The objective of this study was to find out the effect of tibial position and orientation to patellofemoral kinetics, especially during deep knee flexion. The data about patellofemoral kinetics is necessary for calculating tibiofemoral joint force which is used to evaluate a design of knee prosthesis, however, there have been no data how it changes by tibial anterior translation or internal rotation which recent prostheses are aiming. We performed a three-dimensional model analysis with axioms of point contact and force equilibrium. The flexion angle was from 0° to 150° by four conditions. The neutral condition was based on the two-dimensional analysis using PS type of the prosthesis, without internal rotation and plenty femoral roll back. The other conditions were with over 20mm of tibial anterior translation, with 15° of tibial internal rotation, and both the translation and rotation during deep knee flexion. As a result, patellofemoral joint force reduced by tibial anterior translation and did not change by tibial rotation. Tensile force of patella tendon did not change by the tibial position/orientation. By rotating tibia internally, medial contact force increased and lateral reduced. Moreover, tibial anterior translation facilitated the dislocation of patellofemoral joint, and lateral side lifted off with tibial internal rotation. The contact force reduced rapidly before the lift off, and medial contact force increased by the lateral lift off. In this case, although the magnitude of the patella tendon force did not change, the direction of the force might change unignorably. Both tibial anterior translation and internal rotation might be necessary to be capable of deep knee flexion, however, it is also necessary to discuss the interaction between tibiofemoral and patellofemoral joints for evaluating the new prosthesis intending deep knee flexion.
Severe head injuries can occur in cyclists involved in traffic accidents. In Japan, head injuries accounted for 62% of cyclist fatalities in 2015 (ITARDA, 2016). The purpose of this study is to estimate head injuries for cyclists and quantify the effectiveness of a bicycle helmet by performing finite element (FE) simulations of head impacts against roads. Impacts with and without a helmet over a range of relative head velocities and head impact angles were simulated. A number of possible head injuries were assessed; skull fracture by skull strain, traumatic intracerebral hematoma (ICH) by brain pressure, brain contusion by brain negative-pressure and von Mises stress, and moderate and severe diffuse axonal injuries (DAIs) by von Mises stress. Results showed that without a helmet, the peak values of all metrics exceeded the 50% probability point for head injury in all impacts. The 50% probability points of moderate and severe DAIs were exceeded under impacts of 8.22 m/s at 26.5 degrees and 10.33 m/s at 15.0 degrees for moderate DAI, and 10.33 m/s at 15.0 degrees for severe DAI, without a helmet. All the peak values were reduced when a bicycle helmet was worn, and the largest reduction was found in the skull strain. These results predict that the risks of head injuries due to road impacts may be considerably decreased by helmet use.
For cycling competitors, the pedaling exercise is typically accompanied by a binding pedal system. The purpose of this pedal system is to attach the body of the pedal and the sole of the cycling shoe together in order to allow the cyclist to rotate the crank efficiently. Although the importance of a pedaling skill that streamlines the muscle activity of the leg muscles recruited in the pedaling exercise has been widely recognized in the field of cycling, no instructional method based on scientific evidence has been established yet. Hence, this study first proposes an evaluation standard for the pedaling skill by using the muscle activity data of a skilled cyclist. Subsequently, the training system based on the proposed evaluation standard is developed. The system measures the surface electromyogram of the leg muscles and the angle of crank rotation during the pedaling exercise. In addition, the system employs principal component analysis to extract the features of the muscle activity pattern from a beginner and an intermediate cyclist. Furthermore, the online visualization of their pedaling skill, based on the results of the principal component analysis, is implemented to enable cyclists to objectively monitor their pedaling skill. The experimental results obtained from the developed training system and the relationship between the pedaling skill and the consistency of the muscle activity pattern are discussed. The experimental results revealed the significant aspects of the pedaling skills, in which the consistency of the muscle activity pattern and the motion of pulling the pedal up were relatively clear in the pedaling of the skilled cyclist.
Currently, there is no definite mathematical model to evaluate damage to blood cells, especially for cardiovascular devices with complex flow profiles due to turbulent flow and moving parts. This paper describes a finite volume technique that can more accurately predict damage of red blood cells and platelets by tracking their shear stress history and calculating their accumulated damage. Three standard power-law models for calculating the damage to the blood cells are compared to a novel modified model which takes into account a particle accumulated history and corrects for issues in previous models that miscount for decreasing shear stress. As an example, the damage to blood cells are determined for specific streamlines along a prosthetic polymer-based aortic valve, which is a cardiac device with low levels of damage, allowing for the sensitivity of these models to be tested. The results suggest that the new modified model provides the most accurate prediction of damage.
Various catheter simulators using a computer or blood vessel biomodels have been developed for training of medical students and young physicians. Moreover, we have developed a system to simulate a guidewire in blood vessels that uses both numerical analysis and experimental observation for the quantitative analysis of treatment technique, surgical planning, intra-operative assistance, and to facilitate the design of new guidewires. However, not limited to our group, there is a lack of studies evaluating the motions of both the guidewire and catheter and their interaction in a blood vessel. Therefore, in the present study, we modified our computer-based system and experimental apparatus to evaluate the catheter motion and compared both results. First, we added a mechanism to the experimental apparatus to move and evaluate the catheter in a poly (vinyl alcohol) hydrogel blood vessel model. Second, we added a new catheter model to the calculation. We subsequently evaluated the behaviors of the medical devices (the guidewire and the catheter) by measuring the three-dimensional position and the contact force between the medical devices and the vessel wall. Comparison of the calculation and experimental results showed that the trajectories and the contact forces of both the experimental and numerically analyzed medical devices had the same tendencies. By considering the flexibility of the catheter in both the experimental and numerical analysis methods, we could reproduce the phenomena seen in clinical situations, such as movement of the catheter during the insertion or removal of the guidewire, and movement of the guidewire during the insertion of the catheter.
Mechanisms of development, growth, and rupture of a cerebral aneurysm have been studied by computational fluid dynamics (CFD), calculating hemodynamic parameters, such as wall shear stress, oscillatory shear index (OSI), and relative residence time (RRT). It is well known that the upstream velocity profile and upstream vessel shape influence the computational results. However, few studies have dealt with cases involving a bifurcation upstream of a cerebral aneurysm. Furthermore, the fluid-dynamic effects of multiple structural elements of upstream vessel shape, such as a bifurcation and a bend, on the results of CFD remain unknown. The purpose of this study was to elucidate the fluid-dynamic effects of multiple structural elements of upstream vessel shape such as bifurcation and bend on blood flow and hemodynamic parameters inside an aneurysm. Computations were performed for blood flow in a cerebral aneurysm with upstream sequential elements of a bifurcation, a bend, and a straight section, using four models with different upstream boundaries, i.e., before the bifurcation, after the bifurcation before the bend, after the bend, and after the straight section just before the cerebral aneurysm. The results were compared to elucidate the effect of each upstream structural element on the blood flow and hemodynamic parameters in the cerebral aneurysm. Differences in OSI and RRT resulting from changes in the velocity distribution were observed locally in the aneurysm between the models. It was also found that the effect of the bifurcation on the velocity distribution was greater than that of the bend.