The sacroiliac joint accounts for approximately 16% to 30% of cases of chronic low back pain, which is often overlooked. Especially young adults, when they complain of pain of the buttock, the reason is often thought to be the lumbar disc herniation, after conventional treatment, the symptoms often did not improve significantly.
In fact, it is difficult to distinguish sacroiliac joint disease from other causes of low back pain based on history alone. Accurate diagnosis is often delayed because of the low incidence of the disease, low clinical suspicion rate, and demonstrating similar symptoms with hip, lumbar and abdominal lesions. Clinical manifestations are often diverse, and symptoms and examination results often indicate more common diseases, such as septic arthritis of the hip, lumbar disc herniation or pelvic abscess. The most likely reason may be that clinicians lack of understanding of the disease, the clinical manifestations are not typical, the infection site is not definite, and imitate the characteristics of hip joint suppurative arthritis, iliac osteoarthritis and lumbar disc herniation[1-3].
Sacroiliac joint infection is relatively rare, representing 1%-2% of all cases of septic arthritis[4], and is usually associated with multiple predisposing factors, including intravenous drug abuse, immune suppression, pregnancy, trauma and infection elsewhere in the body[5]. On the early stage X-Ray and computed tomography(CT) is important to exclude "red flags". With the progress of the disease, CT and Magnetic resonance imaging (MRI) can provide valuable information. Especially MRI clearly demonstrates inflammatory reaction and abscess formation around the sacroiliac joint, which is the best imaging modality for diagnosis. MRI has been proved to be the best tool for early diagnosis of sacroiliac joint infection. However, the infection of sacroiliac joint is initially unsuspected upon hospitalization in 50% of patients with this eventual diagnosis[5]. In fact over 40% of patients with sacroiliac joint infection, the primary site of infection may never be identified[6].
The diagnosis of sacroiliac joint infection depends on the analysis of comprehensive results, such as physical examination results, laboratory examination, imaging findings, etiological examination and treatment response. Etiological examination is of great significance in the diagnosis of sacroiliac joint infection. Puncture of abscess may get the most accurate diagnosis by biopsy, but the specimen may be contaminated, or the abscess location is not easy to puncture. Sacroiliac joint infection is a rare but important diagnosis because failure to treat can lead to high incidence rate, such as joint instability and systemic spread of infection.