summary SI Joint Infections are rare infections in the pediatric population most commonly associated with progressive low back and buttock pain. Diagnosis is generally made with MRI studies. Treatment is nonoperative with antibiotics targeted towards the specific organism in the majority of cases. Surgical debridement is indicated in the presence of abscess or lack of response to antibiotics. Epidemiology Incidence rare and only accounts for 1-2% of cases of septic arthritis Demographics more common in children over the age of 10 than adults Risk factors in adults intravenous drug abuse immune suppression pregnancy trauma infective endocarditis sepsis TB Etiology Pathophysiology microbiology staphylococcus aureus login to view 1 more bullet mycobacterium tuberculosis login to view 1 more bullet Salmonella login to view 1 more bullet Presentation Symptoms progressive low back and buttock pain unable to bear weight on affected side secondary to pain fever Physical exam pain worsened by compression of the iliac wings palpation of the right sacroiliac (SI) joint motion normal hip range of motion provocative tests Faber test login to view 1 more bullet Imaging Radiographs indication painful SI joints views AP and lateral pelvis optional views inlet/outlet views findings joint destruction partial or complete fusion periarticular osteopenia widening and cavitation MRI is the most sensitive diagnostic study for SIJ infection findings in the acute phase intra-articular fluid or gas subchondral bone marrow edema articular and periarticular post-gadolinium enhancement and soft tissue edema findings in chronic phase periarticular bone marrow reconversion replacement of articular cartilage by pannus bone erosion subchondral sclerosis joint space widening or narrowing and ankylosis outcomes more sensitive than CT scan Studies Serum labs elevated WBC elevated ESR (>50) elevated CRP (>70) Blood cultures may be positive and should be obtained prior to starting antibiotics Treatment Nonoperative antibiotics targeted towards the specific organism indications login to view 1 more bullet technique login to view 1 more bullet Operative surgical debridement only - rarely needed in children indications login to view 3 more bullets debridement and SI joint arthrodesis indications login to view 3 more bullets outcomes login to view 2 more bullets Complications chronic pain recurrent infection delayed wound healing hardware complications sepsis