Abstract:Knee joint is the largest joint in human body, with the most complex anatomy and the highest demand on motor function. The number of patients who receive the total knee arthroplasty (TKA) grows at the rate of over 10% annually around the world. TKA was developed from total hip arthroplasty, and has been developed rapidly during the thirty years' development. In this paper, evolution of prosthesis types, geometric shape and size of prosthesis and breakthrough in biomechanics of knee joint were reviewed; controversial issues in contemporary TKA studies were discussed; and the development of TKA in future was forecasted.

Abstract:Researches on mechanical properties of biological hard tissues are of great importance to the prevention and treatment for both bone diseases and oral diseases. Meanwhile, biological materials possess superior mechanical properties due to long-term evolution, and studies on the structure and mechanical properties of these materials can provide useful solutions for the design of engineering materials. However, unlike engineering materials, mechanical studies on biological materials need specific methods to accurately characterize the mechanical performance. This paper summarized the research methods on mechanical properties of biological hard tissues, including routine mechanical tests, fracture mechanics tests, nanoindentation tests, as well as numerical simulation techniques in nano, micro and macro scales.

Abstract:Mechanical environment and intervention do have effects on both structure and function of musculoskeletal system, prevention and treatment of related disorders as well as its rehabilitation. With rapid advancement in cellular and molecular biology, biomechanics in musculoskeletal research has extended from organ and tissue level to cellular, molecular and gene level. The development of medical biomechanics promotes research and development of mechanical stimulation-based medical devices and accordingly, how mechanical stimulation can enhance osteogenesis and bone regeneration has become a hot basic and applied research area in orthopaedics. The Journal of Medical Biomechanics has published a series of basic and applied research work on potentials of biomedical stimulations for musculoskeletal systems. In this issue, the Journal specifically selected a few original efficacy and mechanistic research on mechanical stimulation for enhancing osteogenesis and bone regeneration in challenging osteoporotic fracture repair. Such efforts would help to facilitate more clinical orientated scientific research.

Abstract:Objective To investigate the effects of different vibration durations on expression level of osteogenesis-related proteins by loading low intensity mechanical vibration in the ovariectomized (OVX) rats. Methods Twenty-four 6-month old female Wistar rats were ovariectomized and then randomly divided into 8-week-control group (C8), 12-week-control group (C12), 8-week-vibration group (V8), and 12-week-vibration group (V12). Vibration treatment was started one week after all the rats were ovariectomized. Rats in both V8 and V12 groups were loaded with 35 Hz, 0.25 g low intensity mechanical vibration for 15 minutes per day. C8 and C12 groups served as control without any treatment. Rats were executed in batch at 8th and 12th week, respectively, to analyze expression level of osteogenesis-related proteins, including BMP-2, p-ERK, Runx2 and OCN. Results Low-intensity mechanical vibration enhanced the osteogenesis related protein expression in OVX rats (P<0.01). With the extension of vibration duration, the osteogenesis related proteins BMP-2、p-ERK、Runx2 and OCN in V12 group were increased by 22.61% (P<0.05), 27.96% (P<0.01), 25.85% (P<0.01), 27.05% (P<0.01), respectively, as compared with V8 group. But for the control groups, no significant differences were found in expression level of osteogenesis-related proteins. Conclusions The low intensity mechanical vibration could elevate expression level of osteogenesis-related proteins, and the osteogenesis was enhanced with the extension of vibration duration.

