Journal of Mechanics in Medicine and Biology

Reconstruction of the condyle after an ablative procedure for mouth neoplasms remains a surgical challenge because these patients with advanced cancer involving the condyle are subjected to massive ablative surgery, and subsequent major reconstruction with free flap and/or reconstruction prosthesis, the prognosis being poor. Therefore, reports of condylar prosthesis in head and neck cancer reconstruction are rare and with mixed results. This report is for the review of the literature and case series study of the condylar prosthesis. As with virtual technique improvement nowadays, an innovation CAD CAM technique is applied for the treatment plan for these patients. We analyze a serial case of advanced oral neoplasms who receives tumor ablation, i.e., mandibulectomy and disarticular resection, and gains symmetrical mandibular architecture after reconstruction with plate and condylar prosthesis. There is still high complication rate (41.7%) noted, namely condylar prosthesis displacement (two cases), impinge on external ear canal (two cases), and erosion of cranial base (one case). The reasons are attributed to massive flap burden, scar contraction, poor dental articulation, and possible technique error during the operation. According to the outcome analysis, virtual technique including with reconstruction plate and condylar prosthesis in conjunction with flap reconstruction are feasible treatment modality for this serial case of advanced oral neoplasms.

Vertebral screw failure by cutting through or pulling out of the vertebral body is common in intraoperative and postoperative stages of anterior thoracolumbar surgery, especially in osteoporotic patients. This biomechanical study was conducted to investigate the maximum shear force thoracolumbar vertebrae can withstand and the corresponding displacement of screws and analyze their correlation with vertebral bone mineral density. Forty individual vertebra specimens (T11-L3) were obtained from eight fresh adult cadaveric thoracolumbar spine specimens and randomly divided into an experimental group and a control group. Screws were placed in the center point of vertebrae and penetrated the contralateral cortex. Shear loading and axial pullout tests were conducted on the experimental group while only axial pullout test was conducted on the control group. The maximum shear forces and maximum axial pullout forces were recorded. The conditions of vertebral body destruction and screw channel were observed and the maximum axial pullout forces were recorded and analyzed. A large amount of thread bone debris was observed in the control group. In the experimental group, however, only a small amount of thread bone debris was observed; the widths of screw paths were larger than those in the control group and gradually increased from screw tips in the direction of loading. The vertebral bodies had an average shear strength of $536.63\pm 82.99$N, and the corresponding average screw displacement was $8.79\pm 1.08$mm. Linear regression analysis showed that the shear strength had a significant positive correlation with vertebral bone mineral density (BMD) (r$=$0.958, P$<$0.01), while the screw displacement had a significant negative correlation with vertebral BMD (r$=$−0.933, P$<$0.01). No significant difference in bone density was found between the destruction and the control groups (P$>$0.05); the difference in maximum axial pullout strength between the destruction and the control groups was significant (P$<$0.01). These results indicated that vertebral BMD positively correlated with the maximum shear force and negatively with the screw displacement. It is important that the corrective strength for spinal deformity may affect bone–screw interface in anterior thoracolumbar surgery.

Atherosclerotic plaque tends to occur and develop in carotid artery sinus, where stenoses and other lesions can cause cerebral disturbances. The hemodynamics and the platelet profiles in the carotid artery are simultaneously simulated in the present study to reveal the mechanism of the atherosclerotic plaque formation. Firstly, an unsteady PISO solver on unstructured tetrahedral grids is developed to simulate the hemodynamics of carotid artery bifurcation. And small platelets are treated as spherical solid particle described by Newtonian motion equation in the simulation, including inertial force, drag force, shear lift force, virtual mass force and pressure gradient force. Secondly, the visualization experiment for the platelet flow in the straight micro-channel is setup to validate the numerical model. Using the present method, the platelet flow in a carotid artery bifurcation is analyzed. The results show that the outer vascular wall near the bifurcation is more vulnerable in carotid artery sinus, which is mainly due to the lower wall shear stress (WSS) and platelets backflow in the region.

Microfluidics technology has emerged as an attractive approach in physics, chemistry and biomedical science by providing increased analytical accuracy, sensitivity and efficiency in minimized systems. Numerical simulation can improve theoretical understanding, reduce prototyping consumption, and speed up development. In this paper, we setup a 3D model of an integrated microfluidic system and study the multi-physical dynamics of the system via the finite element method (FEM). The fluid–structure interaction (FSI) of fluid and an immobilized single cell within the cell trapping component, and the on-chip thermodynamics have been analyzed. The velocity magnitude and streamline of flow field, the distribution of von Mises stress and Tresca stress on the FSI interface have been studied. In addition, the on-chip heat transfer performance and temperature distribution in the heating zone have been evaluated and analyzed respectively. The presented approach is capable of optimizing microfluidic design, and revealing the complicated mechanism of multi-physical fields. Therefore, it holds the potential for improving microfluidics application in fundamental research and clinical settings.

