Correction of the Lumbosacral Fractional Curve vs. Thoracolumbar Major Curves in Adult Spinal Deformity Surgery: How Much Do We Correct Each Curve?

Abstract

In adult spinal deformity (ASD) surgery, lumbosacral fractional curve (LSF) is stiffer and harder to correct than thoracolumbar major curve (MC). In patients undergoing ASD surgery, we aimed to:1) assess correction rate of LSF vs. MC, 2) determine association between their correction and postoperative alignment and complications. A retrospective cohort study (2009-23) including patients undergoing ASD surgery with evaluated LSF and MC. Outcomes were postoperative coronal malalignment (CM) (CVA≥3cm), sagittal malalignment, and mechanical complications. Multivariable regression controlled for age, sex, body mass index, and preoperative alignment. Among 174 patients (mean age:60±19 years; 73% females), mean preoperative LSF and MC were 13±10° and 32±18°. Mean preoperative/postoperative CVA were 26±25mm and 20±21mm. LSF and MC and were corrected by median 35% (IQR:0.7%-68%) and 17% (IQR:3.0%-61%). Postoperative CM was seen in 35 (20%) patients. Improvement in LSF and MC occurred in 55% vs. 76% (p<0.001). Among 4-groups based on each curve correction, no significant difference was seen in postoperative CM (p=0.060) or CVA (p=0.216). Among patients with LSF-only vs. MC-only corrected, LSF-only group had higher-risk of postoperative CM (33% vs. 10%, p=0.038, OR=5.0, 95%CI:1.0-24.4, p=0.048). LSF-only group had the highest postoperative SVA (p=0.010), but this was lost on multivariable regression (β=0.2, 95%CI:-4.9-5.3, p=0.940). LSF was corrected less frequently than MC. CM was more commonly seen when only-LSF was corrected compared to only-MC. No significant differences were noted in postoperative alignment or complications. These findings emphasize the importance of reconciling correction of both LSF and MC to avoid global CM.