3.5-mm rescue screws and self-tapping Luhr, Champy, and AO 1.5- and 2.0-mm screws. Ten measurements were made for each screw type/bone thickness combination using a piezoelectric washer and torque screwdriver. It was apparent that for 1- and 2-mm bone thicknesses the use of self-tapping screws resulted in the highest compression values. In 3- and 4-mm bone thicknesses, pretapped screws offered the highest compression values. As expected, self-tapping screws had the highest torque values on insertion owing to torque loss in cutting the screw threads. The 2.7-mm screw offered no advantage over the 2.0-mm screws in 1- and 2-mm bone thicknesses but resulted in higher compression values in 3- and 4-mm bone thicknesses.     

Improving physician performance by continuing medical education.

In 1973 the division of continuing medical education of the University of Saskatchewan initiated a 3-year study to determine the effect of hospital-based education on the prescribing accuracy of physicians. This study was undertaken in response to an urgent need to develop more effective methods of continuing medical education and improved techniques of measuring their effectiveness. The educational program focused on common prescribing problems that had previously been defined by experts in the field. Problem frequency was determined by the monitoring of hospital records prior to institution of the educational program and at 3, 6 and 12 months after the program had concluded; this was found to be a satisfactory method of identifying educational needs and is considered to provide a measure of the quality of medical care. Fifteen physicians at three rural hospitals participated in the study. Seventeen physicians at two similar hospitals served as controls. The average problem frequency for topics selected at the study hospitals was reduced by 63% (the percentage of possible improvement), whereas at the control hospitals the frequency of the same problems declined by 32% over the same period. The results of this study provide evidence that an intensive, problem-based program on therapeutics can improve physician performance.     

医学细胞生物学教学初探

在医学细胞生物学教学过程中,教师以学生为主体,精心备课;采用多媒体教学方式,用适当的手段和教学方法培养学生的兴趣;引导学生利用网络资源提高分析问题、解决问题的能力;注重反馈信息,多与学生接触和沟通,取得了较好的教学效果。     

Prospective survey of performance of medical students during preclinical years.

The performance during the preclinical course of 517 students who had applied to this medical school for admission in 1981 and who had been accepted by the school or by another British medical school was analysed in relation to variables measured at the time of application to find factors that predicted success in the preclinical course, whether students chose to take an intercalated degree, and the class achieved in the intercalated degree. Thirty one of the 507 students who entered medical school withdrew from the course or failed their examinations; these students were particularly likely not to have an A level in a biological science. O level grades were of minimal predictive value for performance during the preclinical course. A level grades discriminated between successful and unsuccessful students but had too low a specificity or sensitivity to be of use in individual prediction. Mature entrants performed better overall than school leavers. Background variables accounted for only 14.2% of the variance in performance, implying that motivation and personality may be more important in determining performance. The 80 students who chose to take an intercalated degree were more likely to be men and not to be mature entrants; for a further 50 students intercalated degrees were obligatory. Performance in the intercalated degree related to performance during the preclinical course and to assessments made at the selection interview but not to achievement at O or A level.     

Pullout strength of suture anchors: Effect of mechanical properties of trabecular bone

This study investigated the relationships between trabecular microstructure and elastic modulus, compressive strength, and suture anchor pullout strength. Twelve fresh-frozen humeri underwent mechanical testing followed by micro-computed tomography (μCT). Either compression testing of cylindrical bone samples or pullout testing using an Arthrex 5 mm Corkscrew was performed in synthetic sawbone or at specific locations in the humerus such as the greater tuberosity, lesser tuberosity, and humeral head. Synthetic sawbone underwent identical mechanical testing and μCT analysis. Bone volume fraction (BVF), structural model index (SMI), trabecular thickness (TbTh), trabecular spacing (TbSp), trabecular number (TbN), and connectivity density were compared against modulus, compressive strength, and pullout strength in both materials. In cadaveric bone, modulus showed correlations to all of the microstructural properties, while compressive and pullout strength were only correlated to BVF, SMI, and TbSp. The microstructure of synthetic bone differed from cadaveric bone as SMI and TbTh showed little variation across the densities tested. Therefore, SMI and TbTh were the only microstructural properties that did not show correlations to the mechanical properties tested in synthetic bone. This study helps identify key microstructure–property relationships in cadaveric and synthetic bone as well as illustrate the similarities and differences between cadaveric and synthetic bone as biomechanical test materials.     

