P172. The longitudinal effects of posterior spinal fusion with derotation on axial deformity in adolescent idiopathic scoliosis

BACKGROUND CONTEXT Correction of axial spine alignment is one of several objectives in posterior spinal fusion (PSF) surgery for adolescent idiopathic scoliosis (AIS). Limited data exists regarding longitudinal maintenance of axial derotation over time postoperatively. PURPOSE To characterize the change in angle of trunk rotation (ATR), axial vertebral rotation (AVR), and body surface rotation (BSR) in patients with adolescent idiopathic scoliosis (AIS) undergoing posterior spinal fusion (PSF) with en-bloc derotation across multiple postoperative visits. STUDY DESIGN/SETTING Retrospective review of data from a single-center prospective registry. PATIENT SAMPLE Inclusion criteria for this retrospective study were a diagnosis of AIS, ages 11-20 at index surgery, PSF with en-bloc derotation, minimum of 3-month follow-up. Patients with a previous spine surgery were excluded. OUTCOME MEASURES ATR, AVR, and BSR at preoperative and six-week, three-month, six-month, one-year and two-year postoperative visits. METHODS ATR was measured with a scoliometer, AVR with EOS radiographic imaging, and BSR via surface topographic scanning in the EOS pose. Curve angle was measured by an orthopedic surgeon. Data collection occurred at the: preoperative, six-week, three-month, six-month, one-year, and two-year postoperative timepoints. BSR and AVR were tracked at the preoperative apical vertebral level at each timepoint. Generalized estimating equations were used for statistical analysis using the Chi-square with significance set at p ≤0.05. Covariates included age, sex, and body mass index. A t-test was done between the curve angle at the 6-week timepoint and the 1 or 2 year time point to understand the change in curve postoperatively. RESULTS The cohort included 49 patients (73.4% female, mean age 14.6±2.2 years, average preoperative major coronal curve angle of 57.9°±8.5, and 67% thoracic curves). ATR and AVR demonstrated significant improvement at all postoperative timepoints compared to pre-surgery. ATR correction was greatest at three-months (84%) but decreased to 70% at two years. AVR correction was greatest at the six-week visit (87%), decreased to 48% at two years. Loss of AVR correction from the six-week to the one-year visit was significant (p=0.032). BSR was significantly improved at the three-month and one-year visits when compared to baseline. The highest BSR correction was at the three-month visit (88%), and correction decreased to 44% at two years. There was no statistically significant loss of Cobb angle correction at 1 or 2 years. CONCLUSIONS Clinical assessment and radiographic imaging of axial deformity demonstrated significant improvement across all postoperative timepoints through two years without significant correction loss of ATR or AVR. Surface topographic measurements did not demonstrate significant axial correction after the one-year interval. FDA Device/Drug Status This abstract does not discuss or include any applicable devices or drugs.