Application of finite element analysis in the study of artificial hip joint

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Abstract: Objective To summarize the application of finite element analysis (FEA) in the research of artificial hip joint at home and abroad


Abstract: Objective To summarize the application of finite element analysis (FEA) in the research of artificial hip joint at home and abroad, so as to better guide the application of finite element method in the field of artificial hip joint. Methods the literatures about the application of finite element analysis in the research of artificial hip joint were reviewed. The results of finite element analysis method from the engineering application, through technical improvement has been across to the research field of artificial hip joint, including complications after total hip replacement (such as stress shielding and bone resorption, prosthesis wear, prosthesis dislocation, femoral fracture), bone cement prosthesis design and analysis, although there are still shortcomings but, with the rapid development of computer and software industry, the finite element method and other virtual digital technology combine to effectively solve many unable to complete in vivo biomechanical experiment, which provides technical support for the development of the theory of joint surgery, in order to improve the curative effect. Conclusion finite element analysis has been widely used in the field of artificial hip joint research, and will continue to improve, making it an important tool for clinical and research work in joint surgery.

Finite element artificial hip joint

The finite element method (finite element method) is a widely used in Engineering Science and technology in mathematical physics method, is used to simulate and solve a variety of engineering mechanics, thermology, electromagnetism and other physical problems had been raised as early as 1940s. Courant first proposed the finite element analysis in 1943. It was first applied to the analysis of the static and dynamic characteristics of aircraft structures [1]. After the computer was born in 1946, it was an easy task to calculate the complex structure that was difficult to solve in the past. With the accelerating speed of the computer and software continues to improve, making the model by the structure of a single model has gradually developed into the coupling model closer to the actual situation. Finite element analysis gradually from strain, small displacement, elastic material and static analysis to the study of large deformation, thermal analysis, material nonlinear problems and dynamic problems, and many research in the field of biomechanics combined with [2].

The basic idea of the finite element method is "one point one", which is to carry on the unit analysis, and the other is to analyze the whole structure. Finite element method of analysis and calculation of ideas: l) discretization of objects. An engineering structure is discretized into a computing model composed of various elements, and the nodes of the unit and the unit are connected with each other by the discrete element. The nature of the problem, such as the setting, the nature and the number of the unit nodes, and the requirement of the deformation form and the calculation progress. Therefore, the finite element analysis of the structure is not the original object or structure, but with the new material by a large number of units connected in a certain way to discrete objects. If the number of units is very reasonable, the results obtained are consistent with the actual situation. 2) unit characteristic analysis. Is to find the relationship between the nodal displacement and the stress of the corresponding node. 3) unknown node displacement. According to the support given conditions and loading conditions, using finite element software to solve algebraic equations, obtain the displacements of all nodes, can solve all kinds of problems of field distribution, water pipe, circuit, lubrication, noise, temperature, and solid fluid interaction

Function problem.

Since 70s, the finite element method has been applied to the study of biomechanics in Department of orthopedics. After 80s, its application scope gradually extended to the biomechanical study of craniofacial bone, bone structure, bone of the jaw. Because of the advantages of this method in the analysis of the mechanical characteristics of irregular objects, it is very important to study the biomechanical properties of artificial hip joint

Replacement has been widely used. This review is about the application of the following on the finite element analysis method in the research of artificial hip.

