Introduciton It is imperative not only to restore proper lumbar lordosis (LL) by pelvic incidence (PI), but also to re-establish natural lumbar shape by achieving optimal distribution between the proximal and distal lordosis. Then current investigation aims to determine whether creating a specific angle during posterior lumbar interbody fusion (PLIF) at the L4-5-S1 level affects the incidence of postoperative adjacent segment degeneration (ASD).
Methods The present study retrospectively analyzed the radiographic data obtained from patients who underwent PLIF at the L4-5-S1 level between January 2017 and December 2019. The patients were divided into two categories based on the presence of ASD and non-ASD. The study assessed the differences in radiographic parameters between the two groups and performed a correlation analysis to examine the relationship between PI, LL, upper lumbar lordosis (ULL), lower lumbar lordosis (LLL), and lordosis distribution index (LDI). Furthermore, stratification by the size of PI was performed and then compared using an analysis of variance test. The minimum follow-up duration was two years.
Results A total of 155 patients were subjected to analysis, comprising 84 patients in the non-ASD group and 71 in the ASD group. The mean follow-up period of months, during which a revision rate of 7.7% was observed. Postoperatively, a significant PI-LL mismatch (19.48 ± 11.56°) was observed in the ASD group compared to the non-ASD group (9.98 ± 10.07°, p <0.001). The average value of L4-S1 lordosis in the non-ASD group was 30.93 ± 6.97°, which was greater than that in the ASD group (24.73 ± 10.86°, p = 0.005). In the non-ASD group, there was a positive correlation between L1-L4 angle and PI (r = 0.643, p < 0.001), whereas no correlation was found between L4-S1 angle and PI (r = -0.027, p = 0.806). In contrast, the ASD group showed a positive correlation between L4-S1 angle and PI (r = 0.409, p < 0.001). Stratification based on PI revealed that the distal lordosis (L4-S1 angle) remained consistent (28.09 ± 6.31 vs. 28.97 ± 7.73 vs. 30.28 ± 7.73; p = 0.758) among the PI groups in the non-ASD group, whereas in the ASD group, the distal lordosis did not remain consistent (p = 0.003).
Discussion
The study findings suggest that following L4-S1 PLIF, there is a significant variation in the proximal lordosis that correlates with PI. However, distal lordosis demonstrates a narrower range and is independently associated with PI in patients without ASD. Therefore, it is essential for surgeons to analyze the distal lordotic angle carefully during surgical planning to restore optimal LL distribution and prevent ASD after L4-S1 PLIF.