Risk Factors of Adjacent Segment Disease after Transforaminal Inter-Body Fusion for Degenerative Lumbar Disease.

STUDY DESIGN A retrospective study. OBJECTIVE The purpose of this study was to determine the incidence and risk factors of adjacent segment disease (ASD) after transforaminal inter-body fusion (TLIF) for degenerative lumbar disease. SUMMARY OF BACKGROUND DATA ASD is a major complication after spinal fusion. Many reports have been published concerning the risk factors for ASD after TLIF. A number of quantitative relationships to spino-pelvic parameters have been established. A retrospective cohort study was carried out to investigate spino-pelvic alignment in patients with ASD after TLIF. METHODS This study evaluated 263 subjects (150 subjects undergoing floating fusion (FF group), and 113 patients undergoing lumbosacral fusion (LF group)) who underwent TLIF from 2009 to 2012. The mean follow-up period was 37.6 months. Several parameters were measured using pre- and postoperative full-length free-standing radiographs, including lumbar lordosis (LL), sacral slope (SS), pelvic incidence (PI), pelvic tilt (PT), and PI-LL. Multivariate logistic regression analysis was performed to evaluate these parameters as potential risk factors of early onset radiographic ASD. RESULTS Radiographic ASD was found in 65 cases (43.3%) in the FF group, and 49 cases (43.3%) in the LF group. LL improved by 7.5° and 3.9° in each group respectively after TLIF. However, PT worsened by 6.4° in the LF group. When comparing with ASD positive cases and ASD negative cases, a significant difference in preoperative PT was observed in both FF (P = 0.001) and LF groups (P = 0.0001). Logistic regression analysis and receiver operating characteristic analysis revealed that preoperative PT of more than 22.5° was a significant risk factor of the incidence of ASD after TLIF (P = 0.02; odds ratio: 5.1, 95% CI: 1.62-9.03). CONCLUSION Patients with preoperative sagittal imbalance have a statistically significant increased risk of ASD. The risk of ASD incidence was 5.1 times greater in subjects with preoperative PT of more than 22.5°.