Resident Vanderbilt University Medical Center Nashville, TN, US
Introduction: While the suggested L4-S1 lordosis is approximately 35-45°, few studies have corroborated these findings. In patients undergoing ASD surgery, we sought to determine the impact of L4-S1 lordosis on: 1) mechanical complications, 2) reoperations, and 3) PROMs.
Methods: A single-institution, retrospective cohort study was performed for patients undergoing ASD surgery from 2011-21. Inclusion criteria were: ≥5-level fusion, instrumented to the ilium, and at least 2-year follow-up. The primary exposure variable was preop/postop L4-S1 lordosis trichotomized into < 35°, 35-45°, and >45°. The primary outcomes were mechanical complications and reoperations. Secondary outcomes included PROMs. Multivariable analysis controlled for age, BMI, and T-score.
Results: In 153 patients undergoing ASD surgery and instrumented to the pelvis, mean age was 68.9±11.2, 116 (75.8%) were females, and mean total instrumented levels was 10.9±3.2. L4-S1 lordosis worsened from preoperative to postoperative (28.4±15.8° vs. 26.7±12.5°, p=0.363), with a change of -1.2±14.8°. Preoperatively, L4-S1 lordosis was: < 35° (66.0%), 35°-45° (19.0%), and >45° (15.0%). Postoperatively L4-S1 lordosis was: < 35° (75.2%), 35-45° (18.4%), and >45° (6.4%), with a significant change from preoperative to postoperative (p=0.002). A higher preoperative L4-S1 lordosis (>45°) was associated with spinopelvic complications (32.7% vs. 20.7% vs. 56.5%, p=0.023), spinopelvic complications requiring reoperation (21.8% vs. 10.3% vs. 39.1%, p=0.035), and rod fracture (23.8% vs. 13.8% vs. 52.2%, p=0.005). These findings remained significant on multivariable logistic regression analysis. No significant difference was found between preoperative or postoperative L4-S1 groups and PROMs (all p>0.05).
Conclusion : While most patients undergoing ASD surgery presented with L4-S1 lordosis < 35°, a high preoperative L4-S1 lordosis >45° was independently associated with increased spinopelvic complications and rod fractures. Complications were lowest in the preoperative L4-S1 35-45° group. Special attention should be given to patients presenting with a high L4-S1 lordosis, as they may have a higher risk for certain mechanical complications.