Prolonged response following anesthetic-only medial branch blocks: A retrospective analysis of 410 consecutive procedures.

Introduction: Medial branch blocks (MBBs) are procedures using short-acting local anesthetics to identify candidates for radiofrequency neurotomy (RFN) in suspected facet-mediated pain. Although primarily prognostic tools, some studies report therapeutic responses to MBBs done with or without added corticosteroid, with rates ranging from 11% to over 50%. Even if intended as a diagnostic procedure, prolonged responses to anesthetic-only MBBs, defined as persisting days to months, well beyond the hours-long pharmacokinetic window of the local anesthetic, represent a diagnostic issue to physicians with a poorly defined incidence. This study retrospectively evaluated 410 consecutive MBBs to determine the proportion achieving documented sustained pain relief following anesthetic-only MBBs. Methods: We retrospectively analyzed 410 consecutive MBBs performed during 2019 at a single academic institution by 4 fellowship-trained physiatrists. All procedures were performed using either 0.25 mL or 0.5 mL of 2% lidocaine or 0.5% bupivacaine. Therapeutic response was defined as meeting all three criteria: ≥80% pain relief calculated from chart records; no progression to repeat block or radiofrequency neurotomy; and explicit clinical documentation of sustained relief as the rationale for halting treatment. Chart review identified patients who did not progress for other reasons including insurance denial, patient preference, loss to follow-up, or alternative treatments. 95% confidence intervals were calculated for therapeutic response rates. Follow-up was retrospective and based on subsequent available medical record review rather than a standardized prospective assessment interval. Results: 410 patients underwent medial branch blocks of the cervical or lumbar spine in the study period. Eight patients (1.95%; 95% CI: 0.85-3.81%) met criteria for prolonged response with documented sustained benefit. Of these, minimum confirmed durations of relief ranged from 21 to 331 days (median 53 days; mean 86.5 days). An additional 11 patients (2.7%) did not progress but lacked documented rationale. Conclusions: This represents the lowest rate of prolonged pain relief following MBBs reported in published literature. Our findings do not support the premise that routine anesthetic-only MBBs have therapeutic benefit. This study is the first to quantify the incidence of how often a MBB intended for diagnostic purposes halts further treatment due to unexplained pain relief.