The influence of cervical muscles on the head/neck responses to frontal collisions is an important issue in the design of vehicle safety systems. In this study, spring-type muscles based on a Hybrid III 50th percentile dummy were used. A spring was used to simulate the cervical muscle with the instinctual physiological reaction of a driver. A total of 10 volunteers were recruited for the simulated collision tests and the maximum voluntary contraction tests, and test data were used to establish and design the spring-type muscles. Sled tests were performed using a modified dummy with spring-type muscles, which had similar mechanical characteristics to a human body. The results showed that Ax increased 3.58%, Ay decreased $-$10.32%, Az increased 3.21%, Fx increased 12.22%, Fz increased 3.80%, and My decreased significantly ($-$16.70% in average) at first but then increased 5.57%, in average. Cervical muscles with the instinctual physiological reaction may increase the potential head injury and potential cervical longitudinal shear injury while decreasing the potential cervical extension injury. The study provides reference for designing dummies by taking into consideration the instinctual physiological reaction of the driver to a collision.

Blood pressure is an important factor in cardiovascular diseases, and it is impossible to precisely reproduce the physical phenomenon of the arteries by using conventional simulators with modeling blood vessels as air-filled chambers. The purpose of this study was to develop a cardiovascular simulator that replicates the human arterial system. The vessel part was manufactured with silicon which has similar stiffness and arterial tree structure. To evaluate the validity of the developed simulator, the pressure and flow were analyzed in the ascending aorta and radial artery. Measured pressure waves and input impedance of the ascending aorta were compared with clinical data using quantitative indices. The generated pulse by the developed simulator showed a good agreement with the physiological characteristics of the arterial system in the human body.

The aim of this study is to establish a biomechanical model of bone on the basis of cellular structure and then to evaluate its accuracy for the clinical application. The thighbone of swine was scanned by computed tomography (CT). The resulting sectional images were input into MIMICS10.01 to generate a three-dimensional geometric model. A biomechanical model of bone was built on the basis of cellular structure, and calculations of the model were implemented in MATLAB with the finite element method. With this cellular mechanics model, axial compression load was simulated, and load–axial and load–transverse strain at the measurement points were detected. To evaluate the model, a mechanics model derived from an empirical formula was simulated under the same conditions, and an actual biomechanical experiment was also conducted. The simulated results obtained from the two models were then compared with the test results, indicating that the simulated results for the cellular model were closer to the test results than those for the empirical mechanics model. Therefore, the proposed cellular mechanics model shows advantages in accuracy and scope of application for bone modeling.

Stress fracture of the metatarsal (MT) is often reported clinically. This study was aimed to measure and compare the three-dimensional (3D) morphological structure of five MTs, and investigate the in vitro biomechanics of five MTs under simulated stance phase. A total of seven foot-ankle samples of human cadavers were collected for this experiment. All samples were CT-scanned and 3D re-constructed for digital measurements. To simulate the stance phase, each sample was vertically loaded with 700-N through a material testing machine. The 3D-reconstruction-based measurement showed significant differences of the shaft length, vertical height, and inclination angle between the second MT and four others. Experimental strain measurements at dorsal MTs along the principal axis are all compressive. The values are respectively $-63.99\pm 17.86$, $-123.54\pm 18.07$, $-143.16\pm 24.75$, $-25.48\pm 9.16$, and $-61.56\pm 19.52$ micro-strain from the first to fifth MTs. This study proposed a new load condition of plantar-flexed simply supported beam to describe the MT loading mechanism. The second and third MTs have higher risk of stress fracture due to combined effects of inhomogeneous load distribution, unfavorable geometry and structure, and limited joint motion. This finding would be helpful for design of protective equipment.

In recent years, the physiological phenomena of cell displacement and deformation in blood vessels have gradually become an important topic in the field of biomechanics, and also have important theoretical significance and application value in clinical medicine. To study the migration and deformation of blood cell, the influence of elastic modulus on its behavior, and the effect of deformation on its migration. A numerical simulation of a single cell displacement and deformation in a flow chamber was conducted in the present study using a computer program based on the fluid–solid coupling. The displacement and deformation of the cells with different elastic modulus as well as the influence of deformation on the movement of the cell were investigated. The results showed that the cell with greater elastic modulus had a smaller deformation in the direction of gravity and fluid velocity. The deformation of the cell had obvious effect on the displacement in the direction of gravity. The smaller the deformation of the cell in the direction of gravity was, the higher the cell could jump. The three-dimensional numerical calculation method adopted in this paper and the results obtained can provide a reference for the study of the cell mechanic behavior in the vessels.

