Inclusion Criteria:  Evidence of sacroiliitis on earlier standard of care MRE between 2014 and 2018. Confirmed diagnosis of Crohn's Disease Known HLA-B27 status at time of enrollment and most recent clinical ESR and CRP results from chart (from day of visit or within past 4 weeks of study visit) Adults >18 years of age  Exclusion Criteria:  History of other inflammatory arthritis (e.g. rheumatoid arthritis, systemic lupus erythematosus, gout). Contraindication to MRI. History of malignancy <5 years in remission, (except for non-melanomatous skin cancer). Inability to comply with study protocol. Critically ill patients. Pregnant patients. Non-English speaking patients (as the questionnaires used in this study are not validated in other languages)