| In recent years, with the development of society, especially in transportation and construction industries, and with the changes of people’s work and life styles, the incidence of cervical disease is increasing with the trend of younger onset. It has become a common and frequent clinical one, which does great harm to the community, 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, anterior cervical decompression and fusion (ACDF) has become the most effective treatment and the "gold standard"of cervical degenerative disease, trauma, cancer and other diseases. What is more, by long-term follow-up of patients after ACDF, we knew more about the surgical complications, such as, the integration of postoperative graft collapse, pseudarthrosis, chronic pain and adjacent segment degeneration and other donor site. Among them, the most common complication is the controversy that activity of adjacent segments compensatory because of biomechanical changes in the spine after the fusion surgery, which leaded to the acceleration of secondary surgery. In order to prevent adjacent segment degeneration occurring 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. The US FDA has approved CDR for the treatment of cervical disc herniation of single segment. The latest randomized prospective clinical results showed that the 5-year follow ProDisc-C artificial cervical disc replacement surgery in the treatment of single segment radiculopathy and myelopathy cervical disc disease, retained activity of surgery segment in improving neck pain frequency, relieved neck pain and reduce the extent of the adjacent segments reoperation rates, and were better than ACDF group.Artificial disc in the treatment of single cervical disc herniation has achieved good clinical results. However, there is more 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. With the further research on the cervical spine biomechanics and artificial cervical disc application, it has achieved good clinical efficacy in the use of multi-segmental cervical artificial disc replacement for multi-segmental cervical disc herniation in early follow-up, but it still need long-term follow-up and observation. However, due to limited technical and economic conditions, if there existed serious segment degeneration it would not be suitable for replacement. In order to retain the activities of the cervical spine as far as possible, some scholars have proposed the hybrid surgery (HS) combined ACDF with CDR in recent years. Hybrid surgery avoids the continuous fusion of multi-segment by the use of prosthesis, so as to preserving the cervical activity, reducing the risk of adjacent segment degeneration. At the same time, the appropriate segment fusion can reduce the potential risk of continuous use of artificial disc and medical costs. The compromised surgical technique intrigues surgeon. Dong Ah Shin et al. in a continuous two-level cervical disease clinical studies with 40 patients enrolled in,20 taken to double segment fusion (2-ACDF group), and 20 accepting hybrid surgical approach (HS group, Mobi-C prosthesis), were followed up for two years. They concluded that HS group was better than 2-ACDF groups. However, the choosing of the replacement segment in hybrid surgery still lacks a more general consistent standard. There is no slippage to select the replacement segment just as Shin, and in the case of both the two segments are suitable for prosthesis, the prosthesis was placed in the larger activity segments according to the ROM of the segment (C5-C6> C4-C5> C6-C7> C3-C4), then Barbagallo et al though it would not choose the replacement segments if surgical segment ROM is greater than 3°,no bilateral uncovertebral joint degeneration, no facet joint degeneration, no significant loss of disc height, and no significant vertebral slippage. Cardoso’ oppoins are, with no root and (or) spinal cord symptoms or neck pain, autoimmune diseases, osteoporosis, neck trauma, spinal tumors, vertebral displacement of more than 3.5mm, ossification of the posterior longitudinal ligament, serious small joint disease, if replacement surgery segment conditions are met, would select the ROM large segment for replacement. Ren et al suggested that fusion for the unstable or severe withdrawal renegade section and a larger segment replacement in activity of the remaining patients. In addition, clinical reports showed the treatment of adjacent segments disease after ACDF in the use of artificial cervical disc replacement therapy. But the lack of research on a large sample of all long-term clinical follow-up, the lack of relevant evidence, the selection criteria replacement segment, and its clinical effectiveness and impact on adjacent segments, all of which need more literature to gradually form a consensus. Therefore, biomechanical studies will undoubtedly provide a theoretical basis for the choice of surgical approach.It is complex in biomechanics of the cervical spine, which consists of three joint complex (disc and two side facet joint), forming a semi-restriction system to ensure the normal physiological activity and avoid excessive flexion and extension activities. Artificial intervertebral prosthesis contains non-constrained prosthesis (Mobi-C, Bryan), semi-constrained prosthesis (Prestige, PCM, Prodisc-C) and restrictive prosthesis according to the biomechanical characteristics. Unconstrained prosthesis exceeds the normal physiological activity; semi-constrained prosthesis ensures the normal physiological activity, while constrained prosthesis is less than the range of normal physiological activities. Cunningham et al found semi-constrained and