Needle Trajectory Influences Foraminal Contrast Distribution and Pain Reduction Following Paramedian Cervical...

Background and Objectives: Paramedian cervical interlaminar epidural steroid injection (CESI) is commonly used for cervical radicular pain and is considered safer than the transforaminal approach. However, its clinical effectiveness may be influenced by contrast distribution patterns, although these may not fully reflect actual drug delivery. This study aimed to evaluate the association between needle trajectory, foraminal or periradicular contrast distribution patterns, and short-term pain reduction following paramedian cervical interlaminar CESI. Materials and Methods: This single-center retrospective study included 109 patients who underwent paramedian cervical interlaminar CESI. Needle trajectory was classified as inward or outward. Contrast distribution was graded based on anteroposterior (AP) spread patterns. Pain intensity was assessed using a numeric rating scale (NRS) at baseline and 2 weeks after the procedure. Group comparisons were performed using Welch's t-test and chi-square or Fisher's exact test, as appropriate. Effect sizes were calculated using Cohen's d and η². Multivariable linear regression analysis was performed adjusting for age, sex, baseline NRS, and target level. Results: The outward trajectory group demonstrated a significantly higher proportion of Grade 2 contrast spread compared to the inward group (69.8% vs. 8.9%, p < 0.001). Higher AP contrast spread grades were associated with greater pain reduction (β = 0.83, 95% CI: 0.44-1.22, p < 0.001; η² = 0.14). In addition, patients in the outward trajectory group showed greater NRS reduction than those in the inward group (2.96 vs. 1.71, mean difference: 1.25, 95% CI: 0.74-1.76, p < 0.001; Cohen's d = 0.96). In multivariable analysis, needle trajectory remained significantly associated with pain reduction, whereas AP contrast spread grade was not independently associated. Conclusions: Needle trajectory was associated with contrast distribution patterns and short-term pain reduction following paramedian cervical interlaminar CESI. An outward-directed trajectory was associated with greater foraminal or periradicular contrast spread and greater pain reduction. These findings suggest that needle trajectory may represent a clinically relevant procedural factor influencing clinical outcomes.