Abstract:Objective To study changes in biomechanical characteristics of the femoral head during the progression of avascular osteonecrosis and investigate the mechanism of these biomechanical changes. Methods Twenty-four three-foot weight bearing canine models with osteonecrosis of the femoral head (ONFH) were established by fixing one fore limb of the canine. Osteonecrosis was induced in all experimental animals by randomly injecting 5 mL pure ethanol into one side of the femoral head, and the contralateral femoral head was injected with an equal amount of normal saline as the control group. The canines were killed at 1st, 3rd, 6th, and 12th week after the injection of ethanol, with six canines in each group. The radiographic, histological changes and biomechanical characteristics of the femoral head were observed and analyzed. Results At 3rd week, 29% reduction of indentation stiffness and 32.9% reduction of elastic modulus in the cancellous bone were found in the infected femoral heads compared to the control heads, and a low density area was detected only in MRI and osteonecrosis was the main histological characteristics. At 6th and 12th week, the indentation stiffness in the infected femoral heads was reduced by 45.5% and 48.7%, respectively, and the elastic modulus of the cancellous bone in the infected femoral heads was reduced by 34.1% and 32.4%, respectively, compared to the control heads. At 6th week, uneven bone density of the femoral head was detected in radiographs, and the progression of osteonecrosis and bone healing was found at the same time. At 12th week, areas of reduced bone mineral density beneath the load bearing position of the femoral head were observed on radiographs. Collapse of the articular cartilage surface and narrowing of the joint space were the main histological findings. Conclusions Biomechanics is an important factor in the progression of ONFH. The decreased mechanical properties may be a direct reason leading to the late collapse of the femoral head. The treatment of ONFH should focus not only on acceleration of the bone healing, but also on provision of a favorable and stable biomechanical environment for the infected femoral head.

Abstract:Objective To investigate the effects of low-magnitude high-frequency vibration (LMHFV) on osteoporotic fracture healing and blood supply of distal injured limbs based on osteoporosis fracture model of the ovariectomized (OVX) rats. Methods Ovariectomy was performed in 32 six-month-old female SD rats. 3 months later, closed transverse fractures were created at the right femoral midshafts complicated by femoral artery injuries. The rats were then randomly divided into vibration group and control group. Radiographs were performed in each week to assess the callus size and the status of fracture healing. At 2nd, 4th and 8th week after treatment, pulsed-wave Doppler ultrasonography was utilized to evaluate the blood flow velocity and the resistance index (RI) of the distal femoral artery in injured limbs. The peri-fracture region was reconstructed by Micro-CT for both qualitative and quantitative analysis. Results Pulsed-wave Doppler indicated a significantly higher peak systolic velocity of distal femoral artery in vibration group at 2nd and 4th week (P<0.05) and a lower RI as compared with control group.Radiography and Micro-CT analysis demonstrated that vibration group had better callus formation, mineralization, remodeling, and bridging rate during fracture healing as compared with control group. Conclusions LMHFV can effectively improve the blood supply of distal injured limbs and promote the osteoporotic fracture healing.

Abstract:Objective To make a reasonable selection from internal fixation Methods for treating femoral neck fracture, namely the fixation angle of a single screw, the number of screws and the combination mode of screws, so as to obtain the optimal stability of fracture reduction. Methods Based on the DICOM data and Lindon mode, a three-dimensional finite element model of femoral neck fracture fixation was built including different angles, numbers and combination modes of the screws. The model was attributed to nonlinear material properties based on the relationship between the property parameters of bone materials and the gray value of CT images, and loaded under the simulation of physiological loads. Results Corresponding to different angles of the fracture surface, the optimal fixation angle of the single screw was 65°and 70°in clinic. The more the number of screws, the better the effect of fixation, when the surgical condition was permitted. The inverted triangle placement was better than the triangle placement in case of three-screw fixation, while the triangle placement was superior to two-screw fixation, but the decision on the placement of two-screw fixation in flat form or diagonal form depended on the angle of the fracture surface. Conclusions Different angles of the fracture surface have significant impacts on the effect of fixation, and the loading simulation process on the three-dimensional model can provide a feasible way to the study of the fixation for the femoral neck fracture.