The use of information technology in improving medical performance. Part I. Information systems for medical transactions

Investment in medical information technologies reached $15 billion in 1996. However, these technologies have not had the wide impact predicted in streamlining bureaucracy, improving communications, and raising the effectiveness of care. In this series, we identify how such technologies are being used to improve quality and performance, the future directions for advancement, and the policy and research developments required to maximize public benefit from these technologies. Each of these articles focuses on a different type of information technology: (1) information systems to manage medical transactions; (2) physician-support technologies to improve medical practice; and (3) patient-focused technologies designed to change how people manage their own care. This first article of a 3-part series examines the successes of and opportunities for using advanced information systems that track and manage medical transactions for large populations to improve performance. Examples of such systems include: HEDIS, which gathers standardized data from health plans on quality of care; the USQA Health Services Research Program, which tracks treatment patterns and outcomes for 14 million insurance members; Ford's program to collect medical data for over 600,000 employees; and Harvard Pilgrim Health Care's system of computerized laboratory, pharmacy, ambulatory, and hospital admission records for its 1.5 million members. Data from these systems have led to modest improvements in knowledge and practice patterns for some diseases. Significant barriers are slowing efforts to add outcomes data to these databases and broaden the databases to cover larger populations. Nonetheless, existing data in currently evolving systems could be used to greater benefit in tracking public health and in identifying more effective treatments and causes of diseases.     

Design and testing of external fixator bone screws

In external fixation, bone screw loosening still presents a major clinical problem. For this study, the design factors influencing the mechanics of the bone-screw interface were analysed and various experimental screws designed with the intention of maximizing the strength and stiffness of the inserted screw. Push-in, pull-out and bending tests were then carried out on the three experimental screws, and on two commercially available screws in both a synthetic material and in cadaveric bone; photoelastic tests on different screw threadforms were also performed. The results of the push-in and pull-out tests indicate that both the screw threadform and cutting head have a significant effect on the holding strength of the screw. The photoelastic tests show that most of the applied load is distributed over the first few threads closest to the load, and that the area between the thread crests is subjected to high shear stresses.     

椎弓根螺钉抗拔出强度的生物力学测试

目的:分析骨密度(bone mineral density,BMD)和植入角度对椎弓根螺钉拔出强度的影响.方法:6例新鲜尸体脊柱T10-L2骨,分解为单个椎体30个,共60个椎弓根.根据骨密度检查结果分组,每个标本脊椎左侧使螺钉在椎弓根平行植入,在脊柱右侧使螺打在与椎弓根成7°角植入.将60个椎弓根分别进行拔出测试(5mm/min的速度垂直方向拔出).结果:螺打平行植入与椎弓根成7°角植入,后者其拔出力大20%(P<0.05).骨密度时拔出力的影响,正常组与骨质疏松组相差57%(P<0.05).结论:选择与椎弓根成角度植入螺钉有助于提高螺固定相对稳定性;对于骨质疏松的病例,应注意抗拔出力不能满足生理要求的危险性.     

Tensile strength studies of self-cutting titanium osteosynthesis screws]

The tapping screws of the Medicon Osteosynthese System applied in the jaw and facial area were checked for their mechanical sturdiness. Screwing tests with bones and aluminium were carried out. The minimum fracture moment, the moment transferrable by the screw slot and the required moment for a tight seat of the Osteosynthese plate on the bone surface were calculated. The screws and plates are of titanium alloy TiA16V4 (US standard) for implantats. In a sample taken at random of test screws the fracture moments were measured and examined. All the screws support considerable loads and the fracture moments are almost 20% higher that the minimum fracture moment for TiA16V4 screws specified in DIN 267, part 18.     

