Lumbosacral fusion terminated to S1 for adult degenerative scoliosis: Technical innovation and finite element analysis

Abstract

Background: To evaluated the practicability and reliability of CBT+TT in the treatment of ADS by finite element analysis and the comparison of clinical effects.Methods: 18 cases were enrolled from patients who were admitted to the department of Spine Surgery in Affiliated Hospital of Qingdao University with a strict standard which qualify for the surgical indications of L5-S1 long segment fusion. Based on different spinal-pelvic fusion techniques, those cases were divided into three groups including the groups of IS , S2AI and CBT+TT, 3, 4 and 11 cases recpectively. Clinical data of CBT+TT group such as VAS, ODI, coronal Codd angle, C7PL-CSVL and SVA were acquired preoperatively and compared with those measured at the end of follow-up. DICOM data of CT scan (1mm) of all postoperative patients in those 3 groups were used to created 3D models. The models were imported into software for the finite element analysis under different conditions such as flexion, extension, lateral flexion and rotation, to obtain the stress distribution properties of three fusion techniques.Results: In CBT+TT group, the VAS score was 7.00±0.89 preoperatively and 0.91±0.70 at the end of follow-up. The ODI was 51.09±7.83% and 5.45±1.13%. There was a significant difference between the preoperative data and that at the end of follow-up (P<0.001). The Cobb angle was 49.10±11.51° and 12.33±3.96°. C7PL-CSVL was 27.27±17.61 mm and 12.20±8.04 mm. SVA was 25.33±18.21 mm and 8.60±5.31 mm. The results of the finite element analysis of simulated conditions, such as flexion, extension, lateral flexion and rotation, showed that in the IS group, the average extreme pressure value was 366.1 MPa, 183.1 MPa, 398.4 MPa, and 573.6 MPa; in the S2AI group, the values were 518.4 MPa, 259.2 MPa, 608.2 MPa, and 545.7 MPa; and in the CBT+TT group, the values were 390.0 MPa, 195.0 MPa, 353.7 MPa, and 476.8 MPa. Conclusion: This innovative technique (CBT+TT, terminating at S1) has been proven to be reliable and practical in the treatment of degenerative scoliosis.