Sacroiliac Joint Fusion Versus Sham Operation for Treatment of Sacroiliac Joint Pain

Inclusion Criteria: 1. Age 21-70 at time of screening 2. Patient with suspected SIJ pain for \>6 months or \>18 months for pregnancy induced pelvic girdle pain. 3. Diagnosis of the SI joint as the primary pain generator based on ALL of the following: A. Patient has pain at or close to the posterior superior iliac spine (PSIS) with possible radiation into buttocks, posterior thigh or groin and can point with a single finger to the location of pain (Fortin Finger Test) B. Patient has at least 3 of 6 physical examination maneuvers specific for SI joint pain: 1. Compression 2. Posterior Pelvic Pain Provocation test - P4 (Thigh Thrust) 3. Palpation of the long dorsal ligament 4. Patrick's test (Faber) 5. Leg Raise (ASLR ) 6. Geanslens test C. Patient has improvement in lower back pain NRS of at least 50% of the pre injection NRS score after fluoroscopic controlled injection of local anesthetic into affected SI joint (including previous documented test \<6 months ago) 4\. Baseline Oswestry Disability Index (ODI) score of at least 30% 5\. Baseline lower back pain score of at least 5 on 0-10 point NRS 6\. Patient should have tried adequate forms of conservative treatment with little or no response. 7\. Patient has signed study-specific informed consent 8\. Patient has the necessary mental capacity to participate and is physically able to comply with study protocol requirements. 9\. Patients with unilateral or bilateral pain can be included in the study if they clearly can differentiate between the two sides. It is the most painful side that will be included and randomized to SIJ fusion or sham surgery in the study. Exclusion Criteria: 1. Severe low back pain due to other causes, such as lumbar disc degeneration, lumbar disc herniation, lumbar spondylolisthesis, lumbar spinal stenosis, lumbar facet degeneration, and lumbar vertebral body fracture. 2. Sacroiliac pathology caused by auto-immune disease (e.g. ankylosing spondylitis) and/or neoplasia (e.g. benign or malignant tumor) and/or crystal arthropathy 3. History of recent (\<1 year) fracture of the pelvis with documented malunion, non-union of sacrum or ilium or any type of internal fixation of the pelvic ring. 4. Spine surgery during the past 12 months. 5. Previously diagnosed or suspected osteoporosis (defined as prior T-score \<-2.5 or history of osteoporotic fracture) 6. Documented osteomalacia or other metabolic bone disease 7. Any condition or anatomy that makes treatment with the iFuse Implant System infeasible 8. Patients with prior successful fusion to the contra lateral side are exluded from the study.