Abstract:Objective To study three-dimensional feature of the thickness of subchondral cortical bone, the surface area and space width of the facet joints as well as its morphological characteristics and variation, and to compare the differences of these parameters in patients with low back pains and healthy people, based on three dimensional reconstruction images of the facet joints. Methods CT scanning from L1/2 to L5/S1 at supine position was performed on 90 subjects to obtain two-dimensional images of the facet joints and three-dimensional point-cloud data of the subchondral cortical bone, the surface area and space width of the facet joints after reconstruction. Distributions of these parameters between the superior and inferior facet joints and at different regions of the articular process were investigated, and differences of these parameters in lumbar segments, gender, age and symptoms were also compared. Results (1)At superior facet, the largest thickness was located at the cranial region, while at inferior facet, it was located at the caudal region. The thickness of subchondral cortical bone was significantly smaller at central region than at the other regions. A more obvious difference could be observed at the lower lumbar levels（L4/5, L5/S1）. (2)The average surface area of the facet joints was (173.2±3.6) mm2, and it was increased with the lumbar level and age increasing, especially at the L4/5 level and at the age of more than 40. The surface area of superior facet joints was significantly larger than that of inferior facet joints for patients with low back pains (except at L5/S1 level), who had an obviously larger surface area of the facet joints than healthy people. (3)The average thickness of space width of the facet joints was (1.46±0.08) mm, and it was decreased with age decreasing, especially at the age of more than 40. The female had significantly larger space width than the male, while patients with low back pains had significantly smaller space width. At each facet joint, the space at cranial region was significantly larger than that at caudal region, and it was also significantly larger at central region than at surrounding region. These differences were more obvious at the lower three lumbar levels. Conclusions Computer-assistant image processing and reconstruction analysis techniques can accurately measure the relative parameters of lumbar facet joints with complicated structure in three dimensional space. The feature of the facet joints was correlated with shape of the facet joint surface，stress on the joint and degeneration of the joint, so it was a reflection of adaptive changes in human body structure due to the long-term loading on the facet joint.

Abstract:Objective To observe the obstacle of mandible to the cervical spine with the aid of dual fluoroscopic imaging system, explore the optimal perspective Methods of in vivo kinematics of cervical spine, and verify the feasibility of cervical in vivo kinematic researches. Methods A dual fluoroscopic imaging system composed of two C-arms placed in different angles was utilized. X ray images of the cervical spine for five healthy volunteers (4 male, 1 female) with standing, flexion extension, twisting and bending positions were obtained with the C-arms in the angle of 90°, 60°and 45°, respectively. The obstacles of mandible to the cervical spine in different positions were compared and the obstacle degree of mandible to the cervical spine was evaluated to screen the optimal perspective Methods. The perspective images under conventional head rotation and coaxial trunk rotation were collected during cervical twisting to compare the obstacle of mandible to cervical images. Results There were significant differences in mandibular obstacle degrees among the three angles measured in standing, flexion-extension, twisting and bending positions（P<0.05）. With two C-arms in 45°, the cervical spine was best imaged with the least obstacle. With two C-arms in 60°, significant differences could be found between the coaxial trunk rotation and the head rotation group. Conclusions For in vivo kinematics study of cervical spine, the obstacle of mandible to the cervical spine can be minimized with C-arms of dual fluoroscopic imaging system in 45°, and the coaxial trunk rotation can decrease the mandibular obstacle degrees as compared with the head rotation, which satisfy the requirement of 2D-3D image matching.

Abstract:Objective To propose some detailed methods for diagnosis of fractured stem failure in clinic by studying the mechanical mechanism of fractured stem failure and the specific causes of fracture occurrence after the total hip arthroplasty (THA). Methods The correlations between fracture stem failure and production, clinical situation and patients were analyzed by 2D and 3D finite element analysis (FEA) method to study the biomechanical mechanism of fracture processes. Results The reasoning route for fractured stem failure analysis after THA was proposed, and mechanical analysis and validation on fractured stem failure were conducted by FEA methods successfully. Conclusions Fracture should not occur on the artificial stem, for those that gone through the strength design and experimental test; statistical analysis on fractured stem failure showed that the occurrence of such fractured stem is a kind of little probability random event, which could be induced by a variety of non-normal factors, such as fluctuations in product quality, technical errors in clinic, patient accidents and so on. Strict controls on these factors can reduce the fractured stem occurrence; the reasoning route for fractured stem failure can help to discover the reasons of failure occurrence; the mechanical mechanism of specific fracture stem occurrence can be detected by 2D and 3D FEA methods.

