The purpose of this study is to evaluate the long term safety and effectiveness of SI joint fusion using the iFuse Implant System in patients with degenerative sacroiliitis (DS) and/or sacroiliac joint disruptions (SD).

Study Design: This study is extended follow-up from two ongoing multicenter prospective US clinical trials. All participants have already undergone the surgical procedure of interest (SI joint fusion with iFuse Implant System). The two ongoing trials are:

• SIFI:( Sacroiliac Joint Fusion with iFuse Implant System) a single-arm trial of patients with degenerative sacroiliitis or sacroiliac joint disruption who underwent iFuse placement, and
• INSITE(Investigation of Sacroiliac Fusion Treatment): a randomized clinical trial of the same patient population who underwent either non-surgical treatment or iFuse placement

Inclusion Criteria:

1. Patient enrolled and treated in SIFI or patient initially randomized to iFuse and treated in INSITE. Note: Patient may be in the initial follow up period associated with SIFI or INSITE at the same time they consent for this study and "extend" their post-operative follow up.
2. Patient has signed study-specific LOIS informed consent form.
3. Patient has the necessary mental capacity to participate and is physically able to comply with study protocol requirements.

Exclusion Criteria:

1. Treated with iFuse as a "crossover" in INSITE.
2. Currently pregnant or planning pregnancy within 5 years of iFuse Implant.
3. Patient is a prisoner or a ward of the state.
4. Known or suspected active drug or alcohol abuse.
5. Inadequately treated psychiatric illness (e.g., schizophrenia, major depression, personality disorders) that could interfere with study participation.
6. Unwilling to perform the long-term follow up requirements of this study.
7. Patient has any condition that could substantially prevent long-term follow-up.
8. Unwilling to return to site at pre-specified study visits.

Subjects with degenerative sacroiliitis or sacroiliac joint disruption who underwent iFuse placement.