 Current practice is to perform the SIJ posterior sensory blocks and RFA under fluoroscopic guidance. Research has confirmed that SIJ RFA can provide significant relief, however, the success rate and magnitude of relief are variable. Part of this variability may relate to the challenging nature of identifying key anatomical landmarks under fluoroscopy - their location may not be clearly evident with fluoroscopy particularly if the patient is obese, has low bone mineral density or has abundant bowel gas andor stool in the pelvis. 