Impact of High Pelvic Incidence on Reoperation Rates and Sagittal Alignment Following Anterior Lumbar Interbody Fusion for Isthmic Spondylolisthesis

Introduction: Pelvic incidence (PI) determines spinal alignment, and a high PI has been linked to increased risk of complications. There is limited research exploring how a high PI affects surgery for the common condition of isthmic spondylolisthesis. Among a cohort of patients undergoing anterior lumbar interbody fusion (ALIF) for isthmic spondylolisthesis, we assessed the impact of high PI on: 1) reoperations, 2) PI-lumbar lordosis (PI-LL) mismatch.

Methods: A retrospective, cohort study was conducted for patients undergoing ALIF Grade-1/2 isthmic spondylolisthesis from 2011-23. Patients with multilevel spondylolisthesis, revision surgeries, or concomitant deformity procedures were excluded. The primary exposure variable was a high preoperative PI, defined as >80º. Patient demographics, preoperative sagittal parameters and intraoperative variables were compared between the cohorts. The primary outcome was reoperation. The secondary outcome was PI-LL mismatch, defined as >10º, and assessed pre and postoperatively. Descriptive and bivariate statistics were performed.

Results: Among 58 patients undergoing ALIF for isthmic spondylolisthesis, mean age was 47.0±12.6 years, mean BMI 30.7±5.3, and 44.8% (26) were male. There were 9 (15.5%) patients with PI >80º. The high PI cohort had a mean PI of 89.8±10.8º; the lower PI cohort had a mean PI of 63.0±10.2º. Preoperatively, patients with PI >80º had significantly greater lumbar lordosis (71.3±6.6 vs. 56.0±12.2º, p=0.001), pelvic tilt (33.8±11.6 vs. 21.1±7.7º, p< 0.001), and sacral slope (56.7±4.1 vs. 43.1±10.2º, p< 0.001) compared to patients with PI ≤80, with no difference in L4-S1 lordosis (42.3±15.1 vs. 37.6±10.9º, p=0.260). There was no difference in estimated blood loss, operative time, length of stay or length of follow up. Patients with a PI >80º required significantly more reoperation (22.9% vs. 2.0%, p=0.012) than patients with PI ≤80. There was no difference in PI-LL mismatch preoperatively (66.7% vs. 44.9%, p=0.230) or postoperatively (22.2% vs. 26.5%, p=0.786) between patients with PI >80º or with PI ≤80º.

Conclusion : Patients with a high PI undergoing ALIF for isthmic spondylolisthesis are at significantly greater risk for reoperation compared to those with lower PI despite similar rates of PI-LL mismatch postoperatively. These findings underscore the importance of thorough preoperative patient counseling to address the elevated risk of reoperation in this group.