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Abstract:ObjectiveTo automatically measure anatomic parameters of proximal femur by establishing three-dimensional (3D) coordinate system of the femur based on bony landmarks, so as to assist pre-operative planning and design of customized femoral stem. MethodsThe software named "Femeter" was independently developed for anatomic measurement of the femur, which allowed importing the femur models with STL format and manually locating the targeted anatomic landmarks. The 3D modeling of femoral medullary canal was rapidly created by semi-spherical iterative searching algorithm, and 16 key anatomic parameters of proximal femur, including femoral head radius, neck-shaft angle, anterversion were automatically calculated by least-squares fitting algorithm. ResultsBy experimenting on 30 femur STL models, the average execution time of single measurement was (0.95±0.16) seconds, and the intra-class correlation coefficient of 9 anatomic parameters was between 0.907 and 0.999, which showed high intra-rater and inter-rater reliability. ConclusionsThe automatic modeling and execution time of measuring algorithm by Femeter are fast, with satisfactory measurement repeatability and easy interaction, which is easily applicable to clinical practice. The 3D anatomic measurement of proximal femur can provide solid data for pre-operative planning of total hip arthroplasty, selection of commercialized femoral stem and design of customized femoral stem.

Abstract:Objective To investigate the effects of different stent parameters on the development of restenosis, so as to provide references and basis for the design of stent forms. Methods Stents were categorized into groups according to stent unite length, strut number, strut cross-section diameter, stent depth into fluid, strut cross-section shape. The influence of different parameter settings on wall shear stress distributions was investigated based on three-dimensional computational fluid dynamics (CFD) simulation. Results The strut cross-section diameter had the most obvious impact on wall shear stress. It would lead to the increase of low wall shear stress area with shorter stent unite length, more strut number, larger strut cross-section diameter and deeper stent depth into the fluid. In comparison with triangular and square cross-section shape, the low shear stress area was much smaller by using stent with circular cross-section. Conclusions It is suggested that the circular cross-section shape should be adopted in stent design, with preference to reducing strut cross-section diameter, strut number and stent depth into the fluid, while increasing stent unite length.

Abstract:Objective To analyze the relationship between structure characteristics and longitudinal flexibility of the self-designed NiTi coronary stents by using finite element method. Methods A new type of stent geometric model was designed with the CAD software Soildworks, and then the finite element stent model was established with Hypermesh, MATLAB and ABAQUS software. In ABAQUS, the angular displacement loads were applied on the stent in 9 bending directions within one structural cycle to maintain the stent in a pure bending state. Results The stent flexibility appeared no significant difference before the self-contact occurred, while it showed obvious anisotropy after the self-contact occurred. In addition, the bending deformation occurred under in-plane pure bending loads, accompanied with the out-of-plane deflection and torsion deformation around the axis. Conclusions The bending behavior of the stent is determined by its structural characteristics, and the stent always shows anisotropic flexibility due to its spiral arrangement of the connecting body and self-contact, which will provide a scientific guidance for clinical application of the stent.

Abstract:Objective To demonstrate the relationship between modified Hausdorff distance (MH) and the spatial change of arterial vasculature in residuum. Methods Data of the vascular model were obtained from CT scans of clinical cases, and a centerline model of the residuum vasculature was established by setting the appropriate parameter of distance between control points (DCP) in MIMICS 10.0. Deformation was applied on the model through compiling the program in MATLAB. The MH values before and after the deformation were calculated and analyzed. According to different locations of the rotation axis, the deformation was divided into four cases (C1, C2, C3, C4) on the basis of growth order in node numbers and total length of the vasculature. Results MH increased with the increment of the vascular rotation angle, but due to different maximum rotation radius and total length of the vascular vessel, 4 deformed models showed different growth trends. With the rotation angle increasing, MH gradually increased from C1 to C4. The maximum change occurred from C2 to C3, and minimal change occurred from C3 to C4. Specifically, the maximum rotation radius and total length of the vessels from C1 to C2 increased by 22.2% and 91.3%, while those from C3 to C4 increased by 14.1% and 26.8%, respectively. Moreover, the maximum change of MH value was 60.4% from C1 to C2 and 4.5% from C3 to C4. Conclusions MH can be an effective parameter to indicate spatial change of the residuum vasculature. MH of the residuum vasculature is proportional to deformation angle of the vessel, and the maximum rotation angle has a significant influence on MH. Moreover, when DCP is smaller than 3 mm, the influence of parameter setting can be avoided effectively. In addition, MH can also be applied in the studies of vasculature change and comparison.

