A Finite Element Analysis Of Mobi-C Cervical Disc Replacemnt In The Treatment Of Multi-level Cervical Disc Disense

[Background]Cervical vertebra is prone to prolapse of intervertebral disc, peripheral soft tissue injury and so on, as the largest activity amount and the most frequent use of spinal segment in spinal joint. And with the accelerated pace of modern life, more and more people are in study and work pressure,these leading to overfatigue around cervical muscles and ligaments,proceed to induce various cervical disease. Domestic and international research shows:the incidence of cervical disease is gradually increasing and with the trend of younger. It has become a common and frequent clinical one, which dose great harm to the society,the family and the patient.Since Robison-Smiht (1955) and Cloward (1958) reported that the surgery technique of anterior cervical discectomy and fusion for the treatment of cervical disease, surgical treatment of cervical disease has made rapid progresses. In 60 years development and improvement, anterior cervical decompression and fusion (ACDF) has become the most effective treatment and the "gold standard"of cervical degenerative disease, cancer, trauma, and other diseases. ACDF can relieve symptoms of nerve compression in practicing full decompression,and what’s more, after fusion which can provide support for the stability of the spine.Clinical curative effect is good, operation is relatively simple, can also achieve good effect in improving clinical symptoms. However, with the long-term follow-up of patients after ACDF, there are also many complications after the operation.such as, the decompression and fusion of postoperative graft collapse, pseudarthrosis, chronic pain and adjacent segment degeneration and other donor site. The secondary degeneration of the adjacent segments and lead to recurrence after the decompression and fusion of operative and should be treated by operation again is considered to be the most common and serious complications. Studies have shown that, after fusion surgery the activity of the adjacent segment disc (range of, motion, ROM), intradiscal pressure (intradiscal pressure, IDP) compensatory increase because of biomechanical changes in the spine, which is an important reason for adjacent segment degeneration accelerated after ACDF. In order to reduce and prevent the degeneration of the adjacent segments, in recent years, the concept of surgical treatment gradually is shifted to non-fusion technology, from trying to keep fixed by the strong integration of motion segment, to the elastic fixed way, therefore, the application of artificial disc replacement in order to restore the intervertebral disc anatomy and function, namely cervical artificial disc replacement surgery (cervical disc replacement, CDR) came into being.Compared with cervical fusion surgery, artificial cervical disc arthroplasty may retain activity segments, and provide the stability for the cervical spine and the adjacent segments carrying capacity and kinematics normalize, theoretically reduce adjacent segment degeneration. And after the surgery, patients treated by CDR have faster recovery than the patients treated by ACDF, only one to two weeks.What’s more, patients treated by ACDF need to wear orthosis fusion which is beneficial to the fusion of bone graft, so compared to ACDF, patients treated by CDR can effectively avoid neck muscle atrophy and limited sense because of neck braking for longterm.There have the similar characteristics between prosthesis materials used by CDR and natural disc, at the same time,which has a certain buffer function, and does not need to get the material from the ilium,avoids local complications. Single segment of artificial disc replacement for cervical disc herniation treatment has been approved by the US FDA. The latest randomized prospective clinical experiment results show that the 5-year follow ProDisc-C artificial cervical disc replacement surgery in the treatment of single segment radiculopathy and myelopathy cervical disc disease, retains activity of surgery segment in improving neck pain frequency, relieves neck pain and reduces the extent of the adjacent segments reoperation rates, and were better than ACDF group.Recent research shows artificial disc in the treatment of single cervical disc herniation has achieved good clinical results. However, there is also controversial for patients with double segment and above cervical disease to choose the surgery technique. We can choose different surgical approaches according pressure areas, compression segment length and cervical curvature change, such as, anterior cervical discectomy and fusion (anterior cervical discectomy and fusion, ACDF), anterior cervical corpectomy and fusion (anterior cervical corpectomy and fusion, ACCF), anterior cervical decompression and fusion hybrid surgery (anterior cervical hybrid decompression and fusion, ACHDF), and artificial cervical disc arthroplasty (cervical disc replacement, CDR) and so on.Double or multi segment fusion compared with single segment fusion, has more effect of ROM, IDP on adjacent segments,and will more likely lead to ASD. Artificial disc replacement has achieved good clinical effect in the treatment of single segmental cervical intervertebral disc herniation, but further comparative evaluation of fusion and replacement is still to be more long-term clinical observation.The application has also been more and more widely in the clinical work of artificial cervical disc replacement for the treatment of double segment cervical disease. A prospective multicenter controlled clinical trial was designed to comparative analysis the clinical effect in application of PCM prosthesis between multi and single segmental cervical disease by PimentaCome to the conclusion:The clinical treatment effect was significantly