summary Sacroiliitis is an inflammatory condition of the sacroiliac joint that can cause persistent low back and posterior pelvic pain. Diagnosis is made with MRI studies with contrast showing fluid/inflammation at the SI joint and possible abscess. Treatment is usually nonoperative with NSAIDs and rest, with IV antibiotics reserved for infections. Surgical debridement is indicated in the presence of an abscess. Epidemiology Demographics most commonly presents in teen to middle-aged individuals males > females Associated conditions commonly part of ankylosing spodyliitis or Reiter's syndrome Etiology Pathophysiology can stem from traumatic event or infection pregnancy may lead to increased incidence in some females often stems from chronic inflammation of SI joints can lead to fibrosis and ossification within SI joint Associated conditions ankylosing spodyliitis associated with HLA-B27 1-2% of all individuals will have HLA-B27 Reiter's syndrome oligoarticular arthritis, conjunctivitis and urethritis joint arthritis Presentation Symptoms pain with prolonged standing difficulty climbing stairs generalized low back pain weakness from hip musculature on affected side morning stiffness Physical exam FABER test pain with flexion, abduction, and external rotation of hip ankylosing spondylitis associated with spinal flexion deformities starting in T and L spines Imaging Radiographs may show some erosive changes in the bone, but it’s not specific may show calcifications or sclerosis within SI joint MRI is study of choice use gadolinium T2’s show fluid/inflammation at the SI joint and maybe an abscess Studies Labs WBC usually normal can be elevated with infection ESR/CRP usually elevated blood cultures are positive in 50% HLA-B27 check for rheumatoid factor (should be negative for true Ankylosing spondylitis) Treatment Depends on cause infection IV antibiotics until symptoms and the CRP resolve then put on orals antibiotic surgery may be necessary if this fails or if there is a large abscess trauma or overuse rest, activity modification, NSAIDS, corticosteroid injections indications most resolve with soft tissue rest and activity modification pregnancy observation typically resolves after childbirth part of larger spondylopathy aggressive PT, NSAIDs, TNF inhibitors severe symptoms may require TNF inhibitors or other similar medications Prognosis Depends on cause but most patients will eventually resolve the episode and continue without issues