 The sacroiliac SI joint is a common source of low back pain. Radiofrequency ablation RFA can be used to treat low back pain from the SI joint , and is often recommended by physicians to provide long lasting pain relief. However, the use of RFA for SI joint pain has not been as successful as RFA for pain in other areas of the back and neck. X-ray guidance fluoroscopy is currently used to perform this procedure. Under fluoroscopy, however, it can be difficult for physicians to identify necessary landmarks, and there are risks to the patient because of radiation exposure. In contrast, ultrasound may provide better image guidance than fluoroscopy, and there is no radiation risk. The purpose of this study is to examine if ultrasound guided SI joint RFA is effective. 