Risk Factors for Adjacent Segment Disease in Short Segment Lumbar Interbody Fusion-A Case Series

BACKGROUND: Adjacent segment disease (ASD) is a common problem after lumbar spinal fusions. Ways to reduce the rates of ASD are highly sought after to reduce the need for reoperation. OBJECTIVE: To find predisposing factors of ASD after lumbar interbody fusions, especially in mismatch of pelvic incidence and lumbar lordosis (PI-LL). METHODS: We conducted a retrospective cohort study of all patients undergoing lumbar interbody fusions of less than 4 levels from June 2015 to July 2020 with at least 1 year of follow-up and in those who had obtained postoperative standing X-rays. RESULTS: We found 243 patients who fit inclusion and exclusion criteria. Fourteen patients (5.8%) developed ASD, at a median of 24 months. Postoperative lumbar lordosis was significantly higher in the non-ASD cohort (median 46.4 degrees +/- 1.4 degrees vs 36.9 degrees +/- 3.6 degrees, P <.001), pelvic tilt was significantly lower in the non-ASD cohort (16.0 degrees +/- 0.66 degrees vs 20.3 degrees +/- 2.4 degrees, P =.002), PI-LL mismatch was significantly lower in the non-ASD cohort (5.28 degrees +/- 1.0 degrees vs 17.1 degrees +/- 2.0 degrees, P <.001), and age-appropriate PI-LL mismatch was less common in the non-ASD cohort (34 patients [14.8%] vs 13 [92.9%] of patients with high mismatch, P <.001). Using multivariate analysis, greater PI-LL mismatch was predictive of ASD (95% odds ratio CI = 1.393-2.458, P <.001) and ageappropriate PI-LL mismatch was predictive of ASD (95% odds ratio CI = 10.8-970.4, P <.001). CONCLUSION: Higher PI-LL mismatch, both age-independent and when adjusted for age, after lumbar interbody fusion was predictive for developing ASD. In lumbar degenerative disease, correction of spinopelvic parameters should be a main goal of surgical correction.