When performing anterolateral foraminotomy for the treatment of cervical spondylotic radiculopathy, the extent of uncinate process resection affects the stability of the cervical spine. The aim of this study was to determine the stability of the cervical spine after resection of various amounts of the uncinate process. Based on computed tomography (CT) scans of an adult male volunteer, a three-dimensional geometric model of the cervical spine (C4-C6) was established using Mimics 13.1, SolidWorks 2012, and ANSYS 15.0 software packages. Next, the mechanical parameters of the tissues were assigned according to their different material characteristics. Using the tetrahedral mesh method, a three-dimensional finite element model of the cervical spine was then established. In modeling uncinated process resection, two excision protocols were compared. The first excision protocol, protocol A, mimicked the extent of resection used in current clinical surgical practice. The second excision protocol, protocol B, employed an optimal resection extent as predicted by the finite element model. Protocols A and B were then used to resect the left uncinate process of the C5 vertebra to either 50% or 60% of the total height of the uncinate process. The stability of the cervical spine was assessed by evaluating values of deformation and maximum equivalent stress during extension, flexion, lateral bending, and rotation. After protocol A resection, the total deformation was increased as was the maximum equivalent stress during left and right rotation. After protocol B resection, the total deformation was little changed and the maximum equivalent stress was visibly decreased during left and right rotation. As evidenced by these results, protocol B resection had relatively little effect on the stability of the cervical spine, suggesting that resection utilizing the limits proposed in protocol B appears to better maintain the stability of the cervical spine when compared with current clinical surgical practice as replicated in protocol A.

Advanced three-dimensional (3D) models have played more and more essential roles in orthopedics surgical interventions. In order to improve the clinical outcomes of knee surgery (KS) including minimally invasive knee surgery (MIKS), the melted extrusion modeling (MEM), a rapid prototyping (RP) technique, was used efficiently to fabricate real life-size 3D physical models of interesting knees. The applications and advantages of the tangible RP-constructed 3D models in KS were elucidated in this study. As a result, better preparation including optimal preoperative planning was made so that KS could be performed in an accurate, safe and fast manner for each case. Besides, the surgical skills of MIKS were substantially improved. Therefore, the results suggest that KS can benefit much from the advanced 3D modeling technique.

Tortuous saphenous vein graft (SVG) hemodynamics was investigated using computational fluid dynamics (CFD) techniques. Computed tomography (CT) technology is used for noninvasive bypass graft assessment seven days after surgery. CT investigation shows two regions with severe shape remodeling, one is an angle type contortion and the other one is a sharp curvature with tortuous area reduction. The numerical analysis carefully examines the effect of an SVG geometry remodeling through flow separation, particle deposition, and wall shear stress (WSS). During the cardiac cycle, overall pressure drop increases from 2.6mmHg to 4.4mmHg. In the accelerating part of the systolic phase, particles released in the inlet section move downstream toward the first narrowed part (elbow type contortion) with a helical motion. WSS range along the cardiac cycle varies from 2Pa to 42Pa, enough to damage the endothelial cells. Vessel torsion induced helical flow can reduce the flow disturbance and separation. Additionally, in the distal end of the graft, the high particle concentrations can promote the inflammatory processes in the vessels.

For patients with severe joint deformity or defect, the conventional knee implant cannot meet the installation requirements. A patient-specific prosthesis is a rational choice for these patients. The purpose of this study was to develop a patient-specific knee implant and evaluate its mechanical properties. A mobile-bearing type of knee implant was designed for a young patient with severe rheumatoid arthritis. The stress characteristics were studied by the finite element (FE) method. Results show that the stress distribution of the mobile-bearing knee implant is much better than that of a hinged knee implant designed before. But the stability of the mobile-bearing knee implant should be investigated in more detail before its application.

