Analysis of factors associated with sagittal alignment deterioration after correction of degenerative scoliosis by in situ contouring

Introduction: In situ contouring is one of the surgical techniques used for scoliosis reduction. The initial correction could change over time, with deterioration of the sagittal balance. The purpose of this study was to analyze the loss of correction after degenerative lumbar scoliosis surgery using in situ contouring. Materials and methods: Full spine radiographs of 73 patients (mean age 63.3 years, mean follow-up 27 months) were analyzed before surgery, after surgery, and at the final follow-up. The following radiographic parameters were measured: C2-C7 lordosis, T4-T12 kyphosis, L1 -S1 lordosis, pelvic tilt, pelvic incidence, sacral slope, SVA C7, SVA C2, Cobb angle. Bayesian inference was used to compare the changes in these parameters. A probability > 0.95 was considered as a significant change. Results: After surgery, lumbar lordosis increased from -28.4 degrees to -37.8 degrees (probability 0.999), then decreased to -32.1 degrees at the final follow-up (probability 0.953). Thoracic kyphosis increased from 29.6 degrees to 37.4 degrees after surgery (probability 1.00) and continued to increase to 41.6 degrees at the final follow-up (probability 0.999). SVA C7 increased from 38.5 mm to 62.3 mm (probability 0.999) and pelvic tilt from 19.4 degrees to 25.1 degrees (probability 1.00) during the follow-up period. Ten patients had to be reoperated because of a surgical site infection. Infection (14%) was associated with an increase of SVA C7 (probability 0.989) and thoracic kyphosis (probability 0.987). Nonunion (16%) was associated with a decrease in lumbar lordosis (probability 0.756). Conclusion: Correction of degenerative lumbar scoliosis by in situ contouring resulted in sagittal balance correction; however, some of this correction was lost during the follow-up period. The main risk factors were deep wound infection and nonunion. (C) 2021 Elsevier Masson SAS. All rights reserved.