P73. Change of cervical sagittal alignment after surgery for adolescent idiopathic scoliosis (AIS): comparison of vertebral body tethering (VBT) versus posterior spinal fusion

BACKGROUND CONTEXT VBT takes advantage of the Hueter-Volkmann principle, and modulates growth across intervertebral disc spaces with a tensioned tether secured at the lateral aspects of vertebral bodies. Cervical deformity in AIS patients is associated with lower health related quality of life. PSF constructs have been shown to improve cervical deformity, however, to date, these relationships have not been described in patients treated with VBT. PURPOSE Determine if cervical sagittal alignment parameters following VBT for correction of AIS are similar to what is observed following PSF. STUDY DESIGN/SETTING Multi-center retrospective cohort study. PATIENT SAMPLE Patients with AIS that undergo correction surgeries with LIV in the lumbar spine from 2013 to 2021 with pre- and 2-year postop standing full body plain films available. OUTCOME MEASURES Outcome measures: Age, height, weight, BMI, Risser score, LIV and levels instrumented. Radiographic analysis included pre- and postop C2 to C7 sagittal vertical axis (cSVA), cervical lordosis angle (CL), T1 slope and thoracic kyphosis (TK). METHODS Measures were compared using independent samples t-tests, significance set at p<0.05. RESULTS A total of 99 patients: 49 VBT and 50 fusions. The VBT cohort Lenke class breakdown is 23% 1A, 13% 1C, 31% 3C; 18% 5C, and 15% 6C, while the PSF cohort consisted of 42% 1A, 6% 1B, 2% 2C, 2% 3B, 12% 3C, 2% 5B, 24% 5C, and 10% 6C. There were no significant differences with regard to patient age or number of levels instrumented. Patients included in the VBT cohort had a lower level of bone maturity as defined by Risser class (1.6±0.9 vs 2.6±1.8, p=0.001). The VBT cohort had higher baseline cSVA (3.4mm±1.6 vs -1.0mm±3.1, 0.001) and less CL (-0.6°±18.2 vs 11.6°±12.8, p=0.001) than the fusion cohort. No differences in baseline T1 slope or Thoracic Kyphosis was observed. VBT patients also had higher 2-year cSVA (3.4mm±1.4 vs -3.7mm±2.1, p=0.001) and less CL (-4.0±18.5 vs 7.0±12.2, p=0.001) compared to fusion patients. The PSF group had a significantly greater correction in cSVA than the VBT group (2.8mm±4.0 vs 0mm±1.6, p=0.001). Both groups displayed improvement in radiographic parameters of cervical and thoracic alignment including CL (VBT 3.3°vs 4.3°, p=0.74), T1 slope (VBT -4.3°vs -4.9°, p=0.81) and TK (VBT -6.1°vs -3.9°, p=0.47). After PSM for Lenke classification, 66 patients remained: 33 VBT, 33 PSF. The PSF group continued to demonstrate greater improvement in cSVA than the VBT group (3.2mm±3.0 vs -0.3±1.8, p=0.001. CONCLUSIONS VBT and PSF both improve radiographic parameters of cervical alignment in AIS patients; however, PSF showed greater correction of cSVA at 2-year followup. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs. VBT takes advantage of the Hueter-Volkmann principle, and modulates growth across intervertebral disc spaces with a tensioned tether secured at the lateral aspects of vertebral bodies. Cervical deformity in AIS patients is associated with lower health related quality of life. PSF constructs have been shown to improve cervical deformity, however, to date, these relationships have not been described in patients treated with VBT. Determine if cervical sagittal alignment parameters following VBT for correction of AIS are similar to what is observed following PSF. Multi-center retrospective cohort study. Patients with AIS that undergo correction surgeries with LIV in the lumbar spine from 2013 to 2021 with pre- and 2-year postop standing full body plain films available. Outcome measures: Age, height, weight, BMI, Risser score, LIV and levels instrumented. Radiographic analysis included pre- and postop C2 to C7 sagittal vertical axis (cSVA), cervical lordosis angle (CL), T1 slope and thoracic kyphosis (TK). Measures were compared using independent samples t-tests, significance set at p<0.05. A total of 99 patients: 49 VBT and 50 fusions. The VBT cohort Lenke class breakdown is 23% 1A, 13% 1C, 31% 3C; 18% 5C, and 15% 6C, while the PSF cohort consisted of 42% 1A, 6% 1B, 2% 2C, 2% 3B, 12% 3C, 2% 5B, 24% 5C, and 10% 6C. There were no significant differences with regard to patient age or number of levels instrumented. Patients included in the VBT cohort had a lower level of bone maturity as defined by Risser class (1.6±0.9 vs 2.6±1.8, p=0.001). The VBT cohort had higher baseline cSVA (3.4mm±1.6 vs -1.0mm±3.1, 0.001) and less CL (-0.6°±18.2 vs 11.6°±12.8, p=0.001) than the fusion cohort. No differences in baseline T1 slope or Thoracic Kyphosis was observed. VBT patients also had higher 2-year cSVA (3.4mm±1.4 vs -3.7mm±2.1, p=0.001) and less CL (-4.0±18.5 vs 7.0±12.2, p=0.001) compared to fusion patients. The PSF group had a significantly greater correction in cSVA than the VBT group (2.8mm±4.0 vs 0mm±1.6, p=0.001). Both groups displayed improvement in radiographic parameters of cervical and thoracic alignment including CL (VBT 3.3°vs 4.3°, p=0.74), T1 slope (VBT -4.3°vs -4.9°, p=0.81) and TK (VBT -6.1°vs -3.9°, p=0.47). After PSM for Lenke classification, 66 patients remained: 33 VBT, 33 PSF. The PSF group continued to demonstrate greater improvement in cSVA than the VBT group (3.2mm±3.0 vs -0.3±1.8, p=0.001. VBT and PSF both improve radiographic parameters of cervical alignment in AIS patients; however, PSF showed greater correction of cSVA at 2-year followup.