Incidence and Risk Factors for L5-S1 Complications After Long-level Floating Fusion in Adult Degenerative Scoliosis

Abstract Background Whether to preserve L5-S1 with no pre-existing pathology in the fusion for patients with adult degenerative scoliosis (ADS) remains controversial. This study is to determine the predictors of L5-S1 diseases for the distal fusion to L5 in the long instrumented fusion for ADS. Methods A total of 159 patients with ADS who had undergone long floating fusion were evaluated with a minimum 2 year follow-up between 2014 to 2018. The patient- and surgical-related risk factors for each individual were identified by using univariate testing. All patients were divided into groups with and without L5-S1 diseases. Univariate testing was used to identify the potential risk factors. Independent risk factors of L5-S1 diseases were identified using multivariate logistic regression. Results BMD of the patients with L5-S1 diseases were much higher than that without L5-S1 diseases (P = 0.003). Postoperative sacral slope in L5-S1 diseases group was much higher than that without L5-S1 diseases group (P = 0.000). Patient-related independent risk factors for the development of L5-S1 diseases included gender (OR = 0.41, P = 0.016) and BMD (OR = 0.42, P = 0.000). Surgical-related independent risk factors for the development of L5-S1 diseases included fusion level (OR = 2.64, P = 0.033) and postoperative sacral slope (OR = 1.43, P = 0.000).ConclusionsGender and BMD were the most common patient-related independent risk factors, Fusion levels and postoperative sacral slope were the most common surgical-related independent risk factors. Prevention of these risk factors can reduce the incidence of L5-S1 diseases in patients with long floating fusion.