Computational Modelling of Patella Femoral Kinematics During Gait Cycle and Experimental Validation

The effect of loading and boundary conditions on patellar mechanics is significant due to the complications arising in patella femoral joints during total knee replacements. To understand the patellar mechanics with respect to loading and motion, a computational model representing the patella femoral joint was developed and validated against experimental results. The computational model was created in IDEAS NX and simulated in MSC ADAMS/VIEW software. The results obtained in the form of internal external rotations and anterior posterior displacements for a new and experimentally simulated specimen for patella femoral joint under standard gait condition were compared with experimental measurements performed on the Leeds ProSim knee simulator. A good overall agreement between the computational prediction and the experimental data was obtained for patella femoral kinematics. Good agreement between the model and the past studies was observed when the ligament load was removed and the medial lateral displacement was constrained. The model is sensitive to ±5 % change in kinematics, frictional, force and stiffness coefficients and insensitive to time step

Similar TKA designs with differences in clinical outcome: A randomized, controlled trial of 77 knees with a mean follow-up of 6 years

Contains fulltext : 96347.pdf (publisher's version ) (Open Access)Background and purpose To try to improve the outcome of our TKAs, we started to use the CKS prosthesis. However, in a retrospective analysis this design tended to give worse results. We therefore conducted a randomized, controlled trial comparing this CKS prosthesis and our standard PFC prosthesis. Because many randomized studies between different TKA concepts generally fail to show superiority of a particular design, we hypothesized that these seemingly similar designs would not lead to any difference in clinical outcome. Patients and methods 82 patients (90 knees) were randomly allocated to one or other prosthesis, and 39 CKS prostheses and 38 PFC prostheses could be followed for mean 5.6 years. No patients were lost to follow-up. At each follow-up, patients were evaluated clinically and radiographically, and the KSS, WOMAC, VAS patient satisfaction scores and VAS for pain were recorded. Results With total Knee Society score (KSS) as primary endpoint, there was a difference in favor of the PFC group at final follow-up (p = 0.04). Whereas there was one revision in the PFC group, there were 6 revisions in the CKS group (p = 0.1). The survival analysis with any reoperation as endpoint showed better survival in the PFC group (97% (95% CI: 92-100) for the PFC group vs. 79% (95% CI: 66-92) for the CKS group) (p = 0.02). Interpretation Our hypothesis that there would be no difference in clinical outcome was rejected in this study. The PFC system showed excellent results that were comparable to those in previous reports. The CKS design had differences that had considerable negative consequences clinically. The relatively poor results have discouraged us from using this design

Design improvements in Total Knee Arthroplasty

Contains fulltext : 30127_desiimint.pdf (publisher's version ) (Open Access)The thesis deals with three questions concerning the knee joint and total knee arthroplasty. 1. Are there parameters which can be changed to reduce bone resorption, caused by TKA, without affecting other relevant parameters? A debonded anterior flange of the femoral TKA component reduces bone resorption without jeopardizing the implant fixation. 2. Can the design of the femoral component be changed to obtain more physiological patellar kinematics? The orientation of the natural trochlea is significantly different (even opposite) to the orientation of the patella groove of an implanted femoral TKA component. The patellar kinematics are strongly correlated to the orientation of the trochlea and the groove. A more anatomical groove design is proposed. 3. Is it possible to increase the range of motion without adversely affecting the mechanical performance in high flexion TKA? Dynamic FE models were used. High flexion TKA shows a similar mechanical behavior as conventional TKA in normal flexion (120 degrees). It should be noted that high flexion TKA still creates relatively high stress levels in high flexion even if the prosthetic components are optimized for high flexion.RU Radboud Universiteit Nijmegen, 12 januari 2007Promotor : Kampen, A. van Co-promotores : Verdonschot, N.J.J., Waal Malefijt, M.C. de149 p

[Research methods in dentistry 5. The finite element method]

Contains fulltext : 58892.pdf (publisher's version ) (Open Access)The finite element method is a commonly applied experimental research technique. The method comprises computer simulation of constructions under load and of internal mechanical processes, which enables the study of effects of geometrical and material variations. The analysis shows internal stresses and, consequently, predictions can be made of possible failure. In dentistry, the method is applied in disciplines, such as orthodontics, oral and maxillofacial surgery, implantology en restorative dentistry

Benefit of textured CIGS cells for low reflecting nanogrid application

Metallization of the front contact can increase the conductivity. We show the optical benefit by combining nanowire with a texture of the thin film stack. The parallel nanowires are placed in crevices of a texture in the optical model. Texturization reduces the reflection of both the stack and the nanowire. For a period of 500 nm, the reflection is virtually independent of the nanowire width for a texture height/period ratio of only 1. For a texture height of 1000 nm, the reflection is minimized with maximum of 3% (between 600 nm and 750 nm wavelength) and this would mean that the surface would appear as black, even with a surface metal coverage of 30%. Moreover, outside this wavelength range, the reflection is below 1% and marks a significant increase in current density up to 38 mA/cm2 compared to the flat layer stack (27 mA/cm2)

Integrated Front–Rear-Grid Optimization of Free-Form Solar Cells

Free-form solar cells expand solar power beyond traditional rectangular geometries. With the flexibility of being installed on objects of daily use, they allow making better use of available space and are expected to bring in new possibilities of generating solar power in the coming future. In addition, their customizable shape can add to the aesthetics of the surroundings. Evidently, free-form solar cells need to be efficient as well. One wayto improve their performance is to optimize the metallization patterns for these cells. This work introduces an optimization strategy to optimize the metallization designs of a solar cell such that its performance can be maximized. For the purpose of optimization, w

Optimized grid design for thin film solar panels

There is a gap in efficiency between record thin film cells and mass produced thin film solar panels. In this paper we quantify the effect of monolithic integration on power output for various configurations by modeling and present metallization as a way to improve efficiency of solar panels. Grid design and finger dimension optimization was performed monolithically integrated solar panels by modeling under standard conditions and with variation of boundary conditions such as transparent conductor used, conductivity of the metallic pattern and low light intensity. For each, the optimal cell and grid dimensions as well as the power output is presented. In contrast to previous studies that focus on 100. μm wide grid lines, our grid finger width was varied between over a wide range and a finger width of 20. μm was shown to give optimal results. We included mapping the power output for 20. μm, 60. μm and 100. μm wide grid lines as function of cell length, finger spacing and TCO sheet resistance and show that also for wide fingers efficiency improvement of more than 15% is possible. This provides not only optimization of grid dimensions, but also the sensitivity of the power output with respect to the finger dimensions, TCO sheet resistance and the cell length. These results indicate that the application of a grid is a robust solution which allows for a considerable variation (>25%) in the parameter window around the optimum configuration with only small impact (<2%) on the power output. cop. 2014 Elsevier Ltd