Incidence and Predictors of Hardware Failure After Instrumentation for Spine Metastasis: A Single-Institutional Series

Objective: We report a retrospective analysis of hardware failure in patients requiring instrumentation for spinal metastasis. Methods: In a retrospective study at a single institution, we identified 58 patients who underwent spinal instrumentation for metastasis from 2012 to 2018. Hardware failure was defined as screw pullout/loosening, cage migration, progressive kyphosis, or an otherwise-noticeable instrumentation deficit detectable on imaging. Risk factors for hardware failure with a P < 0.05 in in univariate were included in multivariate logistic regression models controlled for age, sex, and previously identified risk factors for hardware failure. Results: In total, 58 patients required instrumentation for metastatic spine disease. Median age was 60.2 years (interquartile range 49.0–66.3), 38 patients (65.5%)were male, and median follow-up was 8.1 months (interquartile range 3.1–20.7). Eight patients (13.8%)developed signs of hardware failure during follow-up, of whom 2 patients (3.4%)underwent operative revision. In univariate analysis, Eastern Cooperative Oncology Group performance status >2 (P = 0.049)and multiple myeloma lesions (P = 0.010)were significant predictors of failure. Both factors maintained significance in a multivariate logistic regression model controlled for age, sex, history of spine radiation, and number of fused levels with P = 0.047; odds ratio 12.7 (95% confidence interval 1.03–156.4)for Eastern Cooperative Oncology Group performance status over 2 and P = 0.012; odds ratio 31.5 (95% confidence interval 2.2–460.0)for multiple myeloma lesions. Conclusions: The rate of hardware failure in this cohort was 13.8%, although operative revision rate was 3.4%. Spinal instrumentation in patients with poor preoperative functional status or multiple myeloma may be more likely to develop instrumentation failure.