increased for disc replacement in multi segmental cervical compared to single. The cervical biomechanical is complex, intervertebral disc and facet joint in two sides form a three joint complex. This kind of structure is both to ensure the normal physiological activities, and at the same time limit excessive activity.Artificial disc can be divided into two types according to the different types of application materials:one is metal-metal prosthesis, with strong abrasion resistance; the other is metal-polymer prosthesis, with better shock absorption ability. It can be divided into non restrictive prosthesis (Mobi-C, Bryan), semi restrictive prosthesis (Prestige, PCM, Prodisc-C) and restrictive prosthesis according to biomechanical characteristics. Non restrictive prosthesis activity is more than the normal physiological range, semi restrictive prosthesis is to ensure the normal physiological activity, and limit the type of prosthesis is less than the normal physiological range. Cunningham found that the non restrictive semi restrictive prosthesis can provide consistent mobile instantaneous axis of rotation as normal cervical spine.What’s more, requirement is relatively low in the operation position.But it may cause bearing greater rotary load and the shear force in the zygapophysial joints.At present, clinical related reports on restrictive prosthesis are still not have. In addition, Cunningham believes that restrictive prosthesis theoretically has fixed center of rotation prosthesis,The shear stress in joint surface will be reduced to a minimum, at the same time due to need more stringent requirement in the placement, surgeons need to be accurately placed into the corresponding anatomical position. If there is dissimilarity between the rotating axis and normal cervical spine,which is highly possible to lead to damage facet because of abnormal stress.Multi-segment cervical disease refers to find these signs in imaging, including osteophyte formation of multi segmental posterior cervical vertebrae, and degeneration and prominent of the intervertebral disc and so on in the continuous or discontinuous cervical vertebral.Meanwhile, multiplanes are compressd in cervical spinal cord and dural sac, and has the corresponding clinical symptoms of cervical diease. At present, there is a big controversy in the choice of operation of patients with the three or more segments of cervical spine involvement. Biomechanical study of different operation modes is relatively rare to do with disc replacement in cervical three segment operation. Zheng Yuchen comparative analyzed the biomechanical difference between 2-ACDF plus Mobi-C and 3-ACDF treatment of cervical degenerative disease in three segments by the finite element method. Come to the conclusion is that prosthesis is less prone to sinking when use Hybrid operation of Mobi-C prosthesis in the treatment of multi segment cervical disease.More segments’ fusion can well maintain the facet joint stress in the adjacent section. At present, there is lack of systematic biomechanical research to three segment disc replacement and the hybrid operation of two segment cervical artificial disc with one segment fusion in treatment for continuous three segment cervical intervertebral disc herniation.The rapid development of digital medicine lead medical research into a new field,what’s more,it’s status is more and more important. Experimental study on biomechanical has these disadvantages,such as experimental specimens and equipment cost much, can not carry on complex condition analysis.But,the finite element analysis has its unique superiority in the alternative, repeatability and controllability and so on.The finite element analysis, meaning finite element methods (Finite Element, Method, FEM) is a method of using mathematical approximation simulate the real physical system (geometry and load), which is a kind of the most effective methods in the theoretical research in biomechanics. Finite element analysis is to replace the complicated problems with relatively simple problems and then solving.It regard solving domain as constitute from many interconnection of small subdomain in finite element.For each unit assumingan appropriate (simpler) approximate solution, then solve the domain satisfying conditions (such as structural equilibrium conditions), so as to get the solution of the problem.This solution is not exact solution, but the approximate solution,because the actual problem is replaced by a more simple question.Most practical problems is difficult to obtain precise solution, while the finite element is not only high accuracy, but also can adapt to various of complex shapes, and thus it become an effective method of engineering analysis.The concept of "finite element" was first proposed in 50 years in the last century.The analysis method is an effective numerical analysis method with the application in Continuous mechanical field, such as analysis of aircraft structural static and dynamic characteristics.And,Soon afterward, widely used in solving continuous problem in heat conduction, electromagnetic field and fluid mechanics.In 1973, Belytschko first introduced the finite element analysis method in the research on the biomechanics of spine,it marks the beginning of application of finite element analysis in biomechanics analysis in department of orthopedics.In recent years, with the development of computer technology, the finite element analysis method has been more widely used in the field of biomechanics research,also cause widespread concern in clinical workers, and is becoming a hot research area day by day. The scope of clinical application for finite element analysis method is more extensive, involving the spine, skull, pelvis, tendon, joint prosthesis and so on.The biggest advantage lies in it can reflect the change of stress inside