Abstract:Objective To study the expansion behavior of stent in stenotic vascular, in stent blood flow and fatigue life of stent by finite element method. Methods ANSYS was used to simulate the expansion of stent in stenotic vascular. The blood flow model was created by constructing the entities based on deformation of the related nodes from the result of dilation process. A sample model was also built to simulate the in stent blood flow. Stent fatigue life was evaluated based on Goodman’s method and accumulated damage method, respectively. Results (1) Plastic deformation appeared on most parts of struts. The major stresses were localized in the corner of the slots. (2) Turbulent flow occured near the stent. Stresses of stent in cross section of bridge struts along the direction of blood flow were highest. (3) Goodman’s method showed that the stent was safe, and cumulative damage indicated that the largest cumulative damage occured in the second cross section of bridge struts. Conclusions Finite element method can be effectively used to simulate the stent expansion, in stent blood flow and stent fatigue life.

Abstract:Objective To investigate the edge contact behavior of conformal spherical hip joint replacements under the given dynamic contact displacement condition. Methods Based on the developed spherical-grid-data model, the contact behavior and corresponding edge contact behavior of a typical metal-on-metal hip joint replacement was simulated under the increasing displacement between the acetabular cup and femoral head. Results It was found from the obtained results that the vertical and horizontal component of the support force due to contact pressure increased with the dynamic contact displacement increasing. The vertical component of support force for the edge contact showed a slower variation tendency than that for the non edge contact, while the corresponding horizontal component of support force increased more significantly with the dynamic displacement. In addition, the corresponding contact pressure distributions and the contact areas of hip joint replacements for edge contact and non-edge contact were different. Conclusions The significant edge contact behavior of hip joint replacements with bigger cup inclination angle occurrs with the increasing displacement of femoral head to the acetabular cup, which will cause the sliding between contact surfaces and additional wear since the horizontal support force increases. This provides a reference for the wear assessment and manufacturing of hip joint replacements.

Abstract:Objective To study the characteristics of upper airway airflow dynamics during inspiration after unilateral total maxillectomy by means of computer numerical simulation. Methods Based on postoperative CT images of three patients with unilateral maxillary tumor, three-dimensional upper airway structures of the patients were reconstructed, and the upper airway airflow was simulated numerically by computational fluid dynamics method. Results The upper airway airflow trends of the patients during inspiration after unilateral maxillectomy were obtained. Airflow in the defect nasal cavity was separated, and made the spacious vortices of low velocity occurred throughout the entire maxillary defect cavity. Conclusions The upper airway trends of the three patients were generally in conformity with each other after their unilateral total maxillectomy, which illustrated that the respiratory patterns of such patients were of universality. Unilateral total maxillectomy resulted in structure changes of patients’ upper airway, which could disturb the upper airway airflow patterns，and affect the physiological functions of patients’ upper airway. Numerical simulation of patients' upper airway airflow after unilateral total maxillectomy could help to explain the phenomena of nasal drying and crusting, secretion accumulation as well as other symptoms of the kind of patients.

Abstract:Objective To construct and validate the 95th percentile finite element model of Chinese human head, evaluate the relative displacement between the skull and brain according to four types of skull brain relative displacement experiments as references, and investigate the shear strain distributions on the brain. Methods By comparing the relative displacement curve derived from the experiment and simulation and referring to conclusions from animal and physical experiments, the position of higher shear strain was investigated. Results High correlations could be found between the simulated and experimental results for skull brain relative displacement. Peaks and troughs could always appear in curves of skull brain relative displacement due to the fact that the brain tissue tended to return to its initial state. The results that higher strain could occur at temporal lobe of the brain, corpus callosum and brain surface were consistent with conclusions from the animal and physical experiments. ConclusionsT he 95th percentile finite element model of Chinese human head is validated with good biofidelity. Due to the rotational motion of human head, higher shear strain will occur on brain surface and in deep brain, leading to injuries, which provids a scientific theoretical basis for the study on injury mechanism of human head in traffic accidents.

