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.
Gwak et al. (Fri,) studied this question.