| Spinal pathologies such as degeneration,infection,fracture,and congenital malformations commonly result in the progressive compression of the spinal cord.This compression may lead to clinical symptoms such as limb numbness and pain,significantly affecting patients’quality of life.Anterior cervical discectomy and fusion(ACDF)is a widely utilized surgical procedure in spine surgery.It directly relieves spinal cord compression by removing overgrown osteophytes and herniated disc material.Additionally,robust internal fixation and fusion effectively restore intervertebral height and correct kyphotic deformities,thereby alleviating related symptoms.However,the fusion surgery necessitates the near-total removal of one vertebra,fusion of two spaces,and fixation of three cervical vertebrae,resulting in a 40%loss of motion in the lower cervical spine.This can lead to stress concentration,increased load,adjacent segment degeneration(ASD),nonunion and pseudarthrosis,as well as postoperative complications such as donor site hemorrhage,infection,and pain.To solve the those problems,the concept of"physiological reconstruction of the spine"emerged,which has become a research hotspot in recent years.Its main design principle is to restore the stability of cervical structure while maintaining the physiological movement of the cervical spine by mimicking the normal biomechanical environment of the functional unit of the spine.However,at present,there is no kind of cervical mobility preserving implant that has been applied clinically around the world,which can replace the anterior cervical corpectomy and fusion,and can achieve the effect of both stabilizing the cervical spine and preserving the mobility.To address this issue,our group developed an artificial cervical joint complex system based on porous titanium substrates constructed by 3D printing technology and conforming to the idea of physiological reconstruction of the spine.Objective:To research and develop a novel 3D printed artificial cervical joint complex to replace the surgery of ACCF,and evaluate its safety and efficacy through finite element tests,biomechanical experiments and preliminary clinical studies,so as to provide a basis for its further clinical application.Methods:1.Improvement the redesign:Summarize and analyze the experimental results and design defects of the previous generation of ACJC,on the basis of which,improve and optimize the design of the new generation of ACJC,and manufacture it through 3D printing technology and high-precision numerically controlled machine tools.2.Finite element analysis:Using the CT scan data of the cervical spine of normal adult men,establish a complete C3-C7 three-dimensional finite element model,and verify its effectiveness.Establish a three-dimensional finite element model of ACJC implantation,anterior cervical corpectomy and fusion(ACCF)and double-segment artificial cervical disc replacement(ACDP).The biomechanical characteristics of range of motine,the adjacent intervertebral disc stress and the fatigue of the new ACJC prosthesis was studied to verify its safety and reliability.3.Biomechanical test:Nine fresh and healthy corpses(including 6 males and 3females,and the possibility of trauma,tumor,malformation,severe degeneration and osteoporosis has been excluded by X-ray examination)were selected to collect cervical spine specimens of C3-C7 segment.Nine specimens were randomly divided into three groups(including 2 males and 1 female in each group),the control group was intact cervical spine without surgical treatment,and the fusion group was conventional ACCF surgery on C5 vertebra,The artificial cervical joint group was treated with C5 cervical subtotal vertebrectomy and ACJC replacement.Three groups of specimens were fixed on the ABB IRB-1600 six-axis mechanical arm experimental system,and the flexible pressure sensor was placed at the center of the upper intervertebral disc(C3-4)and the lower intervertebral disc(C6-7).The experimental parameters of the spinal motion simulation test system were set.During the whole experiment,the torque of 2.5 Nm was maintained on the C3 vertebral body,and the flexion and extension,left and right lateral bending Rotate the range of motion(ROM)in six directions,and simultaneously record the C3-4 and C6-7 intervertebral pressure when the maximum ROM is reached in six directions.4.Preliminary clinical experiment:A single-center,prospective,small-sample,non-randomized controlled clinical trial design was adopted.The patients were divided into two groups according to their own wishes.The patients who underwent subtotal vertebrectomy and internal fixation and fusion surgery were in the ACCF group,and the patients who underwent artificial cervical arthroplasty were in the ACJC group.Record the operation