Pelvic incidence is a risk factor for lower instrumented vertebra failure in adult spinal deformity patients who underwent corrective fusion terminating at the L5 vertebra

Background: Factors related to postoperative mechanical failure after long fusion with lower instru-mented vertebra (LIV) at L5 have not been well investigated. Elucidating such factors may allow us to perform alternatives to spinopelvic fusion for adult spinal deformity (ASD) cases. We investigated the incidence and risk factors of LIV failure in patients with ASD who underwent surgical treatment of long corrective fusion until the L5 vertebrae.Methods: Between 2009 and 2018, 52 patients who underwent corrective fusions to L5 were followed-up for at least one-year. We evaluated the associated patient factors for LIV failure which include loosening of the pedicle screw of LIV, fracture of LIV, distal junctional kyphosis (DJK).Results: The mean age of the participants was 71.2 +/- 7.59 (range, 44-84). LIV failure occurred in 20 patients (38.5%), and 6 patients (11.5%) underwent secondary surgery for caudal segments. The mean pelvic incidence (PI) was 52.5 +/- 9.8 in the failure group versus 45.3 +/- 11.4 in non-failure group (P = 0.02) and pelvic tilt (PT) was 39.1 +/- 9.0 versus 32.4 +/- 13.0. There were no significant differences in sex, age, body mass index, number of levels fused, and other radiographic data. Logistic regression analysis that included T1 pelvic angle, PT, PI -postoperative LL and PI also identified PI as the only significant determinant of LIV failure (OR = 1.07, P = 0.034). Receiver operating characteristic analysis demonstrated that a PI over 50.0 degrees was associated with LIV failure (sensitivity 63%, specificity 70%, AUC 0.694).Conclusion: LIV failure was frequently observed after long corrective fusion for patients with ASD. High PI was found to be a significant risk factor for the LIV failure.(c) 2021 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.