The more the better? Integration of vertebral pelvic angles (VPA) PJK thresholds to existing alignment schemas for prevention of mechanical complications after adult spinal deformity surgery

Abstract

Purpose: While existing adult spinal deformity (ASD) alignment schemas acknowledge the dynamic relationship between the pelvis and spine, consideration of vertebral pelvic angles (VPA) thresholds for PJK may provide further insight into the relationship of each individual vertebra to the pelvis, which may allow for greater individualization of operative targets. Herein, we examine VPA's utility in preventing mechanical complications and its possible unification with prevalent scoring systems.

Methods: In a retrospective cohort study of a prospectively collected database, operative ASD patients ≥ 18 years with complete baseline (BL) and two-year (Y) operative, radiographic, and health-related quality of life data were included. Descriptive analyses, means comparison, and logistic regression tests were applied to explore demographic and surgical differences, as well as the impact of alignment goals on outcomes. Cohorts were grouped as patients who met VPA non-PJK thresholds, as defined by Duvvuri et al. 2023 alone versus traditional GAP/SAAS alignment matching versus combined VPA + SAAS + GAP. The Non-PJK VPA validated mean for L1PA was 10.4 ± 7.0 and T9PA 8.9 ± 7.5.

Results: 398 patients met inclusion criteria (mean age 61 ± 14 years, 78% female, BL BMI 27 ± 6, BL CCI 2 ± 2). At baseline, mean vertebral pelvic angles were as follows: T1PA: 24 ± 14; T4PA 20 ± 13, T9PA 15 ± 12, L1PA 11 ± 10, L4PA 11 ± 6. Mean vertebral pelvic angles at 6 W postoperatively: T1PA 16 ± 10, T4PA 12 ± 10, T9PA 8 ± 9, L1PA 9 ± 8, L4PA 11 ± 5. 240 (60%) patients attained optimal L1PA, while 104 patients (26.1%) reached non-PJK mean for T9PA. 89 patients (22%) were optimal by both VPA standards. VPA-Optimal group demonstrated significantly lower rates of 1Y PJK (17% v 83%, p = 0.042) and PJF by 2Y (7% v. 93%, p = 0.038). When patients attained VPA goals in addition to GAP/SAAS goals at 6 W, they demonstrated significantly lower rates of Y1 PJK (p = 0.026) and Y1 and Y2 PJF. Those with optimal VPA registered greater SRS-22 scores across multiple domains (p < 0.02) as well as a greater rate of normal neurological examination at 6 W (p = 0.048).

Conclusions: Vertebral pelvic angles are a reliable measure of global alignment, and respecting certain targets may help prevent development of PJK/PJF. The value of VPA can be augmented through integration with GAP/SAAS frameworks to prevent complications and improve quality of life.

Keywords: Alignment; Deformity; Sagittal; Spine.