Parameters in electrode positioning in thoracic percutaneous facet denervation: an anatomical study

The purpose of the present study was to verify if needle placement in thoracic percutaneous facet denervation (PFD), based on bony landmarks, and under fluoroscopic guidance, would lead to constant anatomical positioning; and hence to an adequate placement at the assumed target, i.e., the medial branch of the dorsal ramus of the spinal nerve; and furthermore to determine if interpretation of the needle position by CT is more reliable than by fluoroscopy. The procedures were carried out bilaterally at all 12 levels on two cadavers, simulating the clinical setting as much as possible. In 44 cases the position of the needles was determined on hard copies of fluoroscopic images, 1.5 mm interval CT-images, surface-photographs, and on counterstained 25 microns sections obtained by a multirange heavy duty cryomicrotome. The sections established that standardized use of bony landmarks under fluoroscopic control can result in reproducible anatomical needle positioning in thoracic PFD. Nervous tissue was hit in 27 (61%) cases, but the supposed target structure, i.e., the medial branch "stem" was never hit. In none of the procedures was an accidental pleural puncture observed. The correlation between fluoroscopic images and sections was poor. The correlation between CT and sections was better, except for the mediolateral direction. The results of the present study suggest that "pure" anatomical positioning based on bony landmarks analogous to those used in the lumbar region is not reliable enough for thoracic PFD, and that corrections after electrostimulation substantially contribute to obtaining an adequate position of the needle.