The relationship between distal lumbar lordosis correction and early postoperative L1-pelvic angle changes in adult spinal deformity surgery.

Abstract

To evaluate the early postoperative relationship between changes in distal and proximal lumbar lordosis and the L1-pelvic angle in adult spinal deformity surgery. A retrospective review was performed of 120 adult spinal deformity patients undergoing ≥ 6-level thoracolumbar fusion to the pelvis with a UIV at T10 or higher. Spinopelvic parameters were assessed preoperatively and at an early postoperative window (minimum 6 months to maximum 1 year) to isolate initial alignment mechanics, ideal L1-pelvic angle was defined as (0.5 × pelvic incidence - 19) ± 2, and uni- and multivariable regression analyses examined associations between changes in lumbar lordosis components and L1-pelvic angle, with stratification by postoperative L1-pelvic angle deviation. The cohort (mean age 65.7 years; 64.1% female) had a mean pelvic incidence of 55.2°. L1-pelvic angle improved from 13.7° preoperatively (deviation 5.1°) to 9.2° postoperatively (deviation 0.1°), with increases in distal and proximal lumbar lordosis of 10.5° and 9.5°, respectively. Change in distal lumbar lordosis strongly correlated with change in L1-pelvic angle (ΔL1PA =  - 0.5ΔDLL + 0.4; r =  - 0.80; p < 0.001). Patients with postoperative L1-pelvic angle increase had greater preoperative thoracic kyphosis, thoracolumbar kyphosis, and L4-S1 lordosis (all p ≤ 0.017). Distal lumbar lordosis change is strongly associated with early postoperative L1-pelvic angle alignment in adult spinal deformity, with each 1° of L4-S1 correction producing a 0.5° L1-pelvic angle reduction. This relationship provides a descriptive framework for understanding early lumbopelvic behavior after major reconstruction, while the lack of association with proximal lordosis and ideal preoperative L1-pelvic angle suggests sagittal deformity drivers beyond the distal lumbar spine.