Pediatric Sacroiliac Joint: Normal Development and Pathologic Disorders.

The sacroiliac joint (SIJ) is a critical anatomic structure that connects the axial skeleton with the lower limbs. Compared with its adult counterpart, the pediatric SIJ exhibits unique anatomic features, and imaging evaluation may then present significant challenges due to overlapping features between normal developmental manifestations, anatomic variants, and true pathologic conditions. Two frequently observed developmental findings can resemble pathologic conditions: subchondral irregularities and subchondral flaring. These are commonly seen on MR images of the developing pelvis. A diverse range of anatomic variations has been documented in both the cartilaginous and ligamentous components of the SIJ. Though overall innocuous, some variations are linked to mechanical overload and pain. True sacroiliitis can arise from inflammatory, infectious, or traumatic causes. Inflammatory conditions may exhibit similar imaging characteristics and are best differentiated through MRI. The presence of unilateral sacroiliitis should prompt consideration of an infectious cause, with imaging indicators such as capsular edema and abscess formation suggesting infection. Traumatic injuries to the SIJ are uncommon in children and usually occur in the context of high-energy trauma. Mechanical overload or repetitive stress in the pediatric population can result in bone marrow edema in the weight-bearing regions of the SIJ and, less commonly, in sacral stress fractures, most often involving the sacral ala. It is crucial to accurately differentiate these imaging features to avoid functional impairments, morbidity, and unnecessary interventions. The authors aim to enhance radiologists' understanding of the pediatric SIJ by examining its unique anatomic characteristics, key imaging features, and pertinent differential diagnosis. © RSNA, 2026 Supplemental material is available for this article.