the body in finite element model.This is difficult to do in the biomechanical and other experimental methods.For the collected information for stress distribution and the internal energy change from local information of vertebrae, intervertebral disc, facet joints and internal fixation device,which has relatively high clinical value.In recent years, the finite element technology is more and more used in clinical trials,it can reflect the changes of the body’s internal stress.Summary of the introduction of the background, this project will establish a three-dimensional finite element model of the complete C2-C7, meanwhile simulating segmental motion in flexion, extension, lateral flexion,and rotation, change in rear facets and the adjacent intervertebral disc pressure between Mobi-C artificial disc replacement of C3-C6 three segment using the finite element method and normal condition.Through the finite element analysis results to investigate the feasibility of C3-C6 three segment Mobi-C artificial disc replacement operation in clinical application.To provide biomechanical basis for the clinical operation mode selectionChapter 1 Establishment of normal three-dimensional finite element model of C2-C7 cervical vertebra in normal adult maleObjective:To establish the complete three-dimensional finite element model of normal C2-C7 cervical bertebra by the use of CT scanning data of cervical normal adult male,in addition to verify its effectiveness, which provide the experimental basis for the follow-up study of the cervical biomechanical stimulant surgery.Material and Methods:Gave a healthy adult male volunteer cervical CT scan to obtain tomographic images and stored in DICOM format. Apply Mimics10.01 software for three-dimensional reconstruction models, Geomagic Studio 12 to optimize the model, and HaperMesh10.0 and ANSYS14.5 software to establish the finite element model. In the model, using 1.5Nm torque to simulate the motion of flexion, extension, lateral bending and rotation, calculating the intervertebral activity under different conditions, and comparing with the biomechanics of the experimental results in previous literatures to verify the effectiveness of the model.Results:There are a total of 887,245 units and 1,340,596 nodes in the C2-C7 cervical vertebra finite element model in this study, including the C2-C7 cervical vertebrae cortical and cancellous bone, cervical disc annulus and the nucleus, endplate, bilateral facet joints, pedicle, vertebral plate, transverse process, spinous process, the anterior longitudinal ligament, posterior longitudinal ligament, fiavum ligament, supraspinous ligament, interspinous ligaments and capsule ligaments. In the simulation of various conditions, the intervertebral activity of the various segments was consistent with previous findings. Therefore, the model is considered to be effective, and can be used in clinical and experimental research.Conclusions:In our study, biomechanical data which from three-dimensional finite element model of normal male C2-C7 under various working conditions is consistent with previous research results,it is accurate and effective,which can provide the basis of three-dimensional finite element modefor in the next step of the simulate operation comparative analysis.Chapter 2 A Finite Element Analysis of Mobi-C Cervical Disc Replacemnt in the Treatment of Multi-level Cervical Disc DisenseObjective:To analysis cervical activity, rear facet pressure and adjacent intervertebral disc pressure in C3-C6 three segments Mobi-C cervical artificial disc replacement model compare with the normal model of cervical using the three-dimensional finite element, and to provide biomechanical basis for clinical operation.Material and Methods:To establish C3-C6 three Mobi-C cervical artificial disc replacement model.Exert 50N preload and 1.0 Nm torque load on C3-C6 three Mobi-C model and normal model which established in Chapter 1, simulate forward bends, stretch, the left elbow and left rotating motion, and record the intervertebral motion of each model, the facet joint stress and stress distribution characteristics of artificial implants.Results:In the simulation of loading, the postoperative model under various conditions of the intervertebral activities were measured, and the results were compared with normal model group.The results showed that Mobi-C replacement segment ROM (C3-C6) had a little increase compared with the normal group.In the simulation of loading, the facet joints under various conditions of postoperative model stress was measured, and the results were compared with normal model group.The results show that the facet joint pressure with a slight increase in the replacement segment, and decreased slightly in non replacement segment in normal group compared with Mobi-C replacement group.In the simulation of loading, the adjacent intervertebral disc under various conditions on the upper and lower vertebral body contact pressure was measured on the postoperative model, and compared with normal model group.The results show that the intervertebral disc pressure were decreased in C2-C3, C6-C7 in the replacement group compared with the normal group.Conclusions:Through the comparison study between the finite element model of Mobi-C replacement in 3 segments and normal model,We concluded that it is safe and effective in theory,using of cervical artificial disc Mobi-C treatment of multi segmental cervical spondylosis, and preventing of adjacent segment degeneration.But at the same time it still has the possibility of increased ROM in the displacement segmental and increased joint stress, as well as has a risk of accelerated degeneration in the displacement section. It still needs a multicenter, large sample of the long-term follow-up data to prove the long-term effect of Mobi-C replacement in 3 segments operation.