Abstract
Pelvic incidence (PI)-based lumbar lordosis (LL) restoration is crucial for spinal balance. Proper proximal and distal LL distribution reduces mechanical complications, but the effect of segmental lordosis at L4-S1 on adjacent segment degeneration (ASD) remains unclear. This study aims to determine whether the lordotic angle achieved during L4-5-S1 posterior lumbar interbody fusion (PLIF) is associated with the incidence of postoperative ASD. This retrospective study analyzed radiographic data from L4-5-S1 PLIF patients (January 2019-December 2021) with at least 2 years of follow-up. Patients were categorized into ASD and non-ASD groups. Radiographic parameters, including PI, LL, upper lumbar lordosis, lower lumbar lordosis, and the lordosis distribution index, were compared. Correlation and stratification analyses were performed. A total of 155 patients were included (84 non-ASD, 71 ASD). The mean follow-up was 39.60 ± 20.33 months, with a 7.7% revision rate. The ASD group had a significant PI-LL mismatch (19.48 ± 11.56° vs 9.98 ± 10.07°, P < .001) and a lower L4-S1 lordosis angle (24.73 ± 10.86° vs 30.93 ± 6.97°, P = .005). In the non-ASD group, the L1-L4 angle correlated positively with PI (r = 0.643, P < .001), but L4-S1 did not (r = -0.027, P = .806). In contrast, the ASD group showed a positive correlation between L4-S1 and PI (r = 0.409, P < .001). PI stratification revealed stable distal lordosis (L4-S1) in the non-ASD group (P = .758) but significant variation in the ASD group (P = .003). These observations led the authors to infer that the stability of distal segmental lordosis - particularly at L4-S1 - across varying PI values may be a distinguishing feature associated with lower ASD risk. Proximal lordosis varies with PI, whereas distal lordosis remains stable in non-ASD patients. Insufficient distal lordosis may contribute to ASD, highlighting the importance of optimizing LL distribution during L4-S1 PLIF.