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

Retrospective Cohort Study. 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). 80 consecutive patients who underwent single-level L5-S1 ALIF were divided into 3 groups based on the degree of change (∆) in index-level segmental lordosis: 10° (n = 28). Radiographic parameters measured included global lumbar, segmental, and adjacent level lordosis, sacral slope, pelvic tilt, pelvic incidence, and PI-LL mismatch. Patients with ∆SL 5°-10° or ∆SL >10° both showed significant increases in global lumbar lordosis from preoperative to final follow-up. However, patients with ∆SL >10° showed statistically significant losses in adjacent level lordosis at both immediate postoperative and final follow-up compared to preoperative. When comparing patients with ∆SL >10° to those with ∆SL 5-10°, 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. 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.