The Effect of Changes in Segmental Lordosis on Global Lumbar and Adjacent Segment Lordosis After L5-S1 Anterior Lumbar Interbody Fusion

Study Design Retrospective Cohort Study. Objective Restoration of lordosis in lumbar fusion reduces low back pain, decreases adjacent segment degeneration, and improves postoperative outcomes. However, the potential effects of changes in segmental lordosis on adjacent-level and global lordosis remain less understood. This study aims to examine the relationships between segmental (SL), adjacent-level, and global lumbar lordosis following L5-S1 Anterior Lumbar Interbody Fusion (ALIF). Methods 80 consecutive patients who underwent single-level L5-S1 ALIF were divided into 3 groups based on the degree of change ( increment ) in index-level segmental lordosis: <5 & DEG; (n = 23), 5 & DEG;-10 & DEG; (n = 29), >10 & DEG; (n = 28). Radiographic parameters measured included global lumbar, segmental, and adjacent level lordosis, sacral slope, pelvic tilt, pelvic incidence, and PI-LL mismatch. Results Patients with increment SL 5 & DEG;-10 & DEG; or increment SL >10 & DEG; both showed significant increases in global lumbar lordosis from preoperative to final follow-up. However, patients with increment SL >10 & DEG; showed statistically significant losses in adjacent level lordosis at both immediate postoperative and final follow-up compared to preoperative. When comparing patients with increment SL >10 & DEG; to those with increment SL 5-10 & DEG;, there were no significant differences in global lumbar lordosis at final follow-up, due to significantly greater losses of adjacent level lordosis in these patients. Conclusion The degree of compensatory loss of lordosis at the adjacent level L4-L5 correlated with the extent of segmental lordosis creation at the index L5-S1 level. This may suggest that the L4 to S1 segment acts as a harmonious unit, able to accommodate only a certain amount of lordosis and further increases in segmental lordosis may be mitigated by loss of adjacent-level lordosis.

Automated summary

This study aimed to examine the effects of L5-S1 anterior lumbar interbody fusion on segmental, adjacent-level, and global lordosis. The results showed that an increase in segmental lordosis following the fusion procedure significantly increased global lordosis, but also caused a decrease in adjacent-level lordosis. This suggests that an increase in segmental lordosis may lead to a compensatory loss of lordosis at the adjacent level.