Prevalence of accessory sacroiliac joint anatomy and associated clinical features

The accessory sacroiliac joint (ASIJ) is the most common sacroiliac joint anatomical variant; however, its literature-reported prevalence is inconsistent. Previous CT-based studies of the ASIJ have used thick axial slices, which may not adequately detail ASIJ anatomy. The aims of this study are to (1) evaluate ASIJ prevalence and radiographic features in a large age- and sex-balanced cohort using thin-section CT and (2) determine associations between ASIJ anatomy, patient features, and treatment strategies.

Thin-section CTs (0.75 to 2.00 mm) of the pelvis from 800 patients were reviewed by two musculoskeletal radiologists. Degree of degenerative change and ankylosis at ASIJs were detailed. The EMR was used to capture demographics, lower back or sacroiliac joint symptoms, and treatments.

The ASIJ was present in 25.8% of patients and bilateral in 53.3% of those with any ASIJ. ASIJs were more common at the S2 than S1 neural foramen level (75.7% and 27.2%). There was a statistically significant difference between age and presence of any ASIJ anatomy (mean (SD) 69.0 (19.8) with ASIJ versus 55.9 (22.1) years without ASIJ). Degenerative changes and ankylosis were found in 93.5% and 20.3% of ASIJs, respectively. There was a higher odds ratio of having received a sacroiliac joint corticosteroid injection in those with ASIJ anatomy.

Radiologists should be familiar with the ASIJ and consider its age-related association, propensity to show ASIJ degenerative change, and ability to serve as a potential pain generator. Steroid injections may be considered for diagnostic and therapeutic purposes.