THE ABILITY OF LUMBAR MEDIAL BRANCH BLOCKS TO ANESTHETIZE THE ZYGAPOPHYSIAL JOINT - A PHYSIOLOGICAL CHALLENGE

Study Design. Randomized, controlled, single-blinded study. Objectives . To determine the physiologic effectiveness of lumbar medial branch b locks. Summary of Background Data. Zygapophysial joint pain can be dia gnosed by anesthetization of the joint or its nerve supply (the medial branch divisions of the dorsal rami). The physiologic effectiveness o f lumbar medial branch blocks has been assumed but not proven. Methods . Eighteen asymptomatic individuals were randomly assigned to either L 4-L5 or L5-S1 zygapophysial joint injections with contrast medium unti l capsular distention elicited pain without extracapsular contrast spr ead. One week later, 15 blinded individuals underwent two randomized s aline or 2% lidocaine medial branch injections that correlated to the innervation of the previously injected joint. Medial branch injections were performed such that inadvertent venous uptake was avoided in 14 individuals. Thirty minutes after medial branch injections, these 14 i ndividuals underwent repeal capsular distention of the same zygapophys ial joint provoked the prior week in an attempt to elicit another pain ful response. Results. All five control individuals who received salin e medial branch injections felt pain on repeat capsular distention. Ni ne individuals received 2% lidocaine medial branch blocks; eight fell no pain, and one felt pain on repeat capsular distention. Conclusions. There was a significant effect of 2% lidocaine (versus saline) medial branch injections on anesthetization of the zygapophysial joint when venous uptake was avoided during these injections. When properly perfo rmed, lumbar medial branch blocks successfully inhibit pain associated with capsular distention of the lumbar zygapophysial joints at a rate of 89%.