non-constrained prosthesis provides basic activities, whose opinion consistent with normal cervical movable instantaneous axis of rotation, leaded to a relatively easy placement technique, and also produce the greater shear force and rotational load in the facet joints. There still no relevant clinical reports on constrained prosthesis yet. Cunningham considered constrained prosthesis should have a fixed center of rotation so that the articular surface of the shear stress will be minimized, which requests a relatively high standard to accurately place to the appropriate anatomical position when putting the prosthesis. If the rotation axis of the prosthesis and normal cervical rotation axis is inconsistent, it will make damaged on the articular surface because of the abnormal stress.Currently in vitro biomechanical study on cervical artificial disc replacement mainly concentrated on the adjacent segment ROM, adjacent segment IDP and other aspects. It has been widely reported on biomechanical studies of single segment artificial cervical disc. Puttlitz comparatively analized the ProDisc-C artificial cervical disc replacement group and the normal group through 6 cases in vitro experiments, found that, there was no significant difference in two groups in surgical activity segment with adjacent segments, and the coupled motion compared with the normal group has also been retained after the replacement of the cervical spine. Jaumard and Bauman found there is no significant difference in facet joint pressure compared to the normal group after the ProDisc-C replacement for single segment. In recent years, there are cervical artificial disc biomechanical studies on double cervical levels. However, in the literature it has not been reported on the biomechanics characteristic of the facet joint of the different surgery techniques in the treatment of the two-level cervical spondylopathy in vitro experiments. So far, semi-constrained prostheses (Prestige, PCM, Prodisc-C) were mostly used in vitro experiments. Unrestricted prosthesis Mobi-C was the only one approved by the US FDA for both single and double segment artificial cervical disc replacement prosthesis, which is not yet demonstrated by experimental research on biomechanics.With the increase for multi-segmental cervical disease in clinical, the treatment methods are challenging. For a single segment, considing of the anterior approach, there are two options, fusion or replacement. For multi-segment diseases, the approaches include select multiple segmental fusion (including corpectomy), multi-segment replacement and hybrid surgery. This will produce a variety of permutations and combinations of surgery. In general, when the lesion is greater than or equal to 3 segments, it will not suitable for replacement therapy for all segments. Kang et al. conducted a comparative analysis of 3-ACDF and two segments cervical disc replacement combining intermediate section fusion in 2 years follow-up. Postoperative neck pain and NDI scores after surgery improved compared to before. But the hybrid surgical group resume preoperative ROMC2-C7 after 2 years, and 2 years ROMC2-C7after the 3-ACDF is significantly reduced. The superior and inferior adjacent segments in the hybrid constructs group had a significantly decreased ROM at 1 month postoperatively (P<0.05). The ROM at 3,6,12, and 24 months postoperatively did not differ significantly from that pre-operatively (P>0.05). The superior and inferior adjacent segments in the 3-level ACDF group displayed a significantly decreased ROM at 1 month postoperatively (P<0.05). The ROM increased at 3 and 6 months and increased significantly at 12 and 24 months postoperatively when compared with preoperative ROM (P<0.05). Meanwhile, the ROM in the superior and inferior adjacent segments showed significant differences between the 2 groups at 12 and 24 months postoperatively (P<0.05).Currently there are few biomechanical studies on different surgery approaches to cervical disc replacement surgery for 3 segments surgery. Zheng conducted comparative analysis of the biomechanical differences between 2-ACDF combined with Mobi-C and 3-ACDF treatment of three segments cervical degenerative in finite element method and concluded that in the hybrid surgery Mobi-C prosthesis was less prone to sinking and also better maintain the facet joint stress of adjacent segments. At present, it still lacks of systemic biomechanical study on the hybrid surgery combined two-level CDR with one-level ACDF for the treatment of consecutive three-level cervical disease.In summary, this study intends to conduct in vitro biomechanical comparison of different techniques of consecutive two-level cervical disease:effect on the spinal kinematics and facet force using unconstraint Mobi-C prosthesis. Furthermore, we demand to give evaluation of the biomechanical properties of different combinations for three consecutive segments cervical degenerative disease treatment using 2-level Mobi-C combined single-level ACDF in the finite element method.This study was performed in the following aspects:(1) Compare the ROMs of operative segment and the adjacent segment of the different techniques:C4-C6 Mobi-C replacement, hybrid surgery (C4/5Mobi-C combined with C5/6ACDF and C4/5ACDF combined with C5/6Mobi-C) and C4-C6 2-level ACDF under displacement controlled loading conditions (2) A Comparative Study of the effect on the facet joints of the single and double segment Mobi-C replacement or fusion:C4-C5Mobi-C replacement, C4-C5 fusion, C4-C6Mobi-C replacement, C4-C6 and hybrid fusion surgery (C4/5Mobi-C combined with C5/6ACDF and C4/5ACDF combined with C5/6 