Postoperative loss in segmental lumbar lordosis following L5-S1 anterior lumbar interbody fusion

Achieving and maintaining adequate segmental lumbar lordosis through anterior lumbar interbody fusion (ALIF) has been associated with favorable clinical outcomes. However, preoperative and immediate postoperative factors predicting changes in segmental alignment have not been established for ALIF.

Adults who underwent L5-S1 ALIF surgery for degenerative disc disease at a single institution between 2017 and 2022 were included. Multivariate stepwise linear regression analyses were performed to identify modifiable demographic, surgical, and alignment parameters that were predictive of 6-week to 1-year postoperative L5-S1 segmental lordosis loss. Next, multivariate logistic regression analyses were performed to evaluate the association between segmental loss and postoperative mechanical complications. Finally, multivariate logistic regression and receiver operating characteristic (ROC) curve analyses were performed to establish lower and upper thresholds for 6-week postoperative L5-S1 segmental lordosis that mitigated the need for revision surgery and segmental lordosis loss, respectively. Similar thresholds were established for low (< 45°), average (45°-60°), and high (> 60°) pelvic incidence (PI) categories as well.

Among 94 patients, the mean age was 50.2 years, 57% were female, and the mean Charlson Comorbidity Index score was 1.4. Radiographically, patients had 7.6° L5-S1 lordotic correction (p < 0.001) and 10.2-mm L5-S1 anterior disc height increase (p < 0.001) after their ALIF surgery, and these changes were maintained to 1 year postoperatively. Stepwise regression revealed that baseline obesity (coefficient = -2.2, p = 0.047), lack of posterior fixation (coefficient = -2.4, p = 0.045), and larger correction in L5-S1 lordosis (coefficient = -0.4, p < 0.001) were independently associated with postoperative L5-S1 segmental lordosis loss. Cage subsidence was associated with higher odds of postoperative segmental loss (OR 1.2, p = 0.017). ROC curve analyses identified a 6-week postoperative L5-S1 segmental lordosis range of 21.6° to 26.8° (low PI 19.0°-24.8°, average PI 21.0°-26.4°, and high PI 24.1°-28.7°) as that which minimized loss of lordotic correction and the need for revision surgery over a 1-year follow-up period.

ALIF offers powerful restoration of segmental alignment that is maintained after surgery. The extent of subsequent loss can be predicted by baseline obesity, the presence of posterior instrumentation, and the degree of achieved lordotic correction. Preoperative surgical planning should consider correcting L5-S1 segmental lordosis to between the thresholds defined in this study to mitigate the risk of postoperative mechanical complications.