Incidence of Unintentional Flow of Contrast into the Facet Joints during Fluoroscopy-Guided Cervical Interlaminar Epidural Injections: A Retrospective Cohort Study

Objective. We sometimes encounter unintentional flow of contrast into the facet joints during cervical interlaminar epidural injection, which leads to false-positive epidural injection. The purposes of this study were to evaluate the rate of facet flow of contrast and to investigate various factors associated with injection into the space of Okada during fluoroscopy-guided cervical interlaminar epidural injection. Setting and Subjects. Images from consecutive cases of fluoroscopy-guided cervical interlaminar epidural injection performed at a single institution between July 2015 and July 2018 were obtained and reviewed. Methods. Cases of epidural injection were classified as either facet flow or no facet flow. Multivariate logistic regression was used to identify the predictive factors of unintended injection into the Okada space. Results. A total of 2,006 cases were included. Intra-articular flow was identified in 6.0% of cases (121/2,006). All cases of flow of contrast into the facet joints were recognized, and appropriate epidurograms were obtained during the procedures. The highest rate of unintended facet flow of the contrast (10.1%, 44/436) occurred at C5–6. Cervical interlaminar epidural injection at C5–6 and above (adjusted odds ratio [aOR] = 1.929, P = 0.001) and the paramidline approach for epidural injection (aOR = 2.427, P < 0.001) were associated with injection into the space of Okada. Conclusions. We detected injection into the space of Okada during fluoroscopy-guided cervical interlaminar epidural injection in 6.0% of procedures. Cervical interlaminar epidural injection at C5–6 and above and the paramidline approach for epidural injection were positive predictors of unintentional facet flow of the contrast.