 SIJ RFA: Ultrasound-guided RFA of the PSN will be performed using the same technique as the local anesthetic block with the exception that 2 Nimbus multitined electrodes will be used in a bipolar configuration. The electrodes will be placed along the lateral crest using a sequential, leap-frogging technique from the inferomedial aspect of the PSIS at or just above the level of the S1 dorsal sacral foramen if visible, or the S1 spinous process if not to the third transverse sacral tubercle at 1.5-2 cm intervals at the skin surface. A radiofrequency current will be passed for 120 seconds per site thus raising the temperature at the dorsal periosteum and adjacent soft tissue to 80C resulting in thermal coagulation of the plexus. Prior to performing the thermal lesion, electrical stimulation at 2 Hz and 2.0 V will be administered. If the patient perceives, or the operator observes muscle contraction of the leg or anal sphincter, no radiofrequency current will be applied and the needle tip will be adjusted to a position away from where the sacral nerve roots may lie. 