Abstract:Objective To investigate the influence of three extracellular matrix (ECM) proteins, namely, laminin (LN), collagen type I (Col I), fibronectin (FN) on the morphology and contractility changes in airway smooth muscle cells (ASMCs) induced by platelet-derived growth factor-BB (PDGF-BB). Methods ASMCs were seeded on the culture dish coated with LN, Col I, or FN, respectively, and divided into two groups to be cultured either in the absence or presence of PDGF-BB (10 mg/L) for 0~5 d. Subsequently, cell morphology was examined by the optical microscopy and quantified as the ratio of cell width to length, and the KCl/histamine-induced contractile responses of the cell were measured by optical magnetic twisting cytometry (OMTC). Results ASMCs cultured in the presence of PDGF-BB generally appeared in longer and thinner cell shapes, namely, a smaller ratio of cell width to length, but the cell width/length ratio for ASMCs adhered on LN was relatively bigger than that on Col I or FN. In the absence of PDGF-BB, contractility of ASMCs to KCl increased with the duration of culture, which was independent of the ECM proteins. In contrast, in the presence of PDGF-BB, contractility of ASMCs to KCl or histamine decreased in all situations, but degree of the decrease was smaller for ASMCs adhered on LN than those on Col I or FN. Conclusions The morphology and contractility changes in ASMCs induced by PDGF-BB are influenced by ECM proteins on which cells are grown. For ASMCs adhered on LN, the morphology and contractility changes are relatively smaller than those on Col I and FN. The differential effect of ECM proteins on PDGF-BB induced changes in morphology and contractility of ASMCs is important to fully understand the interactions between ECM proteins, inflammatory factors, ASMCs, and their relation to the pathophysiological mechanism of asthma.

Abstract:Objective To measure the rabbit retinal nerve fiber layer(RNFL) thickness in vivo under different intraocular pressures (IOP) and at different time intervals after acute high IOP, and to obtain the regularity on change of RNFL thickness with acute high IOP. Methods Four groups of acute high IOP model were formed by perfusing the saline water into the anterior chamber of rabbit eyes, then RNFL thickness under different IOPs was measured by optical coherence tomography with radial scanning mode whose center was optical papilla and diameter was 6 mm. Results The absolute change values of RNFL thickness were(-27.16±14.24), (-33.33±6.74), (-48.75±5.24), (-67.29±3.89) μm under different IOPs of (4.50±0.35), (6.07±0.31), (7.74±0.26), (10.71±0.07) kPa, respectively. The linear relationship was found between the relative change of RNFL thickness and IOP. IOP could return to the normal level within two days after acute high IOP, while the RNFL thickness could be restored at the second week, and it was easier to restore if the IOP was lower than 6.65 kPa. Conclusions The acute high IOP could cause RNFL thickness to decrease significantly with the increased acute high IOP, but it will be restored after some time.

Abstract:Objective To propose and numerically simulate a novel stent with triangular wire cross-section so as to compare the hemodynamic effect of endovascular stents in aneurysm with circular, rectangular and triangular cross section, respectively. Methods Three aneurysm models were constructed by implanting 3 kinds of stents separately, including one with bare circular wire cross-section stent (named CM), and one with bare rectangular wire cross-section stent (named RM), and one with bare triangular cross-section stent (named TM). An unstented aneurysm model was also constructed to serve as the control (named UM). Four models were preformed with numerical simulation of fluid-structure interaction under the same boundary conditions using finite element method. Results Compared with TM and CM, RM showed lower velocity, higher flow resistance and longer turn over time, which demonstrated that the effect of blood flow pattern on three stents was decreased in the order of RM, TM, CM. RM could reduce the magnitude and fluctuation of wall shear stress (WSS) more significantly than that of TM and CM. However, the pressure rise of TM and CM was lower than that of RM. WSS distribution and deformation results indicated the possibility of aneurysm development along the distal wall was higher than that along the proximal wall, and the top of aneurysm was in the highest risk of rupture. Conclusions Three kinds of stents show differences of hemodynamics in aneurysm treatment, which provides significant references for the structural design and optimization of endovascular stent.

