Risk factors for cage subsidence following anterior-posterior spinal fixation in osteoporotic vertebral fractures: a multicenter retrospective study.

Abstract

Retrospective multicenter cohort study. This study aimed to evaluate the incidence of cage subsidence and its impact on the clinical outcomes of anterior-posterior spinal fixation (APSF) for osteoporotic vertebral fractures (OVFs). It also aimed to identify the risk factors for cage subsidence. The risk factors for cage subsidence after APSF for OVFs remain unclear. This multicenter retrospective cohort study included patients who underwent combined APSF using an expandable cage system, with a minimum 1-year follow-up at multiple centers. Patients were divided into cage subsidence (n=53) and non-subsidence (n=47) groups. Demographic data, surgery-related factors, and radiographic parameters were analyzed. After univariate analysis of factors associated with cage subsidence, multivariate logistic regression was used to identify related factors. The demographic data showed a significant difference in Hounsfield unit (HU) (102.6±28.3 vs. 80.0±30.6, p=0.005) and endplate injury (p<0.001). Furthermore, 1A1B fixation was significantly more common in the subsidence group (p<0.001). Radiographic data showed significant differences in Δlocal kyphosis (supine-standing) (-7.1°±9.2° vs. -14.6°±11.5°, p=0.001). Multivariate analysis showed that Δlocal kyphosis (supine-standing) (adjusted odds ratio [aOR], 12.8; p=0.010), HU (aOR, 8.1; p=0.033), fixation range (aOR, 8.2; p=0.020), and endplate injury (aOR, 18.8; p=0.011) were significant risk factors for subsidence. Intraoperative endplate injury, low HU (<87.5), short fusion, and preoperative vertebral instability (Δlocal kyphosis [supinestanding] <-14) were identified as risk factors for cage subsidence in APSF. Therefore, extending the fusion levels in patients with low HU values and significant preoperative vertebral instability should be considered to avoid intraoperative endplate injury.