duration,intraoperative bleeding volume and hospitalization duration of each patient;Through the comparison of X-ray,CT and MRI of each follow-up before and after the operation,the activity and fusion of the cervical surgical segment,the activity of the adjacent segment and the degeneration of the intervertebral disc,as well as the recovery of the sagittal balance of the cervical spine in the two groups were evaluated;All patients were followed up with visual analogue scale(VAS score)and JOA cervical spine score before and after surgery to assess their pain relief,functional recovery and quality of life improvement.Results:1.A new type of porous titanium alloy artificial cervical composite joint system has been successfully designed and manufactured,which has a motion mode of internal and external double joint design and multi-axis coupling of upper and lower joints.While realizing the concept of non-fusion fixation of"moving in stability and seeking stability in motion",it can provide reliable stability for cervical surgery through the implantation and fusion mode of"bone in prosthesis and prosthesis in bone"with porous titanium structure on the surface.2.Finite element analysis:a 3D finite element model of the lower cervical spine was successfully established,which was contrasted with the in vitro biomechanical experimental data and finite element data reported in the literature,and the results were generally consistent and proved to be correct and effective for lower cervical finite element.Focusing on the C5 vertebral body,four surgical models were successfully established,including ACCF surgery,artificial disc replacement with two segments(ACDP),composite arthroplasty of the ACJC of the third generation(ACJC,3th),and composite arthroplasty of the ACJC of the fourth generation(ACJC,4th).(1)ROM:Compared with the normal human cervical spine model,the all 4 models showed a decrease in the overall relative mobility of the C3-C7 vertebrae in some movement states,such as forward flexion,extension,left-right lateral curvature,and left-right rotation,among which the ACCF group showed the greatest loss of cervical spine overall mobility,with a decrease of-38.3%to-29.7%;The overall reduction in C3-C7 vertebral phase in the ACDP group relative to the vehicle control was approximately-7.1%to-2.3%;The two ACJC groups had slightly less preservation of overall relative mobility of the C3-C7 vertebral bodies than the ACDP group.(2)Adjacent segment disc stress:compared with the human normal cervical spine model,the corresponding upper C3-4 disc and lower C6-7 disc stresses in each group increased when moving in six directions,and the increase was most significant in the ACCF group,where the increment was about 48.2%to 125.5%for the C3-4 disc and45.5%to 93.2%for the C6-7 disc stress,especially in the presence of left-right scoliosis and left-right rotation;The ACJC 2 group had the lowest effect on adjacent segment disc stress,with stress increments of approximately 8.8%to 19.3%at C3-4 discs and 28.3%at C6-7 discs,respectively,relative to the blank control group,whereas the ACDP group was slightly larger than the ACJC 2 group.(3)Posterior facet joint stress:at the C4-6 operative segment,except for the ACDP group,all other three groups significantly decreased posterior facet joint stress when exercising in six directions,with the most significant decrease occurring in the forward flexion and extension motion states,including the ACCF group;The stress on the posterior facet joints of the ACDP and ACJC was lower than that of the ACCF group at non operated segments C3-4 and C6-7 adjacent to both upper and lower levels,with the ACDP group showing the least effect on the posterior facet joints of adjacent segments and the ACCF group showing the most significant increase of 27.8%to 45.2%of the stress on the posterior facet joints compared to the blank control group,characterized by the forward flexion and backward extension motion states.(4)Prothesis stress and vertebral body stress:when moving in six directions,the body of the ACJC prosthesis can share partial stress when it is active,so that the overall stress is more scattered,which is lower at screw fixation compared with the ACCF group,and it is lower at screw fixation compared with the ACDP group,which has less effect on vertebral body stress in the operated segments and adjacent segments.(5)Fatigue analysis:When the new generation of ACJC structural model moves in six directions of forward bending and backward extension,left and right lateral bending and left and right rotation,the maximum equivalent stress of the structure is 258.78 Mpa,244.67 Mpa and 224.99 Mpa respectively,and the fatigue life is 3.37×10~7times,6.15×10~7,4.63×10~7;The maximum stress of the prosthesis is located at the root of the joint between the cobalt chromium molybdenum ball joint and the titanium alloy structure.3.Biomechanical experiment:a surgical model of cadaveric vertebral specimen was successfully established,and postoperative X-ray examination showed that the internal fixation position of each surgical specimen was good.