| Part one Finite element analysis of stress distribution of disc above the upper instrumented vertebrae followed thoracolumbar pedicle screw-rod fixationObjective: To explore the dangerous position of proximal junctional kyphosis after thoracolumbar kyphosis by finite element analysis and provide guidance of reasonable functional exercise for the patients.Methods: Patients with thoracolumbar kyphosis caused by congenital wedge-shaped vertebrae who underwent posterior pedicle screw-rod fixation and anterior subtotal vertebral body resection and reconstruction were recruited.According to the thin-slice CT scan data at 2-year follow-up,the finite element model of thoracolumbar kyphosis was established by the interactive medical image control system,3-matic 5.1 forward engineering software,ANSYS 13.0 finite element analysis software,Pro/Engineer software.The stress of the anterior,posterior,left,right and central regions of the disc above the upper instrumented vertebrae were measured under seven conditions: upright position,flexion,extension,left and right lateral flexion and left and right rotation.Results: The stress of anterior edge of the disc was the highest in the antero-flexion position,the stress of posterior edge of the disc was the highest in the left-hand position,the stress of left edge of the disc was the highest in the left-bend position,the stress of right edge of the disc was the highest in the left-bend position,the stress of center of the disc was the highest in the right-bend position.In the upright position,the stress on the posterior edge of the disc is the greatest;in the forward flexion position,the stress on the anterior edge of the disc is the greatest;in the backward extension position,the stress on the anterior edge of the disc is the greatest;in the left flexion position,the stress on the posterior edge of the disc is the greatest;in the right flexion position,the stress on the right edge of the disc is the greatest.In the left-bend position,the stress on the posterior edge of the disc is the largest;in the right-bend position,the force on the anterior edge of the disc is the largest.Conclusion: After thoracolumbar kyphosis surgery,the stress on the anterior edge of disc above the upper instrumented vertebrae increased in the flexion,left and right dextral position,which may be result in proximal junctional kyphosis.Part two Prevention of proximal junctional kyphosis: are polyaxial pedicle screws superior to monoaxial pedicle screws at the upper instrumented vertebrae?Objective: Evidence regarding whether the polyaxial pedicle screws at the upper instrumented vertebrae(UIV)are superior to monoaxial pedicle screws in prevention of proximal junctional kyphosis(PJK)is less clear.The aim of this study was therefore to explore the influence of different type of pedicle screws at UIV on the incidence of PJK.Methods: 242 patients surgically treated with instrumented segmental posterior spinal fusion at a minimum 4 motion segments were reviewed retrospectively.Polyaxial pedicle screws were used at UIV in 125 patients(Polyaxial group)and Monoaxial pedicle screws were used at UIV in 117 patients(Monoaxial group).According to the occurrence of PJK at final follow-up,patients in both the Polyaxial and Monoaxial groups were then divided into two sub-groups: PJK sub-group and Non-PJK sub-group.To investigate risk factors of PJK,two categorized variables were analyzed statistically:(1)Patient characteristics: age,sex,body mass index(BMI),bone mineral density(BMD),sagittal vertical axis(SVA),thoracic kyphosis(TK),thoracolumbar junctional(TLJ)angle,lumbar lordosis(LL),pelvic incidence(PI),pelvic tilt(PT),sacral slope(SS).(2)Surgical variables: Changes of radiographic parameters include the SVA,TK,TLJ,LL,PI,PT,SS,pedicle-upper endplate angle,the number of instrumented levels,the most proximal and distal levels of the instrumentation.Results: PJK was developed in 26 of 117 patients(22.2%)in Monoaxial group and 30 of 125 patients(24.0%)in Polyaxial group until to the final follow-up,there was no significant difference in the incidence of PJK between Monoaxial and Polyaxial groups.No significant difference in patient characteristics and surgical variables between the two groups,except PJA change.In Monoaxial group,there were no significant difference in patient characteristics between PJK and Non-PJK sub-groups,except BMI,BMD,no significant difference in change of radiographic parameters,except SVA change,PJA change,LL change,and lower instrumented vertebrae location.Multivariate logistic regression analysis revealed that obesity,osteoporosis,lower instrumented vertebra at sacrum,and LL change more than 10 degrees were independently associated with PJK.In Polyaxial group,there were no significant difference in patient characteristics between PJK and Non-PJK sub-groups,except BMI,BMD,no significant difference in change of radiographic parameters between PJK and Non-PJK sub-groups,except P-UP angle,and lower instrumented vertebrae location.Multivariate logistic regression analysis revealed that obesity,osteoporosis,and lower instrumented vertebra at sacrum were independently associated with PJK.Conclusions: Application of polyaxial pedicle screws at UIV is not superior to monoaxial pedicle screws in the prevention of PJK.Obesity,osteoporosis,and lower instrumented vertebra at sacrum are risk factors for PJK no matter the pedicle type at UIV,while the excessive LL reconstruction is the unique risk factor of PJK when Monoaxial pedicle screws were used at UIV.Part three