Abstract:Objective Based on the previous researches of hepatic blood vessel perfusion, using dynamic methods to study and simulate the dynamic behavior of fluid and mechanical properties of vascular wall during perfusion of defected liver (blocked or with foreign matter), and investigate the variation patterns and influencing parameters during liver perfusion. Methods On the basis of medical image data, both the liver straight and bend vessel models were constructed. A mathematics method was proposed to estimate the perfusion speed and simulate the flow of intravascular perfusion liquid. Under the condition of fluid-solid coupling, the mechanical properties of vascular wall were analyzed, and the optimization of perfusion parameters under multiple-coupling condition was suggested. Results When the vascular diameter of the liver changed (such as vascular spasm) or in the case of vascular thrombosis, the hydrodynamic behaviors in blood vessel during liver perfusion were as following: (1) The deformation in the first half part was much more serious than that in the second half part of blood vessel with different blocked degrees. (2) Under the same perfusion condition, the deformation in bend vessel was much larger than that in straight vessel. Conclusions The simulation results show that the proposed estimation method for perfusion speed is feasible, and the results of liquid-solid coupling analysis on both hydrodynamic behavior of fluid inside blood vessel and mechanical properties of vascular wall during simulated liver perfusion accord with the medical practice. The parameters influence vascular wall differently as follows: the blocked degree of blood vessels＞ the shape of blood vessels ＞ the location of foreign matter. The optimal parameter values during liver perfusion are also obtained under the condition of fluid-solid-heat coupling field.

Abstract:Objective To study the influence of laser peripheral iridotomy (LPI) on aqueous humor flow in eyes of patients and fluid shear stress exerted on the corneal endothelial cells. Methods A complete three-dimensional geometric eye model was established by CAD software with references to human eye geometric data from the literature. Numerical simulations on the flow conditions of aqueous humor and the shear stress exerted on corneal endothelial cells after LPI surgery were performed using finite element software. The simulation results of shear stresses at different positions of the laser hole in the iris before and after LPI surgery were compared. Results If the laser hole punched more closer to the pupil axis in iris, the shear stress exerted on corneal inner surface would be smaller. The maximum shear stress exerted on corneal endothelium was 16.5, 25.8, 57.0, 179.8 mPa when the distance between laser hole and the pupil axis was 4.0, 4.5, 5.0, 5.5 mm, respectively. With laser hole at 3 and 6 o’clock orientation, the maximum shear stress exerted on corneal inner surface was 13.7% and 4.2% greater than that at 12 o’clock position (56.95 mPa). ConclusionsLPI can influence the intraocular aqueous humor flow and shear stress exerted on corneal endothelial cells. The suitable position can decrease the shear stress exerted on corneal endothelial cells and reduce the risk of postoperative bullous keratopathy for patients after LPI surgery.

Abstract:Objective To study the effects of high pressure environment on human cochlea, so as to supplement inadequate study on cochlea behavior under high pressure conditions due to insufficient experimental methods, and provide new ideas for the targeted research on cochlea in future. Methods Based on CT scan images of normal human cochlea and combined with self-compiling program and the software PATRAN, a three-dimensional finite element model of spiral cochlea was constructed. The fluid-solid coupling frequency response analysis and transient response analysis were made by using NASTRAN. The effect of high pressure on cochlea was then investigated by numerical simulation. Results The simulated results of ratio of displacement at 12 mm from basilar membrane to that at the oval window were consistent with those reported in the literature, which verified the correctness of the model. In high pressure environment, the amplitude of cochlea basilar membrane at characteristic frequency point would decrease with the pressure increasing. Conclusions High pressure conditions can ultimately lead to the loss of human hearing. The research findings provide the theoretical support for developing high pressure buffer devices in clinic.