1 evolution of finite element method

In the finite element analysis of hip joint in human skeletal anatomy due to the complexity and irregularity of the accuracy of modeling presents a great challenge to the biomechanical study of the Department of orthopedics, makes the finite element analysis of most of the time spent in the establishment of model. Zhong Shizhen established the first virtual human data at home by grinding, slicing method, the cutting precision, increase the VHP and VKH of 0.33mm and 0.2mm to the space of fault in 0.1mm; there will be no distinction between the vascular filling arteriovenous, through perfusion filling technique given in much improved display; cutting cutting equipment, more efficient simple; in human samples selection more standardized, a representative of [3]. However, it is difficult to obtain the uniform thickness of the cross section under the condition of thin section, because of cutting and destroying the model. And the need for adequate time to prepare the model and the geometric shape of the section, and the error has been eliminated. This method is only an extreme simplification of the real anatomy, the lack of computational accuracy. Kuroda by laser surface scanning by laser surface modeling, measurement equipment will scan the surface profile of the object, then the data input software to establish the solid model and then reverse into the finite element pre-processing module. Three dimensional measurement of high cost, data processing time is longer, the surface structure can only be established, can not reflect the tissue material properties inherent in medical research, mainly used in some may not consider the analysis of the internal characteristics of the structure such as prosthesis model, dynamic analysis of [4]. Song Hongfang [5] used Photoshop reconstruction by CT conversion of the original data obtained after a series of bitmap file, such as denoising, enhancement, segmentation and registration of image processing work, according to the image information and the 3D coordinates of each fault, the method using 3D visualization data to establish femur model. This method requires manual each picture conversion of CT image on the computer can recognize the bitmap format, and the need for accurate alignment of the image processing software of artificial, para inaccuracy will directly affect the accuracy of the model, this method also need to spend a lot of manpower and material resources. Yan Shigui [6] using DlCOM (Digital Imaging and of Medicine Communication) data to establish a model of hip joint replacement after the analysis of femoral stress changes. DICOM medical digital image communication is the core of the field of medical image information system, which mainly relates to the storage and communication of medical image information system is the most important and most difficult, can be directly applied to radiology information system (RIS) and picture archiving and communication system (PACS) in recent years, the booming in medical information field. Using the DICOM format data file directly modeling does not need to convert the data, you can directly read data and processing, to avoid repeated operations caused by data distortion or loss, greatly improve the accuracy of the model. With the advent of powerful integrated medical image processing function of finite element software, and the finite element method combined with other virtual digital technology, the future more powerful computers and software can automatically extract the characteristic parameters from the CT/MRI or virtual human data or important geometric details, direct finite element model. With the help of the finite element model, it can be used for noninvasive examination of the tissues in the body, the establishment of the auxiliary surgical treatment plan and the simulation of the quantitative surgery. The development trend of finite element modeling technology will be intelligent, integrated and network oriented.

Finite element analysis of 2 hip replacement related complications

1 stress shielding and bone resorption

After total hip arthroplasty through stress to femoral prosthesis, the stress is different from physical joint directly through small bone to bone Liang Conggu femur, caused by stress shielding and the bone absorption and atrophy, reducing its carrying capacity. Lin Fengfei [7] using three dimensional finite element method of single hip after total hip arthroplasty were standing biomechanical testing, analysis of the femoral and acetabular prosthesis implantation before and after the overall stress patterns and various combinations of the prosthesis after implantation of bone interface stress distribution. It is concluded that there is no significant difference in the stress of the interface between the femur and the acetabulum, whether it is a metal, ceramic, ceramic or polyethylene. Li Wei and [8] were used to compare the performance of titanium alloy, carbon fiber composite, CoCrMo alloy and stainless steel prosthesis. The results show that the titanium alloy and carbon fiber composite prosthesis have better stress distribution than CoCrMo alloy and stainless steel prosthesis, and its clinical application effect will be more ideal. The stress shielding is produced because the mechanical properties of the metal prosthesis and the bone are not compatible, and the prosthesis designed by the biocompatibility of the composite material can replace the metal prosthesis. Three dimensional finite element analysis of Peter[9] shows that the use of Allen phosphate after hip replacement can increase the periprosthetic bone density and reduce the probability of prosthesis loosening.

2) prosthesis wear

The finite element analysis can be used to simulate the wear condition of the prosthesis after implantation, and it can adjust the parameters flexibly. Bevill et al. [10] used finite element model to simulate the prosthesis wear under the one million gait load, and analyzed the influence of the thickness of the polyethylene coating and the size of the femoral head prosthesis on the wear. The finite element analysis shows that the creep behavior of polyethylene takes up 10%-50% of the total amount of acetabular lining, and is mainly in early stage.

3) dislocation

The finite element analysis method can also be used to study the dislocation of the prosthesis after total hip arthroplasty. Display of 3D finite element model of dislocation Li Yong prize [11] cross, finite element simulation of sitting in the corner and legs, input resistance moment value showing femur three distinct stages. Only is the weight of the articular surface of the friction torque, once the neck and lip liner occurred after the collision, the femoral head began to slide into the stage to hit subluxation, should increase the torque force and the value of the cup center. After a moment the platform is a cup of subluxation of the corresponding state, after the stop of force distance gradually reduce until the numerical instability. The impingement and dislocation are two very different biomechanical process, which are separated by the subluxation stage, so in order to reduce the total hip arthroplasty prosthesis dislocation rate, the maximum range of activities before the impact in operation as a reduction of dislocation index should be cautious. The finite element analysis model of Nadzadi [12]'s main guide prosthesis pressure change, joint force, hip joint movement of dislocation position and cause dislocation force, found from the lower risk for standing posture change occurs when the dislocation is the highest, than from the bend to the standing of the dislocation risk 6 times higher.

