SPECIFICITY OF LUMBAR MEDIAL BRANCH AND L5 DORSAL RAMUS BLOCKS - A COMPUTED-TOMOGRAPHY STUDY

Study Design. A cross-sectional study. Objectives. To determine the fa ce validity of lumbar medial branch blocks. Summary of Background Data . Lumbar medial branch blocks have been used increasingly to diagnose zygapophysial joint pain. The course and relations of the medial branc hes of the dorsal rami have been demonstrated in previous anatomic stu dies. What is not known is whether blocks of the medial branches anest hetize these nerves exclusively or whether they anesthetize other stru ctures that are potential sources of pain. Methods. In a cadaveric stu dy, the branches of the dorsal rami were exposed. Spinal needles were placed over the nerves, and plain radiographs were taken to demonstrat e the precise radiographic locations of the nerves. In the second phas e of the study, healthy volumteers underwent injections of radiographi c contrast over the nerves, and plain radiographs and computed tomogra phic images were taken. Injections were performed using different rate s of injection and in two positions for each nerve. Results. Radiograp hic contrast incorporated the medial branches of the dorsal rami in ev ery injection. When injections were performed using the upper position , aberrant flow of contrast medium was demonstrated with extension int o the epidural space or intervertebral foramina. When a position lower on the transverse process was selected, aberrant flow was very uncomm on. Eight percent of injections were found to be intravenous. Conclusi ons. When the appropriate technique is used, medial branch blocks are target specific. To guard against false-negative responses due to intr avenous uptake, contrast medium must be used before the injection of l ocal anaesthetic.