Abstract:Objective To simulate the process of lumbar burst fracture by finite element method, and investigate stress distributions on the cancellous bone of lumbar vertebrae under axial compressive loads. Methods The 3D finite element model of normal human thoracolumbar motion segments (T12-L2) was established. Stress at different levels (0.4, 0.6, 0.8, 1.0, 1.2 kN) was applied on the surface of T12 thoracic vertebra to simulate the different axial compressive loads at the occurrence of lumbar burst fracture. The ligature between concave vertexes of the inferior and superior endplates was divided into 7 portions, and the cancellous bone of the L1 vertebra was then divided into 7 layers with each layer separated into 6 statistic zones. The average stress on 18 statistic zones at 3 layers (Layer 1, 4, 7) of the cancellous bone was calculated, respectively. The average stress on 3 layers under the same loads was analyzed by one-way ANOVA, and stress distribution on the cancellous bone of lumbar vertebrae under different loads was also analyzed. ResultsUnder axial loads at 5 different levels, the average stress on Layer 1 and Layer 7 had obvious statistical significance compared with that on Layer 4(P<0.05), but no significant difference between Layer 1 and Layer 7(P>0.05). The stress on the middle layer (Layer 4) was the minimum compared with that on Layer 1 and Layer 7. Conclusions Under axial compressive loads, the stress concentration occurred in the cancellous bone of lumbar vertebrae. The stress at adjacent vertebral endplates (inferior and superior endplates) was larger, while the stress on the middle layer was relatively smaller. The phenomenon that vertebral stress concentrating on inferior and superior endplates was consistent with the biomechanical mechanism of broken endplates caused by lumbar burst fracture, which indicates that the damage to lumbar structure may be related to the stress concentration on lumbar vertebrae.

Abstract:Objective To analyze the viscoelastic properties of adjacent segments after anterior fusion under prolonged flexion, and further reveal the mechanism of accelerated adjacent segment degeneration after intervertebral fusion. Methods The same prolonged flexion lasted 30 minutes was applied on the two-level ovine lumbar specimen before and after anterior fusion respectively, and the moment relaxation and viscoelastic deformation of adjacent segments were measured. The moment relaxation curves from two groups were then fitted to obtain the quantitative viscoelastic results. Results After fusion，the initial and final moment in two groups significantly increased by 30.68% and 34.34%, and the viscoelastic deformation of the adjacent segments increased by 28.21%. The Prony model could perfectly fit the moment relaxation curves (R2=99.50%). The integral stiffness significantly increased by 47.82% and 31.14% for two groups, while the viscoelasticity significantly decreased by 27.19% and 28.16%, respectively(P<0.05). Conclusions After intervertebral fusion, to maintain the same posture with the same time, the joints should bear larger loads than before. The viscoelastic deformation of adjacent segments becomes larger, which increases the risk of instability or injury, and further leads to the accelerated degeneration of adjacent segments. The mechanism of quasi-static daily loading on adjacent segment degeneration should be focused in clinical research.

Abstract:Objective To analyze the mechanical properties of V-bends with different materials, sizes of arch wires, angles, shapes, inter-bracket distances by using finite element method, so as to provide references for clinical practice of V-bends. Methods The finite element models of V-bends were established, including two kinds of materials (stainless steel, titanium-molybdenum alloy), two sizes（0.43 mm×0.64 mm, 0.48 mm×0.64 mm）, two V-bend positions, two angles(150°, 165°),and two inter-bracket distances（7,10 mm）, so as to compare and analyze their mechanical properties after simulative loading. Results The maximum force values produced by V-bends with stainless steel arch wire were greater than that of V-bends with β titanium steel arch wire. The force produced by V-bends with 0.43 mm×0.64 mm arch wire was smaller than that produced by V-bends with 0.48 mm×0.64 mm arch wire. The size of arch wire had a more obvious impact on V-bends with symmetrical arch wire. The force of V-bends with asymmetric arch wire was more evidently influenced by the change of inter-bracket distance. For V-bends with the same shape, the smaller the V-shaped angle, the greater the force on the bracket would be. Conclusions The V-bends with different materials, different sizes of arch wires, different shapes and inter-bracket distances will have different mechanical behaviors. In clinical application, the materials, sizes of arch wires, shapes and angles of V-bends should be adjusted properly according to the inter-bracket distances.

