Clinical Research And Finite Element Method Analysis Of The Long Segment Or Short Segment Fixation For The Treatment Of Adult Degenerative Scoliosis

Objective 1.To compare the clinical outcomes of long-segment?L?fixation or short-segment?S?fixation after surgical decompression of adult degenerative scoliosis?ADS?patiens.2.To explore the changes under different loading conditions of adult degenerative scoliosis?ADS?patients fixed with long segmental or short segment instrumentations,including the range of movement?ROM?of adjacent segment and the biomechanical stress of screws and adjacent structures.Methods 1.A retrospective study on 32 patients treated with surgeries in our department for ADS from 09/2012 to 01/2014 was carried out,including 12 male and 20 female?1:1.7?.The average age was 68?51-86?.All patients underwent surgeries of posterior decompression and fixation.They were devided into long-segment fusion group?L?and short-segment fusion group?S?according to sagittal parameters and coronal balance.During follow-ups?preoperation/3-month postoperation/final?,clinical outcomes were assessed by means of visual analog scale?VAS?and Oswestry disability index?ODI?.Radiographic evaluation on full-length standing film included coronal Cobb's angle,distant between C7 plumb line and center sacral vertical line?C7PL-CSVL?,thoracic kyphosis angle?TK?,lumbar lordosis angle?LL?,pelvic incidence?PI?,and pelvic tilt?PT?,PI-LL,sagittal vertical axis?SVA?.Postoperative complications were also recorded.2.Two postoperative ADS patients with long segment fixation?range T11?Si?and short segment fixation?range L2?L5?respectively were chosen to download their Dicom files of CT scanning images.Then data were imported to Mimics and 3-Matic softwares to establish the 3-dimension?3D?models.3D models of screws and rods were modified by Pro/E software.Assembly of 3D models of spine with those of screws and rods was then followed by the formation of finite element mesh model by Hypermesh with appropriately meshing.ABAQUS was used to add material properties,boundary conditions of construction.Finite element models of long-segment fixation ??Range:T11?S1?,long-segment fixation ??Range:L₁^S₁?and short-segment fixation?Range:L₂^L₅?were set up successfully.Under the physiological and ultimate loads,finite element method?FEM?was employed to compare range of movement?ROM?of the same segment and biomechanical change of screws and adjacent structures between them during flexion,extension,lateral bending and rotation.Results 1.All patients were followed up for average 2.2 years?range:1.5-3.5 years?.No significant difference of was found in age or gender between two groups?L:17,S:15?of patients?P=0.275,1.000,respectively?.As for the fusion segments,group L?5.9±1.6?was more thangroup S?2.8±0.7??P<0.001?.Operation time and blood loss of group L were statistically more than group S?P<0.01?.Postoperative VAS sores of back pain and leg pain as well as ODI were all improved significantly in two groups?P<0.05?.At the final follow-up,back pain VAS was more in group L than group S?P<0.05?,but no significant difference was found in leg pain VAS between two groups?P>0.05?;at the final follow-up,group L's ODI showed better functional recovery than group S's[?12.8±9.3?%VS.?25.4±11.4?%,P<0.05].In coronal plane,there was no significant difference of Cobb' angle between two groups?P>0.05?.The Cobb's angle and C7-CSVL distance were corrected significantly in group L?P<0.05?,while not statistically significant in group S?P>0.05?.Saggital imbalance was found in group L before surgery and restored to nomal alignment with increase of LL and decrease of SVA,PI-LL and PT postoperatively.No obvious sagittal imbalance was found in group S before and after operation.The overall incidence of postoperative complications was 34.4%.Group L showed more incidence of complication than group S with no statistical significance?P=0.147?.2.In the condition of ultimate loads and lateral bending,the caudal second screw on the right of long segment fixation I reached the maximum stress of 569.6Mpa.Distribution analysis showed that the stress concentrated on rear 1/3 part of the screw.Long-segment fixation ? showed more ROM of the same segment than long-segment fixation I in all loads and movments.In physiological loads and flextion,the adjacent disc and vertebrae of the long-segment fixation I showed the maximum stress of 2.87MPa and 10.46MPa respectively.Proximal adjacent posterior ligment complex in two long segment fixations showed more stress in flexion and rotation.In the physiological load conditions,short segment fixation showed greater amounts in the stress of adjacent structures?vertebrae,intervertebral disc and ligament?and screws than those of long segment fixation.Conclusions 1.Surgical treatment was testified to be efficient for the ADS patients.Long-segment fixation had abbility to correct the coronal and sagittal deformities with increased blood lose and peri-operation complication incidence;however,short-segment fusion showed lower peri-operational risks with relatively weaker correction effect.Appropriate internal fixation method should be chose based on carefully assessment of patient's deformity.2.The caudal screws showed more stress in long segment fixation when lateral bending,so it should bear in mind to prevent screw breakage by avoiding lateral bending or modifying the screw design.Long segment fixation to the thoracic vertebrae will compromise ROM of proximal segement and increase the stress of the adjacent vertebrae,while the stress of adjacent posterior ligment complex decrease.The surgical choice of long segment fixation crossing thoraco-lumbar transional region should be prudently made based on the patient's specific situations.In the biomechanical perspective,long segment fixation was more suitable for the treatment of ADS than short segment fixation.