2025 Lumbar Lordosis Distribution in Adult Spinal Deformity: Targets Based on Pelvic Morphology

INTRODUCTION: The lumbar lordosis distribution index (LDI) is an important constituent of achieving adequate correction of adult spinal deformity (ASD). While previous literature has evaluated LDI, targets can vary based on pelvic morphology that remains to be evaluated in the ASD population. METHODS: Operative ASD patients fused from at least L1 and proximal to the pelvis with two-year follow-up were included. Patients were stratified into three categories based on pelvic incidence (PI) [P1: PI<45°, P2 PI 45-60°, P3 PI >60°]. LDI was assessed based on lumbar lordosis distribution (LDI) [L4-S1 lordosis / L1/S1 lordosis]. LDI based on Lafage and GAP were evaluated. Thresholds were determined by conditional inference tree (CIT) analysis. RESULTS: 334 patients met the inclusion criteria. Overall, 49% had mechanical complications, with 32% considered major and 22% undergoing reoperation for mechanical complications. 54% had PJK, while 13% developed PJF. No difference in mechanical complication rate when meeting Lafage LDI (48 vs 49%, p=.8) or GAP LDI targets (46 vs 51%, p=.4). CIT analysis determined thresholds based on PI (all p<.05). PJK rates were reduced in P1 (low PI) if LDI was corrected to >0.6. While those in P2 (mid PI), with PT <23° had reduced rates of early PJF when LDI was corrected to >0.4. In P3 (high PI) with preoperative PT <48°, reduced rates of PJF if postoperative LDI was <85%, while reduced major mech comp with LDI <68. CONCLUSIONS: Correction of lumbar lordosis distribution based on pelvic morphology reduced rates of PJK and PJF. Reduced rates of PJK were seen with thresholds for LDI correction of at least 60% for low PI, and lower than 85% in those with high IP.