summary Sacroiliitis is an inflammatory condition of the sacroiliac joint that can cause persistent low back and posterior pelvic pain Diagnosis is made with contrast-enhanced MRI demonstrating fluid/inflammation in the SI joint and possible abscess formation Treatment is usually nonoperative, consisting of NSAIDs and rest, with IV antibiotics reserved for infection. Surgical debridement is indicated in the presence of an abscess Epidemiology Demographics most commonly presents in teenagers to middle-age adults login to view 1 more bullet Associated conditions commonly part of ankylosing spondylitis or Reiter's syndrome Etiology Pathophysiology can stem from a traumatic event or infection pregnancy may predispose often stems from chronic inflammation of the SI joints can lead to fibrosis and ossification within the SI joints Associated conditions ankylosing spondylitis login to view 2 more bullets Reiter's syndrome login to view 1 more bullet Presentation Symptoms pain with prolonged standing difficulty climbing stairs generalized low back pain weakness of the hip musculature on the affected side morning stiffness Physical exam FABER test login to view 1 more bullet ankylosing spondylitis may be associated with the following: login to view 2 more bullets Imaging Radiographs may show some erosive changes in the bone, although these findings are nonspecific may show calcifications or sclerosis within the SI joint MRI is the study of choice with gadolinium T2-weighted images may show fluid/inflammation in the SI joint and/or a possible abscess Studies Labs WBC login to view 2 more bullets ESR/CRP login to view 1 more bullet blood cultures login to view 1 more bullet HLA-B27 login to view 1 more bullet Treatment Depends on underlying cause infection login to view 5 more bullets trauma or overuse login to view 3 more bullets pregnancy login to view 2 more bullets when occurring as part of a broader spondyloarthropathy login to view 2 more bullets Prognosis Depends on the underlying cause, but most cases eventually resolve