Abstract:Objective To study the effects on compressive strength and rigidity of tibia cortical bone from deep-freezing, freeze-drying or radiation treatments, and to discuss the appropriate method for tibia cortical bone treatment. Methods The cortical bone were collected from the middle part in tibial diaphysis from amputated limbs of trauma patients and made into bone plates with the size of 10 mm×10 mm×5 mm each. The bone plates were then divided into seven groups evenly and randomly: control group (Group A), deep-freezing group (Group B), freeze-drying group(Group C), deep-freezing plus 60Co (25 J/g) radiation group(Group D), deep-freezing plus 60Co (50 J/g) radiation group(Group E), freeze-drying plus 60Co (25 J/g) radiation group(Group F), freeze-drying plus 60Co (50 J/g) radiation group(Group G). The compressive strength and rigidity of allograft cortical bone were tested by mechanical testing machine. Results The largest compressive strength of the tibia cortical bone was in the range of 6.089-9.089 kN. Compared with Group A, the strength in Group B, C, D and F showed no significant difference, and the rigidity in Group B and C showed no significant difference, while the rigidity in Group D and F was decreased by 9.6% (P<0.05) and 8.7% (P<0.05), respectively. Compared with Group A, the strength in Group E and G was reduced by 29.6% (P<0.05) and 33.1% (P<0.05), respectively, and the rigidity was reduced by 16.7% (P<0.05) and 14.8% (P<0.05), respectively. Conclusions The strength and rigidity of tibia cortical bone are not changed significantly after deep-freezing or freeze-drying treatment. Compared with the untreated group, the strength of tibial cortical bone with the small dosage of 60Co treatment is not significantly changed after deep-freezing or freeze-drying, but the rigidity is decreased; the strength and rigidity with the large dosage of 60Co treatment are decreased obviously. For application of cortical bone used in spinal fusion, radiation sterilization dosage should be controlled in the range of 15-25 J/g.

Abstract:Objective To investigate the effects of exposure to glucocorticoids with different dosage on skeleton of normal 3-month-old rats by dual energy X-ray absorptiometry (DXA), biomechanical testing and bone histopathology. Methods Thirty-one 3-month-old female clean level SD rats were randomly divided into 3 GC-treated groups, with tail intravenous injections of dexamethasone (Dex) at the dosage of 1, 2.5, 5 mg/kg twice per week for 8 weeks, respectively, and 1 normal control group treated with saline. At the end of experiment, bone mineral content (BMC) and bone mineral density (BMD) of the femur and the 3rd lumbar vertebrae in rats were measured by DXA. The 3-point bending test of the total femur and compression test of the 5th lumbar vertebrae were also conducted, respectively. Microstructure of the trabecula in proximal metaphysis of the tibia was observed by bone pathological section for quantitative analysis. Results Compared with control group, the body weight was significantly decreased in all Dex-treated groups, while no obvious decrease in vertebral BMC, BMD and maximum compressive loads was found. The total femoral BMC was also reduced significantly in all Dex-treated groups, while the total femoral BMD, proximal and distal femoral BMD were reduced only in Dex 1mg group. The fracture load, maximum load and elastic load for 3-point bending test were all evidently decreased in Dex 1mg group, while the Dex 2.5mg group and Dex 5mg group only showed a decline in elastic load. All Dex-treated groups showed an unevenly spatial distribution of the trabecula, which indicated a low bone metabolic state. Conclusions The exposure to GC for 8 weeks brings negative effects on skeleton of the 3-month old rats, which will cause more bone loss and worse mechanical properties in femur than in lumbar vertebrae. Higher dosage of Dex does not increase bone mass loss or change the mechanical properties. Both the decline in bone mechanics, especially elastic load, and unevenly density distribution of trabecula indicate that Dex will affect more bone quality other than bone mass. The side effects of GCs on skeleton in clinical application should be evaluated with various methods.