Left pulmonary artery sling (LPAS) is a kind of severe congenital anomaly, where the stenoses usually occur at trachea and main bronchi for the external compression of the artery sling. Computed tomography (CT) images can provide accurate morphological analysis, but the airflow and its effects on the airway wall are unknown and seldom investigated. In the present study, a uni-directional coupling fluid–structure interaction (UCFSI) method is employed to simulate the deformation and stress of tracheal and main bronchial wall for four LPAS subjects and one health control. Much higher airflow velocity is observed for LPAS subjects due to the stenosis, and the deformation and equivalent stress of airway wall are about 50–900 and 90–1000 times of the health control, respectively. The direction of tracheal shift may be related to the airway shape, and is opposite to the net reaction force. The influences of inlet flow velocity and wall thickness on the deformation and stress are significant and their relationship is non-linear. These results suggest that the UCFSI simulation is helpful for the quantitative analysis on the deformation and stress of the airway wall and better understanding of LPAS mechanism.

A C-arm fluoroscopy is a useful instrument for finding out the position of a needle in a minimally invasive surgery, but its use means that the surgeon and patient are exposed to radiation while the surgeon places the C-arm into the previous position and orientation as well as he/she regularly uses it to take X-ray images. In this paper, a two-bar link system and moving mechanism added on a C-arm are proposed to reduce the dose of the exposure. The two-bar link system consists of two bar links and three absolute encoders. It measures the relative position and angle between the C-arm and the surgical table in real time and stores the measurements in the system. The moving platform of C-arm is proposed to have two switchable casters for both passive freewheeling and active motor driving. Passive freewheeling allows the C-arm to be freely moved by human force and active motor driving returns the C-arm to its original position automatically. A simple experiment is performed to verify the feasibility of C-arm repositioning using a two-bar link system.

Based on the negative exponential pair potential ($1∕R^n$), the interaction potential between curved surface body with negative Gauss curvature and an outside particle is proved to be of curvature-based form, i.e., it can be written as a function of curvatures. Idealized numerical experiments are designed to test the accuracy of the curvature-based potential. Compared with the previous results, it is confirmed that the interaction potential between curved surface body and an outside particle has a unified expression of curvatures regardless of the sign of Gauss curvature. Further, propositions below are confirmed: Highly curved surface body may induce driving forces, curvatures and the gradient of curvatures are the essential factors forming the driving forces.

Toward improving the real-time property and stability of the micro-pipetting process of an automatic enzyme-linked immunoassay analysis system, the fault detection of the process was studied by monitoring the pressure. A new method that combines the absolute degree of grey coefficients (ADGC) with the double extremes method (DEM) for monitoring pressure is proposed. The ADGC is used to demonstrate the variation of the pressure signal. In particular, the sectioning used is more flexible and is not constrained by the key timings of the micro-pipetting process. The data for a single point can be calculated in real time to obtain the double extremes (the extremes of the pressure and the first derivative) using the DEM. The DEM can therefore be performed without the need to reduce the sampling frequency, thereby guarantying the information integrity. By comparing the double extremes with the preset threshold, the fault types such as tip blockage, presence of air bubbles, and sample shortage can be distinguished. Moreover, a grey filtering technique based on the GM (1, 1) model is used to improve the stability of the pressure sensor output and significantly reduce the real-time computation requirements. Experiments were performed to verify the feasibility of the combined pressure monitoring method, and it was confirmed that it could be used to ensure real-time integrity of the information of the pressure curve. It can thus be confidently concluded that the method can be used to improve the accuracy and stability of monitoring the pressure of micro-pipetting.

This study aims to explore the biomechanics of positive intrathoracic pressure and its effects on left ventricle (LV) filling in healthy subjects. 30 healthy subjects were enlisted to perform a Valsalva maneuver (VM) with a load of 40mmHg lasted 10s. LV filling parameters were measured by echocardiography at rest and at 10s during the VM. Compared with the at rest values, LV early inflow velocity (E) decreased significantly ($p<0.05$), late inflow velocity (A) decreased insignificantly ($p>0.05$), while the E/A ratio decreased significantly ($p<0.05$) after 10s of the strain phase of the VM. LV septal early tissue velocity ($e_{\mathrm{\text{sep}}}$) and lateral early tissue velocity ($e_{\mathrm{\text{lat}}}$) of the mitral did not change ($p>0.05$), while the $E∕e_{\mathrm{\text{sep}}}$ ratio and the $E∕e_{\mathrm{\text{lat}}}$ ratio decreased significantly ($p<0.05)$ after 10s during the VM. Based on these results, biomechanical analysis suggests that the effects of positive intrathoracic pressure on the LV free wall impede LV diastolic motion, which may be one of the factors contributing to a decrease in E and the E/A ratio. Positive intrathoracic pressure also increases the flow resistance of the LV and pulmonary vasculature, which may contribute to a decrease in E, the $E∕e_{\mathrm{\text{sep}}}$ ratio, and the $E∕e_{\mathrm{\text{lat}}}$ ratio.