Mobi-C. (3) Through the establishment of normal cervical vertebra (C2-C7) of three-dimensional finite element model, to further analyze 2-level Mobi-C replacement combined with single segment fusion in treatment for three consecutive cervical spondylitis, using different "hybrid" surgical combination of C3/4, C4/5 and C5/6 segments, a "hybrid" surgical simulation, applying the same load and torque on the reconstruction model, the overall activity of the cervical spine under the comparison of various conditions, each intervertebral motion, the facet joints stress, stress transfer model and the stress distribution of artificial disc. We hope to provide biomechanical evidence for different surgical techniques in clinical application.Chapterl Biomechanical comparison of Two-Level Cervical Mobi-C versus arthrodesis:effect on adjacent-level spinal kinematicsIntroduction The purpose of this experimental study was the biomechanical analysis of the range of motion (ROM) of cervical spine kinematics for a 2-level cervical arthroplasty and compared them with those after anterior cervical arthrodesis (2-ACDF) and hybrid surgery (HS).Methods Seven human cadaveric spines (C1-T2) were biomechanically evaluated between Levels C2 and T1 in the intact condition and under the following reconstructions:2-level arthroplasty (C4-C6) using Mobi-C devices (LDR, Troyes, France),2-level anterior cervical discectomy and fusions (2-ACDFs), and hybrid surgery of both (HS). Multidirectional flexibility testing used the Panjabi hybrid testing protocol, including pure moments for the intact condition with overall spinal motion replicated under displacement control for subsequent reconstructions. Unconstrained intact moments of ±1.5 NM were used for flexion/extension (FE), axial rotation (AR) and lateral bending (LB).Results MM group compared with the II group, except to the ROM increasing significantly in C4-C5 level, the ROM in each level have no significant different under each condition. MF group compared with the II group, in operated levels, the ROM in C5-C6 level were significantly decreased under all conditions (P<0.05), while the ROM in C4-C5 level were significantly increased (P<0.05); in the adjacent levels, except to the ROM in C3-C4 level decreasing under the axial condition, the ROM in the other levels led to a compensive increase under all conditions and has no statistical difference. FM group compared with the II group, the ROM in C4-C5 level were significantly decreased under all conditions (P<0.05), while the ROM in C5-C6 level were significantly increased (P<0.05); the ROM in the adjacent levels were compensatory increased under all conditions and has no statistical difference. FF group compared with the II group, the ROMs in operated levels were significantly decreased under all conditions (P<0.05), and the ROMs in adjacent levels were larger than those in the other groups.ConclusionIn conclusion, two-level Mobi-C produced kinematics similar to intact spine with slightly increased ROM at implated segments. Hybrid construct (ACDF plus Mobi-C) leaded to a hypermobility of prosthesis, however, it is not known whether the hypermobility of the ROM is a shortcoming or has an adverse impact on the spinal structure in vivo. Considering of the adjacent level, two-level Mobi-C and Hybrid construct generated better biomechanical conditions than two-level ACDF by limiting contribution of these segments to global ROM. These biomechanical findings support the concept of two-level arthroplasty and Hybrid construct in the cervical spine and suggest that two-level TDR or HS should be considered as alternative options to treat two-level consecutive disc disease, even if long-term and large cohort follow-ups are necessary to shed more light on two-level Mobi-C and HS.Chapter 2 Biomechanical comparison of the single and double segment Mobi-C replacement versus arthrodesis:effect on facet joints of the surgery segmentsObjective To investigate the effect on facet force after the single or double segment fusion, single or double segment displacement and "hybrid" surgery, and to provide biomechanical basis of the choice of different surgical technique for clinical applications.Methods A total of 6 fresh adult cervical specimens, respectively, were made to six model groups according to the experiment, such as C4-C5 replacement, C4-C5 fusion, C4-C6 replacement, C4-C5 replacement combined with C5-C6 fusion, C4-C5 fusion combined with C5-C6 replacement and C4-C6 fusion. We applied 1.5Nm pure torque on the specimen at the direction of flexion, extension, left and right axial rotation and the left lateral bending, and measured the left facet force of C4-C5 and C5-C6 using FlexiForce pressure sensor. Compare the facet force in all loads and directions within the facet joint C4-C5, C5-C6 in each group, and SPSS 13.0 statistical package was used for statistical analysis.Results 1. Single segment treatment groups:the force in the facet joints in ACDF group was significantly reduced compared with the intact spine and the replacement group in all loding condition (P<0.05). The facet joint force in Mobi-C group increased compared with intact spine, however, only in flexion and extension, left lateral bending loading condition, the difference was statistically significant (P<0.05), the left and right rotation loding conditions were effective to maintain the inter-facet normal physiological force. Compared with the intact spine, the adjacent segments C5-C6 facet force of ACDF group increased to some extent, but only in the extension, right rotation and left lateral bending loading condition, the difference was significant (P<0.05); and adjacent segments C5-C6 facet force of Mobi-C group was reduced in varying degrees, but the difference was not statistically significant.2. Compared with the intact spine, C4-5 and C5-C6 facet force of 2-level Mobi-C group increased in flexion, extension, left and right rotation, left lateral bending motion, but the difference was not statistically significant (P> 0.05); In MF group, compared with the intact spine, the left facet force of replacement segment C4-C5 significantly increase in all conditions; facet joints force of arthrodesis segments C5-C6 leded to a reduce, however, the difference was statistically significant only in extension and ipsilateral bending and right rotation motion (P<0.05); Compared with the intact spine, FM group, the facet joints of arthrodesis segments C4-C5 was reduced significantly (P<0.05), the C5-C6 facet joint pressure of the replacement segment increased to varying degrees, but only in left lateral bending loading with on the motion a statistically significant difference(P<0.05). The left C4-C5 and C5-C6 facet force of FF group resulted in a significant decrease compared with the intact spine (P<0.05).Conclusions Firstly, facet force after ACDF in single segment surgery significantly decreases compared with the intact spine, but a significant increase in the adjacent segments facet joint, which may be caused by the occurrence of degeneration or accelerated degeneration at adjacent segment after ACDF; and after a single segment Mobi-C replacement, facet force of segmental replacement is increased in flexion, extension, lateral bending loding, but its lower adjacent segment C5-C6 facet force do not develop a significant impact, which may be a factor of cervical disc replacement prevent adjacent segment degeneration; at the same time, it is possibly an important cause to surgical segment facet joint degeneration; secondly, there is no significant differences but an increasing trend in the segment facet joint force of cervical double segment Mobi-C artificial cervical disc replacement surgery compared to the intact, suggesting double segment Mobi-C cervical artificial disc replacement can rebuild cervical facet biomechanics but its long-term effect need further clinical observation; thirdly, cervical double segment hybrid surgery led to a significant facet force increase compared with the intact spine, which may accelerate the facet joint degeneration of replacement segment.Chapter3 Establishment of normal three-dimensional finite element model of C2-C7 cervical vertebraObjective:To establish the dimensional finite element model of normal C2-C7 cervical bertebra, and to verify its effectiveness.Methods:Gave a healthy adult male volunteer cervical CT scan to obtain tomographic images and stored in D1COM format. Apply Mimics 10.01 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, vertebral 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.Conclusions:It is accurately and efficiently for the C2-C7 cervical finite element model established in this study, which can be used for the biomechanical research after surgery in future.Chapter 4 The three-dimensional finite element analysis of "hybrid" surgical treatment for cervical spondylosisObjective:To evaluate cervical spine biomechanics characteristics of four different surgical methods using three-dimensional finite element, and to provide biomechanical basis for clinical operation.Methods:We set up four different finite element model of postoperative surgical respectively:(1) in the third part we built C2-C7 finite element model of cervical spine and simulate 3 segmental anterior cervical decompression and fusion model at C3 to C6 segments (FFF); (2) give ACDF at C3-C4 segment, and Mobi-C at C4-C6 double segments (FMM); (3) ACDF at C4-C5 segment, Mobi-C at C3-C4 and C5-C6 segments model (MFM); (4) make artificial disc replacement Mobi-C at the C3-C5 segments, ACDF in C5-C6 segment model(MMF). Exert 50 N preload and 1.0 Nm torque load on four kinds of models and normal model, 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:(1) Under each loading condition, the intervertebral ROM of arthrodesis has been greatly reduced compared to normal group, however, after Mobi-C placement the segment is increased; the ROMs of adjacent segmental C2-C3 and C6-C7 were also increased, with the the most increase in the FFF model. (2) The stress of the facet joint of arthrodesis have greatly reduced compared to intact spine; however, the facet joint stress of Mobi-C segment was increased; the stress of the facet joint of adjacent C2/3 and C6/7 segments had no obvious difference compared to intact group. (3) There is no obvious stress concentration phenomenon in the FFF mold, and the maximum stesee of various loading conditions are at the very back of the peek. Mobi-C is divided into three parts, under various conditions, the stress of superior endplate is greater than the inferior endplate, maximum stress concentration on the superior endplate is in the sawtooth, and stress value is bigger, the inferior endplate stress concentration is in the central region; the maximum stress concentration of the artificial intervertebral disc is on both sides of the central lining.Conclusions:Through the comparison study between the three kinds of "hybrid" operation, the normal finite element model and the full fusion model, we concluded that:it is beneficial for cervical activity when using two artificial disc replacement combined with a single segmental fusion surgery, 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 "hybrid" operation. |
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