iFuse Implant System® Minimally Invasive Arthrodesis

Inclusion Criteria: 1. Age 21-70 at time of screening 2. Patient has lower back pain for \>6 months or \>18 months for pregnancy induced lower back pain 3. Diagnosis of the SI joint as the primary lower back 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), and b. Patient has at least 3 of 5 physical examination maneuvers specific for SI joint pain, and 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(s) (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 50 on 0-100 point VAS 6. Patient has signed study-specific informed consent form 7. Patient has the necessary mental capacity to participate and is physically able to comply with study protocol requirements Exclusion Criteria: 1. Severe lower 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. Known allergy to titanium or titanium alloys 9. Use of medications known to have detrimental effects on bone quality and soft-tissue healing 10. Prominent neurologic condition that would interfere with physical therapy 11. Current systemic infection or local infection at the SI joint 12. Currently pregnant or planning pregnancy in the next year 13. Known or suspected drug or alcohol abuse 14. Diagnosed psychiatric disease (e.g., schizophrenia, major depression, personality disorders) that could interfere with study participation 15. Patient is participating in an investigational study or has been involved in an investigational study within 3 months of surgery