Abstract:Objective To analyze and summarize the gait characteristics of patients with sciatica, so as to assist with diagnosis and evaluation for such patients in clinic. Methods Forty-three patients with lumbar disc herniation accompanied by siatica were fitted with portable gait analyzer, and required to walk at the self-selected comfortable speed for a distance of 120 m. Forty-three healthy subjects with matched age, gender and body mass index (BMI) were recruited as control. The gait data including 7 spatial-temporal parameters (single-support duration, double-support duration, ratio of single-support duration to double-support duration, duration of gait cycle, step speed, step frequency, step length) and 4 acceleration parameters (pulling acceleration, swing power, ground impact, foot fall) were collected to compare the gait differences between patients and healthy subjects, as well as between affected and healthy limbs of patients. Results The single-support duration, ratio of single-support duration to double-support duration, step speed, step frequency, step length and four acceleration parameters of patients with sciatica were obviously smaller than those of healthy subjects, while the double-support duration of patients with sciatica was increased. The affected limb of patients with sciatica showed a significant decrease in single-support duration, step frequency and all four acceleration parameters but increase in step length as compared to their healthy limbs. Conclusions Patients with sciatica have significant gait abnormalities due to their affected limbs, which influence their walking ability. Portable gait analyzer can be used for objectively characterizing the walking abnormalities of patients, so as to provide additional information for the clinical diagnosis and evaluation.

Abstract:Ankle sprains are one of the most common surgical injuries in clinic. In this article, the foot anatomy structure was elaborated, and the biomechanics of ankle ligaments during sports was mainly reviewed. At the same time, the mechanism of ankle sprains was analyzed, the principal means of ankle sprains, prevention and rehabilitation at present were summarized, and the use of ankle braces to prevent ankle sprains as well as its research progress were introduced emphatically. The classification and characteristics of ankle braces were then summarized, and the prevention of ankle sprains and development of ankle braces were prospected. The multiple ankle lateral ligament damage was due to the physiological structure differences between lateral and medial ligaments of the ankle joints, and such structure characteristic should be considered while improving ankle braces and designing new ankle braces. Wearing ankle braces plays a key role in ankle sprains protection, which can shorten the recovery time and avoid re-injury in clinical rehabilitation. For rehabilitation of severe ankle sprains, semi-rigid ankle braces are better than elastic ones.

Abstract:The traditional method of in vitro biomechanical study cannot simulate the realistic environment in human body due to the limitation of in vitro technology. Using advanced imaging techniques and testing methods, in vivo biomechanical studies of cervical spine kinematics can directly observe the cervical spine motion of living subjects. The data obtain repeats physiological situations and has important implications for improvement in clinical practice. In this paper, the biomechanical research methods of cervical spine kinematics, as well as the development process and current status were reviewed. The postoperative changes in cervical spine kinematics and the effects on adjacent segments following cervical spine fusion and cervical disc arthroplasty surgery were analyzed. The future developments in cervical spine research were also discussed.

Abstract:The rupture of carotid atherosclerotic plaques and thrombosis are the main risk factor for ischemic stroke. The risk of carotid plaque rupture is closely related with the local biomechanical situation, morphology, components and biological activity of the carotid plaques. In this article, the research progress on methodology for studying carotid stenosis biomechanics, the risk of vulnerable plaque rupture in carotid stenosis and decision-making in clinical treatment, the animal modeling and experiment on vulnerable carotid plaques, and the components and biological activities of carotid plaques was summarized, the existing problems were analyzed, and the in-depth prospective about the biomechanical mechanism and quantitative assessment indices for vulnerable carotid plaques was also proposed, expecting to provide necessary theoretical guidance for feasible decision-making on the treatment of carotid stenosis.