(1)ROM:Compared with the normal cervical spine group,the ROM of the lower cervical spine in the ACJC group in six directions has no significant difference(p≤0.05).The ROM of the fusion group in forward flexion,backward extension and left and right torsion was significantly lower than that of the normal cervical spine group and the prosthesis implantation group,and there was no significant difference in left and right lateral bending activities(p>0.05).(2)Adjacent segment disc stress:Compared with the normal cervical spine group,the ACJC group had little effect on the pressure of the intervertebral disc of the upper and lower adjacent segments in the cervical lateral bending and rotation movement(p>0.05).Although the stress of the adjacent intervertebral disc would be increased in the forward bending and backward extension movement,there was no statistical significance between the two groups(p>0.05);The movement in six directions in the ACCF group will increase the stress of the adjacent intervertebral disc,but the difference between the two groups is statistically significant(p≤0.05)only in the forward flexion and extension movement;There was also a statistical difference between ACJC group and ACCF group in flexion and extension(p≤0.05).4.Preliminary clinical experiment:According to the relevant inclusion and exclusion criteria,a total of 8 patients(2 women and 6 men)were included,including 4 patients in the ACCF group and 4 patients in the ACJC group.(1)Surgical data:the mean operative time was 156.3min in the ACCF group and172.5min in the ACJC group;The mean intraoperative blood loss was 62.5 ml in the ACCF group and 125.0 ml in the ACJC group;The mean hospital stay was 7.5 days in the ACCF group and 6.8 days in the ACJC group.The above results were not statistically different between the two groups(P>0.05).(2)Radiographic evaluation:postoperative radiographs and 3D CT reconstruction of the cervical spine showed that the prosthetic position of the prosthetic cervical spine joint was good and in close contact with surrounding bone.After the operation,imaging follow-up was performed on 8 patients,and the ACCF group showed successful fusion except for case 8 whose follow-up time was shorter and no fusion determination was made;Both cases 1 and 2 in the ACJC group had regained cervical mobility compared with their degenerative status preoperatively,which was restored to 16.5°and 11.7°by 2.3°and9.4°preoperatively,respectively,and cases 3 and 4 had maintained cervical mobility preoperatively,which was 21.1°and 26.5°at last follow-up,respectively;Cases 5 and 8in the ACCF group and cases 1,2 and 4 in the ACJC group maintained preoperative cervical lordosis within normal limits postoperatively,case 3 in the ACJC group recovered from preoperative cervical curve straightening to within normal limits,and case 6 in the ACCF group had preoperative cervical curve straightening that did not recover;None of the 8 patients experienced complications such as prosthesis loosening,fracture,fusion failure,adjacent segment degeneration,or heterotopic ossification during follow-up.(3)Pain and function scores:the JOA score and VAS score at the last follow-up in both groups were significantly lower than those before surgery,and there was no statistical difference in the improvement of pain and function evaluation between the two groups(P>0.05).Conclusions:1.While maintaining the cervical spine sequence and interbody relationship,the artificial cervical spine composite joint system largely retains the mobility of the cervical spine,avoids the acceleration of degeneration of adjacent segments caused by fusion,and has a small impact on the posterior facet joints of the cervical spine,which can effectively reduce the possibility of cervical instability and heterotopic ossification,and realizes the non-fusion fixation concept of"seeking stability while moving,seeking stability while moving".2.In the surgical treatment of cervical spondylosis,the artificial cervical spine composite joint system can effectively maintain or improve the postoperative cervical spine activity and sagittal balance of the cervical spine.Compared with the ACCF operation,it does not significantly increase the length of operation,intraoperative bleeding,and the length of hospitalization of the patient,and there are no obvious related complications.It is a safe and effective choice for internal fixation of cervical spine surgery. |
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