| Background Cervical spinal stenosis(CSS)is a common disease of orthopedics,mostly caused by the ossification of the posterior longitudinal ligament(OPLL),multilevel disk herniation(MDH)and cervical spondylotic myelopathy(CSM).Normally clinic surgery was adopted for the treatment of the CSS.The surgery method single-door cervical laminoplasty(SDCL),first introduced by Hirabayashi et al.in 1977,has been widely utilized in clinical treatment of CSS.In order to reduce the incidence of postoperative complications associated with the traditional silk suspension method,Centerpiece titanium plate has been widely used in the new posterior cervical plate fixation system in recent years.Currently,there are generally two clinical unsolved problems associated with SDCL.The first of them is the standard for the optimal width of the door to open on the lamina;the second one is on which side(left or right)to open the door.During the clinical SDCL,the laminoplasty opening size(LOS)played a critical role on the increment of both the spinal sagittal canal diameter(SCD)and cross-sectional area.Either an over-or under-increment of the LOS would lead to unexpected adverse consequences.Therefore,it is the main highlight to achieve an optimal LOS in SDCL.Currently,there are undergoing researches investigating the relationship between the LOS and the increment of postoperative SCD,as well as the spinal cross-sectional area.However,the study results have not yet been widely applied on the clinic treatment, mainly due to the complex equations and biological anatomical differences.Meanwhile,most of the clinic study failed to take into consideration the loss of lamina tissue at the operation,which clinically reduced the accuracy and effectiveness for the surgery treatment.To the author's knowledge,for most of the SDCL it is the operator's habit to determine the location(left or right)of the open door.However,according to the geometrical study,alternating left and right door openings would achieve a high level of mechanical balance.Note that finite element method(FEM)has been widely used to simulate the change of biomechanical characteristics of cervical vertebra.The computational simulation has advantages over experimental study by reducing the dependence on quite a number of patient or research animals.Additionally,the simulation,to a certain extent,is capable to predict the range of motion(ROM),as well as the interaction between the internal fixation and lamina,before and after cervical spine surgery.In past decades,quite amount of FEM has been performed at the SDCL by both domestic and international scholars,whereas there are yet few reports on the effects of surgery with alternating left and right open doors.Objective 1.A geometric model was established according to the variation of LOS before and after the surgery operation.A set of modeling formula was derived to characterizing the actual LOS,increment of the cross-sectional area and the SCD in the SDCL.Clinical data were collected and analyzed to confirm the high accuracy and reliability.The formula would be applied to assess and predict postoperative data before the surgery,as well as assist the surgery operator to achieve a more satisfactory treatment results.2.The second goal of the proceeding research focused on the computational simulation of the SDCL.Based on the medical CT imaging technique,FEM was utilized to simulate and analyze the cervical spine surgery with different selection of opening the door(full left open,full right open,left and right cross open);the result would provide some theoretical guidance for clinical SDCL.Methods 1.Based on the variation of the LOS before and after the surgery operation,a theoretical model was established and developed to characterize the relationship between the actual LOS and the enlargement of cross-sectional area,as well as the increment ofSCD.2.A new measuring device was invented and designed based on the derived formulation,enabling the clinical operation to be more precise and efficient.3.The clinical data were collected to verify the theoretical results.The PACS system and the new measuring device were used to measure and calculate the preoperative and postoperative parameters to confirm the accuracy and functionality of the characterizing formula and the new measuring device.4.Three-dimensional reconstruction of C1-C7 structure of human cervical vertebrae was performed based on medical CT imaging technique.In addition,three-dimensional FEM simulation was performed to compare with the clinical results.The relative ROM data was further analyzed to verify the accuracy of simulation.5.In different movement styles such as the flexion,extension,left/right lateral flexion,and left/right rotation,FEM was conducted to study their effects on different styles of opening lamina(full left open,full right open,crossing left/right open),to compare corresponding ROM and stress data.Results 1.A theoretical formula was established to characterize the geometric relation of the actual LOS and increment of cross-sectional area in the SDCL: where a is the transverse canal diameter(TCD),b the LOS,c the size of titanium plate,and d the diameter of surgery drill bit;a formula was developed to unveil the relationship between the actual LOS and increment of SCD: y(mm)=2a×sin(?/2)+ d,where y is the targeted SCD,a the TCD,? the laminoplasty opening angle(LOA),and d the diameter of the drill bit used in the surgery operation.2.During the research,preoperative and postoperative CT imaging data were collected from the patients included in the study.There was no significant difference(P> 0.05)between the increase of cross-sectional area of vertebral canal from the clinical data and that calculated by formula.Moreover,there was no significant difference(P> 0.05)in the increment of SCD of each segment calculated by formula and that from clinical measurements.Furthermore,there was no significant difference(P> 0.05)between the parameters measured by the PACS system and the parameters measured by the proposed new measuring device.The above-mentioned statistical analysis verified the accuracy of the proposed formula and the reliability of the invented new measuring device.3.The finite element model of normal cervical vertebrae was applied with the same loading as that studied by Panjabi and Zhang et al.Relative ROM value of vertebral body under different biomechanic loadings such as flexion,extension,left and right side bending,left and right rotation simulation,were respectively derived and compared with the data from Panjabi,Zhang,et al.The relative activity and the deformation agreed very well with their reports,which confirmed the accuracy and effectiveness of the present research.4.The FEM analysis indicated that the flexion motion had relatively more significant influence on the increment of general ROM.The general ROM value were increased by about 5.73% after all-left and all-right single-door operation,while the increment of general ROM value under either left-right crossing or right-left crossing under the 6 types of motion tends to be located between the all-left and all-right open surgery.Especially,the results were more stable compared to the all-left and all-right open door surgery in the motion of left/right side bending and left/right rotating.Discussions 1.A mathematical modeling was built based on the geometrical relationships of spine canal.With measurements of the corresponding variables,the derived formula enables an accurate estimation of the increment of SCD and canal cross-sectional area in the SDCL.This technique would be widely applied on the clinical surgery as a quantitative standard to achieve more accuracy and efficiency of the surgery operation.2.In the present research,the 3D reconstruction of medical imaging,as well as the FEM,was performed for numerical simulation of the cervical spine surgery with different open-door patterns.The results of ROM and stress variations indicated that the left/right mixing open-door surgery proved more mechanical balance and stability than the unilateral open-door in motions such as flexion,extension,lateral flexion,and rotation.Theoretically,these discoveries provided guidance for the biomechanical effects of the SDCL. |
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