Effects of sleep disruption on cognitive performance and mood in medical house officers.

Twelve medical house officers were tested on a battery of memory, concentration, and work related tasks after three conditions: a night spent off duty; a night spent on call; and a night spent admitting emergency cases. Short term recall, but not digit span, concentration, or work related abilities, was impaired after a night of emergency admissions. A night spent on call had no effect on cognitive performance. Self reported mood scores showed that house officers were more deactivated (indicating a lack of vigour and drive) after nights of emergency admissions but not after nights on call. Significant between subject differences were found for five of the eight cognitive tests. Though loss of sleep and long hours of work have an effect on memory and mood, the individual differences among doctors are the main source of the variance in performance of tasks.     

Constructing complex 3D biological environments from medical imaging using high performance computing

Extracting information about the structure of biological tissue from static image data is a complex task requiring computationally intensive operations. Here, we present how multicore CPUs and GPUs have been utilized to extract information about the shape, size, and path followed by the mammalian oviduct, called the fallopian tube in humans, from histology images, to create a unique but realistic 3D virtual organ. Histology images were processed to identify the individual cross sections and determine the 3D path that the tube follows through the tissue. This information was then related back to the histology images, linking the 2D cross sections with their corresponding 3D position along the oviduct. A series of linear 2D spline cross sections, which were computationally generated for the length of the oviduct, were bound to the 3D path of the tube using a novel particle system technique that provides smooth resolution of self-intersections. This results in a unique 3D model of the oviduct, which is grounded in reality. The GPU is used for the processor intensive operations of image processing and particle physics based simulations, significantly reducing the time required to generate a complete model.     

The use of information technology in improving medical performance. Part II. Physician-support tools

Increasing data from a few sites demonstrate that information technologies can improve physician decision making and clinical effectiveness. For example, computer-based physician order entry systems, automated laboratory alert systems, and artificial neural networks have demonstrated significant reductions in medical errors. In addition, Internet services to disseminate new knowledge and safety alerts to physicians more rationally and effectively are rapidly developing, and telemedicine to improve rural access to specialty services is undergoing substantial growth. However, even technologies demonstrated to yield beneficial effects have not yet achieved widespread adoption, though the pace of change appears to be increasing as the Internet takes hold. Scientific evaluation of many technologies is also lacking, and the dangers of some of these technologies may be underappreciated. Research on the effects of specific technologies should be a priority. Policies should be developed to press information technology companies, such as pharmaceutical and medical device manufacturers, to recognize the importance of clinical evaluation. Research could also analyze the characteristics of effective technologies and of physicians and organizations who implement these technologies effectively.     

Pedicle Screw Fixation Study in Immature Porcine Spines to Improve Pullout Resistance during Animal Testing

The porcine model is frequently used during development and validation of new spinal devices, because of its likeness to the human spine. These spinal devices are frequently composed of pedicle screws with a reputation for stable fixation but which can suffer pullouts during preclinical implantation on young animals, leading to high morbidity. With a view to identifying the best choices to optimize pedicle screw fixation in the porcine model, this study evaluates ex vivo the impact of weight (age) of the animal, the level of the vertebrae (lumbar or thoracic) and the type of screw anchorage (mono- or bi-cortical) on pedicle screw pullouts. Among the 80 pig vertebrae (90- and 140-day-old) tested in this study, the average screw pullout forces ranged between 419.9N and 1341.2N. In addition, statistical differences were found between test groups, pointing out the influence of the three parameters stated above. We found that the the more caudally the screws are positioned (lumbar level), the greater their pullout resistance is, moreover, screw stability increases with the age, and finally, the screws implanted with a mono-cortical anchorage sustained lower pullout forces than those implanted with a bi-cortical anchorage. We conclude that the best anchorage can be obtained with older animals, using a lumbar fixation and long screws traversing the vertebra and inducing bi-cortical anchorage. In very young animals, pedicle screw fixations need to be bi-cortical and more numerous to prevent pullout.