Distal hyperlordotic distribution does not increase the risk of mechanical complications in adult spinal deformity patients undergoing long-construct fusion to the pelvis with optimal global sagittal alignment.

PURPOSE: To assess whether distal hyperlordotic distribution (DHD), defined by the Lordosis Distribution Index (LDI) from the Global Alignment and Proportion (GAP) score, increases the risk of mechanical complications (MC) in adult spinal deformity (ASD) patients with optimal postoperative global sagittal alignment and total lordosis after long-construct fusion to the pelvis.

METHODS

Retrospective analysis of a prospective, multicenter database. ASD patients undergoing fusion from L2 or higher to the pelvis with ≥ 2 years follow-up and optimal postoperative global alignment (RSA = 0) and total lordosis (RLL = 0), according to the GAP score, were included. Patients were classified into Ideal (LDI = 0) and DHD (LDI = 3) groups. Rates of MCs (stratified in PJK or PJF), reoperations, and functional outcomes were compared. A post-hoc non-inferiority analysis utilizing a 10% clinical margin was performed.

RESULTS

A total of 125 patients met criteria (91 Ideal; 34 DHD). The DHD group, compared to the Ideal group, had a significantly lower preoperative pelvic incidence (50.9° vs. 57.2°, p = 0.014) and more frequently underwent three-column osteotomies (35.3% vs. 18.7%, p = 0.050). At 2-year follow-up, DHD was statistically non-inferior to the Ideal distribution regarding PJFs (absolute risk difference was -7.3%, 90% CI: -16.1% to 1.5%) and for PJKs (absolute risk difference was 1.5%, 90% CI: -6.0% to 9.0%). Reoperation rates (38.2% vs. 28.6%, p = 0.299) and patient-reported functional outcomes were comparable.

CONCLUSION

In ASD patients with pelvic fixation and optimal global alignment, DHD is statistically non-inferior to ideal distributions regarding the risk of MCs, including PJK and PJF, and reoperations. In addition to this, DHD represents a physiological scenario in patients with lower pelvic incidence. Future predictive models should focus on penalizing distal hypolordosis rather than universally penalizing DHD.

LEVEL OF EVIDENCE: III.