Abstract:Objective To measure the bone mass, the shape of bones and the bone strength through segmentation of the bone cortex in CT images, and to calculate the corresponding parameters in histomorphometry. Methods CT images were first interpreted through the DCMTK to draw information of the corresponding images, then the OpenCV are used for preprocessing on the basis of ROI (range of interest), and the texture features of the image were extracted as the input vector. Results of the manual segmentation were used as the mentor signal to train BP neural network, which were then used for segmenting the bone cortex in a sequence of CT images. Results of the segmentation were further processed and displayed. Results The segmentation efficiency of the bone cortex in CT images through neural network met the needs of the practical application. The separation results showed an obvious shape of the bone cortex with easy distinguishing from the surrounding tissues, which could satisfy the demand of the clinical diagnosis. Conclusions When the texture features of the bone cortex are evident, this method can achieve a more satisfying segmentation effect with smooth contours, high segmentation accuracy and strong adaptability. With less artificial intervention in the process of the image segmentation, this method can be used for batch CT image segmentation of a complete set of the bone cortex. The inadequacy of the method lies in relatively longer training time demanded for the neural network training.

Abstract:Objective To study the self-adaptive anti-control of a single H-R neuronal system transformed from periodic dynamics pattern to chaos. Methods Numerical analysis was performed by adding sine function self-delay feedback while coupling intensity and time-delay, respectively, as the control parameters. Results By numerical simulation and analysis, it was found that in a certain range of the combination of coupling intensity and time-delay, the time-interval sequences of the dynamical pattern of a single H-R neuronal system could be controlled from a periodical pattern of 3 spikes onto chaos and other periodical patterns. Conclusions The method of self-adaptive feedback of sine function is effective for the anti-control of H-R neuron, and the coupling intensity and time-delay are both important parameters. The particular self-adaptive dynamics of information identification to neuron is reflected in the control process.

Abstract:Objective To study the effect of continuous strain on the proliferation and osteogenic differentiation of rat bone marrow stromal cells(BMSCs) in vitro. Methods Rat BMSCs were obtained from adult female Sprague-Dawley rats (3-month old), and purified by full-blood attachment culture. BMSCs between passage 3—5 were seeded on Flexercell mechanical loading system(10%, 1 Hz), and divided into 1 h group, 6 h group, 12 h group, 24 h group, 48 h group, respectively, according to the time subjected to strain. Effects of continuous strain on the morphology, proliferation and osteogenic differentiation of BMSCs were observed and analyzed. Results (1) Compared with the control group, cells subjected to 10% strain showed the particular orientation. Their alignment elongated mostly in the direction perpendicular to the strain axis in a time-dependent manner. (2)10% continuous strain could significantly decrease the proliferation of BMSCs. (3) Continuous strain could increase mRNA expression of ALP, COLⅠand Runx2 in a time-dependent manner. Compared with the control group, mRNA expression of ALP was increased significantly at 24 h, COLⅠat 24 h and 48 h, and Runx2 at 6 h. mRNA expression of osteocalcin (OC) ascended greatly in the beginning, but went down gradually and was significantly lower than that of control at 48 h（P＜0.05）. (4) Continuous strain could induce an increase in Runx2 protein level. A sharp increase in Runx2 protein was observed at 6 h(P＜0.05) , then Runx2 protein level decreased slowly with its mRNA expression being significantly lower than that of control at 24 h（P＜0.05） Conclusions Continuous strain could induce rat BMSCs to orient in an orderly manner, suppress its proliferation activity, but stimulate the osteoblastic differentiation at the early stage.

Abstract:As a new technique of determining the viscoelasticity of soft biomaterials and cell cytoplasm in living cells, particle tracking microrheology (PTM) is mainly applied in the biomechanical research field, such as cell movement, embryo development, laminopathies. PTM has many advantages over the conventional detection methods in cell mechanics. Using this technique, the Brownian motion of probe particles embedded in the medium could be measured by the video-microscopy, and the movement trajectories of the probe could be mathematically transformed into the mean squared displacements (MSDs) thus to extract the parameters such as the frequency-dependent viscoelastic modulus or the creep compliance from the time dependent MSDs of the probes. The basic principles of PTM technique and its application in biomechanics will be reviewed in this paper.