Background: Septic sacroiliitis is often difficult to diagnose because the clinical findings can be misleading and the radiological signs delayed.
Case report: A 16-year-old adolescent was hospitalized with a history of fever and painful hip. The initial hypothesis of hip osteoarthritis was not confirmed by ultrasonography or CT-scan. The bone scan was also normal. The definitive diagnosis of sacroiliitis was made 1 week later based on the clinical evolution and a positive blood culture. It was confirmed by a second bone scan and MR imaging.
Conclusion: Examination of the sacroiliac joint needs several different tests. Although the initial bone scan may be normal, an osteoarticular infection cannot be definitively ruled out and iterative radiological investigation is warranted. MR imaging may be an additional diagnostic tool for detecting sacroiliitis.