4) femoral fractures

On the new [13] that total hip arthroplasty before the proximal femoral calcar and subtrochanteric region of high stress, when the greater trochanter was suddenly high violence, easy to cause the intertrochanteric fracture. After total hip arthroplasty, femoral calcar and subtrochanteric region stress decreased significantly, the proximal femur in high stress area is located at the terminal level of prosthesis after total hip replacement patients, the greater trochanter is violent, femoral shaft fracture easily occurred in prosthesis end level. Because of the stress concentration at the end of the total hip arthroplasty, the violence is along the prosthesis to the end of the prosthesis, leading to the fracture of the site, which is the reason why most of the ipsilateral femoral fractures occur at the end of the prosthesis. Study on Bessho [14] that finite element analysis can accurately predict bone strength, contribute to a better understanding of the changes in the mechanical analysis of fracture, and the femoral neck fracture in the elderly to make an accurate prediction, so as to strengthen the prevention, reduce the incidence of such fractures.

3 prosthesis design

The matching of prosthesis and marrow cavity determines the stability of the prosthesis and the quality of the stress conduction, and reduces the bone resorption. Zheng Xiaowen [15] by three dimensional finite element analysis of artificial femoral stem inverted tapered hollow helps to reduce the human proximal femur and prosthesis contact stress shielding effect; the cement coating in the femoral stem, can enhance the bonding strength of femoral stem and bone cement interface, to reduce the prosthesis in hip replacement postoperative loosening; have obvious effects on the human femur stress uncemented stem microporous coating, microporous coating range is too large is not conducive to maintaining suitable human femur stress and stem fixation. The finite element study of Joshi confirmed that the proximal fixed prosthesis has good biomechanical effect, the matching of prosthesis and pulp cavity is closer to the anatomical state, and the stress shielding is less. New

The femoral stem length and cross-sectional shape comparison of [16] under static and dynamic loading effect of stress and fatigue of the stem, with stress drum shaped cross section and 90mm long stem has the best mechanical properties - smaller in 30 femoral model and micro displacement, fatigue high safety coefficient. Keaveny study on the pearl surface, 2/3 surface and pearl pearl face and neck biomechanical effect under the condition of no confirmed, pearl face neck prosthesis before and after each level to the internal and external direction and the axial direction of the difference of stress and living status; and the pearl surface is larger, torsional and axial the more load to the distal conduction. In recent years, hip resurfacing is gradually rising, Lin Lijun [17] reconstruction of metal on metal hip resurfacing with the finite element analysis model, virtual load and simulation calculation of the model. Objective to compare the stress distribution of the femur side after metal to metal hip resurfacing arthroplasty. It is found that the metal on metal hip arthroplasty, the stress mainly concentrated in the medial femoral neck prosthesis and head and neck junction, and the femoral bone under the presence of stress shielding, stress concentration and stress shielding and after hip resurfacing femoral neck fracture occurred between hip resurfacing arthroplasty after. But the Little [18] finite element analysis method is applied to prove that after hip resurfacing, osteoporosis and bone under normal conditions in normal walking, and will not produce can cause stress fracture in the proximal femur, so after hip resurfacing complicated with femoral neck fracture may be a result of various factors.

4 finite element analysis of bone cement application

Finite element analysis of Mann and [19] was used to analyze the interface of bone cement, and the results showed that the porosity of bone cement was >, 30%, the interface micro motion increased significantly. The improvement of bone cement technology can improve the long-term survival rate of total hip prosthesis. Through the finite element method confirmed that the distal prosthesis bone cement layer makes the bubble interface stress increases, and increases with the increase of the bubble, the bone cement interface bone cement thickness 2mm than 5mm thick or above force 50%, the third generation of bone cement technology and clinical requirements, prevent the generation of bubbles, ensure the distal bone cement prosthesis the thickness of 5mm layer. The application of finite element simulation analysis method and experimental method of bone cement interface fiber organization should effect on the stress distribution around the prosthesis, the results show that the finite element analysis and the experimental results are basically consistent, fibrous tissue and bone cement interface can greatly increase the stress of bone cement, and the relatively small impact on the cortical bone should be force.

The finite element analysis of hip joint is a very effective research method, it can effectively solve many problems that can not be completed in the biomechanics experiment. Although there are still shortcomings, but with the rapid development of computer and software industry, combined with the finite element method and other virtual digital technology, finite element analysis will increasingly become an important tool in clinical department of orthopedics and scientific research, promote the development of hip joint surgery forward.


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