Clinical Outcomes of Two Institution-Specific Cervicothoracic Interlaminar Epidural Steroid Injection Protocols (C7/T1–6 mL vs. T1/T2–8 mL) in Cervical Radiculopathy: A Multicenter Retrospective Cohort Study

Background: Cervical radiculopathy is a common and disabling condition with both nociceptive and neuropathic pain components. Epidural steroid injections (ESIs) are widely used as an interventional treatment modality; however, the optimal cervicothoracic interlaminar access level and injectate volume remain subjects of ongoing debate. Because injection level and injectate volume have historically been varied together in routine practice rather than independently, prospectively designed comparative data are lacking. Methods: In this retrospective, multicenter cohort study, 166 patients with MRI-confirmed cervical radiculopathy treated between January 2022 and December 2025 at three participating institutions received fluoroscopy-guided cervicothoracic interlaminar epidural steroid injections with dexamethasone and bupivacaine at either C7/T1 (6 mL; n = 87) or T1/T2 (8 mL; n = 79), with protocol determined by the treating institution rather than randomization. The prespecified primary outcome was the baseline-adjusted between-group difference in arm-pain Numeric Rating Scale (NRS) score at 3 months, analyzed by analysis of covariance (ANCOVA) adjusted for a directed acyclic graph-informed covariate set (age, symptom duration, baseline pain severity, number of stenotic levels, DN4 score, and treatment center); the same covariates were used in a generalized estimating equation (GEE) model with a group-by-time interaction and in a multivariable logistic regression for treatment response. Secondary outcomes—neck-pain NRS and VAS, neuropathic pain (DN4), functional disability (NDI), quality of life (SF-36, EQ-5D), Patient Global Impression of Change (PGIC), analgesic consumption, and cardiovascular/metabolic safety outcomes—were assessed at baseline, 3 months, and 6 months. Results: Both groups showed significant within-group reductions in arm-pain NRS (C7/T1: 8.7 ± 0.4 to 3.5 ± 0.4 at 3 months and 4.1 ± 0.6 at 6 months; T1/T2: 9.2 ± 0.7 to 3.9 ± 0.5 at 3 months and 4.9 ± 0.7 at 6 months; both p < 0.001). Baseline pain scores and symptom duration were not balanced between groups (baseline-adjusted analysis was therefore used). After adjustment for baseline severity, age, symptom duration, and center, the T1/T2–8 mL protocol was associated with higher (worse) adjusted arm-pain NRS than the C7/T1–6 mL protocol at 3 months (adjusted difference 0.41 points, 95% CI 0.21–0.61) and 6 months (0.66 points, 95% CI 0.35–0.97); a multivariable-adjusted logistic regression model likewise showed lower odds of achieving a ≥50% arm-pain reduction at 3 months with the T1/T2–8 mL protocol (adjusted OR 0.18, 95% CI 0.04–0.82). NDI decreased from a mean of 48.1 points at baseline to 28.1 points at 3 months (pooled cohort, score capped at the 0–50 scale maximum; the majority of baseline NDI source records could not be individually verified and this is reported as a limitation), and analgesic consumption decreased over follow-up. Among hypertensive patients (45/166, 27.1%), 78% experienced transient blood pressure elevation and 40% required temporary antihypertensive adjustment; among diabetic patients (13/166, 7.8%), 92% developed transient hyperglycemia. Because injection level, injectate volume, and treatment center were confounded by design, these findings should be interpreted as a comparison of two center-specific treatment protocols rather than an isolated effect of anatomical level or volume. Conclusions: Both center-specific cervicothoracic interlaminar epidural steroid injection protocols were associated with improvements in pain and function over six months, with no catastrophic procedural complications documented; however, near-complete confounding of injection level with injectate volume and treatment center, together with imbalanced baseline pain severity, precludes conclusions about the comparative effectiveness of C7/T1 versus T1/T2 access. Transient cardiovascular and metabolic effects were common and support consideration of post-procedural monitoring in patients with pre-existing hypertension or diabetes.