Do Intraoperative LIV-Tilt and Disk Angle Remain Stable at 2-year Follow-up Compared With Upright Radiographs in Patients With Idiopathic Scoliosis?: A Retrospective Cohort Study.

STUDY DESIGN: This study was a retrospective chart and radiographic review. OBJECTIVE: The aim of this study was to determine if lowest instrumented vertebra (LIV) tilt and disk wedging measured intraoperatively correlated to their respective values on standing radiographs at intermediate follow-up. SUMMARY OF BACKGROUND DATA: No guidelines exist regarding an acceptable intraoperative LIV-tilt. MATERIALS AND METHODS: After IRB approval, a consecutive series of patients with adolescent idiopathic scoliosis (AIS) and structural lumbar curves treated with posterior spinal fusion (PSF) at a single institution between 2007 and 2010 was identified. A total of 163 patients with AIS underwent PSF during this time period. Seventeen patients had fusion of structural lumbar curves with adequate imaging and a minimum 2-year follow-up. The LIV-tilt and disk angle below the LIV was measured on the preoperative standing, intraoperative supine fluoroscopy and postoperative standing radiographs, and coronal balance was measured on the preoperative and postoperative standing radiographs using a standardized method separately by 2 authors. RESULTS: The curve distribution was as follows: Lenke 3 (29%), Lenke 5 (47%), and Lenke 6 (24%). There was agreement on radiographic measurements between the 2 authors with a correlation coefficient of 0.98 for coronal balance, 0.91 for LIV-tilt, and 0.65 for disk angle. LIV-tilt improved from 19.4 degrees preoperatively to 3.6 degrees intraoperatively. At minimum 2-year follow-up, LIV had on average progressed to 8.6 degrees. The disk angle improved from 5.4 degrees preoperatively to 2.5 degrees intraoperatively. This improvement was maintained at 2 years (2.8 degrees). Coronal balance also improved during the postoperative period from 17.9 mm immediately following surgery to 11.1 mm at the last follow-up. CONCLUSIONS: Compared with prone intraoperative fluoroscopic images, disk wedging below LIV remains stable at 2 years postsurgery on standing radiographs in patients with AISundergoing PSF, including structural lumbar curves, whereas LIV-tilt improvement is not maintained. Intraoperative fluoroscopy provides a reliable prediction of disk wedging below LIV, 2 years after surgery on standing radiographs.