Does Achievement of Ideal L1 Pelvic Angle with MIS Techniques in Adult Spinal Deformity Correction Lead to Better Outcomes?

Abstract

Retrospective cohort study using a multicenter, prospectively collected adult spinal deformity (ASD) database. To determine whether achieving the ideal L1 pelvic angle (L1PA) in minimally invasive surgery (MIS) for ASD correction is associated with reduced mechanical failure and improved clinical outcomes. Prior research has shown that achieving ideal L1PA-defined as (0.5×pelvic incidence)-21-is linked to lower reoperation risk in open ASD correction. Its relevance in MIS has not been well established. A total of 1,104 ASD patients across 13 centers were included (criteria: scoliosis ≥20°, SVA ≥5 cm, PT ≥25°, or TK ≥60°, with ≥2-year follow-up). Radiographic parameters and patient-reported outcomes (PROs) were collected preoperatively, at 6 weeks, and at final follow-up. Ideal L1PA was defined as within±5° of the calculated target. MIS was defined as circumferential MIS (LLIF/ALIF with percutaneous posterior fixation). Associations between alignment and outcomes (reoperation, PROs) were analyzed using linear regression and t-tests. Ideal L1PA was achieved in 63% of MIS cases and 61% of open cases (P=.342). Among MIS patients, ideal L1PA correlated with lower reoperation rates (15% vs. 33%, P <.01) and greater improvement in SRS-22 total (Δ0.85 vs. Δ0.40, P <.01) and SF-36 PCS scores (Δ9.1 vs. Δ4.6, P=.04). In contrast, ideal L1PA was not associated with reduced reoperation in the open group. Across all patients, each 1° deviation from ideal L1PA increased reoperation risk by 1.8% (P=.04). Ideal L1PA is achievable in MIS at similar rates as open surgery. In MIS-treated ASD patients, achieving ideal alignment is associated with reduced reoperation and improved clinical outcomes, supporting its role as a key surgical target.