Prevalence and prognosis of coronal malalignment following circumferential minimally invasive surgery (CMIS) for adult spinal deformity (ASD) correction.

Introduction: The coronal balance results and the prognosis of any postoperative coronal malalignment (CM) after circumferential minimally invasive surgery (CMIS) for adult spinal deformity (ASD) correction is underreported. We aimed to study coronal balance change and correlation to clinical outcomes after CMIS.

Methods: We prospectively collected data registry of 312 ASD patients who underwent CMIS correction from Jan2011 to Sep2022. Inclusion criteria were having ASD ,4+levels fused and at least1-year follow-up. Based on the preoperative distance between the C7 plumb line and central sacral vertical line (C7PL-CSVL) and the relationship between C7PL and the main lumbar curve, these patients were classified as: Bao A (C7-CSVL < 3cm, coronal aligned, CA); Bao B (C7-CSVL>3cm, shifted toward the concavity of the main lumbar curve); and Bao C (C7-CSVL>3cm, shifted toward the convexity of the main lumbar curve). Preoperative and 1-year postoperative standing radiographs and clinical outcome measures (VAS, ODI, SRS-22) were used to make the comparisons.

Results: A total of 120 patients (mean age 66.6yrs (24-84)) were grouped: 81 pts (67.5%) type A, 19pts (15.8%) type B, and 20pts (16.7%) type C. The radiological measures (CVA, coronal Cobb angle, LSF curve, SVA, LL, PI-LL) and the clinical outcomes, were significantly improved in each of the 3 groups postoperatively. At 1-year follow-up, 10patients (12.4 %) of type A had CM, 4 patients (21.1%) of type B, and 8 patients (40%) of type C remained CM. Comparing CA to CM patients at the 1-year follow-up in each Bao subtype revealed that CA patients had better radiographic outcomes, but the differences were not significant. Clinical outcomes of CA and CM patients of each Bao subtype were not significant (except for the CA type A patients that had significantly better ODI scores than CM type A patients).

Conclusion : Our study suggests that CMIS for ASD correction significantly improves radiographic and clinical outcomes, regardless of the preoperative coronal alignment status. Bao type C is more prone to have postoperative CM than types A and B. However, the 1-year clinical and radiographic outcomes were not significantly different between the postoperative CA and CM patients in all preoperative Bao subtypes.