Instrumentation-Related Complications Following Nonfusion Posterior Fixation in Patients with Metastatic Spinal Tumors: Incidence and Risk Factors

<b>Background/Objectives</b>: Previous studies have reported satisfactory outcomes and low rates of instrumentation-related complications (IRCs) following nonfusion posterior fixation in patients with metastatic spinal tumors (MSTs). However, to adequately assess the longevity and durability of nonfusion instrumentation in patients with longer life expectancy, an extended follow-up period is essential. This study aims to evaluate the incidence of and risk factors for IRCs in patients with MSTs who underwent nonfusion posterior fixation and had radiographic follow-up data available for at least one year postoperatively. <b>Methods</b>: Consecutive data were collected from patients who underwent pedicle screw-based posterior fixation without fusion for MSTs in the thoracic and/or lumbar region from 2005 to 2018. The IRCs included screw loosening, screw pull-out, and metal breakage. The IRC-free survival and related factors were analyzed by Kaplan-Meier survivorship analysis with the log-rank test within a minimum follow-up period of one year. A multivariate analysis was performed using a Cox proportional-hazards regression model. <b>Results</b>: In total, 61 patients were included. The mean follow-up period was 28.3 months (range: 12.0-102.6 months). There were 27 cases (44.2%) of IRCs, including 22 cases of screw loosening, four cases of screw pull-out, and one case of rod breakage, at an average of 9.6 months (range: 1.0-38.1 months). The median IRC-free survival was 38.1 months (range: 1.0-102.6 months). Only three patients experienced pain aggravation with IRCs. No revision surgery was performed. A multivariate analysis identified that fixation length was a risk factor for IRCs (odds ratio: 0.358, 95% confidence interval: 0.114-0.888; <i>p</i> = 0.027). <b>Conclusions</b>: IRCs are frequent but mostly asymptomatic after nonfusion posterior fixation in patients with MSTs followed up for at least one year. Overall, the IRC-free survival was long enough considering the patient survival. Fixation length was a significant risk factor for IRCs regardless of MST location.