The goal of this observational study is to learn if Nevro1 Sacroiliac Transfixing and Fusion System can treat sacroiliac joint dysfunction in males or females over 21. The main questions it aims to answer is what percentage of patients have clinically important pain relief with no adverse events, and what proportion of patients have fusion of the sacroiliac joint at 1 year and 2 years.

Inclusion Criteria:

1. Has medical insurance that covers this standard of care procedure and all other anticipated and unanticipated procedure-related care, and all coverage criteria required by insurer are met, which may include but are not limited to:

   • Has had low back and/or buttock pain for at least 6 months that is inadequately responsive to non-surgical care
   • Has a positive Fortin's test
   • Has a diagnosis of SIJ dysfunction (degenerative sacroiliitis or SI disruption) with pain elicited on at least 3 of 5 provocative tests (FABER, Gaenslen, Distraction, Thigh Thrust, Compression).
   • At least 75% reduction in pain for the expected duration of two anesthetics (on separate visits each with a different duration of action), and the ability to perform previously painful maneuvers, following an image-guided, contrast-enhanced intra-articular (diagnostic) SIJ injection
   • A trial of at least one therapeutic intra-articular SIJ injection (i.e. corticosteroid injection)

2. Has an ODI score ≥30% at enrollment

3. Has a SI joint pain score of at least 5 out of 10 on numerical rating scale at enrollment.

4. Be at least 21 years of age at enrollment

5. The patient's physician has decided that the best treatment for the patient's SIJ dysfunction is the Nevro1 SI Fixation System, and the patient has agreed to the treatment

6. Be willing and capable of giving written informed consent

7. Be mentally and physically able to comply with study-related requirements and procedures and attend all scheduled visits

Exclusion Criteria:

1. Has current severe back pain due to other causes, such as lumbar disc degeneration, lumbar disc herniation, lumbar spondylolisthesis, lumbar spinal stenosis, lumbar facet degeneration, lumbar radicular pain, and lumbar vertebral body fracture
2. Has SIJ pain secondary to inflammatory conditions or other known sacroiliac pathology such as: Sacral dysplasia, inflammatory sacroiliitis (e.g., ankylosing spondylitis or other HLA-associated spondylo-arthropathy), tumor, infection, acute fracture, and crystal arthropathy
3. Has had a previous SIJ implant placement, including an allograft
4. Has had an injection with corticosteroid into the index SIJ within the last 30 days
5. Has had a sacral radiofrequency ablation within the last 6 months
6. Has a history of recent (<1 year) major trauma to pelvis
7. Has previously diagnosed or suspected severe osteoporosis (defined as prior T-score < -2.5 or history of osteoporotic fracture)
8. Has a chronic rheumatologic condition (e.g., rheumatoid arthritis)
9. Has a known allergy to titanium or titanium alloys
10. Has a current local or systemic infection that raises the risk of surgery
11. Is currently receiving or seeking short- or long-term worker's compensation related to the SI joint or low back pain, is currently receiving disability remuneration related to SI joint or low back pain, and/or is currently involved in injury litigation related to the SI joint or low back pain
12. Is participating in an investigational study or has been involved in an investigational study within 3 months prior to enrollment
13. Has any condition or anatomy that makes treatment with the Nevro1 SI Fixation System infeasible
14. Is taking a medication known to have detrimental effects on bone quality and soft tissue healing
15. Has a prominent neurologic condition that would interfere with physical therapy
16. Be pregnant or plan on becoming pregnant in the next two years.
17. Has a medical condition or pain in other area(s), not intended to be treated in this study, that could interfere with study procedures, accurate pain reporting, and/or confound evaluation of study endpoints, as determined by the Investigator

Cohort will be selected from participating clinics

Study data will be reported with descriptive statistics describing group level outcomes, not individual outcomes.