Incidence and risk factors of adjacent segment disease following posterior decompression and instrumented fusion for degenerative lumbar disordersObjective: To explore incidence and risk factors of adjacent segment disease following posterior decompression and instrumented fusion for degenerative lumbar disorders and hope to provide references in decision making and surgical planning for both spinal surgeon and surgically treated patients.Methods: By retrieving the medical records from January 2011 to December 2013 in our hospital,237 patients were retrospectively reviewed.According to the occurrence of adjacent segment disease at follow up,patients were divided into two groups: ASD and N-ASD group.To investigate risk values for the occurrence of adjacent segment disease,three categorized factors were analyzed statistically: Patient characteristics: age,sex,body mass index,bone mineral density,duration.Surgical variables: surgical strategy,number of fusion levels,surgery segment,surgery time,blood loss,intraoperative superior facet joint violation.Radiographic parameters: preoperative lumbar lordosis,preoperative angular motion at adjacent segment,preoperative adjacent segment disc degeneration,preoperative paraspinal muscle degeneration.Results: Postoperative adjacent segment disease was developed in 15 of 237 patients(6.3%)at final follow up.The mean follow-up duration was 2.6 ± 0.2 years in ASD group and 2.5 ± 0.3 years in N-ASD group.There was no statistically significant difference between the two groups in patient characteristics of age,sex composition,bone mineral density,duration,while the body mass index was higher in ASD group than that in N-ASD group.There was no difference in surgical variables of surgical strategy,number of fusion levels,surgery segment,surgery time,blood loss,while intraoperative superior facet joint violation was more common in ASD group than that in N-ASD group.There was no difference in radiographic parameters of preoperative lumbar lordosis,preoperative paraspinal muscle degeneration,while preoperative adjacent segment disc degeneration was more severe in ASD group than that in N-ASD group.The Logistic regression analysis revealed that,BMI > 25 kg/m2,preoperative disc degeneration,and superior facet joint violation were independently associated with adjacent segment disease.Conclusion: Higher BMI,preoperative disc degeneration at adjacent segment and intraoperative superior facet joint violation are risk factors for adjacent segment disease.Patients who are overweight or obesity and with preoperative disc degeneration at adjacent segment should be fully informed the risk of adjacent segment disease.For surgeons,it is essential to prevent superior facet joint violation in pedicle screw insertion procedure.Part four Incidence and Risk Factors of Postoperative Adjacent Segment Degeneration Following Anterior Decompression and Instrumented Fusion for Degenerative Disorders of the Cervical SpineObjective: The aim of this study was to explore the incidence and risk factors of postoperative adjacent segment degeneration following anterior decompression and instrumented fusion for degenerative disorders of the cervical spine and hope to provide references in decision making and surgical planning for spinal surgeons.Methods: By retrieving the medical records from January 2005 to September 2011,283 patients were retrospectively reviewed.According to the occurrence of adjacent segment degeneration at follow up,patients were divided into two groups: ASD group and N-ASD group.To investigate risk values for the occurrence of adjacent segment degeneration,three categorized factors were analyzed statistically.Patient characteristics: age,sex,body mass index,bone mineral density,duration of disease,neurological function,diagnosis.Surgical variables: surgical strategy,number of fusion levels,surgery segment,surgery time,blood loss.Radiographic parameters: preoperative sagittal alignment,cervical mobility,adjacent disc degeneration of both above and below the surgical segment,congenital stenosis,plate-to-disc distance.Results: Postoperative adjacent segment degeneration was developed in 68 of 283 patients(24.0%)at final follow up.There was no statistically significant difference between the two groups in patient characteristics of age,sex composition,body mass index,bone mineral density,duration,neurological function,and diagnosis.There was no difference in surgical variables of surgical strategy,surgery time and blood loss.The number of patients received two level spinal fusion was higher in ASD group than that in N-ASD group.The upper instrumented vertebrae at C5 was more common in ASD group than that in N-ASD group.There was no difference in radiographic parameters of cervical sagittal alignment,cervical mobility,adjacent disc degeneration of both above and below the surgical segment,congenital stenosis.The plate-to-disc distance was much smaller in ASD group than that in N-ASD group.The Logistic regression analysis revealed that,upper instrumented vertebrae at C5,plate-to-disc distance less than 3.0mm,two-level anterior cervical fusion were independently associated with the adjacent segment degeneration.Conclusions: Patients with degenerative disorders of the cervical spine,who receive two-level cervical fusion and with upper instrumented vertebrae at C5,are at high potential risk of adjacent segment degeneration.Plate-to-disc distance less than 3.0mm is another risk factor and should be prohibited. |
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